Overview of Process PlantPiping System Design

Participants Guide

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Overview of Process PlantPiping System Design

By:

Vincent A. CarucciCarmagen Engineering, Inc.

Copyright 2000 by

All Rights Reserved

TABLE OF CONTENTSPART 1: PARTICIPANT NOTES ..............................................................................3

PART 2: BACKGROUND MATERIAL .................................................................................... 73

I. Introduction ....................................................................................................................... 73II. General ............................................................................................................................. 73

A. What is a piping system .......................................................................................... 73B. Scope of ASME B31.3............................................................................................. 73

III. Material selection considerations...................................................................................... 75A. Strength................................................................................................................... 75B. Corrosion Resistance.............................................................................................. 77C. Material Fracture Toughness .................................................................................. 77D. Fabricability ............................................................................................................. 78E. Availability and Cost ................................................................................................ 78

IV. Piping Components........................................................................................................... 79A. Fittings, Flanges, and Gaskets................................................................................ 79B. Flange Rating .......................................................................................................... 85Sample Problem 1 - Determine Flange Rating ................................................................. 88Solution ............................................................................................................................. 88

V. Valves ............................................................................................................................... 89A. Valve Functions....................................................................................................... 89B. Primary Valve Types ............................................................................................... 90C. Valve Selection Process ......................................................................................... 98Exercise 1 Determine Required Flange Rating ............................................................. 99

VI. Design ............................................................................................................................. 100A. Design Conditions ................................................................................................. 100B. Loads and Stresses............................................................................................... 101C. Pressure Design of Components .......................................................................... 105Sample Problem 2 - Determine Pipe wall thickness ....................................................... 110Sample Problem 3 .......................................................................................................... 116Exercise 2: Determine Required Pipe Wall Thickness .................................................. 121

VII. System Design ................................................................................................................ 122A. Layout Considerations .......................................................................................... 122B. Pipe Supports and Restraints ............................................................................... 123C. Piping Flexibility..................................................................................................... 129D. Required Design Information for Piping Stress Analysis ...................................... 132E. Criteria for Allowable Equipment Nozzle Loads.................................................... 132F. When Should A Computer Analysis Be Used ....................................................... 134G. Design Considerations for Piping System Stress Analysis ................................... 134

VIII. Fabrication, Assembly, and Erection .............................................................................. 140A. Welding and Heat Treatment ................................................................................ 140B. Assembly and Erection.......................................................................................... 144

IX. Quality Control ................................................................................................................ 151A. Inspection .............................................................................................................. 151B. Testing................................................................................................................... 154

X. Other Considerations ...................................................................................................... 156A. Nonmetallic Piping................................................................................................. 156B. Category M Fluid Service...................................................................................... 157C. High Pressure Piping............................................................................................. 158

XI. Summary......................................................................................................................... 160

3Part 1:Participant Notes

41

OVERVIEW OF PROCESS PLANT PIPING

SYSTEM DESIGNBy: Vincent A. Carucci

Carmagen Engineering, Inc.

Notes:

2

Piping SystemPiping system: conveys fluid between locations Piping system includes: Pipe Fittings (e.g. elbows, reducers, branch

connections, etc.) Flanges, gaskets, bolting Valves Pipe supports

Notes:

53

ASME B31.3

Design Materials Fabrication

Petroleum refineries Chemical plants Pharmaceutical plants Textile plants

Paper plants Semiconductor

plants Cryogenic plants

Erection Inspection Testing

Provides requirements for:

For process plants including

Notes:

4

Scope of ASME B31.3 Piping and piping components, all fluid

services: Raw, intermediate, and finished chemicals Petroleum products Gas, steam, air, and water Fluidized solids Refrigerants Cryogenic fluids

Interconnections within packaged equipment Scope exclusions specified

Notes:

65

Strength Yield and Tensile Strength Creep Strength Fatigue Strength Alloy Content Material Grain size Steel Production Process

Notes:

6

Stress - Strain DiagramS

AB

C

E

Notes:

77

Corrosion Resistance Deterioration of metal by chemical or

electrochemical action Most important factor to consider Corrosion allowance added thickness Alloying increases corrosion resistance

Notes:

8

Piping System CorrosionGeneral orUniform

Corrosion

Uniform metal loss. May be combined with erosion ifhigh-velocity fluids, or moving fluids containingabrasives.

PittingCorrosion

Localized metal loss randomly located on materialsurface. Occurs most often in stagnant areas or areas oflow-flow velocity.

GalvanicCorrosion

Occurs when two dissimilar metals contact each other incorrosive electrolytic environment. Anodic metal developsdeep pits or grooves as current flows from it to cathodicmetal.

Crevice Corrosion Localized corrosion similar to pitting. Occurs at placessuch as gaskets, lap joints, and bolts where creviceexists.

ConcentrationCell Corrosion

Occurs when different concentration of either a corrosivefluid or dissolved oxygen contacts areas of same metal.Usually associated with stagnant fluid.

GraphiticCorrosion

Occurs in cast iron exposed to salt water or weak acids.Reduces iron in cast iron, and leaves graphite in place.Result is extremely soft material with no metal loss.

Notes:

89

Material Toughness

Energy necessary to initiate and propagate a crack

Decreases as temperature decreases Factors affecting fracture toughness

include: Chemical composition or alloying elements Heat treatment Grain size

Notes:

10

Fabricability Ease of construction Material must be weldable Common shapes and forms include:

Seamless pipe Plate welded pipe Wrought or forged elbows, tees, reducers,

crosses Forged flanges, couplings, valves Cast valves

Notes:

911

Availability and Cost

Consider economics Compare acceptable options based on:

Availability Relative cost

Notes:

12

Pipe Fittings

Produce change in geometry Modify flow direction Bring pipes together Alter pipe diameter Terminate pipe

Notes:

10

13

Elbow and Return

Figure 4.1

90 45

180 Return

Notes:

14

Tee

Figure 4.2

Reducing Outlet Tee Cross Tee

Notes:

11

15

Reducer

Figure 4.3

Concentric Eccentric

Notes:

16

Welding Outlet Fitting

Figure 4.4

Notes:

12

17

Cap

Figure 4.5

Notes:

18

Lap-joint Stub End

Figure 4.6

Note square corner

R

R

Enlarged Section of Lap

Notes:

13

19

Typical Flange Assembly

Figure 4.7

Flange

Bolting

Gasket

Notes:

20

Types of FlangeAttachment and Facing

Flange Attachment Types Flange Facing Types

Threaded Flanges Flat Faced

Socket-Welded Flanges

Blind Flanges Raised Face

Slip-On Flanges

Lapped Flanges Ring Joint

Weld Neck Flanges

Table 4.1

Notes:

14

21

Flange Facing Types

Figure 4.8

Notes:

22

Gaskets Resilient material Inserted between flanges Compressed by bolts to create seal Commonly used types

Sheet Spiral wound Solid metal ring

Notes:

15

23

Flange Rating Class Based on ASME B16.5 Acceptable pressure/temperature

combinations Seven classes (150, 300, 400, 600, 900,

1,500, 2,500) Flange strength increases with class

number Material and design temperature

combinations without pressure indicated not acceptable

Notes:

24

Material Specification List

Table 4.2

Notes:

16

25

Pressure - Temperature Ratings

Table 4.3

MaterialGroup No. 1.8 1.9 1.10

Classes 150 300 400 150 300 400 150 300 400Temp., F-20 to 100 235 620 825 290 750 1000 290 750 1000

200 220 570 765 260 750 1000 260 750 1000300 215 555 745 230 720 965 230 730 970400 200 555 740 200 695 885 200 705 940500 170 555 740 170 695 805 170 665 885600 140 555 740 140 605 785 140 605 805650 125 555 740 125 590 785 125 590 785700 110 545 725 110 570 710 110 570 755750 95 515 685 95 530 675 95 530 710800 80 510 675 80 510 650 80 510 675850 65 485 650 65 485 600 65 485 650900 50 450 600 50 450 425 50 450 600950 35 320 425 35 320 290 35 375 5051000 20 215 290 20 215 190 20 260 345

Notes:

26

Sample Problem 1Flange Rating

New piping system to be installed at existing plant.Determine required flange class. Pipe Material: Design Temperature: 700F Design Pressure: 500 psig

Mo21Cr4

11

Notes:

17

27

Sample Problem 1 Solution Determine Material Group Number (Fig. 4.2)

Group Number = 1.9 Find allowable design pressure at

intersection of design temperature and Group No. Check Class 150. Allowable pressure = 110 psig < design pressure Move to next higher class and repeat steps

For Class 300, allowable pressure = 570 psig Required flange Class: 300

Notes:

28

Valves Functions

Block flow Throttle flow Prevent flow reversal

Notes:

18

29

Full Port Gate Valve1. Handwheel Nut2. Handwheel3. Stem Nut4. Yoke5. Yoke Bolting6. Stem7. Gland Flange8. Gland9. Gland Bolts or

Gland Eye-bolts and nuts10. Gland Lug Bolts and Nuts11. Stem Packing12. Plug13. Lantern Ring14. Backseat Bushing15. Bonnet16. Bonnet Gasket17. Bonnet Bolts and Nuts18. Gate19. Seat Ring20. Body21. One-Piece Gland (Alternate)22. Valve Port

Figure 5.1

Notes:

30

Globe Valve Most economic for throttling flow Can be hand-controlled Provides tight shutoff Not suitable for scraping or rodding Too costly for on/off block operations

Notes:

19

31

Check Valve

Prevents flow reversal Does not completely shut off reverse flow Available in all sizes, ratings, materials Valve type selection determined by

Size limitations Cost Availability Service

Notes:

32

Swing Check Valve

Figure 5.2

Cap

Hinge

DiscBody

Pin

SeatRing

FlowDirection

Notes:

20

33

Ball Check Valve

Figure 5.3

Notes:

34

Lift Check Valve

Figure 5.4

SeatRing

Piston

FlowDirection

Notes:

21

35

Wafer Check Valve

Figure 5.5

Notes:

36

Ball ValveNo. Part Names1 Body2 Body Cap3 Ball4 Body Seal Gasket5 Seat6 Stem7 Gland Flange8 Stem Packing9 Gland Follower10 Thrust Bearing11 Thrust Washer12 Indicator Stop13 Snap Ring14 Gland Bolt15 Stem Bearing16 Body Stud Bolt & Nuts17 Gland Cover18 Gland Cover Bolts19 Handle

Figure 5.6

Notes:

22

37

Plug Valve

Figure 5.7

Wedge

Molded-In Resilient Seal

Sealing Slip

Notes:

38

Valve Selection Process

General procedure for valve selection.1. Identify design information including

pressure and temperature, valve function, material, etc.

