June 2000

Process Industry PracticesPiping

PIP PNC00004Piping Flexibility Analysis Criteria

for ASME B31.3 Metallic Piping

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES

In an effort to minimize the cost of process industry facilities, this Practice hasbeen prepared from the technical requirements in the existing standards of majorindustrial users, contractors, or standards organizations. By harmonizing thesetechnical requirements into a single set of Practices, administrative, application, andengineering costs to both the purchaser and the manufacturer should be reduced. Whilethis Practice is expected to incorporate the majority of requirements of most users,individual applications may involve requirements that will be appended to and takeprecedence over this Practice. Determinations concerning fitness for purpose andparticular matters or application of the Practice to particular project or engineeringsituations should not be made solely on information contained in these materials. Theuse of trade names from time to time should not be viewed as an expression ofpreference but rather recognized as normal usage in the trade. Other brands having thesame specifications are equally correct and may be substituted for those named. AllPractices or guidelines are intended to be consistent with applicable laws andregulations including OSHA requirements. To the extent these Practices or guidelinesshould conflict with OSHA or other applicable laws or regulations, such laws orregulations must be followed. Consult an appropriate professional before applying oracting on any material contained in or suggested by the Practice.

This Practice is subject to revision at any time by the responsible Function Teamand will be reviewed every 5 years. This Practice will be revised, reaffirmed, orwithdrawn. Information on whether this Practice has been revised may be found athttp://www.pipdocs.org.

Process Industry Practices (PIP), Construction Industry Institute, TheUniversity of Texas at Austin, 3208 Red River Street, Suite 300, Austin,Texas 78705. PIP member companies and subscribers may copy this Practicefor their internal use.

Not printed with State funds

June 2000

Process Industry Practices Page 1 of 7

Process Industry PracticesPiping

PIP PNC00004Piping Flexibility Analysis Criteria

for ASME B31.3 Metallic Piping

Table of Contents

1. Introduction..................................21.1 Purpose ............................................. 21.2 Scope................................................. 2

2. References ...................................22.1 Process Industry Practices ................ 22.2 Industry Codes and Standards .......... 2

3. General .........................................3

4. Flexibility ......................................3

5. Design Basis ................................35.1 Thermal Effects ................................. 35.2 Weight Effects ................................... 35.3 Friction Effects ................................... 35.4 Wind Effects ...................................... 45.5 Seismic Effects .................................. 45.6 Pressure Relief Systems ................... 45.7 Water Hammer/Slug Flow ................. 45.8 Flanges .............................................. 45.9 Maximum Pipe Spans

and Deflections .................................. 45.10 Special Requirements........................ 4

6. External Load Limits onEquipment.................................... 56.1 General .............................................. 56.2 Rotating Machinery............................ 56.3 Reciprocating Compressors .............. 56.4 Air Cooled Heat Exchangers ............. 56.5 Pressure Vessels and Heat

Exchangers........................................ 56.6 Tank Nozzle Loads ............................ 5

7. Pipe Flexibility Requirements..... 6

8. Piping Flexibility AnalysisRecord Keeping........................... 6

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1. Introduction

1.1 PurposeThe purpose of this Practice is to outline the minimum basic requirements foranalyzing aboveground metallic piping systems for flexibility.

1.2 ScopeThis Practice provides basic piping flexibility analysis, design conditions, anddocumentation requirements for the flexibility analysis. All piping systems shall beevaluated and, where appropriate, analyzed for applicable conditions in accordancewith ASME B31.3 (henceforth referred to as the Code) and this Practice.

2. References

When adopted in this Practice, the latest edition of the following references in effect on thedate of contract award shall be used, except as otherwise noted. Short titles will be usedherein when appropriate.

