procedure for piping stres analysis offshore)
TRANSCRIPT
308-7080-ST-54-102Page 1 of 26
H A L L I B U R T O N K B R
Procedure for Piping Stress Analysis (Offshore)
Document Number 308-7080-ST-54-102
______________________________________________________________________
P R O P R I E T A R Y I N F O R M A T I O N
This document contains proprietary information belonging to Halliburton KBR and mayneither be wholly or partially reproduced nor be disclosed without the prior writtenpermission of Halliburton KBR.
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R E V I S I O N R E C O R D
Rev. Date Description By Check. Review App._____________________________________________________________________D1 15/11/99 Draughted MOD2 18/10/00 Checked PRD3 13/06/01 Reviewed RTD4 24/04/02 Issued for Use MO PR RT IB
_______________________________________________________________________
DOCUMENT RESPONSIBILITY
The Piping Department Manager is responsible for authorisation of revisions of thisdocument.
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CONTENTS1.0 PURPOSE
2.0 SCOPE
3.0 REFERENCES
3.1 Applicable Codes, Standards and Regulations3.2 Other Requirements
4.0 PROCEDURES
4.1 System of Units4.2 Critical Line List4.3 Stress Isometric Index4.4 Studies4.5 Stress Isometrics4.6 Piping General Arrangement Drawings4.7 Stress Calculations4.8 Supplier Drawings and Data4.9 Approval of Nozzle Loads4.10 Piping Isometric Drawings for Construction4.11 Pipe Supports4.12 Offshore Riser and Topsides Piping Interface
5.0 DESIGN
5.1 Design Conditions5.2 Stress Limitations5.3 External Loads5.4 Loads Applied to Mechanical Equipment5.5 Design and Analysis of Flanged Joints5.6 Clamp Connectors5.7 External Loads Due to Blast Over pressure5.8 Use of Fabricated Lateral Connections in Process Piping5.9 High Strength Stainless Steels5.10 Use of Mechanical Joints5.11 Transportation Loads
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6.0 ATTACHMENTS
Attachment 1 Overview of Caesar II Program
Attachment 2 Requirements for Stress Isometrics
Attachment 3 Typical Stress Isometric
Attachment 4 Restraint Symbols for Stress Isometrics
Attachment 5 Flow-Chart for Stress Analysis
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1.0 PURPOSE
This procedure provides an overview of piping stress department activities, withparticular regard to the information interface with other sections and disciplines.In addition, requirements are outlined for engineering of piping systems, withregard to internal and external effects upon the piping and connected equipment.
Further advice regarding working practice and calculation methods is available inStress Analysis Working Methods, document No. 308-7080-ST-54-104.
This Corporate Document may be renumbered and revised to suit specific Projectrequirements.
2.0 SCOPE
2.1 The document is applicable to offshore platform design.
2.2 The objective of piping stress analysis is to obtain a safe and economical layoutfor piping elements whilst ensuring that the following is prevented:
(i) Piping stresses in excess of those permitted by the referenced Codes andStandards (Ref. Section 3.1 and 3.2).
(ii) Leakage at Joints.
(iii) Excessive forces and moments applied to connected equipment.
(iv) Excessive stresses in the supporting or restraining elements.
(v) Unintentional disengagement of piping from its supports.
(vi) Excessive interference with thermal expansion or contraction of the pipingsystem or connected equipment.
(vii) Resonance due to externally imposed vibrations or fluid inducedvibrations.
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(viii) Excessive sag in piping spans, particularly those requiring a drainageslope.
(ix) Damage to piping or components due to strain during jacking to remove orinstall blinds for isolation.
(x) Fatigue Failure due to high cycle loading not covered in ASME B31.3 e.g.wave induced displacements of bridge pipework.
2.3 It is the responsibility of the stress section to perform the following activities:-
(i) Carry out the necessary calculations to ensure that all loading conditionsthat may be experienced by a piping system are considered and catered forwithin the design.
(ii) Ensure that piping systems comply fully with the stress analysisrequirements specified by the Codes and Standards listed in Section 3.1and 3.2.
(iii) Issue approved stress isometrics for critical lines as required.
(iv) Prepare a Stress Analysis Report containing calculations and informationfor each piping system analysed, at the end of the project.
