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TIP 0402-35ISSUED – 2009

©2009 TAPPI

The information and data contained in this document were

prepared by a technical committee of the Association. The

committee and the Association assume no liability or responsibility

in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade

secret laws. The user is responsible for determining that thisdocument is the most recent edition published.

TIP Category:Automatically Periodically Reviewed (Five years)

TAPPI

Post-fabrication cleaning of stainless steel in the pulpand paper industry

Scope

All owners and operators of pulp and paper mills want to keep their facility continuously and reliably on stream for

as long as possible with the minimum of maintenance. Post-fabrication cleaning maximizes technical and corrosion

performance.

Stainless steel relies on its invisible, exceedingly thin, passive film of chromium oxide to protect its surface againstthe onset of corrosion. Post fabrication cleaning is the single most important factor in maximizing and maintaining

the corrosion performance of fabricated stainless steel in any particular application, not just in the pulp and paper industry.

Safety precautions

Refer to the “Health and Safety Concerns” section and Appendix F.

Definitions and expressions

Post fabrication cleaning is the process of cleaning after fabrication to remove all contamination associated with the

fabrication process. Contamination might include foreign metals, excessively thick oxide films, grease and oil.

Cleaning generally involves various different chemical and mechanical processes either individually or incombination.

Pickling is the removal of the heavy oxide film or metallic contamination and some stainless steel using aggressive

acid solutions.

Passivation is defined in ASTM A 380 (1), and more recently in ASTM A 967 (2), as a treatment that is effective

for removal of foreign material (not originating from the stainless steel) from the surface of the stainless steel. Free

iron, usually resulting from contact with steel tooling during fabrication or shipment is the most common concern.

The protective oxide film starts to form immediately and spontaneously on the clean surface of the stainless steelwith exposure to oxygen in the environment, a process sometimes called auto-passivation. A clean stainless steel

surface will form the passive film when exposed to oxygen and does not require chemical treatment to achieve the

passive film. Some “passivation” methods also chemically promote and strengthen the inherent protective oxide film

on the surface of the stainless steel, simply by increasing the oxygen content close to the surface.

Fabrication may reduce the overall corrosion performance of stainless steel to below its “normal” level because of

transfer of foreign material to the surface of the stainless steel. In reality, it is difficult, if not impossible, to completethe fabrication of a significant facility or piece of equipment without some surface contamination.

Further discussion is provided in Appendix A.



TIP 0402-35 Post-fabrication cleaning of stainless steel in the pulp and paper industry/ 2

Economic benefits

Cost of cleaning is small compared to the initial capital expenditure on a piece of equipment and compared to the

continuing operational cost of not cleaning. The economics of post fabrication cleaning can be considered in two

stages, the cost of cleaning and the economic implications of cleaning to long-term performance.

Cost of cleaning

Stainless steel is the material of choice in large areas of the pulp and paper industry because of its superior

characteristics in comparison with carbon steels with regard to:

• Corrosion resistance

• Cost of maintenance

• Long life

• Good life cycle cost characteristics

Areas that have not been post fabrication cleaned are essentially the weak link in the chain as they generally have

relatively poor corrosion performance compared to the surrounding material. Consequently, if post fabrication

cleaning is not completed, the owner/operator is not maximizing the payback on the investment.

Post fabrication cleaning is not expensive. In the context of constructing a vessel, post fabrication cleaning mightcost as little as 1-3% of the cost of material and fabrication depending on the extent of cleaning required (3).

Economic implications of post fabrication cleaning

Some time ago in Canada, most bleach plant equipment was put into service without pickling or cleaning after

fabrication primarily because it was believed that the process environment itself would provide the cleaning of thestainless steel in service. Much more corrosion was experienced in these Canadian mills than in similar mills in the

U.S. where most bleach plant equipment was cleaned. The severe corrosion problems in Canada led to the use of

electro-chemical protection systems, with their associated ongoing operating costs, in an effort to reduce the

corrosion rate (4). The overall experience suggests that cleaning after fabrication could have been a more

economical approach to avoiding corrosion.

This example clearly illustrates how avoiding a relatively small capital expenditure resulted in considerable and continuing operating expenditure. The basic premise should be to “justify why post fabrication cleaning should not

be carried out” rather than having to justify the cost of cleaning.

Classification of surface cleaning need

Systematic approach

Many owner/operators are not well acquainted with the concept of cleaning; thus discussions of and decisions about

cleaning are sometimes difficult. In many cases cleaning is decided after the fact, as a remedy, based on the amount

of oxide formed. The decision is often based on the color of the oxide; an indication of how much damage was doneto the corrosion resistance by the fabricating process. For example a “light straw” color implies relatively little

damage to corrosion resistance and opens the possibility of leaving this light fabrication oxide in place, while a

“burnt sugar” color indicates sufficient loss of effective chromium in the surface that removal is necessary to obtainthe expected corrosion resistance from the grade selected. Absolute reliance on these color differences is not

recommended.

A classification system established ahead of time enables the equipment owner to decide and specify the necessary

cleaning at the time of purchase. By specifying the required cleaning, this essentially economic decision is not left to

the equipment seller or service supplier, and can be accomplished with minimal cost.

The working group for this TIP recommends the following approach:



3 / Post-fabrication cleaning of stainless steel in the pulp and paper industry TIP 0402-35

• Classify the need of cleaning, equipment-by-equipment, surface-by-surface

Based on the classification for each surface:

• Select cleaning method

• Select inspection method

•

Decide unambiguous acceptance criteria

Classification of cleaning need

As mentioned, stainless steel relies on the continuity and integrity of its exceedingly thin oxide passive layer or film

to provide corrosion resistance. The integrity of the oxide film can be damaged by:

• Retained heat treatment oxide (much coarser and thicker than the passive film)

• Welding heat tint (also much coarser than the passive film but not as coarse as the heat treatment oxide)

• Contamination, particularly by other metals, but by any non-stainless material

• Localized chromium reduction from extended high temperature exposure sometimes called “chromiumdepletion”

To maximize corrosion performance all of these damages should be identified and should be removed by anappropriate cleaning procedure. In many cases it is clearly impractical and uneconomical to apply the same cleaning procedure in every situation; preferably a system should be applied where different pieces of plant or equipment in

the pulp and paper mill will have different requirements in terms of cleaning.

Given a systematic classification system, both surfaces of each piece of equipment can be classified and a cost

effective system put in place to apply the post fabrication cleaning policy.

Table 1. Basic rules of cleaning for different operating conditions

Require post fabrication cleaning May not require post fabrication cleaning

Wetted surfaces Fully dry surfaces

Process contact surfaces Non-contact surfaces

Surfaces in contact with halogens or

halides, particularly chlorine or chlorides

Surfaces in contact with alkali andcaustic solutions

Low temperature surfaces(temperatures <~280

oF / 140

oC)

High temperature surfaces(temperatures >~1000

oF / 550

oC)

Aesthetic surfaces

Vessels, etc., where the implications of failure or coming off stream for extendedperiods of maintenance are prohibitive

Vessels where there are no significanthealth and safety or production implications

The deciding factor is the corrosion environment in which each surface is operating. The TIP has classified a total of

111 surfaces from 1 (most stringent requirements) to 6 (least stringent) in the following process environments:

• Kraft pulping

• Kraft recovery systems

• Tall oil acidulation process

• Magnesium sulfite processing

• Mechanical pulping

• Recycled fiber pulping

• Bleach plant systems

• Paper machines




Every piece of steel has two sides, so that one side may be in a severely corrosive environment, in which case post

fabrication cleaning will be essential, while the other side may be in a relatively benign environment in which case

post fabrication cleaning is not critical. Therefore, both the “internal” and the “external” surfaces need to be

described (see Figure 1).

Fig. 1. External and internal equipment surfaces

From Table 2 it can be seen that the peroxide reactor, for example, has the most stringent need of cleaning. TheKraft pre-steamer is classified as “3” as later described after normal pre-cleaning operation, the surfaces will be

mechanically cleaned, and the formation of the passive film chemically promoted. In contrast, the liquor heater shellwould normally be electro polished. No information was available as a basis for suggesting an appropriate practice

for the chlorination tower. An interval is given for the brown stock washers based on diverging views.

Detailed consideration is given to specific pieces of equipment and plant in Appendix B.

These classifications are intended to serve as a first approximation of the cleaning need. A plant operator may adopt

the TIP classifications or create an internal scale based on experience. In the future we hope to update and extend the

list.




Table 2. Examples of classification: 1= most stringent, 6 = least stringent.

Corrosion performance of different cleaning methods

The more stringent the classification, the cleaner the surface needs to be. The influence of the surface cleanliness on

the corrosion performance is well documented (3-7 ).

The corrosion performance of 316L is dramatically reduced in some environments by the presence of an oxide film

that is normally regarded as a good quality “light straw” colored welding heat tint (3). The localized corrosion performance of the weld is improved with the removal of the heat tint. The performance continues to improve as the

final surface is left with a smoother and smoother surface (Fig. 2).

When pickling is used after mechanical cleaning, the corrosion performance is essentially independent of the surface

roughness. The pitting corrosion performance of the weld is brought back to parent material levels. The chemicalcleaning operations are much less intensive, time consuming and skill sensitive than mechanical cleaning techniques

(Fig. 3).

The chromium content at the surface of the stainless steel is reduced (“chromium depletion”) as a result of oxidation

during hot processing. This loss of corrosion resistance is associated more with solution annealing heat treatment

than with hot rolling. Significant chromium depletion occurs such that the corrosion rate was increased by a factor of

as much as 50 times as a result of this chromium depletion. (6 )

Any of the post fabrication cleaning techniques used improved the corrosion performance but the degree of

improvement was different from one treatment to another (6). Pickling gave the greatest improvement and always

considerably improved the corrosion performance. Passivation or chemically enhancing a new passive layer, using

less aggressive chemicals, had a small beneficial effect but, on its own, passivation is not effective at removing

Section Equip Equipment Classification

SpecialRequirements Process Stream

1 1 Pre-Steamer 3 Kraft Paper

1 3 Liquor Heater Shell etc 3 Electro polish Kraft Paper

1 6 Brown Stock Washers 2-5 Kraft Paper

1 8 Chlorination Tower No Data Kraft Paper

1 9 Peroxide Reactor 1 Ferroxyl test Kraft Paper

2 7 Soap Storage Unclassified Kraft Paper

4 1 Reactor Shell 4 Tall Oil: Acidulation Process

4 1 Reactor Paddle 4 Tall Oil: Acidulation Process

4 2Spent acid/brine NeutralizingTank 4 Tall Oil: Acidulation Process

6 5Red Liquor Tank (FromWashers) 2 Mg Sulfite Processing

6 6 Sulfur Burner Gas Cooler 2 Mg Sulfite Processing

6 7 Fortification Tower 2 Mg Sulfite Processing

7 2 Digester No Data Neutral Sulfite Pulping

8 2 Steaming Tube 4 High Yield Mechanical Pulping

8 3 Refiners 4 High Yield Mechanical Pulping

8 4 Separators Unclassified High Yield Mechanical Pulping

9 1 Pulper 2-4 Waste Paper Recycling

9 2 Heavy Duty Cleaner 4 Waste Paper Recycling

9 3 Coarse Screens 4 Waste Paper Recycling




Parent

Material

Weld,

Ground

Heat Tint no tRemoved50

250

450

0.0 0.5 1.0 1.5

Surface Roug hness (Ra microns)

P i t t i n g P o t e n t i a l ( @

2 0

o C m v )

Impro v ing Pi t t ing

Resistance

Parent

Mater ia l .

