ISO Norsok Analysis Fabrication Jackets Final Report Task 3

NORSOK M-503, Edition 3May 2007Cathodic protection4 SUMMARYIn Table 4-1 below a summary of the gaps identified for each group of topics are presented.The summary is made by simple summation of the score given without any weighing due to thesignificance of the gaps.Table 4-1Summary of rating for the various topics 5.1.1Minimum designPractical limit is -30 C for ISOtemperatureLimit for NORSOK is -14 C. 5.1.2ISO describes two differentMethod fordetermination of steelspecifications andaccompanying fabrication,welding and inspectionrequirements. 5.2MaterialsDifferences affectingfabrication costCommentDifferences affectingstructural integrityGroup of TopicsDifferences in what iscovered by the codeTotal score positive andnegative 1000000-10-1000-10-10-20-3000-5200000systems, NORSOK only one.ISO opens for use of alternativesystems which may lead to lessreliable structures.ISO cover less material types,specifies unnecessary low Charpyimpact test temperatures for thinmaterials and in addition too lowCharpy impact energy values. 5.3Fabrication, weldingand weld inspectionISO does not cover all theaspects as in NORSOK and havesome requirements that can leadto increased cost. 5.4GroutingISO gives overall requirementsfor grouting operations.DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 4

5.5Fabrication ofaluminium structuresDifferences affectingfabrication costCommentDifferences affectingstructural integrityGroup of TopicsDifferences in what iscovered by the codeTotal score positive andnegative 0-2000-20-10-1000-10000More details of fabrication ofaluminium given in NORSOK, andISO restrict the use of weldedhigh strength alloys. 5.6Mechanical fastenersMore requirements given inNORSOK. ISO does not restrictyield strength above water. 5.7 5.8GeometrictolerancesNORSOK gives morerequirements relevant for topsidestructures.5.8Corrosion protectionISO does not cover coating0-10-100 5.9Quality assuranceNo gap identified0000003-100-40-9TotalThere are noted 3 rating points on topics where ISO is giving requirements where NORSOK is not, butthere are 10 cases where the opposite is the case.No requirements are found where ISO will lead to more reliable structures than NORSOK while there aregiven 4 rating points where fabrication according to NORSOK will improve the structural integrity.9 rating points are recorded where fabrication according to ISO will imply increased cost compared withthe use of NORSOK.DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 5

5 DETAIL REVIEW OF TOPICS5.1 General5.1.1 Minimum design temperatureTable 5-1Difference rating for the topicType of differenceDifferences in what is covered by the codesDifferences affecting structural integrityDifferences affecting fabrication costDifferencerating 1) 1CommentISO is applicable to temperature below -14 C001) For definition of rating codes see Table 2 -1Table 5-2Summary and commentsSummary: ISO 19902 has no lower limit for minimum design temperature.The minimum design temperature by use of NORSOK is -14 C (ref.N-004, section 5.2, and M101, section 1).Comments: (reference to other codes, important information in the Commentary etc.) ISO 19902 has no lower limit for minimum design temperature (―LAST‖ lowest anticipatedservice temperature). For the most important parts of the structure, ISO specifies that Charpyimpact testing shall be carried out at a temperature 30 C below LAST, both for base materialsand for welding procedure qualification tests. In practice this means that ISO can be useddown to a LAST of -30 C. This as Charpy impact testing of carbon steel at temperatures lowerthan -60 C is not realistic.Table 5-3Identified gapsGaps ISO 19902 has no lower limit for minimum design temperature. However, due to the specifiedCharpy impact test temperatures, the practical minimum design temperature is -30 C. The minimum design temperature by use of NORSOK is -14 C (ref. N-004, section 5.2, and M101, section 1).DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 6