2.1 Process Industry Practices (PIP) PIP PNFS0001 - Miscellaneous Pipe Support Details PIP RESE002 - Allowable Piping Loads on Rotating Machinery Nozzles

2.2 Industry Codes and Standards

American Petroleum Institute (API) API 618 - Reciprocating Compressors for Petroleum, Chemical, and Gas

Industry Services API 661 - Air-Cooled Heat Exchangers for General Refinery Services

American Society of Civil Engineers (ASCE) ASCE 7 - Minimum Design Loads for Buildings and Other Structures

American Society of Mechanical Engineers (ASME) ASME Boiler and Pressure Vessel Code

Section VIII - Pressure Vessels ASME B31.1 - Power Piping ASME B31.3 - Process Piping

Welding Research Council (WRC) WRC 107 - Local Stresses in Spherical and Cylindrical Shells Due to External

Loadings WRC 297 - Local Stresses in Cylindrical Shells Due to External Loadings on

Nozzles - Supplement to WRC 107

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3. General

3.1 The designer shall consider the most severe anticipated coincident pressure andtemperature condition(s).

3.2 The flexibility analysis shall consider the most severe specified temperaturecondition anticipated during start-up, normal operation, steam out/decoking,depressuring, shutdown, defined upset, cold branch, and regeneration. Analysis ofthis situation may require the combination of more than one load case to determinethe total displacement stress range.

Note: Cold branch shall include cases dealing with parallel lines where at leastone line (not always the same one) may be cold at any time. An example is threeparallel pumps where one pump (not always the same one) is normally shut down.

4. Flexibility

4.1 Any computerized pipe flexibility calculations shall be performed using owner-approved software.

4.2 Piping systems shall be analyzed for expansion, contraction, differential settlement,relief valve reactions, and effects due to weight, wind, seismic, and other mechanicalloading per the Code.

4.3 Expansion joints shall not be used unless approved by owner.

5. Design Basis

5.1 Thermal EffectsThe analysis shall be for the maximum temperature differential. Climatic effectsshall be considered in determining maximum differential temperature. The metaltemperature from the effect of solar radiation in the summer and the winter dry bulbdesign temperature should be used. Process conditions listed in Section 3.2 shall alsobe considered.

5.2 Weight EffectsThe weight of piping, piping components, refractory lining, piping insulation, fluidtransported, and fluid used for testing shall be taken into account in the analysis.Snow and ice loads shall be considered when required by project specifications.

5.3 Friction EffectsThe effect of frictional resistance to thermal movement of the pipe shall beconsidered in the design of piping systems. Frictionless unrestrained movement ofthe piping system shall be assumed only when the entire system is supported bymeans of rod or spring hangers. The effect of friction shall not be added to theanalysis to reduce either piping loads or stresses.

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5.4 Wind EffectsThe wind loads on piping systems shall be determined by the procedure outlined inASCE 7 or as specified by owner.

5.5 Seismic EffectsSeismic loads on piping systems shall be considered when required by owner or byjurisdiction, and as outlined in project specifications.

5.6 Pressure Relief SystemsThe discharge piping shall be restrained to contain the thrust loads. Forces andmoments due to valve discharge may be calculated by any method acceptable to theowner, such as ASME B31.1, Appendix II.

5.7 Water HammerPiping systems subject to water hammer shall be analyzed accordingly. Forces due towater hammer shall be determined and suitable pipe restraints shall be provided.

5.8 FlangesExternal bending moments on flanges shall be considered. External loads may beanalyzed by the equivalent pressure method or other methods acceptable to owner.Acceptance criteria shall be in accordance with project specifications.

5.9 Maximum Pipe Spans and DeflectionsIn determining pipe spans, maximum sag deflections shall be limited to 5/8 inch.Any deviations shall be approved by owner.

5.10 Special Requirements5.10.1 The increased stiffness of piping systems caused by a refractory lining shall

be included in the piping flexibility analysis. The increased stiffness due torefractory shall not be included in either the span calculations or thesustained load case (to protect against incremental collapse due to creep).

5.10.2 Large diameter thin wall (D/T 100) lines shall be analyzed for crushingloads at local stress points and reinforced as necessary.

5.10.3 When piping lifts off a support due to thermal movements, either thatsupport shall be removed for sustained load calculations or spring supportsshall be considered.

5.10.4 Attachments on welded ells or within two pipe diameters of the welds of anell decrease its flexibility. This reduced flexibility shall be considered in thepiping flexibility analysis. In the absence of better information, thisdecreased flexibility may be simulated (in a computer analysis) by placing aflange pair at the nearest weld. Although not addressed directly byAppendix D of the Code, 45 degree ells shall have their flexibility reducedby placing a flange pair at each end.