We ld ,

G r o u n d

We ld ,G r o u n d a n d

Pick led

100

300

500

0.0 0.5 1.0 1.5

Sur face Rough ness (Ra m ic ron s )

P i t t i n g P o t e n t i a l ( @

2 0

o C m v )

Im prov ing P i t t ing R es is tanc e

coarse oxide contamination or chromium-depleted areas. Belt grinding resulted in better corrosion performance than

silica sand grit blasting, and the corrosion performance as a result of sand blasting was better than that from chilled-

iron grit blasting. Grit blasting should never be used unless followed by pickling or passivation because the grit itself

may transfer to the cleaned surface and act as a site for corrosion.

Fig. 2. Effect of mechanical cleaning and surface roughness on the pitting corrosion performance of 316l(5)

Fig. 3. The effect of pickling of mechanically cleaned surfaces on their pitting corrosion performance (3, 5)




Various grades of welded stainless steel with different post fabrication cleaning finishes were exposed to the

corrosive environment of a paper mill. Pickled surfaces always gave superior corrosion performance compared to

stainless steel wire brushed surfaces; glass bead blasted surfaces probably performed better than the brushed

surfaces although this improvement was not as consistent or conclusive (4).

The effects of various cleaning techniques on the corrosion performance of 2205 duplex stainless steel were

considered (7 ). There was very little difference in the corrosion performance of ground (60-120 grit) and blasted (blasting angle 45-60o off horizontal) surfaces. In contrast, pickled surfaces gave very good corrosion performance,

(Fig. 4).

It is clear that:

• Post fabrication cleaning should be completed and completed effectively.

• The corrosion performance of both the parent material and the welded joints can be improved by

mechanical cleaning techniques but there is considerable variability from one technique to another.

• The mechanical techniques are skill sensitive and labor intensive and are often difficult to apply evenly

over larger surfaces.

• The best method available to achieve the full value of the stainless steel is to pickle after fabrication.

• The most practical method to maximize the corrosion performance of welded stainless steel may vary from

one fabrication shop or application to the next but it will typically involve mechanical cleaning (usuallygrinding) followed by pickling.

Fig. 4. The effect of different post fabrication cleaning methods on the corrosion performance of duplexstainless steel 2205 [data after Gumpel (7)]

Surface BlastedGround

Pickled

0.4

0.8

1.2

1.6

1 2 3

Surface Treatment

C o r r o s i o n P o t e n t i a l ( V )

Improving Performance




Surface smoothness influences the in-service characteristics and service costs.

The rougher the surface, the greater is the tendency for crevice corrosion associated with deposits to occur. This

effect may be due to the roughness acting as micro crevices, thus initiating crevice corrosion on their own, or by

acting as sites that can hold product or other deposits, thus encouraging crevice corrosion.

A smoother surface drains better than a rough surface. There are obvious benefits in relation to reduced adhesion of

product to the surface, (5, 8, 9). For example, a relatively smooth surface, ASTM No 4 finish (a 2K finish in EN10088) required ~80% less time and water to clean it than a rougher surface (ASTM 2B) (10).

Selection of cleaning method or combination of methods

The basis of all cleaning is that all material that is not stainless steel must be removed from the stainless steel. A

stainless steel cannot extend its protection to non-stainless material on the surface or maintain the corrosion

resistance of any area blocked by a deposit, so any deposits help to initiate corrosion.

For the more stringent classifications the outermost chromium-depleted layer must be removed to restore the surface

to its original corrosion resistance. The efficiency with which any operation is carried out and the effectiveness of that operation is crucial for the result (Table 3). For optimum results a combination of methods is used (Table 4).

Table 3. Effectiveness of common cleaning methods

Method Effectiveness Skill sensitivityLabor Intensity

Grinding, Polishing Metallic contaminations may remain Very high Very intense

Blasting Soft contaminations may remain Medium Low

Brushing Deposits not completely removed Low Low

Mechanical polishing,flat surfaces

Heavy oxide cannot be removed Low Low

Manual polishing of weldareas

Heavy oxide cannot be removed High High

Electro-polishing Smoothens surface Low Low

Passivation Removes light metalliccontamination

Low Low

Pickling by dipping,spraying, pumpingmethods

Removes heavy metalliccontamination and chromiumdepleted layer

Low Low

Pickling by paintingmethod

Removes heavy metalliccontamination and chromiumdepleted layer

Low Medium

One of the main obstacles to properly applied cleaning is adequately addressing the health and safety issues. Thesemight include noise, vibration, thermal and chemical burns, disposal of dusts and waste products and electrical

hazards. The section “Health and Safety Concerns” and Appendix F discuss this in detail.

Grinding is a common method often regarded as a simple operation. From the clean surface point of view though,

grinding requires good judgment and high manual skill as there are no visible signs when both oxide and chromiumdepleted layer are removed. Further, the grinding depth has to be the same at all locations, sometimes over large

areas, which requires manual skill. Chemical methods are usually regarded as difficult because health and environmental training is required to handle the acids and the hazardous waste. From the clean surface point of view

though, once training is performed, chemical methods follow recipes, can be repeated, requires low manual skill and

the removal of material is the same over the exposed surface.




The basis of all mechanical cleaning operations is that all non-stainless steel material must be removed.

It is important to match the cleaning method to the surface classification

Table 4. Selection of cleaning methods for optimum results

Classification Cleaning method(Most stringent to

least stringentclassification)

Pre- Cleaning Mech.Cleaning

Picklinga

Chemicalpromotion of new passive

film

AdditionalCleaningMethod

b

None, As-is

1 Yes (Yes) Yes Yes

2 Yes (Yes) Yes

3 Yes Yes Yes

4 Yes Yes

5 Yes Yes

6 Yes

Unclassified Yesa Any additional cleaning method, e.g., electro-polishing, to be specified at contract stage

b Any additional tests are to be specified as required

Key Yes Should be used(Yes) Optional, use as appropriate

Pre-cleaning

Pre-cleaning should be regarded as an essential first step for all cleaning methods.

Oil, waxes, gross hydrocarbon contamination, etc., retained on the surface to be cleaned can be either smeared

further onto and into the surface by mechanical cleaning or act as a barrier layer to the chemical cleaning methods.

Cleaned surfaces should be Inspected, see the “Selection of inspection methods and coverage” section.

Mechanical cleaning

Grinding and polishing

Grinding and polishing, as manual or mechanized techniques, are very common methods of cleaning a surface. Thefinish achieved depends on the grit size used and on the skill of the operator (Fig. 5). The final finish should be

obtained using fine grit sizes, assuming complete removal of prior surface roughness in each step, and be as smooth

as possible (as shown in the previous section “Corrosion performance of different cleaning methods”) in order to

maximize corrosion performance

In addition to the roughness of the final surface, the final grinding direction can also be important in relation to

efficiency and speed of surface cleaning and draining.

Grinding and polishing do not necessarily remove all metallic contamination. Irrespective of recontamination,existing contamination can be smeared across a surface rather than removed.

These operations are very skill sensitive and labor intensive. The moisture test, as described in the ASTMspecifications, is a simple, straightforward and effective method for identifying the presence of free iron

contamination on the surface of the stainless steel.




Fig. 5. Typical surface roughness produced with different sized grits (11).

Blasting

If blasting is not to be followed by chemical treatment, the grit or shot should be corrosion resistant, either a

stainless steel resistant to the operating condition, or a non-ferrous product, such as alumina, carbide or glass bead. It

should be dedicated to stainless steel to avoid cross contamination.

When blasting, care should be taken to assure the efficiency of the demisters in removing (particularly)

hydrocarbons from the blasting air. Blasting will not necessarily remove “soft” contamination like grease etc.

The blasting angle should be vertical or just off vertical. Blasting at an angle is highly unlikely to fully remove

contamination and is likely to smear contamination into the surface.

Care should be taken to ensure that coverage is even and consistent and that all contamination is removed. A typical blast finish is “Near White Metal” finish as a minimum acceptance criterion (12).

Brushing (manual and power brush)

Brushing, be it power brushing or manual brushing, is normally not adequate for post fabrication cleaning because it

does not completely remove deposits and it certainly does not remove metal. Likewise, brushing does not remove

heat treatment oxides or welding heat tint. Instead, brushing superficially polishes the oxide smooth and making it

invisible, but it does not remove any areas of chromium depletion resulting from oxidation. In this condition asubsequent exposure to a reactive environment may cause corrosion.

A combination of brushing and polishing can remove dust, much gross debris, and possibly some weld spatter.

Brushing by itself is appropriate only for general cleaning.

Weld: Ground

Weld: Ground

and Pickled

0.0

0.5

1.0

1.5

0 100 200 300 400 500 600

Grit Finish No

S u r f a c e R o u g h n e s s ( R a ) ( m i c r o n s )

0

1

2

3

4

5

6

S u r f a c e R o u g h n e s s ( R a ) ( m i c r o

i n c h e s )




Mechanical polishing

The objective when mechanically polishing or buffing is to produce a smooth surface and, as such, it is used in

combination with other methods that remove the gross oxides which polishing cannot. This technique is probably

most commonly applied as a mechanized process to flat plate, before fabrication rather than to a complex shape.Weld zones, etc., are then (generally) manually polished to the required finish, which can be a fairly labor intensive

and skill sensitive operation. There may be issues of consistency of aesthetic appearance over large areas.

Electro-polishing

Electro-polishing is a specialized technique that is useful for chemically cleaning the surface, for smoothing the

surface, and for improving the aesthetic appearance of a surface. It does not necessarily “flatten” the surface.Electro-polishing can smooth a surface as it eliminates short wavelength roughness, e.g. removing the peaks, but it

does not substantially alter long wavelength roughness.

Chemical techniques

Pickling is a method for cleaning and removing heavy oxide layers, such as heat treatment scale and heat tint from

welding, and heavy metallic contamination. In contrast, some forms of passivation remove relatively low levels of metallic contamination.

