creating the plant pipe code

8/6/2019 Creating the Plant Pipe Code

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Creating the Plant Pipe Code

W.N. Weaver, PE

1. INTRODUCTION

Pipes codes are used to standardize piping practices in a facility, to ensure each fluid is

conveyed in the appropriate materials, to control piping costs and to ensure plant safety.There are multiple pipe codes in use in the various industries involved with pipe; some

are listed below:

ASME BPE

ASME B31

For the pharmaceutical industry

Pressure piping

B31.1 Power PipingB31.2 Fuel Gas Piping

B31.3 Process Piping

API

B31.4 Liquid Hydrocarbon Transmission Pipelines

B31.5 Refrigerant PipingB31.8 Natural Gas Transmission Pipelines

B31.9 Building Services

Piping in the Petroleum Industries

ASHRAEAWWA

Refrigerant pipingAmerican Water Works Associations water piping

Local governments Potable water

Local governments Waste waterLocal governments Storm water

Hydraulic systems Tubing and piping for high pressure fluid power systems

NFPANFPA

Sprinkler pipingExtinguishing agent piping

Creating proper pipe codes for your facility is generally a combined effort between

engineering, operations and maintenance. Where available piping, corrosion and welding

engineers should be included in the design group.

It is not necessary to start the creation process with a blank sheet of paper; starting from

an existing national code simplifies the process and gives everyone a view of what the

finished product should look like and contain.Before we go further let us see why we even need a pipe code. Its generally easier to

produce an appropriate document if we understand the reason we need the document inthe first place.

2. WHY HAVE A PIPE CODE?

Most process plants have pipe codes in place which are used for bidding, construction,

new design planning, and repairs. Several points will indicate some of the benefits of

internal pipe codes.

2008 W.N. Weaver, PE Page 2 of 19


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Pressure safety

Ensures proper wall thickness, connection types and gasketing to hold the

required pressure

Consistency of connection types

Ensures proper joint efficiencies, gaskets and flange types to maintain designconditions

Consistency in materials of construction for specific fluids

Ensures corrosion is controlled

Pre use testing of new and or repaired pipe lines

Provides standardized testing for all pipe codes

Proper gasket materials selection

Ensures gaskets reflect corrosion research and pressure requirements

Proper structural support for pipe lines

Provides pipe span details for each pipe size and schedule Control of fugitive emissions from the piping system

Reduces fugitive emissions by reducing leaks from improperly selectedconnections

Reduction or elimination of contamination of raw materials and products

Reduces corrosion contamination by ensuring proper materials for each fluid

Reduction in leakage which results in money saved in raw materials and finishedproduct, reduces environmental problems, reduces fire and injury hazards

Maximizes control of leakage by ensuring proper gaskets and joint types

Some cities and counties have had individual disaster experiences, which have caused

them to institute pipe codes for specific materials within their political jurisdictions.These may well be more restrictive than the recognized national codes.

Certain areas of the country exposed to hazards specific to their locations have added

requirements to piping systems which, are more restrictive than those in other areas. Asan example you would expect California to have more requirements for pipe supports on

hazardous materials than non earthquake prone areas.

Individual facility pipe codes can generally be more restrictive than nationally recognizedcodes. Great care and consultation with the company legal and insurance departments are

called for if the developed pipe code is less restrictive than the national standard.

3. WHY CREATE A PLANT PIPE CODE?

Why not just use an existing nationally recognized code? Lets look at various materials

in pipes and see if we can find justification for facility specific pipe codes.

Compressed Air

Over the years I have seen or installed compressed air piping systems using the followingtypes of pipe:

Carbon steel, schedules 40 and 80

Stainless steel, schedules 5, 10, 20 and 40 using 304 and 316

Copper, K, L and M



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Copper pipe in .065 inch wall and schedule 40

Galvanized steel

PVC

AluminumWhich is the correct one for your facility?

Common to almost all facilities is Potable Water (City Water and Well Water in some

companies)

Types of pipe encountered in use

Carbon steel

Stainless steel, schedules 5, 10, 20 and 40 using 304 and 316Copper, K, L and M

Galvanized steel

PVC, schedules 40 and 80

CPVCGlass

Fiber glassCast iron

Cement lined steel

Rubber lined steel

From these two examples it is obvious there are multiple codes for some fluids. More

importantly each of these codes does the job and is considered as a correct application for

the fluid by someone.