5.1.2 Method for determination of steel specifications andaccompanying fabrication, welding and inspection requirements.Table 5-4Difference rating for the topicType of differenceDifferences in what is covered by the codesDifferences affecting structural integrityDifferences affecting fabrication costDifferencerating 1)-1-10CommentISO 19902 (19.5) is not precise in what iscoveredISO 19902 allows for alternative specifications1) For definition of rating codes see Table 2 -1Table 5-5Summary and commentsSummary: In ISO 19902, section 19.1, two methods are presented for determining the particular steelspecifications to be used and the accompanying welding, fabrication and inspectionrequirements:a) the material category (MC) approach, andb) the design class (DC) approachAs these two methods are informative and not normative, other rational procedures may also beconsidered. NORSOK has one system; the design class (DC) system.Comments: (reference to other codes, important information in the Commentary etc.)DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 7

In ISO 19902, section 19.1, two methods are presented for determining the particular steelspecifications to be used for a specific structure and the accompanying welding, fabrication andinspection requirements. These methods, briefly introduced in 19.2.4 and 19.2.5 in thestandard and described in detail in Annexes C and D, are generally referred to asa) the material category (MC) approach, andb) the design class (DC) approachThe material category (MC) and design class (DC) methods are mutually exclusive. Once themethod has been selected it is not interchangeable at any stage with the other. In section 19.2.3 of ISO 19902 it is stated that Annex C and D provide normative detailsconcerning the implementation of the procedures applicable to its particular method. In section19.5 it is indicated that Annexes C and D not are normative, as it is stated that ―Annexes C andD list commonly used specifications‖ for materials. The annexes themselves (Annex C and D)are identified to be ―informative‖. If Annex C and D are normative or informative is then notfully clear. In 19.2.3 it is also stated that ―as an alternative to the MC and DC approaches, other rationalprocedures may be considered‖. This implies that other methods than the MC and DC methodscan be applied. This would however require development of detailed specifications for materialsand fabrication, and is not considered to be a realistic way in order to satisfy the requirementsof this ISO standard. NORSOK has one system for material selection; the design class (DC) method. Even if the DC method described in ISO is based on the DC method used in NORSOK, thesystems in ISO and NORSOK are not identical.Table 5-6Identified gapsGaps ISO 19902 describes two methods for determining the particular steel specifications to be usedfor a specific structure and the accompanying welding, fabrication and inspection requirements:a) the material category (MC) approach, andb) the design class (DC) approach As an alternative to the MC and DC approach, it is stated in ISO 19902 that other rationalprocedures may be considered. NORSOK has one system for material selection and the accompanying welding, fabrication andinspection requirements; the design class (DC) method. Even if the DC method described in ISO is based on the DC method used in NORSOK, thesystems in ISO and NORSOK are not identical.DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 8

5.2 Materials5.2.1 Material selectionThe material selection process by use of the DC approach in ISO 19902 is described in section 5.6 inTask 2, Design of jacket structures /2/.Section 5.2, Materials, in this document describes the requirements to the selected materials in somemore detail.5.2.2 Material specificationsTable 5-7Difference rating for the topicType of differenceDifferences in what is covered by the codesDifferences affecting structural integrityDifferences affecting fabrication costDifferencerating 1)-100CommentCastings and forgings not covered by ISO1) For definition of rating codes see Table 2 -1Table 5-8Summary and commentsSummary: Material specifications for the following product forms are given in ISO 19902 (Annex D): Plates,rolled sections, hollow sections. References to specifications for cast and forged structural steelare not given. NORSOK has material specifications for the following product forms: plates, rolled sections,hollow sections, cast steel, forged steel.Comments: (reference to other codes, important information in the Commentary etc.) Material specifications for the following product forms are given in ISO 19902 (Annex D):Plates, rolled sections, hollow sections. ISO have no references to specifications for cast andforged structural steel. Material specifications for the following product forms are given in NORSOK:oNORSOK standard M-120: Plates, rolled sections, hollow sections.oNORSOK standard M-122: Cast structural steel.oNORSOK standard M-123: Forged structural steel.DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 9