3.0 REFERENCES
308-7080-ST-51-120 Procedure for Piping Design
308-7080-ST-51-122 Piping Materials Specification Narrative
(PROJECT SPECIFIC) Process Line List
(PROJECT SPECIFIC) Design Premise (Environmental Data)
308-7080-ST-54-101 Specification for Equipment Nozzle Loadingdue to Piping Reactions.
308-7080-ST-54-103 Critical Line List Procedure
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308-7080-ST-54-105 Recommended Installation and Hook-upProcedure for Piping Connected to RotatingCompressors and large Pumps
PCM-WWBV-EN-077 Preparation control and approval ofcalculations
PCM-WWBV-EN-002 Validation and approval of DesignDocuments
3.1 Applicable Codes, Standards and Regulations.
Piping arrangements and piping stress analysis shall be in accordance with therequirements specified in the latest edition of codes and standards listed below:-
ASME B31.3 Chemical Plant and Petroleum Refinery Piping
Client Specifications and Procedures as applicable
3.2 Other Requirements
In addition to ANSI B31.3 and its sub-references, other codes may govern thedesign and installation of some parts of a piping system. Examples of pertinentcodes are:-
ANSI B31.1 Power Piping CodeANSI B16.5 Steel Pipe Flanges and FittingsASME VIII Pressure Vessel and Boiler Code (Div.1 & Div 2)BS 5500 Unfired Fusion Welded Pressure VesselsBS 8010 Pt 3. Code of Practice for PipelinesNEMA SM-23Multi-stage Steam Turbines for Mechanical Drive ServiceMSS SP44 Steel Pipe Line FlangesAPI RP-2A Planning, Design and Construction of Fixed Offshore PlatformsAPI RP-14E Design and Installation of Offshore Production Platform Piping
SystemsAPI RP-520 Recommended Practice for Design of Pressure Relieving SystemsAPI 605 Large Diameter Carbon Steel Flanges
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API 610 Centrifugal Pumps for General Refinery ServiceAPI 617 Centrifugal Compressors for General Refinery ServiceAPI 618 Reciprocating Compressors for General Refinery ServiceAPI 650 Welded Steel Tanks for Oil StorageAPI 660 Heat Exchangers for General refinery ServiceAPI 661 Air Cooled Heat Exchangers for General Refinery ServiceDOE Department of Energy - Offshore Installation Guidelines on Design
and ConstructionDNV Note 30.2 - Det Norsk Veritas - Fatigue Strength Analysis for
Mobile Offshore Structures
Any such codes affecting the piping shall be noted on Stress isometrics.
Should a conflict occur between this Procedure and referred codes then the moststringent requirements shall apply.
4.0 PROCEDURES
4.1 System of Units
The SI system of units shall normally be used. Pipe nominal diameter and wallthickness may be expressed in English units.
4.2 Critical Line List
Critical Line selection and control shall be in accordance with procedures outlinedin following document:
308-7080-ST-54-103 Critical Line Selection Procedure.
4.3 Stress Isometric Index
Generation and use of the Stress Isometric Index is closely allied to selection ofcritical lines and is outlined in the Critical Line Selection Procedure.
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4.4 Studies
The stress section shall review and comment on all piping studies that includecritical lines. The stress section may define approximate locations of major pipesupports and restraints, including spring support locations and vessel attachmentsfor pipe support purposes, with the assistance of the pipe supports section.
Where appropriate, loading on equipment and superstructure shall also bedetermined.
Locations of fixed and sliding ends of horizontal vessels and equipment shall bedefined where appropriate.
One print of each piping study with the issue date is required for review. Thisprint shall be commented upon, signed, dated and retained in stress section files.
A copy with comments shall be returned to the piping section.
4.5 Stress Isometrics
4.5.1 Initial Issue and Approval
The stress section shall issue a critical line list (Ref. section 4.2) indicatinglines to be shown on stress isometrics. Stress isometrics shall be producedin accordance with the guidelines presented in Attachment 2.
The stress engineer shall add to the original any minor routing changesagreed with piping and pipe supports sections, all restraint data, referencenodes, calculated results and notes. The original shall be approved, signedand dated by the stress engineer. The lead stress engineer shall review andissue each completed stress isometric in accordance with the distributionbelow.