4. WHAT DOES THE PIPE CODE ACCOMPLISH?

A fully developed pipe code provides the following:

Allowable design pressures

Allowable temperatures

Acceptable selection of materials of construction

Pipe wall schedule verses fluid pressure

Acceptable valve types

Connections to be used for the pipe: welded, flanged, threaded, etc.

Branch connection table

Bolting for flanges

Acceptable gasket materials

Reinforcing requirements (reinforcing pads)

Surface protection required

Acceptable insulation

Heat Tracing

Heat or cooling jacketing

Allowable unsupported spans

Accepted methods of fabrication of the pipe



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It is not necessary that all pipe codes contain all of the above items, later well see how to

determine what is needed for your facility and how the facility can benefit by using a

home grown pipe code.

5. PIPING CONNECTION OPTIONS

Invariably pipes must be connected to other pipes, valves, instruments and equipment.

How these connections are made is critical to the longevity of the piping system and the

cost of maintenance. Additionally these connections frequently limit the allowable

pressure of the system.Piping connections need to offer some or all of the following characteristics:

Pressure tightness

Fluid tightness

Material compatibility

Temperature capability

Corrosion resistance

Connection rigidity

Connection longevity

Relative ease of use

Commonly used piping connection methods include the following:

1. Socket welded2. Butt welded

3. Threaded

4. Flanged5. Grooved

6. Soldered

7. Brazed8. Flare fittings

9. Silver soldered

10. Compression fittings

11. Adhesives

12. O ring fittings13. Sheet metal couplings (ex. Morris Coupling)

1, 2, 3, 4, and 5 are common in metal piping systems.

6, 7, 8, 9, and 10 are common in metallic tubing systems

10, 11 and 12 are generally useful in plastic piping systems12 and 13 are generally used in duct conveying systems

The acceptable connection systems for each pipe code should be included in the codes

you create.



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6. POINTS TO CONSIDER

Most pipes have several mechanical properties to be considered when being selected for aspecific task. Lets look at the two characteristics most often considered; Pressure Rating

and Allowable Temperature.

PRESSURE

Pipes have four pressures of importance.

MAXIMUM ALLOWABLE PRESSURE. Established by a nationally recognized

organization such as ASME, insurance, local political jurisdiction, or calculations

based on materials of construction structural properties.

DESIGN PRESSURE. Established by the facility pipe code, perhaps a nationally

recognized code or the facility insurance carrier. Usually an arbitrarily selected value

which meets facility needs.

OPERATING PRESSURE. Established by operational needs, the facility pipe code,or a nationally recognized code. Another arbitrarily selected value which meets

facility needs.

BURST PRESSURE. Established by the manufacturer or a national code such as

ASME / ASTM by actual testing or by calculations based on the metal alloy andtemperature.

TEMPERATURE

We also have several temperatures to consider.

DESIGN TEMPERATURE. Established by the facility pipe code, perhaps a

nationally recognized code or the facility insurance carrier. Usually an arbitrarilyselected value which meets facility needs.

OPERATING TEMPERATURE. Established by operational needs, the facility pipe

code, or a nationally recognized code. Another arbitrarily selected value which meets

facility needs. MAXIMUM USABLE TEMPERATURE. Established by the manufacturer or a

national code such as ASME / ASTM by actual testing or by calculations based on

the metal alloy.

Note that metal pipe (actually almost all pipe) has a temperature / pressure curve which

means that Design Pressure and Design Temperature must be considered together. As a

general rule metal pipe will withstand less pressure at higher temperature and in somecases at lower temperatures as well. This tells us we must know the maximum expectedOperating Temperature before we can actually select a suitable material of construction



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for the pipe. We must combine this information with the Design Pressure and potential

for corrosive attack in order to select the proper material.

This should be clearer if we look at some actual pipe ratings verses temperatures. Firstlets see what happens to the allowable stress, S, for A106 steel verses temperature. A106

is a common steel specification for pipe.

TEMPERATURE, F 150 250 350 400 500

ALLOWABLE STRESS, S, psi 12,000 11,520 11,040 10,800 10,320

TEMPERATURE, F 600 700 800 900 950

ALLOWABLE STRESS, S, psi 9,840 9,100 7,250 4,400 2,600

Note that the Allowable Stress decreases with rising temperature, this means we must

reduce the Operating Pressure as the temperature climbs, we must also reduce the Design

Pressure as the temperature rises. For some carbon steel alloys we also have a loweracceptable operating temperature. Although not simply a pressure problem some carbon

steel alloy pipes become brittle below certain temperatures. For A105 that temperature is

about 20 F.