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5.10.5 Branches at angles other than 90 degrees are not addressed by Appendix Dof the Code. For flexibility purposes, testing has shown that these branchesact like unreinforced connections. In the absence of applicable data orrigorous analysis, these branches may be modeled by doubling the defaultstress intensification factor for unreinforced fabricated tees.

5.10.6 Tees with aspect ratios of 3:4 have been found to be non-conservative. Thesetees shall have their stress intensification factor increased by 25%.

5.10.7 Piping systems supported primarily by rod hangers shall accommodate therods rotation and the consequent load impact on near by nozzles.

5.10.8 Unless otherwise approved by owner, use of cold spring for piping systemsthat connect to rotating equipment (compressors, turbine pumps) shall not beallowed.

6. External Load Limits on Equipment

6.1 GeneralLoads imposed on equipment by the piping shall not exceed the lesser of thatallowed by the equipment manufacturer or that listed in the applicable references inthis Practice unless otherwise approved by owner.

6.2 Rotating MachineryAllowable nozzle loads for rotating machinery shall be in accordance withPIP RESE002.

6.3 Reciprocating CompressorsReciprocating compressor piping shall be analyzed in accordance with API 618.

6.4 Air Cooled Heat ExchangersNozzle loads shall comply with the load criteria of API 661 unless otherwise statedin project specifications.

6.5 Pressure Vessels and Heat ExchangersWhere appropriate, nozzle loads shall be evaluated in accordance with WRC 107 andWRC 297, as applicable. If the nozzle/vessel geometry is outside the geometry limitof WRC 107 or WRC 297, other acceptable client-approved local stress analysismethods may be used; extrapolation of the curves in these documents is notacceptable. Allowable stresses shall be based on ASME Boiler and Pressure VesselCode, Section VIII, Division 1 or 2, as applicable.

6.6 Tank Nozzle LoadsNozzle loads shall be evaluated per owners requirements.

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7. Pipe Flexibility Requirements

7.1 All piping systems shall be reviewed to identify those that may be outside therequirements of Section 7.2 and that may still require flexibility analysis.

7.2 A formal flexibility analysis shall be performed on all of the following pipingsystems (see Code, Paragraph 319.4.2):

a. All lines connected to load/stress-sensitive equipmentb. All process, regeneration, and decoking lines to and from steam generators and

fired heatersc. Process lines to and from centrifugal compressors, turbo-expanders, and

blowersd. All working fluid lines to and from turbinese. Suction and discharge lines to and from reciprocating pumps and compressorsf. Lines NPS 3 and larger to and from centrifugal pump nozzlesg. Lines NPS 4 and larger to air cooled heat exchangersh. All relief systems, whether closed or relieving to atmosphere, with

considerations for attached or detached tail pipesi. All piping requiring proprietary expansion devices (e.g., bellows expansion

joints)j. Lines NPS 3 and larger subject to significant differential settlement of vessels,

tanks, equipment, or supports

k. Lines subjected to mixed phase flow (liquid and vapor) and lines identified assevere cyclic or vibrating service

l. Jacketed pipingm. Piping as required by applicable codes and standards (e.g., Code Category M)n. All plastic lined piping systems

7.3 Figures 1 and 2 provide a guide to evaluate situations not covered in Section 7.2.7.4 Analysis for other materials shall be per agreement with owner.

8. Piping Flexibility Analysis Record Keeping

8.1 The designer shall assign calculation numbers and store the flexibility analysis files.8.2 When the project has been completed, the designer shall furnish all stress

calculations and documentation as required by owner.

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Figure 1. Guide for Analysis of Carbon Steel or Low and Intermediate Alloy Steel

Figure 2. Guide for Analysis of Stainless Steel Pipe

Notes:1. Lines in this category may be analyzed by the use of engineering experience or approximate methods.2. Lines in this category require formal analysis. Analysis may be done by approximate or comprehensive

methods. Documentation is required.3. Lines in this category require a comprehensive analysis (typically by computer). Other methods may be

used with owners approval. Documentation is required.