2. Identify potentially appropriate valve types and components based on application and function (i.e., block, throttle, or reverse flow prevention).

Notes:

23

39

Valve Selection Process, contd

3. Determine valve application requirements (i.e., design or service limitations).

4. Finalize valve selection. Check factors to consider if two or more valves are suitable.

5. Provide full technical description specifying type, material, flange rating, etc.

Notes:

40

Exercise 1 - Determine Required Flange Rating

Pipe: Flanges: A-182 Gr. F11 Design Temperature: 900F Design Pressure: 375 psig

Mo21Cr4

11

Notes:

24

41

Exercise 1 - Solution1. Identify material specification of flange

A-182 Gr, F112. Determine Material Group No. (Table 4.2)

Group 1.93. Determine class using Table 4.3 with design

temperature and Material Group No. The lowest Class for design pressure of 375

psig is Class 300. Class 300 has 450 psig maximum pressure

at 900F

Notes:

42

Design Conditions General

Normal operating conditions Design conditions

Design pressure and temperature Identify connected equipment and associated

design conditions Consider contingent conditions Consider flow direction Verify conditions with process engineer

Notes:

25

43

Loading ConditionsPrincipal pipe load types Sustained loads

Act on system all or most of time Consist of pressure and total weight load

Thermal expansion loads Caused by thermal displacements Result from restrained movement

Occasional loads Act for short portion of operating time Seismic and/or dynamic loading

Notes:

44

Stresses Produced ByInternal Pressure

Sl

tP

Sc

Sc

Sl

t

P

=

=

=

=

Longitudinal Stress

Circumferential (Hoop) Stress

Wall Thickness

Internal Pressure

Figure 6.1

Notes:

26

45

Stress Categorization Primary Stresses

Direct Shear Bending

Secondary stresses Act across pipe wall thickness Cause local yielding and minor distortions Not a source of direct failure

Notes:

46

Stress Categorization, contd Peak stresses

More localized Rapidly decrease within short distance of

origin Occur where stress concentrations and

fatigue failure might occur Significance equivalent to secondary stresses Do not cause significant distortion

Notes:

27

47

Allowable StressesFunction of

Material properties Temperature Safety factors

Established to avoid: General collapse or excessive distortion from

sustained loads Localized fatigue failure from thermal

expansion loads Collapse or distortion from occasional loads

Notes:

48

B31.3 AllowableStresses in Tension

Table 6.1

Basic Allowable Stress S, ksi. At Metal Temperature, F.

MaterialSpec. No/Grade

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Carbon Steel A 106 B 20.0 20.0 20.0 20.0 18.9 17.3 16.5 10.8 6.5 2.5 1.0

C - Mo A 335 P1 18.3 18.3 17.5 16.9 16.3 15.7 15.1 13.5 12.7 4. 2.4

1 - Mo A 335 P11 20.0 18.7 18.0 17.5 17.2 16.7 15.6 15.0 12.8 6.3 2.8 1.2

18Cr - 8Ni pipe A 312 TP304 20.0 20.0 20.0 18.7 17.5 16.4 16.0 15.2 14.6 13.8 9.7 6.0 3.7 2.3 1.4

16Cr - 12Ni-2Mopipe

A 312 TP316 20.0 20.0 20.0 19.3 17.9 17.0 16.3 15.9 15.5 15.3 12.4 7.4 4.1 2.3 1.3

Notes:

28

49

Pipe Thickness RequiredFor Internal Pressure

P = Design pressure, psigD = Pipe outside diameter, in.S = Allowable stress in tension, psiE = Longitudinal-joint quality factorY = Wall thickness correction factor

)PYSE(2PDt++++

====

CAttm ++++====

875.0tt mnom ====

Notes:

50 Table 6.2

Spec.No.

Class (or Type) Description Ej

Carbon Steel

API5L

. . .

. . .

. . .

Seamless pipeElectric resistance welded pipe

Electric fusion welded pipe, double butt, straight orspiral seam

Furnace butt welded

1.000.850.95

A 53 Type SType EType F

Seamless pipeElectric resistance welded pipe

Furnace butt welded pipe

1.000.850.60

A 106 . . . Seamless pipe 1.00

Low and Intermediate Alloy Steel

A 333 . . .. . .

Seamless pipeElectric resistance welded pipe

1.000.85

A 335 . . . Seamless pipe 1.00

Stainless Steel

A 312 . . .. . .. . .

Seamless pipeElectric fusion welded pipe, double butt seamElectric fusion welded pipe, single butt seam

1.000.850.80

A 358 1, 3, 452

Electric fusion welded pipe, 100% radiographedElectric fusion welded pipe, spot radiographedElectric fusion welded pipe, double butt seam

1.000.900.85

Nickel and Nickel Alloy

B 161 . . . Seamless pipe and tube 1.00

B 514 . . . Welded pipe 0.80

B 675 All Welded pipe 0.80

Notes:

29

51

Table 6.3

Temperature, F

Materials 900 & lower 950 1000 1050 1100 1150 & up

FerriticSteels

0.4 0.5 0.7 0.7 0.7 0.7

AusteniticSteels

0.4 0.4 0.4 0.4 0.5 0.7

OtherDuctileMetals

0.4 0.4 0.4 0.4 0.4 0.4

Cast iron 0.0 . . . . . . . . . . . . . . .

Notes:

52

Curved and Mitered Pipe

Curved pipe Elbows or bends Same thickness as straight pipe

Mitered bend Straight pipe sections welded together Often used in large diameter pipe May require larger thickness

Function of number of welds, conditions, size

Notes:

30

53

Sample Problem 2 -Determine Pipe Wall ThicknessDesign temperature: 650F

Design pressure: 1,380 psig.

Pipe outside diameter: 14 in.

Material: ASTM A335, Gr. P11 ( ), seamless

Corrosion allowance: 0.0625 in.

Mo21Cr4

11

Notes:

54

Sample Problem 2 - Solution

)PYSE(2PDt++++

====

(((( )))) (((( ))))[[[[ ]]]]

in.577.0t

4.0380,11200,16214380,1t

====

++++

====

Notes:

31

55

Sample Problem 2 -Solution, contd

tm = t + c = 0.577 + 0.0625 = 0.6395 in.

.in731.0875.0

6395.0tnom ========

Notes:

56

Welded Branch Connection

Figure 6.2

DbTb

cNom.Thk.

Nom.Thk.

Dh

Thth

Tr

c

tbMillTol.

MillTol.

d1

d2 d2

L4

ReinforcementZone LimitsReinforcement

Zone Limits

A1

A3

A4A

4

A2 A2

A3

Pipe C

Notes:

32

57

Reinforcement Area

d1 = Effective length removed from run pipe, in.Db = Branch outside diameter, in.Tb = Minimum branch thickness, in.c = Corrosion allowance, in. = Acute angle between branch and header

====

sin)cT(2Dd bb1

Notes:

58

Required Reinforcement Area

Required reinforcement area, A1:

Where: th = Minimum required header thickness, in.

)sin2(dtA 1h1 ====

Notes:

33

59

Reinforcement Pad Provides additional reinforcement Usually more economical than increasing

wall thickness Selection variables

Material Outside diameter Wall thickness

rbp

4 Tsin)DD(

A

====

Notes:

60

Sample Problem 3

Pipe material: Seamless, A 106/Gr. B for branch and header, S = 16,500 psi

Design conditions: 550 psig @ 700F c = 0.0625 in. Mill tolerance: 12.5%

Notes:

34

61

Sample Problem 3, contd Nominal Pipe Header: 0.562 in.

Thicknesses: Branch: 0.375 in.

Required Pipe Header: 0.395 in.Thicknesses: Branch: 0.263 in.

Branch connection at 90 angle

Notes:

62

Sample Problem 3 - Solution

====

sin)cT(2Dd bb1

(((( )))) .in469.1590sin

0625.0875.0375.0216d1 ====

====

21

1h1

in.11.6)90sin2(469.15395.0A

)sin2(dtA

========

====

Notes:

35

63

Sample Problem 3 -Solution, contd

Calculate excess area available in header, A2.

d2 = d1 = 15.469 in. < Dh = 24 in.