If major re-routing of a piping system is required by the stress engineer,the original shall be updated and reissued as above. The lead stressengineer shall agree such action with the relevant piping section leader.
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4.5.2 Changes to Approved Stress Isometrics
A single master file of stress isometrics shall be retained in the stresssection. All changes to critical lines MUST be marked up on the master,signed and dated. The lead stress engineer MUST be informed of all suchchanges. The lead stress engineer shall, in conjunction with the areapiping section leader and the originating stress engineer, make a decisionas to whether re-calculation is required. If so the original stress isometricshall be revised and reissued as above. If a new calculation is notrequired, the lead stress engineer shall annotate the master to this effect.Prior to incorporation of stress isometrics in final stress reports, all suchcomments shall be transferred to the original, including "calculationsvalid".
4.5.3 Distribution of Stress Isometrics
Following approval, the stress isometrics shall be distributed as follows:-
1 copy to piping section leader
1 copy to pipe supports section leader
1 copy to mechanical group, if piping loads are in excess of those stated inSpecification "Loading on Equipment Nozzles due to Piping Reactions",or in the case where allowables lower than those stated have been agreedwith a vendor.
1 copy to (stress section) master file.
The pipe supports group may distribute approved stress isometrics tostructural and civil sections to aid definition of support loads if required.
The original shall be retained by the stress section. When a revised stressisometric is issued, the previous issue master file copy shall be stamped'VOID - SEE LATER ISSUE' and retained in the stress isometric file.Refer to Flowchart, Attachment 5.
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4.6 Piping General Arrangement Drawings
All piping G.A.'s containing critical lines shall be reviewed by the stress sectionprior to issue of each revision in order to ensure that stress analysis requirements,as shown on the stress isometrics have been incorporated in the completed design.One print of each piping G.A. is required for review which shall be commentedupon if necessary.
4.7 Stress Calculations
The CAESAR II computer program (ref. Attachment 1) shall be used forcomprehensive stress calculations. Where less extensive calculations areappropriate, simplified methods such as 'Spielvogel' chart form solutions, guidedcantilever approximation or visual inspection shall be used.
Flexibility analysis shall consider the most severe temperature condition foundduring start-up, normal operation, shut-down, regeneration or steam-out, or anyother condition that may realistically occur. Proper consideration shall be given totemperature excursions and operational combinations, such as those found inmultiple pumps and compressors linked to a common header.
The base case for flexibility analysis shall be "as installed", essentially stress freewith the exception of self weight. Appropriate primary and secondary stress casesand special cases, such as settlement and dynamic or transient loads shall beevaluated as required.
Special consideration shall be given to piping systems in the following categories.
(i) Lines subjected to significant differential deflection due to settlement ofsupports, movement of tank walls, equipment displacement and those linescrossing an inter-platform bridge.
(ii) Category M fluid service as defined by ASME B31.3.
(iii) Lines subjected to two-phase flow or slugging.
(iv) Lines subjected to external pressure, either due to internal vacuum orjacketting.
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(v) Lines subjected to vibration, either by attached equipment or due to flow conditions.
4.8 Supplier Drawings and Data
The stress section shall review and comment on all Supplier drawings ofequipment and vessels. The lead piping engineer shall ensure that the stresssection is included in the IDC circulation and further issues of Supplier drawingsand data.
4.9 Approval of Nozzle Loads
Piping loads applied to mechanical equipment shall normally meet therequirements of Specification for Equipment Nozzle Loading Due to PipingReactions, Document No. 308-7080-ST-54-101.
Approval of any loads applied to equipment nozzles greater than those indicatedin the above specification shall be obtained in writing from the equipmentSupplier by the Mechanical Department.
In the case where allowable loads lower than those indicated have been agreedwith a Supplier, documentary evidence of the revised allowables loads shall befiled with the relevant stress isometrics for inclusion in Stress Analysis Reports.In all cases, applied nozzle loads and respective allowables shall be identified onthe stress isometric, or reference to a load calculation shall be made.
4.10 Piping Isometric Drawings for Construction
The stress section shall review and comment if necessary, prior to the issue ofeach revision, on all piping isometrics. Checks shall be made to ensure that thesystem conforms to stress analysis requirements.