Therefore our Design Pressure / Design Temperature numbers need to take into account

both the reduction in Allowable Stress and the increase in low temperature shocksensitivity for carbon steel pipe. Most pipe materials will experience a range of

temperatures below and above which they should not be used. Polymeric piping materials

have a relatively narrow temperature range between too brittle for use and too weak for

use because of loss of tensile strength caused by an increase in temperature.

The following shows what happens to Maximum Allowable Pressure, psig, for 2 inch

A106 Grade B schedule 40 steel pipe as the temperature rises. Reference ASME B31.1.

TEMPERATURE, F 100 200 300 400 500

ALLOWABLE PRESSURE, psi

TEMPERATURE, F

ALLOWABLE PRESSURE, psi

1,783

600

1,783

1,783

650

1,783

1,783 1,783

700 750

1,712 1545

1,783

Notice that the Allowable Pressure remains constant until we reach over 650 F. This

reflects the decrease in strength for carbon steel as the temperature rises; up to about 650

F the change in allowable stress per 100 degrees temperature rise is around -4%, at 650

the change jumps to -7.5% and continues to rise from there on.

Pipe burst strength and design pressures relate directly to allowable stress. The following

is the burst pressure for various sizes of schedule 40 wrought carbon steel pipe at

constant temperature. The decrease in burst strength is related to the decrease in hoopstrength. Allowable stress remains constant at constant temperature. Hoop strength

calculations incorporate Allowable Stress, diameter and wall thickness. This combination



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causes the burst strength to decrease as diameter increases. Burst Pressure P = 2tS/D

where t = thickness, S = Allowable Stress and D = diameter.

SIZE, INCHES 1 1 & 1 & 2

BURST PRESSURE, PSI 10,380 8,610 8,090 6,745 6,100 5,185

Were only interested in burst pressure in that it reflects on our safety factor; we would

never knowingly design or operate at or even near the burst pressure. ASME, other codes,various government agencies and insurance companies dictate how closely we may

approach the burst pressure for a piece of pipe.

Following all this verbiage we need to select our design pressures based on a variety of

physical properties; most of the time it is easier and safer to accept allowable pressures

from someone like ASME and keep our design pressures at or below these values.

7. WHAT PIPING SYSTEMS ARE INCLUDED IN THE PIPE CODES?

Generally all piping systems should be included in the plant pipe codes. These codes are

a tool for engineering, estimating, maintenance, construction and purchasing to use to

ensure proper piping installation in the plant therefore the maximum number of piping

systems should have specific codes created for them.The field of pipe codes can be broad so to limit the topic we will concentrate on standard

pipe materials and common connection approaches. Understanding the necessary steps to

be used to develop one pipe code applies to all other codes. Most process facilities have

some or all of the following piping systems in use:

Utilities

SteamCondensate

Tower Water

Compressed AirFuel Gas

Potable Water

Fuel OilWaste Water

Nitrogen

Rain Water (from building roof)Storm Water (underground)Hot Oil

Chilled Water

Brine SystemsRefrigerantVacuum

Engine Exhaust PipingDust Collection Systems

Lubricant Systems



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Process

Liquid Raw Materials (solvents, acids, caustics, other chemicals)

Finished Products

Heat Traced PipeJacketed Pipe (heating or cooling)

Pneumatic Conveying Systems

Safety SystemsSprinkler Piping

Safety Shower / Eyewash Stations

Pressure Relief Device Discharge Piping

Fire Lines

8. DEVELOPING THE CODE

A complete pipe code will contain significant information on the requirements the pipesmust meet during operation. Or stated differently, the pipe codes give us the acceptable

ranges of temperatures and pressures under which our facility has agreed a particular typeof pipe can be used. Notice that the authority in this case is our facility; it is no less an

authority than ASME or a local code and a violation of this code puts facility insurance

coverage in jeopardy. In the event of a failure of a piping system which results in lawsuits

the violation of a plant standard pipe code generally can be expected to have negativeeffects in court.

The first activities in developing the code require we establish three process related

criteria:

Corrosion Resistance For example this process requirement determines if we canuse carbon steel pipe or need a stainless alloy to resist the

effects of the fluids.