Passivation

Passivation is a phrase sometimes applied to two different operations. One is the removal of exogenouscontamination. The clearer definition is the re-growth of the passive, protective film. As soon as the surface is clean

the passive film will form by auto-passivation in the presence of oxygen in the environment, either in air or water,

but does not require a separate treatment of the surface. The suggestion that a separate treatment is necessary to

establish stainless steel corrosion resistance is the cause of a lot of confusion.

Passivation is defined in ASTM A 380 as “the removal of exogenous iron or iron compounds from the surface of

stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that willremove the surface contamination, but will not significantly affect the stainless steel itself” (1). Free iron, resulting

from contact with steel tooling during fabrication or shipment is the most common concern. For this purpose nitric

acid (HNO3), stabilized hydrogen peroxide solution (H2O2), citric acid, and phosphoric acid have all been used.

The protective oxide film forms spontaneously on the clean surface of the stainless steel during the first minutes or

hours after passivation (13).

Passivation also chemically promotes and strengthens the inherent protective oxide layer on the surface of thestainless steel, simply by increasing the oxygen content close to the surface. For this purpose, passivation is

undertaken either with an oxidizing mineral acid, frequently nitric acid (HNO3), or with stabilized hydrogen

peroxide solution (H2O2). Citric acid and phosphoric acid may be effective for cleaning the surface from free iron but are inefficient for speeding the formation of the passive film. Concentration and temperatures are discussed in

the “Selection of Cleaning Materials “ section.

A passivation solution, by definition, is incapable of pickling, i.e., the dissolution of stainless steel or oxides

resulting from high temperature exposure, as in welding heat tint or heat treatment oxides. Passivation, by definition,does not produce solutions that are hazardous in the sense of containing chromium or other heavy metals.

Although significantly less aggressive than pickling solutions, passivation acid solutions should be handled, used,

washed off and disposed of in the same way as pickling solutions.

Hydrogen peroxide solution can be run directly to drain under normal circumstances (subject to any localrestrictions).




Pickling

Pickling is an aggressive chemical cleaning capable of removing oxides from the surface of the stainless steel, both

the inherent protective oxide formed by auto-passivation in the presence of oxygen, and the oxides that has been

formed and thickened by welding, heat treatment, or other exposure to high temperatures. Pickling also removesmetallic contamination from the surface of the stainless steel, as well as removing some of the stainless steel surface.

Pickling, as is true of the less aggressive “passivation” treatments, also removes metallic contamination from the

surface of the stainless steel.

Pickling is best applied to a pre-cleaned surface to assure that the exposure of the metal to this aggressive solution is

as uniform as possible. The most common pickling solution for stainless steels uses a solution of nitric (HNO3) and

hydrofluoric (HF) acids, followed by rinsing in water. The presence of the hydrofluoric acid is what enables thedissolution of heat tint and heavy oxides and removal of the surface layer where chromium has been reduced by

formation of the oxide, often called the chromium depleted layer. In special cases, other acid solutions are

sometimes used. Because some stainless steel is dissolved, carrying chromium and other heavy metals into the

pickle liquor, the resulting product is typically considered to be a hazardous waste requiring special precautions indisposal. Because the pickling solution is so aggressive, special safety precautions are required for safety of

personnel.

Once training in acid handling and waste disposal are completed, pickling is not a skill sensitive process nor is it a

particularly labor intensive process.

Pickling can be used as a cleaning process on its own although it is frequently used in conjunction with a pre-

cleaning and mechanical cleaning technique to improve the efficiency and throughput of the cleaning processes.

There are various pickling methods available as described below. The distinguishing characteristics of these

methods generally relate to the method of application of the pickling solution and the subsequent rinsing procedures

Dipping / pickling bath method

Dipping the components to be cleaned into a pickling bath is arguably the most efficient and least labor-intensivemethod of removing oxides and contamination from stainless steel when the components are small enough or

suitably shaped.

The component to be cleaned is dipped into the acid solution, held at the appropriate temperature until it is clean.The time taken to clean the stainless steel will depend on the grade of stainless steel, the extent of oxide that is to be

removed, and the strength and temperature of the acid.

There must be full and efficient drainage of all pickling solutions and wash down waters. Great care must be takenwith air pockets to ensure full treatment, possibly using a separate second stage treatment.

Spraying method

The spray method of pickling is used when a) it is not possible or practical to dip the component; b) there are large

surface areas to clean or c) special production or installation situations make spraying the most effective or the most

economical approach.

Pickling acid is sprayed onto the surface to be cleaned. After the required contact time, the acid is washed off with

high-pressure water hoses.

It is preferable to perform spray pickling in a dedicated facility and with equipment designed especially for spraying,where practical. Spray ball systems, for example, can be utilized for internal surfaces of vessels.




Painting method

Pickling pastes and gels can be painted onto components to be cleaned. This method is particularly appropriate for

cleaning small or local areas, such as weld seams.

Having cooled the component down to essentially room temperature, the pickling paste or gel is painted onto the

area to be cleaned using acid resistant brushes. When the cleaning cycle is complete, the pickling acid is removed

with high-pressure water. Appropriate disposal of rinse water is necessary.

Although this method of pickling is more labor intensive than some other pickling methods, it is not a skill sensitive

operation.

Pumping Method

Pickling bath solutions can be used to clean the bore of tubular systems by circulating the acid in the pipes and tubes

using an acid-resistant pump and acid resistant-plastic connectors. It is important that the rinsing system essentiallyclear the pickling acid from the equipment. This method cleans all wetted surfaces in the bore of the pipe system.

The acid can often be recycled and reused.

Selection o f cleaning materials

All tools and materials must be compatible with stainless steel and dedicated for use on stainless steel. The essential

elements of compatibility are the absence of iron and halides (chlorides), unless chemical treatment will be the finalstep in the process.

Pre-cleaning solutions

Light pre-cleaning:

• Chemicals are generally based on phosphoric acid, concentration about 20%.

• Removal of light organic contamination and light metallic contamination only.

• Alkali cleaners could be used but heavy metallic contamination will not be removed.

Heavier organic contamination

• Grease, oil, or cutting fluid should be removed with a non-chlorinated degreaser.

Mechanical cleaning

Grits for blasting

It is good practice to avoid contamination of the grit with iron or other non-stainless material even if the stainless is

to be chemically cleaned after the mechanical treatment.

Alumina, olivine sand, or glass beads grits tend to give a slightly coarser finish than achieved with carbide grit.

Coarse grits will tend to obtain the desired results more quickly but will result in rougher surface finish. Therefore,

the grit size should be optimized, or applied in a sequence of finer grits, to quickly produce the required surface

finish or roughness.

Grinding, flapper wheels and fine grinding belts

The grit size of carbide or alumina disks and belts should be chosen to suit the job or the specification requirements.

• Removal of heavy oxide: initially done with ~240 grit disc or finer.




• Lighter oxide can probably be removed with ~320 grit disc.

• Start with coarser grits and work through to finer grits.

• The final grit should be as fine as practical or specified.

• Finishing with fine grit is particularly important if the surface is not to be pickled after mechanicalcleaning.

Polishing

All mops (lint free), waxes and lubricants should be iron free and compatible with stainless steel. Care should betaken to remove all waxes and lubricants after polishing.

Chemical cleaning

The main issues are:

• The removal of non-metallic contamination;

• The removal of metallic contamination;

• The removal of gross oxide;

• The removal of local oxide, e.g., heat tint;

•

The retention of a polished, aesthetic finish;• Health and Safety; and

• Environmental acceptability

Passivation solutions

Chemicals are typically:

Nitric acid (HNO3) solutions:

• Nitric acid used historically, concentration 20 – 30%

• Its use, control and disposal must be carefully controlled

Hydrogen peroxide (H2O2) stabilized solutions:

•

Increasingly used in preference to the acid solutions (the health and safety issues associated with their useare not so demanding)

• Effluent can usually be run to normal open drain (subject to any local restrictions)

• Solutions sterilize the surfaces onto which they are sprayed.

These two passivation solutions also boost the formation of the protective oxide film and remove exogenous iron

contamination.

Other acid solutions that do not attack the stainless steel:

• Citric acid (C6H8O7) a weak organic acid that forms a chelate around the iron contamination

• Phosphoric acid (H3PO4)

Passivation is typically performed at ambient temperature.

Pickling solutions

• Generally based on nitric acid (HNO3) and containing hydrofluoric acid (HF).

• Phosphoric acid (H3PO4) is normally inefficient, but at higher concentrations and temperatures it is

sometimes used for “very mild” pickling applications.

• Ingredients and temperature are balanced to give optimum pickling for a specific range of stainless grades,

see the section “Pickling operating window” below and Table 5, i.e. the acid needs to be “stronger” and hotter for “high performance” or “super” grades than for standard grades.




• Pickling solutions can be adopted for spraying, dipping, pumping or brush application.

• Because the pickling solution is used for removal of oxide and is capable of some dissolution of stainlesssteel, the resulting pickling liquor should be considered a hazardous waste and appropriate precautions

taken in its disposal. Read more in Appendix F.

The pickling operating window

In practice, pickling is a balance between acid concentration, temperature and exposure time with two limiting

conditions, metal content of the liquor and NOx fumes.

Pickling is faster and more efficient at higher temperature. The peak performance of a classical mixed acid of 8 -

10% nitric acid with 2 - 3% hydrofluoric acid occurs at 130 - 140°F (55 - 60°C). Further increasing the temperature

is inefficient as hydrofluoric acid starts to boil at 153°F (67°C). If, for practical reasons, the temperature cannot be

raised, both stronger acids and longer pickling times may be used as needed (see Table 5). At ambient temperaturetimes can be very long and any temperature increase is beneficial, even the effect of sunshine, provided the pickling

paste does not dry out and cake onto the surface (see principal diagrams Fig. 6 and 7).

T i m e t o c l e a n s u r f a c e

T i m e t o s a t u r a t e d s o l u t i o n

140ºF

160ºF

80ºF

Operating

window

Time

F l u o r i d e p r e c i p i t a t i o n

HF boil ing

4 0 0

s e r i e s

3 0 0 s e r i e s

H i g h e r a l l o y e d g r a d e s

10 m in 5-10 hours2 min

Fig. 6. Schematic outline of classic acid pickling with 8% HNO3 + 2% HF. The actual pickling times canvary depending on application method and solution agitation. Inspection of the surface is more importantthan simple time.

During the pickling operation, the pickling liquor will be a mixture of acids, water and dissolved metals, iron,chromium and nickel. The dissolved metal may fall back on the steel surface, creating a thin gray film, often called

smut. This film is mainly free iron and needs to be removed by a passivation operation before final rinsing. The

precipitation that occurs when the liquor reaches its saturation point and no longer can hold the metal fluorides in

solution is much worse. Metal fluorides precipitate on every available surface, on the material to be pickled and onall equipment surfaces, liquid container, hoses and pumps. With a classical mixed acid precipitation occurs at 6%

metal content. On the other hand, dissolved metal helps to drive the chemical reaction and between 2% and 5%

metal in solution is beneficial.