4.11 Pipe Supports
4.11.1 Issue of Pipe Support Drawings
Special supports such as those associated with rotating equipment orattached to pressure vessels shall be carefully scrutinised with regard tofitness for purpose.
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4.11.2 Standard Supports
The support section shall check and approve all standard pipe supportdesigns and shall retain records of all calculations.
4.11.3 Spring Supports
Spring supports shall be used to accommodate vertical pipe displacementswhilst controlling dead-weight reactions. Spring locations shall be definedby the stress section. Spring design data sheets shall be completed by thesupports section and reviewed by the stress section. Certified valveweights shall be used for final approval of spring support data sheets.
4.11.4 Special Support Elements
Special pipe support elements such as shock arrestors and snubbers shallbe specified by the stress section and detailed by the supports section.
4.12 Offshore Riser and Topsides Piping Interface
There will normally be an overlap in analysis by the topsides sections andPipelines group of risers, associated piping and receivers or launchers.
The pipe stress section shall model risers down to the dead-weight support, andthe Pipelines group shall include piping up to the launcher or receiver in theirmodel.
The piping stress section shall issue to the Pipelines Department a stress isometricindicating location and type of restraints required for the topsides portion of theriser.
For confirmation, the pipelines group shall provide a copy of their isometricindicating similar locations prior to analysis.
Subsequent to their analysis the Pipelines Department shall issue to the pipingstress section their approved stress isometric of the riser plus topsides pipingtogether with a summary stress report for all load cases considered. This reportmust contain at least the following:-
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i) Maximum calculated stresses with corresponding Design Codecompliance allowable stresses.
ii) Forces and moments at topsides supports (restraint loads).
iii) Forces and moments at flange connections and butt weld valves (datapoints located at butt welds).
iv) A statement of acceptance of data supplied by the Piping Stress section.
The piping stress section shall review the summary report in detail to establish theworst case loads and stresses acting at topsides data points and subsequentlyconfirm that any changes do not compromise the requirements of section 2.2 ofthis procedure.
The piping stress section shall finally update and re-issue to pipelines departmentand piping section the topsides stress isometric to reflect final load and stress data,clearly referencing the source.
Any subsequent changes to the piping stress isometric shall be handled inaccordance with section 4.5 of this procedure and re-issued as required topipelines for further evaluation.
All data supplied to piping stress section by pipelines section shall be placed inthe relevant stress isometric file of the Stress Analysis Report.
5.0 DESIGN
5.1 Design Conditions
The basis of design shall be taken to be the un-deformed and stress free state, withthe exception of weight loads. Stresses and deformations due to transient andother conditions, such as those found during load out and transportation shall betreated as an additional design case, based on available data.
Temperatures and pressures used in stress analysis shall normally be the designtemperature and pressure as quoted in the Line List. Where this may lead to an
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over-conservative design, the Process group shall be consulted and maximumoperating conditions used. In such cases a note shall be added to the Line Listregarding conditions used for stress analysis. The stress isometric shall besimilarly annotated.
5.1.1 Temperature
Selection of temperature range for thermal analysis is dependent upon thetype of plant under consideration.
(i) On-shore PlantWhere thermal displacement of the supporting structure can beconsidered negligible, the base temperature for thermal analysisshall be the installation temperature.
(ii) Offshore PlantThe steel deck of an offshore structure will respond to thermalchanges. It may normally be assumed that structure and pipetemperatures will be equal during construction, and the pipe willtherefore not be thermally stressed, unless some operatingcondition prevails. In this case, the base temperature for thermalanalysis shall be the ambient temperature.
(iii) Both installation (on-shore) and ambient temperature (offshore) arenormally given as a range in the Design Premise document.
(iv) The net algebraic difference between the installation or ambienttemperature and the 'design' temperature (whichever produces thegreatest temperature range) shall be used in thermal stress analysisfor piping reactions. To properly evaluate the net stress range, thealgebraic difference between any minimum and maximumtemperature shall be applied.
(v) In selection of 'design' temperature, consideration shall be given tospecific system requirements outlined in section 4.7. The Processdepartment shall be consulted regarding upset or excursiontemperatures.
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5.1.2 Pressure
Where high stress at an elbow is encountered the difference betweendesign and operating pressures shall be considered, since an increasepressure tends to decrease the stress intensification factor applied. It maybe necessary to run calculations for both conditions to ensure safety.