Operating Temperature This criteria separates polymeric materials from mostmetallic piping materials and is the expected normal or

maximum temperature the system will experience.

Operating Pressure This criteria with the first two provides the data necessary

to determine the required wall thickness for the pipe and isthe expected normal or maximum pressure the system will

see.

Corrosion resistance can be determined from a variety of corrosion tables (PerrysHandbook, pipe manufacturers web sites, etc.), facility chemists and historical data from

the maintenance department. In addition to normal corrosion concerns maintenance

records, industry experience and insurance records may indicate problems with threadedconnections with some raw materials, utilities or finished products.

Design Temperature is selected based on Operating Temperature plus some tolerance to

allow for system deviation from normal operating conditions. Determining the tolerance

required can be complicated and needs to incorporate consideration of items like the

following:



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Possible loss of temperature controls causing a rise in temperature

A change in reaction kinetics which could cause temperature rises.

Only a complete analysis of the system and its range of operations can lead to a

determination of the required tolerance for Design Temperature; for this reason facility

chemists, maintenance, R&D, Operations and engineering should all be involved in thiscriteria development.

Design Pressure is selected based on Operating Pressure plus some tolerance to allow for

system deviation from normal operating conditions. Determining the tolerance required

can be complicated and needs to incorporate consideration of items similar to the

following:

Possible deadheading of pumps

Possible loss of temperature controls causing a rise in pressure

A change in reaction kinetics which could cause pressure rises.

System pressurization using inert gas

Thermal expansion of some fluids

Decisions about these three items will allow us to select the pipe and establish some

boundaries within which it must operate.

9. EXAMPLE: PLANT STEAM PIPING

For our real life example let us assume that the plant has a 150 psig steam system fed

directly from the boiler through a reducing station and protected by a properly set andsized relief device.

Corrosion Potential for Steam Piping System

Operating Pressure 150 psig

Operating Temperature 365.9 F

Pipe Material Corrosion Potential Comments

Carbon Steel

304 Stainless Steel

316 Stainless Steel

LOW

NONE

NONE

INDUSTRY STANDARD

EXPENSIVE

EXPENSIVEGalvanized Steel PLATING PROBLEMS GALVANIZING MAY

FLAKE OFF UNDERCONTINOUS USE

Copper

Cast Iron

PVC

2008 W.N. Weaver, PE

NONE

LOW

NONE

VERY EXPENSIVE

DOESNT MEET SOME

CODES

ABOVE TEMPERATURE

USE LIMITS

Page 10 of 19


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From the table we can see that carbon steel is probably the least expensive choice and has

a long history in this fluid service.

From earlier data we can safely use carbon steel at 650 F, well above our OperatingTemperature.

Now all that is left is to select the applicable wall thickness, or schedule number. There

are multiple sources of allowable pressures, and calculation methods to determine

schedule numbers and burst pressures. So many sources that it sometimes becomes

difficult to select the appropriate data source. See the References section for some

additional sources.

Well use a commonly available source, the ASME table in B31.1 for A106 carbon steel

pipe. The selection of a commonly used national standard as an allowable pressure

reference usually provides adequate liability protection for the engineer. The followingtable for our 2 inch pipe gives us the data we need.

TEMPERATURE, F 100 200 300 400 500

ALLOWABLE PRESSURE, psig

TEMPERATURE, F

ALLOWABLE PRESSURE, psig

1,783

600

1,783

1,783

650

1,783

1,783 1,783

700 750

1,712 1545

1,783

We can now establish the basics for the pipe code for 150 psig steam at 365.9 F to be:

Schedule 40 Carbon Steel Pipe

10. CONNECTIONS

Each pipe code needs to tell the user what method of connection between sections of

pipe, fittings, valves, instruments and equipment is acceptable. We can look at the most

common pipe connections for our steam line with some subjective comments. All of thefollowing connections provide adequate pressure capability when properly applied.

CONNECTION Ease of

Installation

Longevity Maintenance

Concerns

Cost Structural

Integrity

THREADED Easy Fair High Low Fair

WELDED Easy Excellent None Low Excellent

FLANGED Most Involved Excellent Moderate Moderate Excellent

Properly butt welded or socket welded pipe produces joints at least as strong as the pipe.