Table 5-9Identified gapsGaps ISO has references to material specifications for plates, rolled sections and hollow sections. ISOhave no references to specifications for cast and forged structural steel. NORSOK has material specifications for all relevant product forms, i.e. plates, rolled sections,hollow sections, cast steel and forged steel.5.2.3 Charpy Impact test temperatures for base materialsTable 5-10Difference rating for the topicType of differenceDifferences in what is covered by the codesDifferences affecting structural integrityDifferences affecting fabrication costDifferencerating 1)Comment00-1Stricter requirements for small thicknesses inISO 199021) For definition of rating codes see Table 2 -1Table 5-11Summary and commentsSummary: In ISO 19902, Table 19.4-1 (normative), it is specified that steels belonging to a certaintoughness class shall be Charpy impact tested at the same temperature for all thicknesses.Comments: (reference to other codes, important information in the Commentary etc.) Charpy impact testing at the same temperature for all thicknesses is more stringent thanrequired in the fabrication part of ISO 19902, and also more stringent than required byNORSOK (both for base materials and fabrication), which accept higher impact testtemperatures for materials up to a certain thickness.Table 5-12Identified gapsGaps In ISO 19902, Table 19.4-1 (normative), it is specified that steels belonging to a certaintoughness class shall be Charpy impact tested at the same temperature for all thicknesses. Other standards, including NORSOK, accept higher test temperatures for thin materials.DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 10

5.2.4 Charpy Impact energy values for base materialsTable 5-13Difference rating for the topicType of differenceDifferences in what is covered by the codesDifferences affecting structural integrityDifferences affecting fabrication costDifferencerating 1)Comment0-1-1Risk that welded connection may get too lowtoughnessPossible toughness problems will have costimpact.1) For definition of rating codes see Table 2 -1Table 5-14Summary and commentsSummary: The Charpy impact energy values specified for the base materials in ISO 19902, (Table 19.4-1(normative), are too low.Comments: (reference to other codes, important information in the Commentary etc.) Table 5-15Identified gapsGaps The Charpy impact energy values specified for the base materials in ISO 19902, Table 19.4-1(normative), are lower than specified by NORSOK, and are too low in order to guaranteecompliance with the minimum Charpy energy values specified in HAZ after welding (ref. TableF.1 in ISO 19902).5.3 Fabrication, welding and weld inspection5.3.1 Welding and fabrication standardTable 5-16Difference rating for the topicType of differenceDifferences in what is covered by the codesDifferences affecting structural integrityDifferences affecting fabrication costDifferencerating 1)-1CommentISO does not have a specification for fabrication,welding and inspection.0-1Complicated to work to ISO plus a separategeneric specification.1) For definition of rating codes see Table 2 -1DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 11

Table 5-17Summary and commentsSummary: ISO 19902 has just a few specific requirements to welding, fabrication and NDT. Therequirements specified in ISO 19902 shall be used in conjunction with owner specifications,selected international, national or regulatory standards for welding, fabrication and inspection. In the NORSOK system for steel structures, NORSOK M-101 is an independent and ―stand alone‖specification for fabrication, welding and inspection.Comments: (reference to other codes, important information in the Commentary etc.) ISO 19902 has just a few specific requirements to fabrication, welding and NDT. In section20.1 and 20.2.1 of the standard it is stated that fabrication, welding and weld inspection offixed offshore structures shall be performed in accordance with a selected generic specificationor standard (owner specifications, international, national or regulatory standards). Theadditional requirements that shall supplement the requirements of the selected genericspecification are described in section 20 of ISO 19902. The most important complementaryprovisions are specific requirements to weld metal and HAZ toughness (Charpy impact andCTOD test temperatures and energy values). The toughness requirements are further detailedin section 5.3.2.1 and 5.3.2.2 below. The toughness requirements specified in ISO 19902 shalloverrule the corresponding toughness requirements specified in the selected generic standard. Annex A of the standard, which is informative, contains additional information and guidance tothe normative parts of the standard. In section A.20.2.1 of ISO19902 it is stated that NORSOKM-101 is a generic standard that is generally compatible with the DC method. Furthercomparisons between ISO and NORSOK with regard to fabrication, welding and inspection arebased on NORSOK M-101 to be the selected generic fabrication standard.Table 5-18Identified gapsGaps ISO 19902 has just a few specific requirements to welding, fabrication and NDT. In section 20.1and 20.2.1 of the standard, it is stated that fabrication, welding and weld inspection of fixedoffshore structures shall be performed in accordance with a selected generic specification orstandard (owner specifications, international, national or regulatory standards). In the NORSOK system for steel structures, NORSOK M-101 includes all aspects of fabrication,welding and inspection.DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 12