Process conditions which may result in impulse loadings such as pressuresurge or slugging shall be identified by the Process Department andconsidered in the design. The Lead Stress Engineer shall notify the processgroup that this information is required on the P & ID.
5.1.3 Vibration
(i) The effects of vibration in piping systems shall be investigatedwhere appropriate.
(ii) Consideration shall be given to vibration directly or indirectlyimposed upon piping by mechanical equipment.
(iii) The possibility of vibration from the flowing fluid shall beassessed, with particular emphasis applied to valves in continuousflow gas service where a large pressure drop occurs, such asblow-down valves, anti-surge valves and Joule- Thompsonprocess valves. Large pressure drop liquid services such as seawater dump lines shall be similarly investigated. Shock due to'water' hammer shall be considered.
(iv) If significant vibration is probable, the possibility of fatigue in themain piping and components, and in particular, small boreconnections such as instruments, vents and drains shall beassessed. The design shall be modified if required, to prevent anypossibility of damage.
(v) Additional restraints, hold-down supports or shock arrestors shallbe considered in order to moderate vibration. Small bore branchconnections such as instruments, vents and drains may require
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bracing to the header, or re-routing in order to restrain the mass.Refer to section 5.8, high strength steels.
5.2 Stress Limitations
Stresses due to pressure, weight, thermal and imposed displacements, external andoccasional loads, shall meet the requirements of the relevant code listed in section3.
5.3 External Loads
Where appropriate, environmental loads such as snow, ice and wind acting onexposed piping shall be evaluated using project environmental data, andappropriate National Codes. Solar radiation shall be considered in thermalanalysis of exposed piping.
In addition, the effects on piping systems of relative movements between platformmodules, module/deck deflection, platform settlement and other imposeddeflections shall be investigated where appropriate.
5.4 Loadings Applied to Mechanical Equipment
Refer also to section 4.9. Loads applied by piping to pumps, compressors,vessels, exchangers, tanks and package units shall in general comply with therequirements of specification "Equipment Nozzle Loading Due to Pipingreactions".
Refer to document No. 308-7080-ST-54-005 for further information relating toanalysis of piping connected to rotating compressors and large pumps.
Results of analogue studies / mechanical response studies for positivedisplacement equipment shall be incorporated into the design with regard toloadings and pipe support locations.
5.5 Design and Analysis of Flanged Joints
Pressure design of flanges shall generally be in accordance with Section 304.5 ofANSI B31.3.
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When evaluating the effects of piping loads upon flanged joints the followingshall be adopted.
(i) Axial force F (N) and resultant longitudinal moment M (Nmm) shall beexpressed as an equivalent pressure Pe (Nmm-2) as in equation 1.
Pe = 16 M + 4 F ... equation 1πG3 πG2
where G is the gasket reaction diameter (mm)
(ii) Design pressure P (Nmm-2) given by equation 2 shall be used to calculateflange and bolt stresses in accordance with ASME VIII Div. 1 Appendix2.
P = Pi + Pe ... equation 2
where Pi is the internal pressure.
In the case of combined external and pressure loads, flange and boltstresses shall be limited in accordance of the intent of Section 302.3 ofANSI B31.3.
5.6 Clamp Connectors
Where clamp connectors are used in preference to flanged joints the Lead StressEngineer shall liaise with the piping Materials group during the 'bid phase' tospecify the piping loads that can be accommodated by clamp connectors, oversizehubs may be required.
5.7 External Loads Due to Blast Over pressure
At an early stage in the project it shall be agreed with the Client whether blastover pressure effects are to be included in the piping design, or excluded.
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If blast over pressure is included in the stress analysis scope of work, both thepiping systems to be considered and the method of analysis shall be agreed withthe Client and safety group.
5.8 Use of Fabricated Laterals in Process Piping
Due to the high stress intensifications encountered and consequent risk of fatiguecracking in welds, fabricated lateral tees shall be avoided in process pipingsystems. Alternative use of standard forged or (integrally) reinforced 90° branchconnections shall be discussed with the Process Department.