A2 = (2 15.469 - 15.469) (0.875 0.562 -0.395 - 0.0625)

A2 = 0.53 in.2

(((( ))))(((( ))))ctTdd2A hh122 ====

Notes:

64

Sample Problem 3 -Solution, contd

Calculate excess area available in branch, A3.

(((( ))))sin

ctTL2A bb43

====

.in664.0)0625.0375.0875.0(5.2L4 ========

(((( )))) 23 .in003.090 sin

0625.0263.0375.0875.0664.02A ====

====

Notes:

36

65

Sample Problem 3 -Solution, contd

Calculate other excess area available, A4.A4 = 0.

Total Available Area:

AT = A2 + A3 + A4AT = 0.53 + 0.003 + 0 = 0.533 in.2 available

reinforcement.AT < A1 Pad needed

Notes:

66

Sample Problem 3 -Solution, contd

Reinforcement pad: A106, Gr. B, 0.562 in. thick Recalculate Available ReinforcementL41 = 2.5 (Th - c) = 2.5 (0.875 0.562 - 0.0625) =

1.073 in.L42 = 2.5 (Tb - c) + Tr

= 2.5 (0.875 0.375 - 0.0625) + 0.562 (0.875) = 1.16 in

Notes:

37

67

Sample Problem 3 -Solution, contd

Therefore, L4 = 1.073 in.

2432T

223

in.535.00005.053.0AAAA)calculatedpreviously in. 0.003 the (vs. in.005.0A

====++++++++====++++++++====

====

o3 90sin)0625.0263.0375.0875.0(073.12A ====

sinc)t(TL2A bb43

====

Notes:

68

Sample Problem 3 -Solution, contd

Calculate additional reinforcement required andpad dimensions:

A4 = 6.11 - 0.535 = 5.575 in.2

Pad diameter, Dp is:

Tr = 0.562 (0.875) = 0.492 in.

Since 2d2 > Dp, pad diameter is acceptable

3.2716492.0575.5

sinD

TAD b

r

4p =+=+=

Notes:

38

69

Exercise 2 - Determine Required Pipe Wall Thickness Design Temperature: 260F Design Pressure: 150 psig Pipe OD: 30 in. Pipe material: A 106, Gr. B seamless Corrosion allowance: 0.125 Mill tolerance: 12.5% Thickness for internal pressure and

nominal thickness?

Notes:

70

Exercise 2 - Solution From Tables 6.1, 6.2, and 6.3 obtain values:

S = 20,000 psi E = 1.0 Y = 0.4

Thickness calculation:

t = 0.112 in.(((( )))) (((( ))))[[[[ ]]]]04.01500.1000,202

30150)PYSE(2

PDt++++

====

++++====

Notes:

39

71

Exercise 2 - Solution, contd

Corrosion allowance calculation:

Mill tolerance calculation:

.in237.0t125.0112.0CAttm

====

++++====++++====

.in271.0t875.0237.0

875.0tt

nom

mnom

====

========

Notes:

72

Layout Considerations Operational

Operating and control points easily reached Maintenance

Ample clearance for maintenance equipment Room for equipment removal Sufficient space for access to supports

Safety Consider personnel safety Access to fire fighting equipment

Notes:

40

73

Pipe Supports and Restraints Supports

Absorb system weight Reduce:

+ longitudinal pipe stress+ pipe sag+ end point reaction loads

Restraints Control or direct thermal movement due to:

+ thermal expansion+ imposed loads

Notes:

74

Support and Restraint Selection Factors

Weight load Available attachment clearance Availability of structural steel Direction of loads and/or movement Design temperature Vertical thermal movement at supports

Notes:

41

75

Rigid Supports

Shoe Saddle Base AdjustableSupport

Dummy Support Trunnion

Figure 7.1

Notes:

76

Hangers

Figure 7.2

Notes:

42

77

Flexible Supports

Figure 7.3

Load and DeflectionScale

Typical Variable-LoadSpring Support

Small Change inEffective Lever Arm

Large Change inEffective Lever Arm

RelativelyConstantLoad

Typical Constant-LoadSpring Support Mechanism

Notes:

78

Restraints Control, limit, redirect thermal movement

Reduce thermal stress Reduce loads on equipment connections

Absorb imposed loads Wind Earthquake Slug flow Water hammer Flow induced-vibration

Notes:

43

79

Restraints, contd Restraint Selection

Direction of pipe movement Location of restraint point Magnitude of load

Notes:

80

Anchors and Guides Anchor

Full fixation Permits very limited (if any) translation or

rotation

Guide Permits movement along pipe axis Prevents lateral movement May permit pipe rotation

Notes:

44

81

Restraints - Anchors

Figure 7.4

Anchor Anchor Partial Anchor

Notes:

82

Restraints - Guides

Figure 7.5

Guide Guide

Vertical Guide

x

Guide

Notes:

45

83

Piping Flexibility Inadequate flexibility

Leaky flanges Fatigue failure Excessive maintenance Operations problems Damaged equipment

System must accommodate thermal movement

Notes:

84

Flexibility Analysis Considers layout, support, restraint Ensures thermal stresses and reaction

loads are within allowable limits Anticipates stresses due to:

Elevated design temperatures+ Increases pipe thermal stress and reaction

loads+ Reduces material strength

Pipe movement Supports and restraints

Notes:

46

85

Flexibility Analysis, contd Evaluates loads imposed on equipment Determines imposed loads on piping

system and associated structures Loads compared to industry standards

Based on tables Calculated

Notes:

86

Design Factors Layout Component

design details Fluid service Connected

equipment type Operating

scenarios

Pipe diameter, thickness

Design temperature and pressure

End-point movements Existing structural

steel locations Special design

considerations

Notes:

47

87

Equipment Nozzle Load Standards and Parameters

Equipment Item Industry StandardParameters Used To Determine

Acceptable Loads

Centrifugal Pumps API 610 Nozzle size

CentrifugalCompressors

API 617, 1.85 times

NEMA SM-23allowable

Nozzle size, material

Air-Cooled HeatExchangers

API 661 Nozzle size

Pressure Vessels, Shell-and-Tube HeatExchanger Nozzles

ASME Code SectionVIII, WRC 107,WRC 297

Nozzle size, thickness,reinforcement details,vessel/exchanger diameter,and wall thickness. Stressanalysis required.

Tank Nozzles API 650 Nozzle size, tank diameter,height, shell thickness, nozzleelevation.

Steam Turbines NEMA SM-23 Nozzle size

Table 7.1

Notes:

88

Computer Analysis Used to perform detailed piping stress

analysis Can perform numerous analyses Accurately completes unique and difficult

functions Time-history analyses Seismic and wind motion Support motion Finite element analysis Animation effects

Notes:

48

89

Computer Analysis GuidelinesType Of Piping Pipe Size, NPS

Maximum DifferentialFlexibility Temp.

General piping 4

8

12

20

400F

300F

200F

any

For rotating equipment 3 Any

For air-fin heat exchangers 4 Any

For tankage 12 Any

Table 7.2

Notes:

90

Piping Flexibility Temperature Analysis based on largest temperature

difference imposed by normal and abnormal operating conditions

Results give: Largest pipe stress range Largest reaction loads on connections,

supports, and restraints Extent of analysis depends on situation

Notes:

49

91

Normal Temperature Conditions To Consider

StableOperation

Temperature range expected for most of time plant isin operation. Margin above operating temperature(i.e., use of design temperature rather than operatingtemperature) allows for process flexibility.

Startup andShutdown

Determine if heating or cooling cycles pose flexibilityproblems. For example, if tower is heated whileattached piping remains cold, piping flexibility shouldbe checked.

Regenerationand Decoking

Piping

Design for normal operation, regeneration, ordecoking, and switching from one service to theother. An example is furnace decoking.

SparedEquipment

Requires multiple analyses to evaluate expectedtemperature variations, for no flow in some of piping,and for switching from one piece of equipment toanother. Common example is piping for two or morepumps with one or more spares.

Table 7.3

Notes:

92

Abnormal Temperature Conditions To Consider

Loss of CoolingMedium Flow

Temperature changes due to loss of cooling mediumflow should be considered. Includes pipe that isnormally at ambient temperature but can be blockedin, while subject to solar radiation.

Steamout for Airor Gas Freeing

Most on-site equipment and lines, and many off-sitelines, are freed of gas or air by using steam. For 125psig steam, 300F is typically used for metaltemperature. Piping connected to equipment whichwill be steamed out, especially piping connected toupper parts of towers, should be checked for tower at300F and piping at ambient plus 50F. This maygovern flexibility of lines connected to towers thatoperate at less than 300F or that have a smallertemperature variation from top to bottom.

No Process FlowWhile Heating

Continues

If process flow can be stopped while heat is still beingapplied, flexibility should be checked for maximummetal temperature. Such situations can occur withsteam tracing and steam jacketing.