M edium acid pickling: 20% HN O 3 + 5% HF

T i m e t o c l e a n s u r f a c e

140ºF

160ºF

80ºF/

25°C

Operat ing

w i ndow

T i me

F l u o r i d e p r e c i p i t a t i o n

HF bo i l i ng

3 0 0 s e r i e s

H i g h e r a l l o y e d g r a d e s

5–10 hours1 hour

Fig. 7. Effect of stronger acids: schematic outline of medium strong acid pickling 20% HNO3 + 5% HF.The actual pickling times can vary depending on application method and solution agitation. Inspection of the surface is more important than simple time.

Pickling with nitric acid creates a mixture of nitrous gases, often called NOx fumes. The liquor can dissolve a

certain volume of NOx in solution, but above the saturation point fumes are formed. The saturation point varies withthe temperature; cold liquor is able to hold more fumes than hot liquor. The color varies from invisible over light

yellow to heavy brown depending on concentration and temperature. NOx fumes contribute to ground ozone

formation and are regulated. NOx fumes that are generated during pickling can be reduced or effectively eliminated by use of stabilizers, when compared to classic pickling acids with no stabilizer. Hydrogen peroxide (H2O2) is a

common stabilizer. Other stabilizers are often proprietary additions to the acids and are not always declared. Nitric

acid also forms water-soluble nitrates.

Nitric-free pickling methods try to avoid the mentioned disadvantages. Nitric-free pickling solutions are usually

based on a mix of hydrofluoric acid, sulfuric acid and hydrogen peroxide. They are very sensitive to the metal

content and formation of smut as described above is a huge problem. In practice, nitric free pickling often requires a

passivation operation after the pickling and therefore has not gained in popularity.

Selection of chemicals/acids

It is important to match the chemical to be used to the grade(s) being cleaned and the desired effect.

Stainless steels with higher PRE are more resistant to the pickling acids and may require stronger concentrations,

higher temperatures and/or longer exposures. PRE is usually defined as

PRE= % Cr + 3.3 %Mo + 16 %N

In field service and ambient temperature, time has to be extended until the surface is clean.




Table 5. Selection of typical acid mixes for pickling of different grades of stainless steel

Grades PRESurfaceFinish

Acidconcentration

Temperature

Typical acid mixes

140°F(55°C)

8-10% HNO3 + 0.5% HF400 series 12 -22

Fine andEngineering

Mild

Ambient 8-14% HNO3 + 0.5% HF +8–14% H2SO4

Fine Mild As above

140°F(55°C)

8-10% HNO3 + 2–3 % HF

301, 304L,316L

20 -25 Engineering Medium

Ambient 15-20% HNO3 + 1-5 % HF+6–10 % H2SO4

140°F(55°C)

8-10% HNO3 + 3.5–4.5 %HF + 12-14% H2SO4

LDX 2101®, AL-2003®,2304, 309,310, 317LMN

25 -40

Engineering Strong

Ambient 15- 25% HNO3 + 1-6 %HF

2205, 2507,

6%- Mogrades

Above

40

Engineering Aggressive Up to 50% HNO3 + up to

12 % HF

The levels of NOx fumes can be suppressed as schematically shown in Table 6.

For example, an ultra low NOx type solution will minimize NOx fumes while cleaning a fine finish surface whereasthere will be heavy fume generation if no NOx suppression were used. Commercially available pickling solutions

are designed to cover some or all of the below listed combinations. When NOx fumes cannot be suppressed, local

exhaust ventilation may need to be applied.

Table 6. Schematic NOx fume generation at different acids strengths and % suppression

NOx fume Levels, with % SuppressionTypical acidconcentration

% Reduction inNOx emission

Ultra Low90%

Low70%

Medium50%

Classic0%

Mild acids Fine Finishes:PRE <~25

No fumes Little or nofumes

Light fumesat intervals

Yellow fumes

Medium acid EngineeringFinish: PRE<~30

No fumes Little or nofumes

Light fumesat intervals

Heavy brownfumes

Strong acid EngineeringFinish: ~30PRE <40

Light fumes atintervals

Light fumes Yellow fumes Heavy brownfumes

Aggressiveacid

EngineeringFinish: PRE

>40

Light fumes Yellow fumes Heavy brownfumes

Heavy brownfumes

Procedures and techniques

The different stages associated with the various cleaning objectives must all be thoroughly applied in order to

maximize the corrosion performance.




Procedural recommendations and safety precautions for cleaning, descaling, and passivation stainless steel parts are

based on general working practices and on ASTM standards.

The overall cleaning procedures are detailed in Appendix C and can be summarized as shown in Table 7.

Table 7. General cleaning procedures to remove heat tint

Step Activity A: B: C: D: E:

Clean for Appearance

Clean for appearance

and rust stainremoval

Mechanicalcleaning

Restorepassivation by

pickling

Restorepassivation

withoutpickling

1Safety

Precautions Yes Yes Yes Yes Yes

2Safety

Equipment Yes Yes Yes Yes Yes

3 Working area Yes Yes Yes Yes Yes

4 Pre-clean Yes Yes Yes Yes Yes

5 Rinse Yes Yes Yes Yes Yes

6MechanicalCleaning Yes

(a)Yes

(a)As required.

(a)Yes

(a)

7 Brush Clean Yes Yes As required. Yes

8 Pickling Yes

9 Rinse Yes

10 Inspect Yes

11 Passivate Yes Yes

12 Rinse Yes Yes

13Neutralize

rinse waters Yes

14 Inspect Yes

15

Acid Washfor Fe

Removal Yes Yes

16 Rinse Yes Yes

17 Inspect Yes Yes

18

Prepare for subsequentoperations Yes Yes Yes Yes Yes

Notes

a Ensure the correct grit size is used and the grinding direction is correct, particularly for the finaloperation

Selection of inspection methods and coverage

Inspection is an important stage of any operation, including post fabrication cleaning. Recommended inspection for

each cleaning method is discussed in this section. The tests are briefly described in Appendix D.




Table 8. Selection of inspection techniques that are appropriate for the different post fabrication cleaning(PFC) methods

Test

PFCMethod Visual

Water Break Moisture Wipe

CottonBall Ferroxyl

Copper Sulfate Solvent

BlackLight

Add it ionalTests

Grinding Yes Yes Yes (Yes) (Yes) (Yes) II, (I), (III)Blasting Yes Yes (Yes)

a

(Yes) (Yes) Yes Yes II, (I), (III)

Pickling Yesb

Yes Yes (Yes) (Yes)Brushing Yes

c(Yes) (III)

Polishing Yes Yese

Yes Yes (Yes) Yes Yes Yese

Yes I, III, (IV),(V)

Electro-polishing

Yes (Yes) Yes I, (IV), V

Passivation Yesb

Yes Yes Yes (Yes) Yes Yes Yes

Notes and key to tableKey Yes Can be used / probably appropriate

(Yes) Might occasionally be appropriateNotes

aPrimarily to check for retained dust, oil and grease

bLooking for retention of original surface finish through (e.g.) contrast or smoothness

or sheen differences or retained oxidecLooking for absence of gross contamination and dust but not as an acceptance test

for removal of oxide skinsdChecking particularly for absence of retained lubricants, waxes etc from polishing

AdditionalTests

Additional Tests might include:I. Roughness Testing (Ra).II. Compared and contrasted with known / standard finishes, e.g. “Near White Metal”

III. Tactile, for smoothness. Be aware of the implications for contamination of the surfaceand of Health and Safety

IV. Specialist tests available but generally not appropriate for P&P applicationsV. Cotton Ball Test

Selection of tests for each post fabrication cleaning method

It is important to understand which inspection tests are most appropriate for use with the different cleaning

techniques, Table 8. It is not normally necessary to use all of these different tests all of the time. The inspectiontechnique or techniques should be chosen relative to the classification of the surface, type, and extent of cleaning

required.

Tests

It is also important to appreciate the strengths and weaknesses of the different tests that are available to determine

efficiency of cleaning (Table 9).

Selection of coverage of inspection

The minimum inspection requirement is visual examination.

While it is not always appropriate or practical to inspect 100% of all surfaces, a sample inspection of a proportion of the surfaces, such as 10%, should be completed. The inspection procedures and techniques are essentially the same

for sample inspection as for full inspection.




The areas for sample inspection should be identified in advance, together with how extensively these areas are to be

inspected. Areas appropriate for sample inspection obviously vary from one situation to the next but they might

include areas that might be difficult to work in (overhead) or areas where there is “traffic”, e.g., man ways / exit

points.

Consideration needs to be given to the implications of the component failing the sample inspection regime.

Additional cleaning of areas that have failed is normal as well as to increase the inspection level in other areas too.

Table 9. Tests for inspection of post fabrication cleaned stainless steel

Test

Test for Visual Water

breakMoisture Wipe Cotton

ballFerroxyl Copper

sulfateSolvent Black

light Additional

(SeeNotes)

GeneralCleanliness

Yes Yes Yes Yes Yes

More DetailedCleanliness

Yes Yes (Yes) Yes Yes

IronContamination

Yes Yes Yes

HydrocarbonContamination

(Yes) Yes Yes (Yes) Yes

GeneralContamination

Yes Yes Yes Yes Yes

Shadowing Yes Yes

PFC Residues Yes Yes Yes Yes

Smoothness Yes I, III, IVa

Removal of GrossContamination

Yes Yesb

(Yes)b

(Yes)b

IIc, III

Notes and Key to Table

Key Yes Can be used/generally appropriate

(Yes) Might occasionally be appropriateNotes

aSuch tests might include reflectivity. This is generally not appropriate for mechanical

cleaning, pickling and passivation applications due to its sensitivitybIron contamination

cOxide contamination

AdditionalTests

Additional Tests might include:

I Roughness Testing (Ra)II Compared and contrasted with known/standard finishes, e.g. (10)III Tactile, for smoothness. Be aware of the implications for contamination of the surface

and of Health and SafetyIV Specialized tests available but generally not appropriate for P&P applications

Selection of acceptance criteria

The best practice for any piece of equipment may be defined in terms of:

• Classification of need of post fabrication cleaning, (Tables 2 and Appendix B)

• Clearly defined cleaning methods, (Table 4)

• Appropriate inspection techniques (Table 8)

• Acceptance criteria (Table 10)




Different pieces of plant or equipment in the pulp and paper mill will have different requirements in terms of

cleaning and therefore different inspection requirements and acceptance criteria.

Clearly, the more stringent the surface classification, the more important it is that the acceptance criteria actually are

met.

While the acceptance criteria for any cleaning technique may vary from one application to the next, the normal

acceptance criteria are summarized in Table 10.

Table 10. Common acceptance criteria for different inspection methods

Inspection method Common acceptance criteria

Visual Examination No significant visible deleterious components.