Threaded couplings and other fittings are rated by their pressure class and produce some

concern where flexing of the pipe might occur. The table below lists pressure verses

temperature rating for 150# and 300# threaded fittings.



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Temperature, F

200

300

500

150# Class

psig

All Sizes

265

150

to 1

1785

1360

510

300# Class

psig

1& to 2

1350

1050

450

2 & to 3

910

735

385

Pipe flanges also have their own set of classes including 125, 150, 300, 400, 600, 900,

1500 and 2500 # classes. Frequently individuals make the assumption that a 150#flange is only good for 150 psig and end up spending extra dollars for heavier than

necessary flanges.

A 150# flange has the following temperature / pressure curve

TEMPERATURE

F

-20 to

100 200 300 400 500 600 650 700 800 1000

ALLOWABLE

PRESSURE, psig285 260 230 200 170 140 125 110 80 20

A second curve provides additional information necessary for pipe code creation. This

table details Allowable Pressure verses Flange Class at 300 F.

NOTES

FLANGE CLASS, #

ALLOWABLEPRESSURE, psig

150 300 400 600 900 1500 2500

230 655 875 1315 1970 3280 5470

A facility may create pipe codes allowing for multiple methods of

connection; pipe codes allowing both welding and flanges are common.

A single pipe code usually covers a range of pipe sizes and may allow for

threads on small pipe, socket weld on some pipe and flanges only above a certainsize.

A single material of construction, pipe size and schedule number may

occur in several different pipe codes having different design pressures and

temperatures. A pipe code is a Facility Tool and as such needs to be created to match the facilitys

needs and help the facility maintain piping system integrity.

Pipe flanges come in a variety of styles which need to be included in the pipe code:

Connection Type

Weld neck

Socket weld

Back up

Threaded



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Various specialty types

And several gasket face types

Flat faced

Lapped

Ring Joint

Raised face

Large male / female

Small male / female

Various specialty types

For the flange to hold the design pressure several things must be correct:

Gasket surfaces must be flat and in good condition

The proper gasket must be specified The proper bolts torqued to the proper amount must be installed

For welded joints to perform up to the design conditions the welds must be proper and the

pipe fit up correct.

For threaded fittings the threads must be clean, properly cut, have the proper pipe dope

and have the proper amount of thread engagement.

11. WHAT DO WE HAVE SO FAR?

For our steam pipe code we have the following items:

Material of Construction:

Schedule for 150 psig:

Connections:

12. WHAT IS LEFT?

Carbon Steel

Schedule 40 pipe is acceptable being rated at 1783psig at 400 F

150 # flanges or welded

(a 150# flange is acceptable for 200 psig for anoperating temperature of 400 F which gives us a 50

psi and about 40 F tolerance)300# threaded connections are good up to 280 psig(interpolated from table data to 365.9 F)

Determining the extent of the pipe code contents is influenced by the fluid contents of the

pipe, system pressure, temperature, installation environment, facility needs and available

engineering time.The following provides guidance for the remaining items which can be beneficial if

incorporated into a pipe code.



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13. VALVES Generally a code will provide a variety of acceptable valves

depending on the need. Those include gate, globe, ball, plug and

specialty valves. Generally the valve type is listed along with

acceptable model numbers and manufacturers names. Also listedare the acceptable connections for each valve type. Because of it

size the listing of acceptable valves is usually separate from the

pipe code and contains reference numbers for use on P&IDs andpiping arrangements. See the attached sample.

14. BRANCH CONNECTION TABLE A branch connection table provides details

on acceptable branch connections by size. This is generally a twoscale table with Header Size on one scale and Branch Size on the

other. Generally the options available are: Straight Tee (T),

Reducing Tee (R), Reinforced Nozzle Weld (X), Coupling (or half

coupling) welded to Header (C), Weld-O-Let (W)(see BonneyForge in Section 26), Thread-O-Let (L), or Socket-O-Let (S). This

ensures the Header and Branch maintain the pipe pressure rating.The following is a representative table.

HEADER SIZE, in.

11 &

2

2

S

S

WW

T

1 &

R

R

WT

1

R

R

T

R

T

T

The selection of how branch connections are made belongs to the facility and is

influenced by pressure, temperature, fluid and pipe sizes involved. The goal is to produce

branch connections, which maintain the pipe code pressure rating. The sample tableabove is interpreted as follows:

A Branch is connected to a 2 Header using Sock-O-Let (S)

A Branch is connected to a Header using a Reducing Tee (R)

A Branch is connected to a Header using a Tee (T)

15. BOLTING FOR FLANGES All flanges have a specified number of bolts, a

specific bolt size, a specific bolt torque value and a tightening pattern. It is critical

that these values are followed in order to obtain the stated flange pressure rating.