Table 7.4

Notes:

50

93

Extent of Analysis Extent depends on situation

Analyze right combination of conditions

Not necessary to include system sections that are irrelevant to analysis results

Notes:

94

Modifying System Design Provide more offsets or bends Use more expansion loops Install expansion joints Locate restraints to:

Minimize thermal and friction loads Redirect thermal expansion

Use spring supports to reduce large vertical thermal loads

Use Teflon bearing pads to reduce friction loads

Notes:

51

95

System Design Considerations Pump systems

Operating vs. spared pumps

Heat traced piping systems Heat tracing

+ Reduces liquid viscosity+ Prevents condensate accumulation

Tracing on with process off

Notes:

96

System Design Considerations, contd

Atmospheric storage tank Movement at nozzles Tank settlement

Friction loads at supports and restraints Can act as anchors or restraints May cause high pipe stresses or reaction loads

Air-cooled heat exchangers Consider header box and bundle movement

Notes:

52

97

Tank Nozzle

Figure 7.6

NOZZLE SHELL

BOTTOM

Notes:

98

Welding Welding is primary way of joining pipe Provides safety and reliability Qualified welding procedure and welders Butt welds used for:

Pipe ends Butt-weld-type flanges or fittings to pipe ends Edges of formed plate

Notes:

53

99

Butt-Welded Joint DesignsEqual Thickness

Figure 8.1

(a) Standard End Preparationof Pipe

(b) Standard End Preparationof Butt-Welding Fittings andOptional End Preparation of

Pipe 7/8 in. and Thinner(c) Suggested End Preparation,

Pipe and Fittings Over 7/8 in.Thickness

Notes:

100

Butt-Welded Joint DesignsUnequal Thickness

Figure 8.2

(b)

(d)

(c)3/32 in. max.

(a)

Notes:

54

101

Fillet Welds

Figure 8.3

Notes:

102

Weld Preparation Welder and equipment must be qualified Internal and external surfaces must be

clean and free of paint, oil, rust, scale, etc. Ends must be:

Suitably shaped for material, wall thickness, welding process

Smooth with no slag from oxygen or arc cutting

Notes:

55

103

Preheating Minimizes detrimental effects of:

High temperature Severe thermal gradients

Benefits include: Dries metal and removes surface moisture Reduces temperature difference between

base metal and weld Helps maintain molten weld pool Helps drive off absorbed gases

Notes:

104

Postweld Heat Treatment (PWHT)

Primarily for stress relief Only reason considered in B31.3

Averts or relieves detrimental effects Residual stresses

+ Shrinkage during cooldown+ Bending or forming processes

High temperature Severe thermal gradients

Notes:

56

105

Postweld Heat Treatment (PWHT), contd

Other reasons for PWHT to be specified by user Process considerations Restore corrosion resistance of normal

grades of stainless steel Prevent caustic embrittlement of carbon steel Reduce weld hardness

Notes:

106

Storage and Handling Store piping on mounds or sleepers Stacking not too high Store fittings and valves in shipping crates

or on racks End protectors firmly attached Lift lined and coated pipes and fittings with

fabric or rubber covered slings and padding

Notes:

57

107

Pipe Fitup and Tolerances Good fitup essential

Sound weld Minimize loads

Dimensional tolerances Flange tolerances

Notes:

108

Pipe AlignmentLoad Sensitive Equipment

Special care and tighter tolerances needed Piping should start at nozzle flange

Initial section loosely bolted Gaskets used during fabrication to be replaced

Succeeding pipe sections bolted on Field welds to join piping located near

machine

Notes:

58

109

Load Sensitive Equipment, contd

Spring supports locked in cold position during installation and adjusted in locked position later

Final bolt tensioning follows initial alignment of nozzle flanges

Final nozzle alignment and component flange boltup should be completed after replacing any sections removed

Notes:

110

Load Sensitive Equipment, contd

More stringent limits for piping > NPS 3 Prevent ingress of debris during

construction

Notes:

59

111

Flange Joint Assembly Primary factors

Selection Design Preparation Inspection Installation

Identify and control causes of leakage

Notes:

112

Flange Preparation, Inspection, and Installation

Redo damaged surfaces Clean faces Align flanges Lubricate threads and nuts Place gasket properly Use proper flange boltup procedure

Notes:

60

113

Criss-CrossBolt-tightening Sequence

Figure 8.4

Notes:

114

Causes of Flange Leakage Uneven bolt stress Improper flange alignment Improper gasket centering Dirty or damaged flange faces Excessive loads at flange locations Thermal shock Improper gasket size or material Improper flange facing

Notes:

61

115

Inspection Defect identification Weld inspection

Technique Weld type Anticipated type of defect Location of weld Pipe material

Notes:

116

Typical Weld ImperfectionsLack of Fusion Between Weld Bead and Base Metal

a) Side Wall Lack of Fusion b) Lack of Fusion BetweenAdjacent Passes

Incomplete Filling at Root on One Side Only

c) Incomplete Penetration Dueto Internal Misalignment

Incomplete Filling at Root

d) Incomplete Penetration ofWeld Groove

External Undercut

Internal UndercutRoot Bead Fused to Both InsideSurfaces but Center of Root Slightly

Below Inside Surface of Pipe (NotIncomplete Penetration)

e) Concave Root Surface(Suck-Up)

f) Undercut

g) Excess External Reinforcement

Figure 9.1

Notes:

62

117

Weld Inspection GuidelinesType of Inspection Situation/Weld Type Defect

Visual All welds. Minor structural welds.

Cracks.

Slag inclusions.

Radiography Butt welds.

Girth welds.

Miter groove welds.

Gas pockets.

Slag inclusions.

Incomplete penetration.

Magnetic Particle Ferromagneticmaterials.

For flaws up to 6 mm(1/4 in.) beneath thesurface.

Cracks.

Porosity.

Lack of fusion.

Liquid Penetrant Ferrous andnonferrous materials.

Intermediate weldpasses.

Weld root pass.

Simple andinexpensive.

Cracks.

Seams.

Porosity.

Folds.

Inclusions.

Shrinkage.

Surface defects.

Ultrasonic Confirms high weldquality in pressure-containing joints.

Laminations.

Slag inclusions in thickplates.

Subsurface flaws.

Table 9.1

Notes:

118

Testing Pressure test system to demonstrate

integrity

Hydrostatic test unless pneumatic approved for special cases

Hydrostatic test pressure 1 times design pressure

Notes:

63

119

Testing, contd For design temperature > test temperature:

ST/S must be 6.5PT = Minimum hydrostatic test pressure, psigP = Internal design pressure, psigST = Allowable stress at test temperature, psiS = Allowable stress at design temperature, psi

SSP5.1P TT ====

Notes:

120

Testing, contd Pneumatic test at 1.1P Instrument take-off piping and sampling

piping strength tested with connected equipment

Notes:

64

121

Nonmetallic Piping Thermoplastic Piping

Can be repeatedly softened and hardened by increasing and decreasing temperature

Reinforced Thermosetting Resin Piping (RTR) Fabricated from resin which can be treated to

become infusible or insoluble

Notes:

122

Nonmetallic Piping, contd No allowances for pressure or temperature

variations above design conditions Most severe coincident pressure and

temperature conditions determine design conditions

Notes:

65

123

Nonmetallic Piping, contd Designed to prevent movement from

causing: Failure at supports Leakage at joints Detrimental stresses or distortions

Stress-strain relationship inapplicable

Notes:

124

Nonmetallic Piping, contd Flexibility and support requirement same

as for piping in normal fluid service. In addition: Piping must be supported, guided, anchored

to prevent damage. Point loads and narrow contact areas avoided Padding placed between piping and supports Valves and load transmitting equipment

supported independently to prevent excessive loads.

Notes:

66

125

Nonmetallic Piping, contd Thermoplastics not used in flammable

service, and safeguarded in most fluid services.

Joined by bonding

Notes:

126

Category M Fluid ServiceCategory M Fluid

Significant potential for personnel exposure

Single exposure to small quantity can cause irreversible harm to breathing or skin.

Notes:

67

127

Category M Fluid Service, contd Requirements same as for piping in

normal fluid service. In addition: Design, layout, and operation conducted with

minimal impact and shock loads.

Detrimental vibration, pulsation, resonance effects to be avoided or minimized.

No pressure-temperature variation allowances.

Notes:

128

Category M Fluid Service, contd Most severe coincident pressure-temperature

conditions determine design temperature and pressure.

All fabrication and joints visually examined.

Sensitive leak test required in addition to other required testing.

Notes:

68

129

Category M Fluid Service, contd Following may not be used

Miter bends not designated as fittings, fabricated laps, nonmetallic fabricated branch connections.

Nonmetallic valves and specialty components. Threaded nonmetallic flanges. Expanded, threaded, caulked joints.

Notes:

130

High Pressure Piping Ambient effects on design conditions

Pressure reduction based on cooling of gas or vapor

Increased pressure due to heating of a static fluid

Moisture condensation

Notes:

69

131

High Pressure Piping, contd

Other considerations Dynamic effects Weight effects Thermal expansion and contraction effects Support, anchor, and terminal movement

Notes:

132

High Pressure Piping, contd

Testing Each system hydrostatically or pneumatically

leak tested Each weld and piping component tested Post installation pressure test at 110% of

design pressure if pre-installation test was performed

Examination Generally more extensive than normal fluid

service

Notes:

70

133

Summary Process plant piping much more than just

pipe ASME B31.3 covers process plant piping Covers design, materials, fabrication,

erection, inspection, and testing Course provided overview of requirements

Notes:

71

Part 2:Background Material

72

OVERVIEW OF PROCESS PLANT PIPING SYSTEM DESIGN

Carmagen Engineering, Inc.