Water Break Test Absence of any evidence of greases or other contaminants on thesurfaces

Moisture Test No evidence of red rust developing on the surface or other contaminants on the surfaces

Wipe Test No evidence of contaminants on the cloth.

Ferroxyl Test No evidence of free iron

Copper Sulfate Test No evidence of free iron

Solvent Test No evidence of contaminants on the cloth or no discoloration of thedrained down solvent or tide marks on the essentially horizontalsurface after evaporation of the solvent.

Black Light Testing No evidence of fluorescence on any surface.

Roughness Testing The absolute roughness values obtained compare to specified values.

Reflectivity Testing The absolute numeric values obtained compared to specified values

Contrast Tests The sample is either qualitatively equal to or better than the agreedcomparator or is quantitatively satisfactory relative to agreed tests.

Tactile Testing There are no generally accepted criteria for this test. The results arenot to be taken as the absolute basis for acceptance or rejection.

Cotton Ball Absence of fibers retained on the surface

Corrective actions

Inevitably there are some potential problems associated with post fabrication cleaning that may need to be resolved

before delivery. Some of the more common suggested corrective actions are shown in Appendix E.

Specifying cleaning

Just like the majority of fabrication activities, post fabrication cleaning must be correctly and adequately specified.

From a technical point of view, a specification would include:

• Metals to be cleaned

• Surfaces to be cleaned

•

Specific cleaning methods, chemicals, materials etc to be used or not used • Finish required

• Inspection techniques to be applied

• Inspection methods and levels

• Acceptance criteria for each method

• Corrective action requirements/restrictions, etc.

• Post cleaning protection prior to operation, e.g., during shipping or laying-up period

• Quality system requirements

• Any witnessing/sign off requirements




Health and safety concerns

Health and safety is an issue with all fabrication operations. Post fabrication cleaning is no different. Appropriate

equipment should be used and training given in the context of up to date relevant requirements and legislation.

Post fabrication cleaning is best undertaken in a dedicated facility. Should the fabricator not wish to set up such a

facility, specialist companies run so called “metal laundries” that can efficiently and effectively undertake the postfabrication cleaning.

Any fabrication procedure, including post-weld cleaning, requires appropriate safety precautions, techniques, and

personal protection safety equipment (visors, helmets, shields, gloves, etc). Normal manufacturing safety precautions apply. In United States, an EPA waste generator ID number has to be obtained. Some companies require

permits to work. Check with the appropriate department at your organization.

Cleaning may require the use, disposal, or both of chemicals that may present serious health hazards to humans. U.Semployers are required to comply with the requirements of OSHA Hazard Communication Standard (29 CFR

1910.1200). Procedures for the handling of such substances are given in Material Safety Data Sheets (MSDS) that

must be developed by all manufacturers and users of potentially hazardous chemicals and maintained by alldistributors of potentially hazardous chemicals. Prior to the use of this technical information paper, the user should

determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, should strictlyfollow the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use

and disposal of these chemicals.

Appendix F is an overview of the applicable U.S. regulations focusing on small facilities.

Literature cited

1. ASTM Specification A380. Standard Practice for Cleaning, Descaling and Passivation of Stainless Steel

Parts, Equipment and Systems.2. ASTM Specification A 967. Standard Specification for Chemical Passivation Treatments for Stainless steel

Parts

3. Baxter, C., Bornmyr, A., and Stahura, R.,. “Post Fabrication Cleaning: Benefits and Practicalities”.International Conference: Stainless Steel America 2004. Houston, USA Oct 2004. Pages 174 – 178.

4. Garner, A., “Corrosion of Weldments in Pulp Bleach Plants” Welding Journal September 1986 Pages 39 –

44.

5 Baxter, C., and Wendelrup, L., “Post Weld Cleaning of Stainless Steel: Practical Application and Control”.

International Conference: Stainless Steel World 2001. The Hague, The Netherlands. Nov 2001. Pages 467 – 470.

6 Grubb, J., ”Pickling and Surface Chromium Depletion of Corrosion-Resistant Alloys. International

Conference on Stainless Steels. 1991. Chiba, Japan.7. Gumpel et al, Stainless Steel Europe May 1995. Pages 47-51

8. Pickling Handbook, Avesta Finishing Chemicals AB.

9. Backhouse ,A., Private Communication from Outokumpu Stainless Ltd

10. EN 10088. ”Stainless Steels – Part 2: Technical Delivery Conditions for Sheet / Plate and Strip of

Corrosion Resisting Steels for General Purposes”. British Standards Institute. 200511. Baxter , C., Private Communication from Outokumpu Stainless Ltd

12. “White Metal Blast Cleaning,” NACE / SSPC Joint Surface Preparation Standard. NACE No 1/ SSPC-SP

5.

13. Wegrelius ,L,, Sjoden, B., Passivation of stainless steel. Outokumpu Stainless Acom 4-2004.

Keywords

Stainless steel, Cleaning, Corrosion




Addi tional informat ion

Effective date of issue: January 2, 2009

Working Group:Elisabeth Torsner, Chairman, Outokumpu Stainless Inc

Chris Baxter, Outokumpu Stainless Distribution Ltd

Anders Bornmyr, Avesta Finishing Chemicals ABRalph Davison, Technical Marketing Resources Inc

Richard Avery, Nickel Institute

Bob Charlton, Riverside Engineering

Harry Dykstra, Bacon DonaldsonAndy Garner, Andrew Garner & Associates Inc

Margaret Gorog, Weyerhaeuser

John Grocki, RC Inc

John Grubb, Allegheny Ludlum IncWendi Kaiser, Angela Wensley Engineering

John Kish, FP Innovations Paprican

Steve Lukezich, MeadWestvaco Corp / Diamond Power Michael Lykins, MeadWestvaco Corp / New Page Corp /Smurfit

Max Moskal, M&M EngineeringCraig Reid, Bacon Donaldson

Sandy Sharp, MeadWestvaco Corp / Sharp Consultant

Doug Singbeil, FP Innovations PapricanAngela Wensley, Angela Wensley Engineering

Jim Willis, MeadWestvaco Corp

Appendix A. Terminology

Definitions

The terms used in this TIP need to be clearly defined and understood. The terms summarized below generally

correspond to those in ASTM A 380 and A 967 (1, 2).

Cleaning. This is a generic term for the removal of surface contamination from stainless steel (ASTM A380) in

order to:

• Maximize its corrosion performance;

• Prevent product contamination; and

• Achieve a desired surface appearance or finish

Cleaning covers a wide range of specific processes and procedures. The type of cleaning process to be used is

determined by the type of contamination to be removed (e.g., heavy oxides, oil, cutting fluid, welding anti-spatter spray, etc).

Pre-cleaning. The removal of contaminants from the surface of the stainless steel prior to a fabrication process or

prior to addressing issues associated with the quality of the protective passive oxide film (ASTM A 987).

Contaminants might be oil, grease, paint, etc. Light surface rusting can generally be identified and categorized as“removable by light rubbing with a pencil eraser”. Such an approach is not, however, to be regarded as a cleaning

process. Pre-cleaning is unlikely to remove heavy iron contamination of the stainless steel.

Pretreatment. Any operation to be completed prior to undertaking a given operation. (ASTM A 967)

Contamination. Non-stainless steel matter on the surface of the stainless steel (ASTM A967). It is important todistinguish between:

• Metallic contamination: e.g. iron that can be removed by pickling, by passivation or by some pre-cleaningtreatments;




• Non-metallic and organic contaminants (e.g., soil, paint or grease) that will not necessarily be efficiently (if

at all) removed by pickling and passivation and may in fact interfere with these processes; and

• Thickened oxides of the stainless steel (e.g., oxides from thermal exposures).

Pickling and Descaling. Terms often interchanged, incorrectly, but including several distinctly different operations

(ASTM A380).

Descaling is the removal of heavy oxides, generally tightly adherent to the stainless steel, which result from high

temperature operations, e.g., hot forming, heat treatment, and welding. The descaling operation might include

Pickling (Chemical Descaling) or Mechanical Descaling.

Pickling (Chemical Descaling) is the removal of the heavy oxides typically using highly aggressive acid solutions,

such as nitric acid with hydrofluoric acid.

Mechanical Descaling is the removal of the heavy oxides using mechanical or abrasive methods, most typically

grinding or abrasive blasting.

Mechanical descaling and pickling are frequently used in combination.

Passivation. A term that is used for several distinctly different processes (ASTM A 380).

• Cleaning a stainless steel surface of contamination by free iron (iron not originating from the stainless steel

itself) or by iron compounds on the surface of the stainless steel. The contaminating iron is dissolved using

chemicals that do not corrode the stainless steel itself, generally but not necessarily using an oxidizing acid.(This definition of passivation applies unless otherwise indicated.)

• Chemical passivation of stainless steel with an oxidizing acid (most commonly nitric acid) to enhance and

promote the spontaneous formation of the protective passive film.

• Auto-passivation of stainless steel by exposure to an environment containing oxygen in order to form the

protective passive film characteristic of stainless steel.

Post Fabrication Cleaning. The process of cleaning after fabrication to remove all contamination associated with thefabrication process (ASTM A967). Post weld cleaning generally includes the use of various different processes in

sequence or combination.




Appendix B. Classi ficat ion of surface cleaning need of di fferent equ ipment in the pulp and paper mill

The classification given is the result of feedback from different mills. When a single value is given (e.g., “3”), all the

feedback has been either the same or essentially the same classification. Where a range is given (e.g., 2-4), the millclassifications differed by more than 2 points.