16. ACCEPTABLE GASKET MATERIALS Gaskets become a critical part of the

piping system in that they must contain pressure and avoid

degrading the fluid in the pipe. This degradation can take the formof dissolved gasket material or mechanical failure resulting in

particulate in the fluid. Gasket failure creates hazardous situations


BRA

NCH

SIZE,

in.


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including toxic fumes, flammable vapor or liquid releases and

personnel injury.

Gasket selection should be handled by the same team that

established materials of construction for the piping system.Each flange has a gasket surface, which must be protected

from scratches and other damage. Gasket materials have a specific

bolt torque requirement, which may not be the same as theminimum for the flange itself. This torque value is established by

the gasket manufacturer and is designed to prevent gasket blow out

at the rated allowable pressure of the flange. A proper pipe code

will contain gasket types with required torque values and thicknessfor each pipe size, temperature and pressure.

17. REINFORCING REQUIREMENTS (reinforcing pads) Are generally a part of the

Header Branch table and are established by specific calculationsor data from a reference source such as ASME.

18. ALLOWABLE UNSUPPORTED SPANS Whether the pipe is suspended

overhead, attached to a wall or lying on sleepers on the ground

there is a maximum allowable unsupported span for each size,

schedule and material of construction of pipe. Spans should bedetermined based on the weight of the pipe, any insulation and the

contents of the pipe. Spans for pipe are usually limited to the

standards of structural steel or approximately 1/360th

of the span.For a 10 foot span that means the pipe is allowed to sag

approximately 0.33 inches. Allowable sag is a facility decisionrather than a national standard.When specifying the allowable span remember that small pipe also

requires support and generally more frequently than large diameter

pipe. A sch 80 pipe allowable span is about 100 whereas asch 80 1.5 pipe allowable span is about 170. When the pipe

supports are spaced for small diameter pipe then most larger

diameter pipes are adequately supported.

Calculations of sag and span are based on material of construction,wall thickness, pipe outside diameter, moment of inertia and

modulus of elasticity using standard beam formulas from the

structural steel handbooks.An example table of allowable spans for pipe containing water is

shown below.

Nominal Pipe Size,

in.

Schedule # Allowable Span

2008 W.N. Weaver, PE

2

2

40

80

190

200

Page 15 of 19


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19. SURFACE PROTECTION REQUIRED This is another item best determined by

the corrosion and gasket team and is influenced by installation

conditions, materials of construction, insulation, and temperature.

If the plant has a specific Surface Protection standard it should bereferenced in the Pipe Code along with any required color coding

for the pipes contents.

20. ACCEPTABLE INSULATION This is another item best determined by

the corrosion and gasket team with input from the facility

maintenance and energy representatives and is influenced by

installation conditions, materials of construction, insulation type,temperature and energy policy.

21. HEAT TRACING Depending on the type of heat tracing in use there may be a

need for a Heat Trace Pipe Code. Generally heat tracing isaccomplished using hot water, hot oil, steam or electric heat wire.

Most fluid trace system use copper or stainless steel tubing as thetrace piping and details on how it should be specified and installed

should be incorporated into a pipe code.

22. HEAT OR COOLING JACKETING Pipe jackets are a separate pipe code and

require sketches and considerable detail for a pipe code. Jacket

pipe codes contain two sections: one for the core or inner pipe and

one for the jacketing pipe. This is generally a stand alone coderather than a portion of another code and incorporates a variety of

information:Pipe to be jacketedDesired temperature within core pipe

Pressure in core pipe

Materials of construction of core pipeConnection details for branches in core pipe

Jacketing pipe with sizes related to the core pipe

Jacketing pipe schedule

Jacketing termination at valves, fittings and equipmentJacket connections and flow patterns

Jacket spacers designed to hold the jacket off the core pipe

This can quickly become very complicated and it may be necessaryto develop a jacketing standard independent of the pipe codes in

order to put in all the necessary details.