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I. INTRODUCTION

This course provides an overview of process plant piping system design. Itdiscusses requirements contained in ASME B31.3, Process Piping, plusadditional requirements and guidelines based on common industry practice. Theinformation contained in this course is readily applicable to on-the-jobapplications, and prepares participants to take more extensive courses ifappropriate.

II. GENERAL

A. What is a piping system

A piping system conveys fluid from one location to another. Withina process plant, the locations are typically one or more equipmentitems (e.g., pumps, pressure vessels, heat exchangers, processheaters, etc.), or individual process plants that are within theboundary of a process facility.

A piping system consists of:

Pipe sections

Fittings (e.g., elbows, reducers, branch connections, etc.)

Flanges, gaskets, and bolting

Valves

Pipe supports and restraints

Each individual component plus the overall system must bedesigned for the specified design conditions.

B. Scope of ASME B31.3

ASME B31.3 specifies the design, materials, fabrication, erection,inspection, and testing requirements for process plant pipingsystems. Process plants include petroleum refineries; chemical,pharmaceutical, textile, paper, semiconductor, and cryogenicplants; and related process plants and terminals.

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ASME B31.3 applies to piping and piping components that are usedfor all fluid services, not just hydrocarbon services. These includethe following:

Raw, intermediate, and finished chemicals.

Petroleum products.

Gas, steam, air, and water.

Fluidized solids.

Refrigerants.

Cryogenic fluids.

The scope also includes piping that interconnects pieces or stageswithin a packaged-equipment assembly.

The following are excluded from the scope of ASME B31.3:

Piping systems for internal gauge pressures at or above zerobut less than 15 psi, provided that the fluid is nonflammable,nontoxic, and not damaging to human tissue, and its designtemperature is from -20F through 366F.

Power boilers that are designed in accordance with the ASMEBoiler and Pressure Vessel Code Section I and external boilerpiping that must conform to ASME B31.1.

Tubes, tube headers, crossovers, and manifolds that arelocated inside a fired heater enclosure.

Pressure vessels, heat exchangers, pumps, compressors, andother fluid-handling or processing equipment. This includesboth internal piping and connections for external piping.

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III. MATERIAL SELECTION CONSIDERATIONS

Piping system material selection considerations are discussed below.

A. Strength

A material's strength is defined by its yield, tensile, creep, andfatigue strengths. Alloy content, material grain size, and the steelproduction process are factors that affect material strength.

1.0 Yield and Tensile Strength

A stress-strain diagram that is produced from a standardtensile test (Figure 3.1) illustrates the yield and tensilestrengths. As the stress in a material increases, itsdeformation also increases. The yield strength is the stressthat is required to produce permanent deformation in thematerial (Point A in Figure 3.1).

If the stress is further increased, the permanent deformationcontinues to increase until the material fails. The maximumstress that the material attains is the tensile strength (Point Bin Figure 3.1). If a large amount of strain occurs in goingfrom Point A to Point C, the rupture point, the material is saidto be ductile. Steel is an example of a ductile material. If thestrain in going from Point A to Point C is small, the materialis brittle. Gray cast iron is an example of a brittle material.

SA

BC

E

Typical Stress-Strain Diagram for SteelFigure 3.1

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2.0 Creep Strength

Below about 750F for a given stress, the strain in mostmaterials remains constant with time. Above thistemperature, even with constant stress, the strain in thematerial will increase with time. This behavior is known ascreep. The creep strength, like the yield and tensilestrengths, varies with temperature. For a particulartemperature, the creep strength of a material is the minimumstress that will rupture the material during a specified periodof time.

The temperature at which creep strength begins to be afactor is a function of material chemistry. For alloy materials(i.e., not carbon steel) creep strength becomes aconsideration at temperatures higher than 750F.

3.0 Fatigue Strength

The term fatigue refers to the situation where a specimenbreaks under a load that it has previously withstood for alength of time, or breaks during a load cycle that it haspreviously withstood several times. The first type of fatigueis called static, and the second type is called cyclic.Examples of static fatigue are: creep fracture and stresscorrosion cracking. Static fatigue will not be discussedfurther in this course.

One analogy to cyclic fatigue is the bending of a paper clip.The initial bending beyond a certain point causes the paperclip to yield (i.e., permanently deform) but not break. Theclip could be bent back and forth several more times and stillnot break. However after a sufficient number of bending(i.e., load) cycles, the paper clip will break under thisrepetitive loading. Purely elastic deformation (i.e., withoutyielding) cannot cause a cyclic fatigue failure.

The fatigue strength of a material under cyclic loading canthen be defined as the ability to withstand repetitive loadingwithout failure. The number of cycles to failure of a materialdecreases as the stress resulting from the applied loadincreases.

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B. Corrosion Resistance

Corrosion of materials involves deterioration of the metal bychemical or electrochemical attack. Corrosion resistance is usuallythe single most important factor that influences pipe materialselection. Table 3.1 summarizes the typical types of piping systemcorrosion.

General or UniformCorrosion

Characterized by uniform metal loss over entire surface of material.May be combined with erosion if material is exposed to high-velocityfluids, or moving fluids that contain abrasive materials.

PittingCorrosion

Form of localized metal loss randomly located on material surface.Occurs most often in stagnant areas or areas of low-flow velocity.

Galvanic Corrosion Occurs when two dissimilar metals contact each other in corrosiveelectrolytic environment. The anodic metal develops deep pits orgrooves as a current flows from it to the cathodic metal.

Crevice Corrosion Localized corrosion similar to pitting. Occurs at places such asgaskets, lap joints, and bolts, where a crevice can exist.

Concentration CellCorrosion

Occurs when different concentration of either corrosive fluid ordissolved oxygen contacts areas of same metal. Usually associatedwith stagnant fluid.

Graphitic Corrosion Occurs in cast iron exposed to salt water or weak acids. Reducesiron in the cast iron and leaves the graphite in place. Result isextremely soft material with no metal loss.

Typical Types of Piping System CorrosionTable 3.1

For process plant piping systems in corrosive service, corrosionprotection is usually achieved by using alloys that resist corrosion.The most common alloys used for this purpose are chromium andnickel. Low-alloy steels with a chromium content of 1% to 9%and stainless steels are used in corrosive environments.

C. Material Fracture Toughness

One way to characterize the fracture behavior of a material is theamount of energy necessary to initiate and propagate a crack at agiven temperature. This is the material's fracture toughness, which

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decreases as the temperature decreases. Tough materials requirea relatively large amount of energy to initiate and propagate acrack. The impact energy required to fracture a material sample ata given temperature can be measured by standard Charpy V-notchtests.

Various factors other than temperature affect the fracturetoughness of a material. These include the following:

Chemical composition or alloying elements.

Heat treatment.

Grain size.

The major chemical elements that affect a material's fracturetoughness are carbon, manganese, nickel, oxygen, sulfur, andmolybdenum. High carbon content, or excessive amounts ofoxygen, sulfur, or molybdenum, hurts fracture toughness. Theaddition of manganese or nickel improves fracture toughness.

D. Fabricability

A material must be available in the shapes or forms that arerequired, and it typically must be weldable. In piping systems,some common shapes and forms include the following:

Seamless pipe.

Plate that is used for welded pipe.

Wrought or forged elbows, tees, reducers, and crosses.

Forged flanges, couplings, and valves.

Cast valves.

E. Availability and Cost

The last factors that affect piping material selection are availabilityand cost. Where there is more than one technically acceptablematerial, the final selection must consider what is readily availableand what are the relative costs of the acceptable options. Forexample, the use of carbon steel with a large corrosion allowancecould be more expensive than using a low-alloy material with asmaller corrosion allowance.

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IV. PIPING COMPONENTS

A. Fittings, Flanges, and Gaskets

1.0 Pipe Fittings

Fittings are used to make some change in the geometry of apiping system. This change could include:

Modifying the flow direction.

Bringing two or more pipes together.

Altering the pipe diameter.

Terminating a pipe.

The most common types of fittings are elbows, tees,reducers, welding outlets, pipe caps, and lap joint stub ends.These are illustrated in Figures 4.1 through 4.6. Fittings maybe attached to pipe by threading, socket welding, or buttwelding.

An elbow or return (Figure 4.1) changes the direction of apipe run. Standard elbows change the direction by either45 or 90. Returns change the direction by 180.

90 45

180 Return

Elbow and ReturnFigure 4.1

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A tee (Figure 4.2) provides for the intersection of threesections of pipe.

A straight tee has equal diameters for both the run andbranch pipe connections.

A reducing-outlet tee has a branch diameter which issmaller in size than the run diameter.

A cross permits the intersection of four sections of pipeand is rarely seen in process plants.

TeeFigure 4.2

A reducer (illustrated in Figure 4.3) changes the diameter ina straight section of pipe. The centerlines of the large andsmall diameter ends coincide in a concentric reducer,whereas they are offset in an eccentric type.

Concentric Eccentric

ReducerFigure 4.3

A welding outlet fitting, or integrally reinforced branchconnection (Figure 4.4) has all the reinforcement required tostrengthen the opening contained within the fitting itself.

81

Typical Integrally Reinforced Branch ConnectionFigure 4.4

A pipe cap (Figure 4.5) closes off the end of a pipe section.The wall thickness of a butt-welded pipe cap will typically beidentical to that of the adjacent pipe section.