The system is described fully in the “Classification of surface cleaning need” section

Equipment Index Equipment Classification of Surfaces Process Stream

Section Equip Classification InspectionSpecial

Requirements

1-6, U (%) --

1 1 Pre Steamer 3 100 Kraft Paper

1 2 Digester (Batch) 2 100 Kraft Paper

1 2 Digester (Continuous) 3 100 Kraft Paper

1 3 Liquor Heater Shell etc 3 100 Electro polish Kraft Paper

1 3 Liquor Heater Tubing 4 100 Kraft Paper

1 4 Blow Tank 3 100 Kraft Paper

1 5 Flash Tank 3 100 Kraft Paper

1 6 Brown Stock Washers 2-5 100 Kraft Paper

1 7 Brown Stock Recovery Tanks 2 100 Kraft Paper

1 8 Chlorination Tower No Data No Data Kraft Paper

1 9 Peroxide Reactor 1 100 Ferroxyl Test Kraft Paper

1 10 Oxygen Bleach Tower 4 100 Kraft Paper

1 11Washer (After ChlorinationTower) 2 100 Kraft Paper

1 11Washer (After AlkaliExtraction) 2 100 Kraft Paper

1 11Washer (After ChlorineDioxide) 2 100 Kraft Paper

1 12 Alkali Extraction Tower No Data No Data Kraft Paper

1 13 Chlorine Dioxide Tower 4 100 Kraft Paper

1 14 Stock Chests 3 100 Kraft Paper

1 15 Centrifugal Cleaners 4 100 Kraft Paper

1 16 Screener 4 100 Kraft Paper

1 17 Head Box 1 100 Electro polish Kraft Paper

1 18Fourdrinier ComponentsSection 11 1-5 100 Kraft Paper

2 1 Black Liquor Cooler 1 100Kraft Recovery. Brown StockEvaporator

2 2 Black Liquor Storage Tank 3-U 100

Kraft Recovery. Brown Stock

Evaporator

2 3 Concentrators / Vaporizers 3-U 100Kraft Recovery. Brown StockEvaporator

2 4 Condenser 3 100Kraft Recovery. Brown StockEvaporator

2 5 Ejector 4 100Kraft Recovery. Brown StockEvaporator

2 6 Ejector after Condenser 4 100Kraft Recovery. Brown StockEvaporator

2 7 Soap Skimmer 4-U 100Kraft Recovery. Brown StockEvaporator




2 7 Soap Storage U 0

2 8Tall Oil System: See Section4 U 0

Kraft Recovery. Brown StockEvaporator

2 9 Condenser Flash Tank U 0Kraft Recovery. Brown StockEvaporator

2 10 Black liquor storage Tank 3-U 100Kraft Recovery. Brown StockEvaporator

2 11 Heavy Black Liquor Tanks 3-U 100Kraft Recovery. Brown StockEvaporator

2 12 Stripper 4-U 100Kraft Recovery. Brown StockEvaporator

2 13 Foul Oil Decant U 0Kraft Recovery. Brown StockEvaporator

3 1 Salt cake mix tank 1-4 100 Kraft Recovery: Liquor & Lime

3 2 Recovery Boiler: Structure 4 100 Kraft Recovery: Liquor & Lime

3 2Recovery Boiler: CompositeTubes 4-6 100 Kraft Recovery: Liquor & Lime

3 3 Wet Bottom 3 100 Kraft Recovery: Liquor & Lime

3 4 Main Stack 4 100 Kraft Recovery: Liquor & Lime

3 5 Scrubber 3 100 Kraft Recovery: Liquor & Lime

3 6 Main Dissolving Tank 4 (-U) 100 Kraft Recovery: Liquor & Lime3 7 Green Liquor Clarifiers 4 (-U) 100 Kraft Recovery: Liquor & Lime

3 8 Green Liquor Tank 4 (-U) 100 Kraft Recovery: Liquor & Lime

3 9 Slaker 4 (-U) 100 Kraft Recovery: Liquor & Lime

3 10 Caustizers 4 (-U) 100 Kraft Recovery: Liquor & Lime

3 11 White Liquor Clarifier 4 (-U) 100 Kraft Recovery: Liquor & Lime

3 12 White liquor storage tank 4 (-U) 100 Kraft Recovery: Liquor & Lime

3 13 Lime kiln Entry U 0 Kraft Recovery: Liquor & Lime

3 14 Kiln Chains U 0 Kraft Recovery: Liquor & Lime

3 15 Lime kiln scrubber 4-U 100 Kraft Recovery: Liquor & Lime

4 1 Reactor Shell 4 100 Tall Oil: Acidulation Process

4 1 Reactor Paddle 4 100 Tall Oil: Acidulation Process

4 2Spent acid/brine NeutralizingTank 4 100 Tall Oil: Acidulation Process

4 3 Wet Settling Tank 4 100 Tall Oil: Acidulation Process

4 4 Vibrator Screen 4 100 Tall Oil: Acidulation Process

4 5 Centrifuge Feed Tank U 0 Tall Oil: Acidulation Process

4 6 Centrifuge U 0 Tall Oil: Acidulation Process

5 1 NCG & Condensate System 2-4 100 Air Quality / Emissions System

5 2 Stripping Column 2-4 100 Air Quality / Emissions System

6 1 Digester 1 100 Mg Sulfite Processing

6 2 Blow Tank 2 100 Mg Sulfite Processing

6 3 Washers 2 100 Mg Sulfite Processing

6 4 Screens 5 100 Mg Sulfite Processing

6 5Red Liquor Tank (FromWashers) 2 100 Mg Sulfite Processing

6 6 Sulfur Burner Gas Cooler 2 100 Mg Sulfite Processing

6 7 Fortification Tower 2 100 Mg Sulfite Processing

6 8 Acid Filter Unit 2 100 Mg Sulfite Processing

6 9 Cooking Acid Storage Unit 2 100 Mg Sulfite Processing

6 10Weak Red Liquor Tank (toevaporator) 2 100 Mg Sulfite Processing




6 11 Multiple Effect Evaporators 2 100 Mg Sulfite Processing

6 12Strong Red Liquor StorageTank 2 100 Mg Sulfite Processing

6 13 Direct Contact Evaporator 2 100 Mg Sulfite Processing

6 14 MgOH2 Make Up Tank 2 100 Mg Sulfite Processing

6 15 Liquor Heater 2 100 Mg Sulfite Processing

6 16 Recovery Furnace No Data No Data Mg Sulfite Processing

6 17 Scrubber No Data No Data Mg Sulfite Processing

6 18 SO2 Absorption Unit No Data No Data Mg Sulfite Processing

6 19 Stack 4 100 Mg Sulfite Processing

7 1 Liquor tank No Data No Data Neutral Sulfite Pulping

7 2 Digester No Data No Data Neutral Sulfite Pulping

7 3 Blow Tank No Data No Data Neutral Sulfite Pulping

7 4 Live Bottom Bin No Data No Data Neutral Sulfite Pulping

7 5 Double Disc Refiners No Data No Data Neutral Sulfite Pulping

7 6Unwashed Stock StorageTank No Data No Data Neutral Sulfite Pulping

7 7 Washers No Data No Data Neutral Sulfite Pulping7 8 High Density Tank No Data No Data Neutral Sulfite Pulping

7 9 Filtrate Tanks No Data No Data Neutral Sulfite Pulping

7 10 Secondary Refiners No Data No Data Neutral Sulfite Pulping

7 11 Flow Box No Data No Data Neutral Sulfite Pulping

7 12 Machine Chest No Data No Data Neutral Sulfite Pulping

7 13 Semi Chemical Dump Chest No Data No Data Neutral Sulfite Pulping

8 1 Pre-steaming Bin U 0 High Yield Mechanical Pulping

8 2 Steaming Tube 4 100 High Yield Mechanical Pulping

8 3 Refiners 4 100 High Yield Mechanical Pulping

8 4 Separators U 0 High Yield Mechanical Pulping

8 5 Feed Chests No Data No Data High Yield Mechanical Pulping8 6 Screeners 4 100 High Yield Mechanical Pulping

8 7 Reject Chests No Data No Data High Yield Mechanical Pulping

8 8 Screw Press 4 100 High Yield Mechanical Pulping

9 1 Pulper 2-4 100 Waste Paper Recycling

9 2 Heavy Duty Cleaner 4 100 Waste Paper Recycling

9 3 Coarse Screens 4 100 Waste Paper Recycling

9 4 Primary Flotation Cells 4 100 Waste Paper Recycling

9 5 Forward Cleaners 4 100 Waste Paper Recycling

9 6 Alkali Disc Filters 4 100 Waste Paper Recycling

9 7 Bleaching Unit 1-5 100 Waste Paper Recycling

9 8 Peroxide Bleach Tower 1 100 Waste Paper Recycling

9 9 Sulfuric Acid System 4 100 Waste Paper Recycling

9 10 Fine Slot Screeners 4 100 Waste Paper Recycling

9 11 Reverse Cleaners 4 100 Waste Paper Recycling

9 12 Decker Disc Filters 4 100 Waste Paper Recycling

9 13 Screw Presses 4 100 Waste Paper Recycling

9 14 Post Floatation Cell 4 100 Waste Paper Recycling

9 15 Acid Disc Filters 4 100 Waste Paper Recycling




9 16 Sodium Hydrosulfite Unit 4 100 Waste Paper Recycling

9 17 Acid Loop 4 100 Waste Paper Recycling

9 18 Bleach Tower 4 100 Waste Paper Recycling

9 19 De-waterer 4 100 Waste Paper Recycling

10 1 Pumps 4 100 Bleach Plant Systems

10 2 Mixers 4 100 Bleach Plant Systems

10 3 C Stage Chlorination Tower No Data No Data Bleach Plant Systems

10 4D Stage Chlorine DioxideTower No Data No Data Bleach Plant Systems

10 5 H Stage Hypo Tower No Data No Data Bleach Plant Systems

10 6E Stage Caustic ExtractionTower No Data No Data Bleach Plant Systems

10 7EO Stage Caustic OxygenTower No Data No Data Bleach Plant Systems

10 8 P Stage Peroxide Tower No Data No Data Bleach Plant Systems

10 9 Z Stage Ozone Tower No Data No Data Bleach Plant Systems

10 10 O Stage Oxygen Tower No Data No Data Bleach Plant Systems

10 11 Washer 2 100 Bleach Plant Systems

11 1 Stock Approach System 2 100 Paper Machine

11 2 Head box 1 100 Electro polish Paper Machine

11 3 Former 1 100 Paper Machine

11 4 Press 4 100 Paper Machine

11 5 Roll Journals U 0 Paper Machine

11 6 Dryer No Data No Data Paper Machine

11 7 Calender 4 100 Paper Machine

11 8 Coater No Data No Data Paper Machine

11 9 Size Press 5 100 Paper Machine

11 10 Reel No Data No Data Paper Machine

11 11 White Water Shower & Piping U 0 Paper Machine

11 12 White Water Return U 0 Paper Machine




Appendix C. Procedures and techniques

Procedures are based on general working practices (9) and the ASTM standards A 380 and A 967 (1, 2) that include

recommended practices and safety precautions for cleaning, de-scaling, and passivation of stainless steel parts.

The overall cleaning procedures can be summarized as shown in Table 7. The details of the different stages are as

follows:

• Safety precautions: Ensure all staff involved in the operations are familiar with the applicable MSDS's,

general safety precautions, and Health and Safety requirements;

• Safety equipment: Ensure that all appropriate safety equipment is available and that the staff is trained in its

use and the necessity for its use;

• Working area: Ensure working area is safe and, preferably, dedicated to post fabrication cleaning. Guard

against issues including noise, overspray, etc;

• Pre-cleaning: Pre-clean the surface to remove heavy soiling, such as oil, grease, paint, ink from plate

identification or lay out markings, imbedded dirt, etc., using a cleaner appropriate for removal of heavycontamination. Apply by spraying, by immersion, by recirculation in the case of a piping system (using an

acid-resistant pump for acidic cleaners), or by brushing or swabbing. Soak the surfaces until they appear

clean, typically about 15-20 minutes, or as per product directions. If the soiling is light, e.g., fingerprints,

use an appropriate cleaner following the principles described above: solvent or detergent washing may be

appropriate.