23. ANCHORING All pipe requires support (see section on allowable spans) and

how the supporting is accomplished is a critical detail. Supports

include the following items:

Rigid anchorsGuides (to allow for thermal expansion or other movement)

Thrust



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Pipe shoes (protects pipe from structural members which

support it)

Trapeze hangers

Simple rod hangersSpring loaded hangers (hanging and stool)

Rigid clamps (simple U-bolts)

Roller supportsSupporting pipe requires considerable information about the

stresses in the pipe and the resulting loads transferred by or to the

supports. Simple straight runs of pipe rarely cause serious

problems in the determination of the loads generated by the pipe inoperation and for these the selection of techniques for anchoring

the pipe is fairly simple. As pipe stresses increase because of

heating, wind, equipment growth or vibration it becomes more

important to do a detailed analysis of the required supportingsystems. Pipe codes do not usually address any but the simplest

anchoring requirements.

24. TESTING

Testing is an essential part of installation of successful piping systems. Most engineers

test piping systems to 1.5 times the design pressure and generally do this with water.

Several questions always arise:

What do we do when the piping system is to handle hot oil and cannot be completely

drained of the testing water?

What do we do when the design pressure is specified at an elevated temperature?

Is it necessary to test low pressure systems at 1.5 times design pressure?

Can we do pneumatic testing instead of hydrostatic testing?

For systems handling hot oil, chemicals which might react with water and create

corrosive conditions or when the pipe line must be dry or when there might be damage toa lining or freezing using water then fluids other than water may be considered. For

example pressurization might be carried out with non flammable liquids, antifreeze

solutions, or some other compatible liquid.

When the design temperature is higher than the test temperature the following calculation

can be used to establish a minimum test pressure.

Pt = 1.5P St where:

S

Pt = low temperature test pressure (psig)

P = Internal Design Gage Pressure (psig)

St = Allowable stress at test temperature, psiS = Allowable stress at design temperature, psi

Care must be taken using this calculation and it is critical to review ASME B31.3 during

the calculation phase whenever this testing situation occurs.



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When dealing with low pressure systems carrying non toxic, non environmentally

damaging fluids which offer no hazards to life testing may, at the engineers discretion

consist of a tightness test only. Basically a static liquid filled line with no pressure

applied.

The choice of testing fluids (water or air, etc) belongs to some extent to the engineer, to

recognized national standards and codes, the insurance company and local or nationalauthorities. Research in creating the pipe code usually will provide sufficient information

to guide the engineer in selecting the proper test procedure. Incorporating the test

procedure into the pipe code eliminates confusion and problems later.

CAUTION 1: It is generally not a good idea to pressurize equipment connected to piping

systems during pressure testing.

CAUTION 2: Using air for pressure testing must be considered very carefully. Pipe

failure under liquid pressure generally results in a short spurt of water whereas with airthe failure may well become explosive.

CAUTION 3: Frequently instrumentation is removed or valved off during hydrostatictesting.

25. PIPE FABRICATION

Metallic pipe can be fabricated in several ways and is classified in such as way as to

define the manufacturing technique.

Cast Iron Cast in a foundry and generally not part of a process industry except for some

utilities and drainage.Seamless Essentially extruded in some fashion around a mandrel. Considered to be the

best pipe since there is no seam to offer a weak spot or allow corrosion to

begin..

ERW Electric Resistance Welded in an automatic machine as the formed pipe exitsa forming machine.

This becomes a team decision as ERW is usually somewhat less expensive than seamless.

26. CONCLUSION

Properly prepared pipe codes provide a variety of services to the facility engineerincluding:

increased fluid safety

reduced detail creation for bidding purposes

consistent treatment of various chemicals and utility fluids

minimal and consistent piping system costs

simplified instructions transfer to contractors and maintenance

improved detail in P&IDs

satisfaction of legal and insurance requirements



18/18

The effort required may seem significant but by utilizing existing codes as a starting point

the task is simplified and the result worth the effort in future time saved and problems

avoided. A completed pipe code standard relieves the engineer of having to re-invent thecode each time a piping project is approved.

27. REFERENCES

Perrys Chemical Engineers Handbook McGraw-Hill

Marks Mechanical Engineers Handbook, McGraw-Hill

ASME various codesMcCabe and Smith Unit Operations of Chemical Engineering

Engineering Toolbox, www.Engineeringtoolbox.com

Bonney Forge, Mount Union, PA


creating the plant pipe code

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