CapFigure 4.5

A lap-joint stub end (Figure 4.6) is used in conjunction withlap-joint flanges.

Note square corner

R

R

Enlarged Section of Lap

Lap-Joint Stub EndFigure 4.6

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2.0 Flanges

A flange connects a pipe section to a piece of equipment,valve, or another pipe such that relatively simpledisassembly is possible. Disassembly may be required formaintenance, inspection, or operational reasons. Figure 4.7shows a typical flange assembly. Flanges are normally usedfor pipe sizes above NPS 1.

Flange

Bolting

Gasket

Typical Flange AssemblyFigure 4.7

A flange type is specified by stating the type of attachmentand the type of face. The type of attachment defines howthe flange is connected to a pipe section or piece of

83

equipment (e.g., welded). The type of flange face or facingdefines the geometry of the flange surface that contacts thegasket. Table 4.1 summarizes the types of flangeattachments and faces. Figure 4.8 illustrates flange facingtypes.

Flange Attachment Types Flange Facing Types

Threaded Flanges Flat Faced

Socket-Welded Flanges

Blind Flanges Raised Face

Slip-On Flanges

Lapped Flanges Ring Joint

Weld Neck Flanges

Types of Flange Attachment and FacingTable 4.1

84

Flange Facing TypesFigure 4.8

85

3.0 Gaskets

A gasket is a resilient material that is inserted between theflanges and seated against the portion of the flanges calledthe face or facing. The gasket provides the seal betweenthe fluid in the pipe and the outside, and thus preventsleakage. Bolts compress the gasket to achieve the seal andhold the flanges together against pressure and otherloadings.

The three gasket types typically used in pipe flanges forprocess plant applications are:

Sheet.

Spiral wound.

Solid metal ring.

B. Flange Rating

ASME B16.5, Pipe Flanges and Flanged Fittings, provides steelflange dimensional details for standard pipe sizes through NPS 24.Specification of an ASME B16.5 flange involves selection of thecorrect material and flange "Class." The paragraphs that followdiscuss the flange class specification process in general terms.

Flange material specifications are listed in Table 1A in ASME B16.5(excerpted in Table 4.2). The material specifications are groupedwithin Material Group Numbers. For example, if the piping isfabricated from carbon steel, the ASTM A105 material specificationis often used. ASTM A105 material is in Material Group No. 1.1.Refer to ASME B16.5 for additional acceptable materialspecifications and corresponding Material Group Numbers.

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ASME B16.5, Table 1A, Material Specification List (Excerpt)Table 4.2

After the Material Group has been determined, the next step is toselect the appropriate Class. The Class is determined by usingpressure/temperature rating tables, the Material Group, designmetal temperature, and design pressure. Selecting the Class setsall the detailed dimensions for flanges and flanged fittings. Theobjective is to select the lowest Class that is appropriate for thespecified design conditions.

Table 2 of ASME B16.5 provides the information that is necessaryto select the appropriate flange Class for the specified designconditions. ASME B16.5 has seven classes: Class 150, 300, 400,600, 900, 1,500, and 2,500. Each Class specifies the designpressure and temperature combinations that are acceptable for aflange with that designation. As the number of the Class increases,the strength of the flange increases for a given Material Group. Ahigher flange Class can withstand higher pressure and temperaturecombinations. Table 4.3 is an excerpt from Table 2 of ASME B16.5and shows some of the temperature and pressure ratings forseveral Material Groups. Material and design temperaturecombinations that do not have a pressure indicated are notacceptable.

Specifying the flange size, material, and class completes most ofwhat is necessary for selecting an ASME B16.5 flange. The flangetype, facing, bolting material, and gasket type and material must be

87

added to complete the flange selection process. Discussion ofthese other factors is beyond the scope of this course.

Material GroupNo. 1.8 1.9 1.10

Classes 150 300 400 150 300 400 150 300 400Temp., F-20 to 100 235 620 825 290 750 1000 290 750 1000

200 220 570 765 260 750 1000 260 750 1000300 215 555 745 230 720 965 230 730 970400 200 555 740 200 695 885 200 705 940500 170 555 740 170 695 805 170 665 885600 140 555 740 140 605 785 140 605 805650 125 555 740 125 590 785 125 590 785700 110 545 725 110 570 710 110 570 755750 95 515 685 95 530 675 95 530 710800 80 510 675 80 510 650 80 510 675850 65 485 650 65 485 600 65 485 650900 50 450 600 50 450 425 50 450 600950 35 320 425 35 320 290 35 375 505

1000 20 215 290 20 215 190 20 260 345

ASME B16.5, Pressure-Temperature Ratings (Excerpt)Table 4.3

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SAMPLE PROBLEM 1 - DETERMINE FLANGE RATING

A new piping system will be installed at an existing plant. It is necessary todetermine the ASME class that is required for the flanges. The following designinformation is provided:

Pipe Material: 1 Cr Mo.

Design Temperature: 700F.

Design Pressure: 500 psig.

SOLUTION

Determine the Material Group Number for the flanges by referring to ASME Table1A (excerpted in Table 4.2). Find the 1 Cr Mo material in the NominalDesignation Steel column. The material specification for forged flanges would beA182 Gr. F11, and the corresponding material Group Number is 1.9.

Refer to Table 2 for Class 150 (excerpted in Table 4.3). Read the allowabledesign pressure at the intersection of the 700F design temperature and MaterialGroup 1.9. This is only 110 psig and is not enough for this service.

Now check Class 300 and do the same thing. The allowable pressure in thiscase is 570 psig, which is acceptable.

The required flange Class is 300.

89

V. VALVES

A. Valve Functions

The possible valve functions must be known before being able toselect the appropriate valve type for a particular application. Fluidflows through a pipe, and valves are used to control the flow. Avalve may be used to block flow, throttle flow, or prevent flowreversal.

1.0 Blocking Flow

The block-flow function provides completely on or completelyoff flow control of a fluid, generally without throttling orvariable control capability. It might be necessary to blockflow to take equipment out of service for maintenance whilethe rest of the unit remains in operation, or to separate twoportions of a single system to accommodate variousoperating scenarios.

2.0 Throttling Flow

Throttling may increase or decrease the amount of fluidflowing in the system and can also help control pressurewithin the system. It might be necessary to throttle flow toregulate the filling rate of a pressure vessel, or to control unitoperating pressure levels.

3.0 Preventing Flow Reversal

It might be necessary to automatically prevent fluid fromreversing its direction during sudden pressure changes orsystem upsets. Preventing reverse flow might be necessaryto avoid damage to a pump or a compressor, or toautomatically prevent backflow into the upstream part of thesystem due to process reasons.

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B. Primary Valve Types

1.0 Gate Valve

Most valves in process plants function as block valves.About 75% of all valves in process plants are gate valves.The gate valve is an optimum engineering and economicchoice for on or off service. The gate valve is not suitable tothrottle flow because it will pass the maximum possible flowwhile it is only partially open. Figure 5.1 illustrates a typicalfull-port gate valve.

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1. Handwheel Nut2. Handwheel3. Stem Nut4. Yoke5. Yoke Bolting6. Stem7. Gland Flange8. Gland9. Gland Bolts or

Gland-Eye Boltsand Nuts

10. Gland Lug Boltsand Nuts

11. Stem Packing12. Plug13. Lantern Ring14. Backseat Bushing15. Bonnet16. Bonnet Gasket17. Bonnet Bolts and

Nuts18. Gate19. Seat Ring20. Body21. One-Piece Gland

(Alternate)22. Valve Port

Full-Port Gate ValveFigure 5.1

2.0 Globe Valve

The globe valve is the type most commonly used to throttleflow in a process plant. In the smaller sizes, they are

92

typically used as hand-control valves. In larger sizes,applications are limited primarily to bypasses at control valvestations. They provide relatively tight shutoff in control valvebypasses during normal operations; they serve as temporaryflow controllers when control valves must be taken out ofservice.

Because all globe valve patterns involve a change in flowdirection, they are not suitable for piping systems thatrequire scraping or rodding. Globe valves are rarely used forstrictly on/off block valve operations because conventionalgate valves adequately serve that function at a lower costand a much lower pressure drop.

3.0 Check Valve

Check valves prevent flow reversal. Typical check valveapplications are in pump and compressor discharge pipingand other systems that require protection against backflow.Valves which contain a disc or discs that swing out of theflow passage area usually create a lower pressure drop inthe system than those which contain a ball or pistonelement. These latter elements remain in the flowstreamand the port configurations frequently include an angularchange in flow direction. For all process designs, theintended purpose of check valves is to prevent gross flowreversal, not to effect complete leakage-free, pressure-tightshutoff of reverse flow.

The selection of a particular check valve type generallydepends on size, cost, availability, and service. Ball and liftcheck valves are usually the choice for sizes NPS 2 andsmaller, while swing check and plate check valves are usedin the larger sizes.

3.1 Swing Check Valve

The main components of a swing check valve (Figure5.2) are the body, disc, cap, seat ring, disc hinge, andpin. The disc is hinged at the top and closes againsta seat in the valve body opening. It swings freely inan arc from the fully closed position to one thatprovides unobstructed flow. The valve is kept openby the flow, and disc seating is accomplished bygravity and/or flow reversal.