5.9 High Strength Stainless Steels
Where high strength stainless steel such as duplex and super-duplex is used,precautions shall be taken to avoid the possibility of cracking in components dueto vibration induced fatigue. This may require avoidance of integrally reinforcedsmall bore branch connections on thin wall pipe, and use of stub-in or padreinforced branches in preference. Unconnected small bore branches such asvents, drains and instrument connections may require cruciform bracing or othersupport back to the parent pipe.
5.10 Use of Mechanical Joints
Bellows and other such mechanical devices used to limit forces and displacementsdue to pipe movement shall be avoided . The preferred means of absorbingdisplacements shall be by use of the inherent flexibility of the piping system. Priorto specification of bellows etc. in a piping system, the advice of the Corporatestress consultant and Client approval shall be obtained.
5.11 Transportation Loads
Normal practice is to ensure that the modules are supported in the same place inthe yard as offshore. Lead Stress Engineer shall liaise with the Structural group toensure that this is implemented.
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The deflected shape of the platform/module may change from the Fabrication yard(where pipework is initially installed) to the finally installed position i.e. offshore,resulting in additional imposed deflection of the pipework.
Structural deflections during initial installation, transport, and finally installedconditions should be obtained from the structural department and incorporatedinto the stress analysis where relevant.
Consideration shall also be given to inertia loadings and structural deflectionarising from the transportation of the module/platform from the fabrication yard tothe finally installed position.
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6.0 APPENDICES
ATTACHMENT 1
1.0 OVERVIEW OF CAESAR II
CAESAR II is a finite element program based on the direct stiffness matrixsolution method, specifically written for static and dynamic stress analysis of threedimensional piping systems.
The program runs on PC using compiled Fortran files, which cannot be accessedor corrupted by the user. Authorised access for use of the program is controlledby a plug-in electronic security device (dongle).
Calculations may be performed in accordance with several Design Codes.
Full details of the program are available in the User Manual.
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ATTACHMENT 2
REQUIREMENTS FOR STRESS ISOMETRICS
1.0 Stress isometrics shall be produced of critical lines as indicated by the stressengineer in the critical line list.
2.0 Drawing numbers shall be taken from the stress isometric index (ref. Critical LineList Procedures). The Stress Isometric Index is retained, updated and issued bythe Lead Stress Engineer.
3.0 Where possible an entire system should be shown on a single drawing, refer tothe stress section to agree convenient system breaks if more than one drawing isrequired.
4.0 Each stress isometric should contain the following information where applicable:
System title, drawing number and revisionii) Line numbers, sizes and maximum or minimum design conditionsiii) Insulation thickness if anyiv) Valve and component weightsv) All penetrations through decks, walls, firewalls etc.vi) Equipment numbers and nozzle numbersvii) Equipment and vessel fixed pointsviii) Continuation drawing referencesix) Reference dimensions to appropriate grid linesx) Footnotes if anyxi) North arrowxii) At least one elevationxiii) All specification changes, and limits of insulation.
5.0 Unless specifically required otherwise, branch connections below 2" nb need notbe detailed. Such branch locations however must be clearly marked anddimensioned on the header.
6.0 Platform North shall be the negative "x" direction or "top left".
7.0 The "by", "checked " and date boxes shall be completed in all cases.
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ATTACHMENT 3
TYPICAL STRESS ISOMETRIC
REFER TO STRESS SECTION
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ATTACHMENT 5FLOWCHART FOR STRESS ANALYSIS
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S &
ARCH
IVE
SUPP
ORTS
LEAD
STR
ESS
ENGI
NEER
TO
ANNO
TATE
ORI
GINA
LST
RESS
ISOM
ETRI
C
COM
PILE
STR
ESS
ANAL
YSIS
REPO
RTS
INCO
RPOR
ATIN
GRE
FERE
NCE
DATA
, ISO
MET
RICS
,CA
LCUL
ATIO
NS A
ND N
OTES
AT E
ND O
F PR
OJEC
T
PIPI
NG S
TRES
S AN
ALYS
IS -
HAN
DLIN
G O
F IS
OM
ETRI
CS &
DAT
A
YES
1 x
PRIN
T
1 x
PRIN
T TO
STRE
SS S
ECTI
ON(W
ORKI
NG C
OPY)
YES
NO
NO
NO
YES
NEW
REVI
SION