• Rinse: Thoroughly rinse off the active chemicals, ideally by using a high-pressure (> 1600 psi / 110 bars pressure) steam washer. De-ionized water is preferred, particularly if the rinse is the final operation. Drain

and dry to full dryness if this is a final operation or if it will be some time (e.g., more than one day) before

subsequent operations are undertaken. Do not let the chemical treatment or the rinse water puddle and dryout on the material.

• Mechanical cleaning Blast cleaning: select appropriate grit size/type consistent with working instructions and. blast with clean

dry uncontaminated grit suitable for stainless steel in order to remove welding slag, heat tint, etc. Ensure

the air is dry and oil-free.Grinding: When grinding, fine grinding, polishing, etc, select grit size, type, grit sequence, etc. relative to

technique, instructions and requirements. The final grit size should be as fine as practical, particularly when

further chemical treatment is not to be undertaken.

Brushing: Preferably use a clean bristle brush to remove the blasting debris. The use of a dry and oil free air blast has been used historically, being aware that the dust can easily settle back onto the surface being

cleaned (and adjacent surfaces). Air blasting may contravene health and safety regulations.

• Pickling: Ensure the component itself is below about 95oF / 35oC. Apply the pickling acid by spraying,

brushing, dipping or pumping. Visually ensure full coverage (color contrast of the acid) and do not allowthe acid to dry out or cake. The temperature and concentration of the pickling solution should be consistent

with published specifications. The pickling acid can be left to react for between typically 30 min to 4 hours

depending on steel grade and temperature. The solution should be thoroughly rinsed off with a high-

pressure steam wash.

• Inspection: All surfaces should be inspected according to the requirements of the technical specification

and the purchase order. Inspection might include, for example, visual inspection and checking all surfacesfor residual iron contamination using the swab test as detailed in ASTM A 967. Should the results of the

inspection not be satisfactory, preceding stages should be repeated, possibly with adjustments in practice as

required.• Passivation: mineral acid passivation solutions remove the remaining free iron from the stainless steel

surface provided it is not heavily embedded, but do not attack the stainless steel at all. Some, but not all,

passivation solutions also enhance the formation of the passive film. Spray, brush or swab the passivationsolution to the surface and leave it to react, usually about 15-20 minutes, i.e., until the surface looks clean,

unless otherwise directed by specific instructions for a particular product.

• Neutralize rinse waters: Collect all the acidic rinse water in a holding tank and neutralize it using

commercial neutralizers or slaked lime. Allow time for the water to settle and check its pH. The resulting




clear water may be let out into the sewage system or recycled. The resulting sludge should be sent for waste

disposal. All these activities are to be in strict accordance with local wastewater regulations.

• Acid wash for iron removal (see Passivation.)

• Prepare for subsequent operations: The components should be prepared for subsequent operation, e.g.,

wrapping for shipping, as appropriate.

Appendix D. Descript ion of the inspection tests

The objective of this section is to highlight possible uses and shortcomings of the various tests. It does not purport to

give definitive specifications of the tests or the test methods. Full details of each test are given in the appropriate

specifications.

Visual examination

The primary objective of visual inspection is to qualitatively determine the consistency, continuity, and aesthetic

characteristics of the surface.

The surface is examined with naked eye, or at low magnification (×4-5), in good natural light or artificial light. The

illumination and viewing angles can be varied from direct (~90o) to flat (~10-15o) to accentuate different features.

The characteristics that are being considered include geometric/shape effects or color/shading contrasts, as theseeffects might indicate inconsistent or incomplete cleaning. A bore scope should be considered when appropriate.

Acceptance criteria generally include the absence of visible deleterious components or effects.

Water break test

The primary objective of the water break test is to highlight retained oils or greases. A secondary objective might be

to highlight general dirt/dust on surface.

The unit to be inspected is either briefly dipped in a clean water bath (and then removed for inspection) or sprayed

with water. The water should preferably be de-ionized. Greases, oils, etc., will show distinct markings or patterns on

the stainless steel rather than the typical uniformly wetted surface or beaded water on the surface. Retained postfabrication cleaning chemicals will show as unusually low pH of the water. The pH will generally be in the range

~6.5<pH<~7.5; this should be checked locally. Grinding dust, etc., will show as particles in the water globules. Care

should be taken to ensure the surface is fully dried after testing.

Acceptance criteria are generally absence of any evidence of greases or other contaminants on the surfaces

Moisture test

The primary objective of the moisture test is to reveal the presence of free iron contamination on the surface of the

stainless steel. A secondary objective might be to highlight general cleanliness.

Unit to be inspected is sprayed or dipped with water, and then removed but not dried. The component is left

overnight, with the surfaces essentially horizontal, in a warm environment. It may be necessary to leave it for longer in cooler environment. Iron contamination will show as red rust on the surface. General cleanliness may show ase.g., dust in the water droplets. Post fabrication cleaning chemical residues may show as abnormally low pH in

water remaining on the surface.

The acceptance criteria are the absence of red rust developing on the surface and the absence of any other visible

contaminants on the surfaces




Wipe test

The primary objective of the wipe test is to demonstrate the absence or presence of hydrocarbon contamination on

smooth surfaces. A secondary objective might be to show other surface debris.

The test involves wiping the surface with clean, white lint-free cloth and then examining the cloth for discoloration.

Hydrocarbons will tend to be oily with a smeared trace on the cloth. General debris will tend to be powdery and dry.

It is occasionally appropriate to use a colored or black cloth to detect contaminants that would not give sharpcontrast on a white cloth, e.g., a white powder.

The acceptance criterion is normally no evidence of contaminants on the cloth.

Cotton ball test

The primary objective of this test is to check the smoothness of a surface. A secondary objective might be to check

the cleanliness of the surface

A clean ball of cotton wool is gently wiped across the surface in question. This test is particularly appropriate to

smooth surfaces that have been polished.

The acceptance criterion is generally the absence of any fibers retained on the surface or evidence of contaminationon the cotton ball.

Ferroxyl test

The objective of the ferroxyl test is to show the presence of free iron contamination on the surface of the stainless

steel.

A solution of nitric acid and potassium ferricynanide is applied to the surface using non-ferrous equipment. Blue

staining (appearing almost immediately) indicates iron contamination. The solution should be either removed from

the stainless steel as soon as possible or quickly neutralized (1). This is a highly sensitive test suitable for use by“qualified”, experienced personnel only. Its sensitivity is excessive for most applications in the pulp and paper

industry although it is an important test for hydrogen peroxide service.

The acceptance criterion is no evidence of free iron.

Copper sulfate test

The primary objective of this test is to show presence of free iron / carbon steel contamination on the surface.

A solution of copper sulfate in sulfuric acid is swabbed on surface. The surface is rinsed and air-dried after required

exposure time. Copper “red” deposits on surface indicate presence of iron ( 1). This tool is a very sensitive testsuitable for use by “qualified”, experienced personnel only. The test should only be used on 300 series and duplex

grades of stainless steel and on the higher grades in the 200 and 400 series alloys.

The acceptance criterion is no evidence of free iron.

Solvent test

The primary objective of the solvent test is to find hydrocarbon contamination.

The surface to be inspected can be either swabbed with a white lint-free cloth moistened with degreaser

(hydrocarbons typically show as discoloration) or sluiced down with degreaser, draining the solvent to a low point.A surface is considered clean if there is no evidence of contaminants on the cloth or no discoloration of the drained

down solvent or tidemarks on the essentially horizontal surface after evaporation of the solvent.




Black light testing

The objective of black light testing is to determine the efficiency and effectiveness of cleaning or of a cleaningsystem.

Coat or spray all relevant surfaces with riboflavin and then run the wash system (e.g., spray ball) as it would in practice. All surfaces are then checked for retained riboflavin with ultraviolet “black” light. Any surface fluorescing

green has not been cleaned.

The acceptance criterion is that there should be no evidence of fluorescence on any surface.

Roughness testing

The primary objective of this test is to determine the roughness ( Ra) of the surface.

Either portable or solidly mounted equipment can be used to measure the roughness, noting the direction of

measurement. The numerical output is compared to requirements.

The acceptance criterion is that the absolute roughness values obtained compare to required values.

Reflectivity testing

The primary objective of reflectivity testing is the quantitative measurement of reflectance, distinctness of image

and/or of gloss.

This is an extremely sensitive test, applicable only to highly polished surfaces. Its use is limited to dedicated,specialist equipment operated by trained operators and interpreters. Its use is not normally appropriate in pulp and

paper applications.

The acceptance criterion is to compare the measured absolute numeric values to the required specification values.

Contrast tests

The primary objective of contrast tests is to check consistency of a finish.

This test is generally, but not necessarily, a qualitative comparison by visual examination. A sample of the agreed

surface condition is prepared and retained in good condition. Production pieces are then compared with the retained sample looking for consistency with time. Some national and international contrast tests exist, e.g., that for the

quality of grit blasting (12)

The acceptance criterion is that the sample is either qualitatively equal to or better than the agreed comparator or is

quantitatively satisfactory relative to agreed tests.

Tactile testing

The primary objective of tactile testing is to look for the smoothness, continuity and consistency of the surface.

The finger can feel small geometric discontinuities very efficiently and this test is often used in conjunction with

visual testing. It is unlikely any surface will be 100% tested. Be aware that oils and greases will be transferred to thesurface of the stainless steel. This may or may not be significant. Be aware there may also be health and safety

implications with (e.g.) sharp edges.

There are not really any acceptance criteria as such for this test. It is indicative only. The results are not to be taken

as the absolute basis for acceptance or rejection.




Appendix E. Cor rective actions

Inevitably there are some potential problems associated with post fabrication cleaning. Some of the more common

suggested corrective actions are shown in Table E1 (1, 8, 12).

Table E1. Some surface defects associated with post fabrication cleaning, their common causes andpotential corrective actions

DefectSource

Surface defect Caused by or associated with Suggested corrective actions

Blasting

Distortion - Stresses introduced byblasting

- Lower the blast pressure- Finer blast medium- (Note: some distortion of

lighter sections isinevitable)

Inadequatecleaning/Retained oxide

- Poor coverage- Low pressure- Grit too fine- Blasting angle too acute

- Re-blast (Better coverage

or coarser grit or higher pressure)

- Pickle

Rust spots appear (typically after afew days)

- Iron contamination due(generally) to the grit beingcontaminated

- Iron grit being used

- Decontaminate the workarea

- Check for goodsegregation

- Change out the grit and re-blast

- Pickle- Passivate if mild problem

Oxides reappear

after a short time.

- Oxide has been polished

rather than removed.