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Cap

Hinge

DiscBody

Pin

SeatRing

FlowDirection

Swing Check ValveFigure 5.2

3.2 Ball Check Valve

The ball check valve utilizes a ball to prevent flowreversal (Figure 5.3). The basic types are thestraight-through- and globe-type (90 change indirection, similar to a typical globe valve body). Ballcheck valves are available in sizes NPS through 2in all ratings and materials used in process plants.Their low cost usually makes them the first choice forvalves sized NPS 2 and smaller, provided thepressure drop is not a concern.

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Ball Check ValveFigure 5.3

3.3 Lift Check Valve

A lift check valve (Figure 5.4) usually depends ongravity for operation. Under forward flow, a piston ordisc is lifted off the seat by the fluid while beingretained in the valve by guides. On reverse flow, thepiston or disc is forced against the seat to blockfurther flow. Some lift check valves utilize springloading to assure positive seating.

Lift check valves employing the disc- or piston-typemechanism are available in sizes from NPS through 2 in all ratings and materials used in processplants. They are most commonly used in the higherASME B16.5 ratings (Class 300 and greater), andwhere tighter shutoff is required. Valves of this typeshould only be used in clean services.

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SeatRing

PistonFlow

Direction

Lift Check ValveFigure 5.4

3.4 Wafer Check Valve

The wafer body or flangeless valve is a valve bodywithout flanges (Figure 5.5). Valves of this type areplaced between pipe flanges and held in place by thecompressive force between the flanges andtransmitted through the gaskets. The lug-wafer (orsingle-flanged) valve is also shown in Figure 5.5.Valves of this type are mounted between pipe flangesand are held in place by cap screws, machine bolts,or stud bolts which thread into the valve body.

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Figure 5.5

3.5 Ball Valve

Ball valves (Figure 5.6) usually function as blockvalves. Ball valves are well suited for conditionswhere quick on/off and/or bubble-tight shut-off isrequired. The pressure/temperature ratings for ballvalve soft seats above ambient temperatures areusually lower than the ASME ratings for steel valves.This is because of the lower physical properties of thesoft-seat materials. Soft-sealed ball valves are notnormally used for throttling service because the soft-seats are subject to erosion or distortion/displacementcaused by fluid flow when the valve is in the partiallyopen position.

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No. Part Names1 Body2 Body Cap3 Ball4 Body Seal Gasket5 Seat6 Stem7 Gland Flange8 Stem Packing9 Gland Follower10 Thrust Bearing11 Thrust Washer12 Indicator Stop13 Snap Ring14 Gland Bolt15 Stem Bearing16 Body Stud Bolt & Nuts17 Gland Cover18 Gland Cover Bolts19 Handle

Ball ValveFigure 5.6

3.6 Plug Valve

Plug valves (Figure 5.7) usually function as blockvalves. They are well suited for conditions wherequick on/off and/or bubble-tight shutoff is required.The soft-seal-types may have lowertemperature/pressure ratings than the ASME ratingsfor steel valves because of the lesser physicalproperties of the soft-seat materials. Soft-seal plugvalves are not normally used for throttling servicesince the soft seals are subject to erosion ordistortion/displacement caused by fluid flow when thevalve is partially open.

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Wedge

Molded-In Resilient Seal

Sealing Slip

Plug ValveFigure 5.7

C. Valve Selection Process

The steps that follow provide a general procedure for selectingvalves and valve components.

1. Identify the necessary design information. This includes designpressure and temperature, valve function, material, etc.

2. Identify potentially appropriate valve types (i.e., ball, butterfly,check, etc.) and components based on application and function(i.e., block, throttle, or reverse flow prevention).

3. Determine valve application requirements (i.e., design or servicelimitations).

4. Finalize valve selection. Check which factors need consideration iftwo or more valves are suitable.

5. Provide a full technical description. This is done by specifying thevalve type, material, flange rating, etc.

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Exercise 1 Determine Required Flange Rating

For the piping system described below, determine the required flange rating (orClass) in accordance with ASME B16.5.

Pipe: 1 Cr Mo

Flanges: A - 182 Gr. F11

Design Temperature: 900F

Design Pressure: 375 psig

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VI. DESIGN

A. Design Conditions

1.0 General

Normal operating conditions are those expected to occurduring normal operation, excluding failure of any operatingdevice, operator error, and the occasional, short-termvariations stated in the applicable code. Startup andcontrolled shutdown of plants and similar foreseeableevents are included within normal operation.

Design conditions are those which govern the design andselection of piping components, and are based on the mostsevere conditions expected to occur in service. A suitablemargin is used between the normal operating and designconditions to account for normal operating variations.ASME B31.3 does not specify what margins should be usedbetween operating and design conditions; suitable marginsare determined by the user based on his experience.

2.0 Determining Design Pressure and Temperature

The design pressure and temperature are used to calculatethe required thickness of pipe and other design details. Thedesign temperature is used to determine the material basicallowable stress and other design requirements. The valuesfor design pressure and temperature are based on processrequirements.

Piping system design conditions generally are determinedbased on the design conditions of the equipment to whichthe piping is attached. Determining the piping designconditions consists of:

1. Identifying the equipment to which the piping system isattached.

2. Determining the design pressure and design temperaturefor the equipment.

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3. Considering contingent design conditions, such as upsetsnot protected by pressure-relieving devices.

4. Considering the direction of flow between the equipment.

5. Verifying the values with the process engineer.

B. Loads and Stresses

1.0 Classification of Loading Conditions

Pipe loads are classified into three principal types: sustainedloads, thermal expansion loads, and occasional loads.

Sustained loads are those that act on the piping systemduring all or most of its operating time. Sustained loadsconsist of two main categories: pressure and weight. Thepressure load (caused by the design pressure) usually refersto internal pressure, although some piping systems may alsobe designed for external pressure. Design pressure isdefined as the maximum sustained pressure that a pipingsystem must contain without exceeding its allowable stresslimits. Design pressure is normally the governing factor indetermining the minimum required pipe wall thickness.

As shown in Figure 6.1, internal pressure produces bothcircumferential (i.e., hoop) stress and longitudinal stress inthe pipe wall.

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Sl

tP

Sc

Sc

Sl

t

P

=

=

=

=

Longitudinal Stress

Circumferential (Hoop) Stress

Wall Thickness

Internal Pressure

Stresses Produced By Internal PressureFigure 6.1

The weight refers to the total design weight load. The totalweight load includes the weight of the pipe, the fluid in thepipe, fittings, insulation, internal lining, valves, valveoperators, flanges, supports and any other concentratedloads. The weight loads produce a longitudinal stress in thepipe wall.

A piping system will expand or contract due to changes in itsoperating temperature. Thermal expansion loads arecreated when the free expansion and contraction of thepiping is prevented at its end points by connectedequipment, or prevented at intermediate points by supportsand/or restraints that are installed. The resulting loadscause thermal stresses in the pipe. Increasing the restraintin a system increases the loading and results in higherthermal expansion stresses. Another cause of pipe thermalloads can be from the thermal expansion of equipment at

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pipe-to-equipment nozzle attachment points, causingdisplacements in the piping system.

The third type of loading comes from occasional loads.Occasional loads act during a small percentage of thesystems operating time. Occasional loads involve seismicand/or dynamic loading. The degree of seismic loading thatmust be considered varies with geographic location and isdefined by a seismic zone (Ref. ANSI/ASCE 7). Dynamicloads may be caused by safety-relief valve discharges, valveoperation (both opening and closing), steam/water hammer,surge due to pump start-up and shutdown, and wind loads.

2.0 Stress Categorization

To evaluate the stresses in a piping system, it is necessaryto distinguish among primary, secondary, and peak stresses.

Primary stresses are the direct, shear, or bendingstresses generated by the loading.

Secondary stresses are those acting across the pipe wallthickness due to a differential radial deflection of the pipewall. Secondary stresses cause local yielding and minordistortions. Secondary stresses, unlike primary stresses,are not a source of direct failure from a single loadapplication.

Peak stresses are more localized stresses which dieaway rapidly within a short distance from their origin.Peak stresses occur in areas such as welds, fittings,branch connections, and other piping components wherestress concentrations and possible fatigue failure mightoccur. Peak stresses are considered equivalent insignificance to secondary stresses, but they do not causeany significant distortion.

3.0 Allowable Stresses

The basic allowable stress is a function of materialproperties, temperature, and safety factors. The basicallowable stress provides an upper limit for the actualstresses.

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Allowable stresses for sustained loads are established toprevent general collapse or excessive distortion of thepiping system.

Allowable stresses for thermal expansion loads areestablished to prevent a localized fatigue failure.

Allowable stresses for occasional loads are establishedto prevent wind and earthquake type loads fromcollapsing or distorting the piping system.

Actual stresses are calculated for the following load cases:

Sustained loads

Occasional loads

Stress range due to differential thermal expansion

The piping system is designed such that the calculatedstresses are no larger than the appropriate allowablestresses.

Table 6.1 (excerpted from ASME B31.3 Table A-1) listsbasic allowable stresses in tension versus temperature forseveral materials.

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Basic Allowable Stress S, ksi. At Metal Temperature, F.

