surface finish basics for stainless steel rev 1[1]

8/7/2019 Surface Finish Basics for Stainless Steel Rev 1[1]

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Impact of Finish Concerns onEquipment Design

Can it be drained and cleaned? Can it be polished and inspected?

Joins Welds

Elastomeric joints


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ASME BPE-2005

Key Standard for Pharma Surface Finish SF Section

Table SF-1 through SF-9 for acceptancecriteria


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316L Stainless Steel

High corrosion resistance Widely accepted for pharma applications

Properties are understood

L = Low carbon for better welding Good value

Substitutes

AL6XN Hastelloy C

Plastics


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Ra What It Is

Roughness Average An average of absolute values of the profile height deviations

Measured in micrometers m and microinches in

Common industry call outs are 15Ra, 20Ra Unless noted are in microinches

Profilometers

Procedures for Measurement


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Polishing Nomenclature

Mill15 Ra Max240SFF415 MaxPD

32 Ra Max15 Ra Max240SFF415 MaxPM

32 Ra Max20 Ra Max180SFF120 MaxPL

Mill20 Ra Max180SFF120 MaxPC

32 Ra Max32 Ra Max150N/A32 Max7

32 Ra MaxMill150N/A32 Max5

Mill32 Ra Max150SFF132 Max3

MillMill>150N/A>641

OD FinishID FinishGritBPERaPolishing

Code


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Achieving the Desired SurfaceFinish

Materials Polish

Welding Passivation

Electropolish


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Choice of Materials

Traceability Wrought vs. Cast


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Machining

20 Ra finishes now being achieved Require machines with higher speeds and

greater accuracy

Requires the very latest in machine tool and

bit technology

Eliminates potential for residual abrasives,smearing and overworking of surface


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Polishing

Tools of the trade Automatic Polishing

Machines

Manual Pneumatic Air

Guns

Abrasive Materials

Various grits, generally

aluminum oxide Scotch-Brite

Buffing pads and rouge


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Manual PolishingMore Art than Science


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Welding

Proper Materials Proper Procedures

Certified Manual Welders

Weld logs


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Orbital Welding Modern orbital-welding systems offer

computer controls that store welding

schedules in memory. The skills of thecertified welder are thus built into thesystem, enabling the production of identical

welds.


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Heat Affected Zone

Discolored area near weld Surface is modified

Increased potential for corrosion

Need to passivate


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Reasons for Passivating Reasons for Passivating

Increase corrosion resistance of fabricated parts

Removal of weld coloration

Restoration of protective oxide layer Especially in weld areas

What It Does Per ASTM A380, passivation is theremoval of iron compounds from the surface of stainlesssteel by means of a chemical dissolution, typically by atreatment with an acid solution that does not significantly

affect the stainless steel itself. By removing the free ironfrom the surface, a potential corrosion site is eliminated

How Its Done Typically done by dipping the part

into an acidic bath or pumping fluid through system.


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What Passivation Does Per ASTM A380, passivation is the removal of iron

compounds from the surface of stainless steel by means of

a chemical dissolution, typically by a treatment with anacid solution that does not significantly affect the stainlesssteel itself. By removing the free iron from the surface, apotential corrosion site is eliminated

Produces a chemically inactive surface condition obtainedby oxidation of the metal surface

Enriches the chromium and depletes the iron at the metalsurface

Produces a chromium oxide film ranging from 5 50

Angstroms thick (20-30 typical)


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How Passivation Is Done

Exposing surface to acid Nitric, Phosphoric or Citric/Ammonium Citrate

Steps in Passivation

Detergent Pre-Wash

Water Rinse

Acid Wash (Passivating Step)

Final Water Rinse

Ferroxyl Test or (water, humidity or coppersulfate)


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Reasons for Electropolishing

Cleaning Improved surface finish

Improved inspectability

Improved corrosion resistance


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What Electropolishing Does

Removes debris Removes smeared material

Smooths the surface by removing peaks

Passivates the surface by enriching oxygen


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Rouge

What It Is

Typical in Hot WFI

Systems Benign Influence on

Surface

Rarely outside of purewater systems


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Possible Causes of Rouge

Impurities

Ferrite

Impingement

Damage to Passivated

Layer


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Steps to Reduce Rouge

Careful and thorough passivation

Use of wrought materials to lower ferrite


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Specifying for a Good SurfaceFinish

Assure the right material Heat certs

Require the Appropriate Mechanical Polish

Surface Mapping or COCs

Select the Welding Technique

Orbital or Certified Welder Passivation or Electropolish


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Evaluating Surface Finish

Profilometer Visual

Boroscope

Wide field optical microscope

Scanning Electron Microscopy

Electron Spectroscopy Augur Electrospectroscopy


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Documentation

Assures That the Vendor Did What He SaidHe Would

Key for Smooth Validation

More Is Generally Better

On-Line Accessibility through Heat No.


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The Goal

No Corrosion Proper Draining and Cleaning

Simple Validation

Within Budget

surface finish basics for stainless steel rev 1[1]

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