- Grind

- Blast- Pickle

Rusty stainsappear

- Steel brushes used- Contaminated brushes- Initial surface contaminated

with iron

- Decontaminate the area- Check for good

segregation- Blast- Grind- Pickle- Passivate if a mild problem

Fabrication

Rust lines(single lines,probably straight)

- Tooling marks (bending,cutting, spinning etc

- Grind- Pickle- (Passivation: probably not

appropriate except withvery light contamination)

Rust Stains(possibly fanshaped area)

- Overspray (from adjacentgrinding or air arc gougingoperations)

- Grind- Pickle- (Passivation: probably not

appropriate except withvery light contamination)




Grinding

Burnt Surface - Excessive grinding pressure- Moving the grinder over the

surface too slowly- Dwelling too long in one

location being ground

- Regrind- Pickle- (Consider any

metallurgical implications)

Coarse Finish-

Grit too coarse- Alumina grit used

-

Use finer grit finish- Consider using carbide grit

Earlier/previousgrinding still visible

- Not removing earlier grindingoperations

- Change through 90o

whenchanging grinding gritsizes

Rust Streaksappear (maybeafter a few days)

- Iron contamination through(generally) the grinding disc

- Decontaminate the workarea

- Segregate steelprocessing

- Change wheel and regrind- Pickle- Passivate if only slight

problem

Handling Rust Stains(Parallel sidedbands)

- Lifting chains- Iron contaminated or dirty fiber

slings

- Grind- Pickle- (Passivation: appropriate

only with very lightcontamination)

Mechanical Polish ing

Carry over of polishing marks

- Not changing polishing directionbetween finishing media.

- Re-polish from 1 mediafiner than that causing thecarry over, change thepolishing directions by 90°between grit sizes.

Excessive

roughness

- Carry over of polishing marks-

Finishing media too coarse

- Repolish

Pickling

Discoloration - Contaminated rinse water - Decontaminate / Re-passivate

- Use de-ionized water especially for exactingrequirements

- Rinse with high pressurewater

Discoloration - Poor rinsing - Remove spots withcleaning agent

- Final rinse with de-ionizedwater

Discoloration-

Dried on pickling products- Pickling product residues (e.g.,

in crevices)

-

High pressure water jetrinse and re-pickle

Discoloration - Surface contaminants - Pickle- Passivate if mild

Discoloration - Insufficient cleaning - Remove spots

Residual Oxides - Not pickled for long enough- Wrong pickling solution selected

for grade of stainless

- Mechanical pre-treatment- Re-pickle




- Highly adherent welding slag

Rough Surface - Over-pickling- Intergranular attack

- Mechanical treatment, re-pickle

- Mechanical polishing

Smuts(grey/black

shadows on thepickled surface)

- Poor pickling technique- High metal ion concentration in

the pickling bath

- Re-pickle, keep acidsfresh

- Passivate with strongoxidant (HNO3 or peroxide

solutions)

Uneven finish(shading)

- Organic/hydrocarboncontamination

- Uneven application of picklingsolutions

- Sensitive surface- Intergranular corrosion

- Degrease, re-pickle- Re-pickle- Mechanical polishing

improves situation onsensitive surfaces andsurfaces withintercrystalline pickling

Water Stains - Contaminated rinse water - Rinse water puddles- Dust in rinse water or on surface

of stainless

- Re-pickle if bad case- Re-rinse with clean water

Weld showthrough (fromother side)

- HAZ of weld on other side of sheet

- None possible for existingunit (is a welding issue)

- Follow-on units: avoid thewelding, reduce the heatinput

Passivation

Ineffectivedraining (leadingto stains)

- Poor drainage or access points- Poor lifting orientation

- Resolve drainage or lifting- Use peroxide type

solutions

Stains - Incomplete acid removal- Final rinse water not pure

- Re-pickle may benecessary

- Re-passivate plus

improved wash downwater (de-ionized)- Re-passivate with

peroxide




Appendix F. Overview of U.S safety and environmental compliance requi rements

The objective of this section is to give an overview of the applicable regulations, focusing on small facilities.

Regulations do change so it is advisable to check for updates.

Summary

Chemical reactions involved in passivation and pickling are the same, whether brushing on a gel or immersing in alarge tank.

Hazard is dependent on the type of chemical and how concentrated it is. Most passivation and pickling solutions are

dilute.

OSHA Hazard Communication Standard (29 CFR 1910.1200) is valid for all sizes of companies.

Very large quantities of hazardous substances on a site need to be reported to the local fire brigade, local emergency planning committee, State emergency response committee and Department of Homeland Security.

To facilitate, small businesses are often exempt from Federal environmental regulations controlling larger businesses. States may be harder, so always check with local authorities.

On-site safety

• A Hazard Communication Plan is needed for all size companies.

• Warning labels are needed - on the container or posted at the working area.

• Identification labels must not be removed.

• A new label is required when transferring acid from one container to another.

• MSDS (Material Safety Data Sheet) must be easily available in each building.

• Training and documentation of training.

NFPA ratings

The NFPA system is increasingly popular, but not required. The NFPA rating for chemicals and mixtures are oftenstated in the Material Safety Data Sheet (MSDS). NFPA ratings are rather insensitive to acid concentration; there are

only minor differences between the NFPA ratings of the different pickling mixtures.

Health - BlueFlammability - Red

Reactivity - Yellow

Special - White4 = Danger - May be Fatal

3 = Warning - Corrosive, Toxic

2 = Warning - Inhalation

1 = Caution - Irritation0 = No unusual Hazard

Small facility – acids

Federal environmental legislation assumes a small facility uses small quantities of acids and has eased up a number

of requirements. State legislation may be harder.

• Acid storage secondary containment is not required according to Federal rules.

• Used acid or “spent pickle liquor” has to be collected for treatment.

• Used acid can be stored in containers or tanks. A secondary containment is not required.




• Keep on-site quantities low to avoid triggering the Emergency Planning and Community- Right-to-Know

rules, see tables F.1 and F.2.

Small facility – water

• A general storm water permit is needed.

•

Acidic rinse water has to be collected.• Store in containers or a tank and send out for treatment.

or,

• Neutralize acidic rinse water on site and discharge to the POTW after treatment. For this, an Industrial User

permit is needed.

• Nitrates dissolved from the nitric acid remains in the water after neutralization and if you neutralize

yourself you may have to report nitrates.

Small facility – waste

• Obtain an EPA ID #

•

A small facility is “Conditionally exempt” from the hazardous waste rules if it is generating less than 100kg or 220 lbs per calendar month.

• Make sure you are below the limit by keeping count.

• If episodically more in one month, the next step up - Small Quantity Generator - rules must be followed for

waste generated that month.

Conditionally exempt – waste storage

• Collect the hazardous waste, label it, and store in a safe manner and send it out over time. There is no timelimit.

• You are allowed to store 1,000 kg or 2,200 lbs on site.

• A Conditionally Exempt Small Quantity or an Interim (Field) Generator does not need a secondary

containment.

•

You must store in containers or tanks.• A container can be a 55-gallon drum, provided it does not leak, a tanker truck, and a small bucket.

• Send wastes to a federally approved waste treatment facility.

Shipping requirements for acids, hydrogen peroxide, and waste

• Risk Management = Classification of the hazardous material

• Label with the followingo Proper shipping name, usually found in the MSDS.

o Hazard Class: 8 corrosive

o Packaging Group IIo United Nation (UN) number, usually found in the MSDS

o ERG, Emergency Rescue Group number, usually found in the MSDS

• Hazardous waste manifest• DOT placards on carrier - symbols

Department of Homeland Security requirements

DHS requires hydrogen peroxide above 35% concentration and in quantities above 400 lbs or 200 kg to be initially

reported.

DHS reporting requirements for acids are the same as for Emergency Planning and Community Right to know asdescribed in Table F1.




Table F.1. Overview of chemical hazard classifications

Cleaning or passivationmixture

Mild picklingmixture

Mediumpicklingmixture

Aggressivepicklingmixture

Enhancedpassivationmixture

Neutralizer

Active

ingredients

Phosphoric

acid

Hydrofluoric

acidSulfuric acidNitric acids

Hydrofluoric

acidSulfuric acidNitric acids

Hydrofluoric

acidNitric acid

Hydrogen

peroxide

Sodium

hydroxide

Classification Corrosive Corrosive CorrosiveToxic

CorrosiveToxic

Oxidizing Corrosive

OSHA MSDS MSDS MSDS MSDS MSDS MSDS

NFPA Rating Blue 3Red 0Yellow 0

Blue 3Red 0Yellow 0

Blue 3Red 0Yellow 0

Blue 3Red 0Yellow 1

White Oxy Blue 3Red 0Yellow 1

EPCRAEmergencyPlanning andRight to

know

Report to Firebrigade, LECand SECbased on the

contents andconcentrationsreported in theMSDS







Report to Fibrigade, LEand SECbased on th

contents anconcentratioreported in tMSDS

1. First timeon-sitenotification

Not needed Typicallyabove 10,000lbs

Typicallyabove 2,000lbs


Not needed Not needed

2. Spillreporting





Only if above52%concentration


3. InventoryTier II

Typicallyabove 50,000

lbs


lbs


lbs


lbs

Only if above52%

concentration


lbs4. Dep. of HomelandSecurity





Only if above35%concentration


Wastes toreport

Hazardous:K062 (Spentpickling liquor and Picklingsludge)

Acidic rinsewater


Acidic rinsewater Nitrates





Only water Hazardous:D002D007




Table F.2. Typical facility size influence on regulations

Small Field Medium Large

Water permits Storm water POTW Industrialuser

--POTW Industrialuser

Storm water POTW Industrialuser

Storm water POTW IndustrialUser

Own treatmentfacility

Air permit Exempt Exempt Evaluate Title V

Secondarycontainment

Exempt Interim status,exempt

Secondarycontainmentrequired

Secondarycontainmentrequired

Waste Obtain an EPAID#Check thatcontractor hasEPA ID#

Obtain an EPAID#Check thatcontractor hasEPA ID#



HazardousWaste

Generator

Conditionallyexempt

Below 100 kg or 220 lbs per calendar month

Interim Status SmallBetween 220

and 2,200lbs per calendar month

Large Above 1,000 kg

or 2,200 lbs per calendar month

Waste on-siteaccumulation

Time – No limitVolume – 1,000kg or 2,200 lbsand1 kg or 2.2 lbsacute waste, e.g.K062 (spentpickle liquor)

Time – 180 daysor 270 days if shipped morethan 200 milesVolume – 6,000kg or 13,200 lbs

Time – 90 daysVolume – Nolimit

Wastes toreport

Exempt if K062(spent pickle

liquor) is below 1kg or 2.2 lbs per month.Report K062 if above

Either as Smallor Medium

K062 (spentpickle liquor)

Nitrates

K062 (spentpickle liquor)

Nitrates

EPCRA

TRI ToxicReleaseInventoryReport

Exempt if lessthan 10employees

More than 10employeesListed SIC or NAICS codeUsing more than10,000 lbs per year



EmergencyPlanningProgram

Exempt Exempt Exempt CAA 112(r)

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