Material Spec. No/Grade 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Carbon Steel A 106 B 20.0 20.0 20.0 20.0 18.9 17.3 16.5 10.8 6.5 2.5 1.0

C - Mo A 335 P1 18.3 18.3 17.5 16.9 16.3 15.7 15.1 13.5 12.7 4. 2.4

1 - Mo A 335 P11 20.0 18.7 18.0 17.5 17.2 16.7 15.6 15.0 12.8 6.3 2.8 1.2

18Cr - 8Ni pipe A 312 TP304 20.0 20.0 20.0 18.7 17.5 16.4 16.0 15.2 14.6 13.8 9.7 6.0 3.7 2.3 1.4

16Cr - 12Ni-2Mopipe

A 312 TP316 20.0 20.0 20.0 19.3 17.9 17.0 16.3 15.9 15.5 15.3 12.4 7.4 4.1 2.3 1.3

ASME B31.3, Table A-1 (Excerpt),Basic Allowable Stresses in Tension for Metal

Table 6.1

C. Pressure Design of Components

1.0 General

Two different types of pressure may be imposed on a pipingsystem: external or internal. Most piping systems need onlybe designed for internal pressure. Some piping systemsmay be subject to a negative pressure or vacuum conditionduring operation (e.g., process vacuum conditions, steam-out, underwater lines, etc.) and must be designed forexternal pressure. This section only discusses the internalpressure design of straight sections of pipe. Refer to ASMEB31.3 for design requirements for external pressure.

2.0 Required Wall Thickness for Internal Pressure ofStraight Pipe

The required wall thickness for internal pressure iscalculated using the following equation:

)PYSE(2PDt+

=

Where:

t = Required thickness for internal pressure, in.

P = Internal design pressure, psig

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S = Allowable stress in tension (Table 6.1), psi

E = Longitudinal-joint quality factor (Table 6.2)

Y = Wall thickness correction factor (Table 6.3)

The longitudinal-joint quality factor is based on:

Whether the pipe is seamless or has a weldedlongitudinal seam

The pipe material and welding process (if welded pipe)

The wall thickness correction factor is based on the type ofsteel and the design temperature.

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Spec.No.

Class (or Type) Description Ej

Carbon Steel

API5L

. . .

. . .

. . .

Seamless pipeElectric resistance welded pipe

Electric fusion welded pipe, double butt, straight orspiral seam

Furnace butt welded

1.000.850.95

A 53 Type SType EType F

Seamless pipeElectric resistance welded pipe

Furnace butt welded pipe

1.000.850.60

A 106 . . . Seamless pipe 1.00

Low and Intermediate Alloy Steel

A 333 . . .. . .

Seamless pipeElectric resistance welded pipe

1.000.85

A 335 . . . Seamless pipe 1.00

Stainless Steel

A 312 . . .. . .. . .

Seamless pipeElectric fusion welded pipe, double butt seamElectric fusion welded pipe, single butt seam

1.000.850.80

A 358 1, 3, 452

Electric fusion welded pipe, 100% radiographedElectric fusion welded pipe, spot radiographedElectric fusion welded pipe, double butt seam

1.000.900.85

Nickel and Nickel Alloy

B 161 . . . Seamless pipe and tube 1.00

B 514 . . . Welded pipe 0.80

B 675 All Welded pipe 0.80

ASME B31.3, Table A-1B (Excerpt),Basic Quality Factors for Longitudinal Weld Joints, Ej

Table 6.2

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Temperature, F

Materials 900 & lower 950 1000 1050 1100 1150 & up

FerriticSteels

0.4 0.5 0.7 0.7 0.7 0.7

AusteniticSteels

0.4 0.4 0.4 0.4 0.5 0.7

OtherDuctileMetals

0.4 0.4 0.4 0.4 0.4 0.4

Cast iron 0.0 . . . . . . . . . . . . . . .

ASME B31.3, Table 304.1.1 (Excerpt),Values of Coefficient Y

Table 6.3

Two additional thickness allowances must be considered todetermine the final required pipe wall thickness: corrosionallowance and mill tolerance.

Corrosion allowance (CA) is an additional thickness that isadded to account for wall thinning and wear that can occur inservice. The corrosion allowance is based on experienceand data for the particular pipe material and fluid service.Thus:

tm = t + CA

Where:

tm = Total minimum required wall thickness, in.

Mill tolerance accounts for the difference between the actualmanufactured pipe wall thickness and the nominal wallthickness specified in the relevant pipe dimensionalstandard. The typical pipe mill tolerance is 12.5%. Thismeans that the as-supplied pipe wall thickness can be up to12.5% thinner than the nominal thickness and still meet itsspecification requirements. Use the following equation todetermine the minimum required nominal thickness to order:

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875.0tt mnom =

Where:

tnom = Minimum required nominal pipe wall thickness, in.

Each pipe size has several standard nominal thicknessesthat are available. The nominal pipe thickness that isspecified for a system must be selected from those readilyavailable and be at least equal to tnom.

3.0 Curved and Mitered Pipe Segments

The minimum required thickness of curved pipe (elbows orbends) is the same as that required for straight pipesections. A mitered bed is fabricated by welding straightpipe sections together to produce the direction change. Amitered bend is generally less expensive than a wroughtelbow for large pipe sizes (over ~ NPS 24). The minimumrequired thickness for a miter may be greater that that of theconnected straight pipe sections, depending on the numberof miter welds, design conditions, size, etc. Refer to ASMEB31.3 for thickness calculation requirements.

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SAMPLE PROBLEM 2 - DETERMINE PIPE WALL THICKNESS

A piping system must be modified to add a new, spare heat exchanger. Youhave been assigned the responsibility to determine the required wall thicknessfor the pipe from the heat exchanger to several pumps. The piping system willhave a design temperature of 650F. The design pressure is 1,380 psig. Thepipe outside diameter is 14 in. The material is ASTM A335, Gr. P11 (1 Cr Mo), seamless. Corrosion allowance is 0.0625 in.

What is the minimum required thickness for this pipe?

SOLUTION

The following equation applies:

( )PYSE2PDt+

=

Based on the given information:

P = 1,380 psig.

D = 14 in.

For the A335, Gr. P 11 material:

S = 16,150 psi. [Table A-1 of ASME B31.3 at 650F

E = 1.0 [Table A-1B of ASME B31.3]

Y = 0.4 [Table 304.1.1 of ASME B31.3, since thematerial is ferritic and the temperature is below900oF.

Since all the required parameters have now been determined, the requiredinternal pressure thickness may be calculated as follows:

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( ) ( )[ ].in 577.0t

4.0380,11150,16214380,1t

=

+

=

In this case, a 0.0625 in. corrosion allowance has been specified.

Therefore:

tm = t + c = 0.577 + 0.0625

tm = 0.6395 in.

.in0.7310.875

0.6395tnom ==

4.0 Branch Reinforcement Requirements

A pipe with a branch connection is weakened by the requiredopening. Unless the wall thickness of the pipe is sufficientlygreater than that required to sustain the pressure, additionalreinforcement must be provided.

ASME B31.3 contain rules for determining the requiredreinforcement for both welded and extruded outlet-typebranch connections. Branch connections can also be madeusing forged or wrought fittings (i.e., tees, laterals, crosses,couplings, or half-couplings), or an integrally reinforcedbranch connection. Reinforcement calculations are notrequired for forged or wrought type branch connectionsbecause they have adequate inherent reinforcement andhave been designed and tested to meet ASME B31.3requirements. This section discusses only branchconnections that are fabricated by welding a branch pipe tothe run pipe.

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4.1 Area Removed By Branch Connection

A volume of metal is removed from a pipe wall when ahole is cut in it for a branch connection. However, asimplification is made when evaluating branchreinforcement requirements.

An imaginary plane is passed through the branch andrun pipes, and the intersection is viewed in cross-section. The removed volume of pipe wall is thenlooked at as an area (see Figure 6.2).

DbTb

c Nom.Thk.

Nom.Thk.

Dh

Thth

Tr

c

tbMillTol.

MillTol.

d1

d2 d2

L4

ReinforcementZone LimitsReinforcement

Zone Limits

A1

A3

A4A4

A2 A2

A3

Pipe C

Welded Branch ConnectionFigure 6.2

4.2 Limits of Reinforcement Zone

The reinforcing zone is the region where credit maybe taken for any reinforcement that is present. Thebranch connection must have adequate reinforcementto compensate for the weakening caused by cutting ahole in the run pipe. This reinforcement:

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Must be located reasonably close to the openingto provide any practical benefit.

May be located in the branch pipe, the run pipe, orboth.

Additional material located outside of this zone is noteffective for reinforcement.

4.3 Branch Connection Reinforcement

Branch connection reinforcement located within thereinforcement zone may come from one or more ofthe following sources.

Excess thickness available in the branch orheader pipe.

Additional reinforcement added in the form of apad, ring, saddle, or weld metal.

If excess thicknesses in the branch and header pipesdo not provide enough reinforcement, additional metalmay be added.

4.4 Reinforcement Area

The required reinforcement area is based on themetal area removed. This is calculated using:

=

sin)cT(2D

d bb1

Where:

d1 = Effective length removed from the run pipe,in.

Db = Branch outside diameter, in.Tb = Minimum branch thickness, in.c = Corrosion allowance, in.

= Acute angle between branch and header

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The required reinforcement area, A1, is thencalculated using :

)sin2(dtA 1h1 =

Where:

th = Minimum required header thickness, in.

4.5 Reinforcement Pad

Additional branch reinforcement is needed when therequired area exceeds the available area, and may beprovided by locally increasing the thickness of eitherthe header or branch pipe. However, it is usuallymore economical to provide a reinforcement pad tosupply the additional reinforcement