5.3.2 Qualification of welding procedures5.3.2.1Table 5-19Weld metal and HAZ Charpy toughness requirementsDifference rating for the topicType of differenceDifferences in what is covered by the codesDifferences affecting structural integrityDifferences affecting fabrication costDifferencerating 1)Comment00-1For some cases ISO specifies lower testtemperatures than NORSOK.1) For definition of rating codes see Table 2 -1Table 5-20Summary and commentsSummary: There are differences in the requirements to weld metal and HAZ Charpy toughness, both fortest temperatures and energy values. The main differences being that for some cases ISO specifies lower test temperatures thanNORSOK.Comments: (reference to other codes, important information in the Commentary etc.) DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 13

Table 5-21Identified gapsGaps By use of the DC method, the minimum Charpy V-notch toughness requirements for weld metaland HAZ are defined in Annex F of ISO 19902. For a minimum design temperature of -10 C, theCharpy impact test temperature specified by ISO are lower than specified by NORSOK for somestrength groups, toughness classes and thicknesses. ISO specifies the same test temperature forSQL II as for SQL I, while NORSOK specifies higher test temperatures for SQL II than for SQL I.Examples of differences in test temperatures between ISO and NORSOK are shown in the tablebelow.SQL(NORSOK) SMYS (MPa)ThicknessTest temp. ( C)Test temp. ( C)(mm)NORSOKISOI 40025-20-40II 40012 t 250-20II 400250-40II 40025 t 50-20-40II 400, 500 120-20II 400, 50012 t 25-20-40III 400250-20III 40050-20-40For steels with SMYS 500 MPa, the minimum Charpy impact energy values specified by ISOare a few Joules lower than specified by NORSOK (except for SQL II with SMYS 400 MPa,where ISO specifies higher values than NORSOK).5.3.2.2Table 5-22Weld metal and HAZ CTOD toughness requirementsDifference rating for the topicType of differenceDifferencerating 1)Differences in what is covered by the codes-1Differences affecting structural integrity0Differences affecting fabrication cost-1CommentThe requirements to CTOD testing are betterdefined in NORSOK than in ISO.ISO requires higher CTOD values than NORSOK.When CTOD testing is not required by ISO,PWHT shall be carried out.1) For definition of rating codes see Table 2 -1DNV GL – Report No. 2014-1425, Rev. 1 – www.dnvgl.comPage 14

Table 5-23Summary and commentsSummary: There are differences in the requirements to weld metal and HAZ CTOD toughness, bothregarding extent of testing and CTOD values. The requirements for CTOD testing are betterdefined in NORSOK than in ISO.Comments: (reference to other codes, important information in the Commentary etc.) For the comparison, steel with SMYS 500 MPa is considered.Table 5-24Identified gapsGaps NORSOK M-101specifies CTOD testing for thicknesses 50 mm for all strength levels for SQL Iand II and when SMYS 400 MPa for SQL III, both with and without PWHT. The requirement forminimum CTOD value shall be prescribed by the designer. If not specified by the designer, therequirement for minimum CTOD value shall be as for the steel purchase order. This means thatminimum acceptable values shall be as specified by the NORSOK MDS’s; 0,25 mm without PWHTand 0,20 mm with PWHT. In NORSOK maximum qualified thickness when CTOD testing is required is 10% higher than theactual thickness tested. In ISO 19902, requirements to CTOD testing are described in

in the Gap project as the design and fabrication requirements are closely linked. Furthermore ISO 19902 is covering both design and fabrication aspects and making reference to this code will imply that requirements both to design and to fabrication need to be adhered to. 2.2 Basis of comparison of fabrication requirements