NORSOK STANDARD N-004 Rev. 3, February 2013

Transcription

1 NORSOK STANDARD N-004 Rev. 3, February 013 Design o steel structures This NORSOK standard is developed with broad petroleum industry participation by interested parties in the Norwegian petroleum industry and is owned by the Norwegian petroleum industry represented by The Norwegian Oil Industry Association (OLF) and Federation o Norwegian Manuacturing Industries (TBL). Please note that whilst every eort has been made to ensure the accuracy o this NORSOK standard, neither OLF nor TBL or any o their members will assume liability or any use thereo. Standards Norway is responsible or the administration and publication o this NORSOK standard. Standards Norway Telephone: Strandveien 18, P.O. Box 4 Fax: N-136 Lysaker petroleum@standard.no NORWAY Website: Copyrights reserved

2 NORSOK standard N-004 Rev. 3, February 013 FOREWORD 3 INTRODUCTION 3 1 SCOPE 4 NORMATIVE AND INFORMATIVE REFERENCES 4.1 Normative reerences 4. Inormative reerences 4 3 TERMS, DEFINITIONS, ABBREVIATIONS AND SYMBOLS Terms and deinitions 4 3. Abbreviations Symbols 6 4 GENERAL PROVISIONS 9 5 STEEL MATERIAL SELECTION AND REQUIREMENTS FOR NON-DESTRUCTIVE TESTING Design class Steel quality level Welding and non-destructive testing (NDT) 11 6 ULTIMATE LIMIT STATES General Ductility Tubular members General Axial tension Axial compression Bending Shear Hydrostatic pressure Hoop buckling Ring stiener design Material actor Tubular members subjected to combined loads without hydrostatic pressure Axial tension and bending Axial compression and bending Interaction shear and bending moment Interaction shear, bending moment and torsional moment Tubular members subjected to combined loads with hydrostatic pressure Axial tension, bending, and hydrostatic pressure Axial compression, bending, and hydrostatic pressure Tubular joints General Joint classiication Strength o simple joints General Basic resistance Strength actor Q u Chord action actor Q Design axial resistance or X and Y joints with joint cans Strength check Overlap joints Ringstiened joints Cast joints Strength o conical transitions General Design stresses Equivalent design axial stress in the cone section Local bending stress at unstiened junctions Hoop stress at unstiened junctions Strength requirements without external hydrostatic pressure Local buckling under axial compression 35 NORSOK standard Page 1 o 64

3 NORSOK standard N-004 Rev. 3, February Junction yielding Junction buckling Strength requirements with external hydrostatic pressure Hoop buckling Junction yielding and buckling Ring design General Junction rings without external hydrostatic pressure Junction rings with external hydrostatic pressure Intermediate stiening rings Design o plated structures Design o cylindrical shells Design against unstable racture General Determination o maximum acceptable deect size 39 7 SERVICEABILITY LIMIT STATES 40 8 FATIGUE LIMIT STATES General Methods or atigue analysis 41 9 ACCIDENTAL DAMAGE LIMIT STATES General Check or accidental actions 4 10 REASSESSMENT OF STRUCTURES General 4 11 BIBLIOGRAPHY 43 1 COMMENTARY 44 Annex A (Normative) Design against accidental actions 60 Annex K (Normative) Special design provisions or jackets 1 Annex L (Normative) Special design provisions or ship shaped units 158 Annex M (Normative) Special design provisions or column stabilized units 01 Annex N (Normative) Special design provisions or tension leg platorms 41 NORSOK standard Page o 64

4 NORSOK standard N-004 Rev. 3, February 013 Foreword The NORSOK standards are developed by the Norwegian petroleum industry to ensure adequate saety, value adding and cost eectiveness or petroleum industry developments and operations. Furthermore, NORSOK standards are, as ar as possible, intended to replace oil company speciications and serve as reerences in the authorities regulations. The NORSOK standards are normally based on recognised international standards, adding the provisions deemed necessary to ill the broad needs o the Norwegian petroleum industry. Where relevant, NORSOK standards will be used to provide the Norwegian industry input to the international standardisation process. Subject to development and publication o international standards, the relevant NORSOK standard will be withdrawn. The NORSOK standards are developed according to the consensus principle generally applicable or most standards work and according to established procedures deined in NORSOK A-001. The NORSOK standards are prepared and published with support by The Norwegian Oil Industry Association (OLF) and Federation o Norwegian Manuacturing Industries (TBL). NORSOK standards are administered and published by Standards Norway. Annex A, K, L, M and N are normative parts o this NORSOK standard. Introduction This NORSOK standard is intended to ulil PSA regulations relating to design and outitting o acilities etc. in the petroleum activities. The design principles ollow the requirements in ISO NORSOK standard Page 3 o 64

5 NORSOK standard N-004 Rev. 3, February SCOPE This NORSOK standard speciies guidelines and requirements or design and documentation o oshore steel structures. This NORSOK standard is applicable to all type o oshore structures made o steel with a speciied minimum yield strength less or equal to 500 MPa. For steel with higher characteristic yield strength, see Clause 1. NORMATIVE AND INFORMATIVE REFERENCES The ollowing standards include provisions and guidelines which, through reerence in this text, constitute provisions and guidelines o this NORSOK standard. Latest issue o the reerences shall be used unless otherwise agreed. Other recognized standards may be used provided it can be shown that they meet or exceed the requirements and guidelines o the standards reerenced below..1 Normative reerences API RP T, Planning, Designing and Constructing Tension Leg Platorms DNV, Rules or classiication o ships DNV, Classiication Note 30.7 DNV-OS-C101, Design o oshore Steel Structures DNV-RP-C01, Buckling Strength o Plated Structures DNV-RP-C03, Fatigue Strength Analysis o Oshore Steel Structures DNV-RP-C0, Buckling o Shells DNV-OS-C50, Oshore Concrete Structures ISO 19900, Petroleum and natural gas industries General requirements or oshore structures ISO 1990, Petroleum and natural gas industries Fixed steel oshore structures NORSOK G-001, Soil investigation NORSOK M-001, Materials selection NORSOK M-101, Structural steel abrication NORSOK M-10, Material data sheets or structural steel NORSOK N-001, Structural design NORSOK N-003, Action and action eects NORSOK N-006, Assessment o structural integrity or existing oshore load-bearing structures NORSOK Z-001, Documentation or operation NS 3481, Soil investigation and geotechnical design or marine structures NS-EN , Eurocode 3: Design o steel structures - Part 1-1: General rules and rules or buildings NS-EN , Eurocode 3: Design o steel structures - Part 1-5: Plated structural elements NS-EN , Eurocode 3: Design o steel structures - Part 1-8: Design o joints VMO Standards As deined in DNV-OS-H101, Marine Operations, General. Inormative reerences See Clause TERMS, DEFINITIONS, ABBREVIATIONS AND SYMBOLS For the purposes o this NORSOK standard, the ollowing terms, deinitions and abbreviations apply. 3.1 Terms and deinitions can verbal orm used or statements o possibility and capability, whether material, physical or casual 3.1. may NORSOK standard Page 4 o 64

6 NORSOK standard N-004 Rev. 3, February 013 verbal orm used to indicate a course o action permissible within the limits o the standard Norwegian petroleum activities petroleum activities where Norwegian regulations apply operator company or an association which through the granting o a production licence is responsible or the day to day activities carried out in accordance with the licence petroleum activities oshore drilling, production, treatment and storage o hydrocarbons principal standard standard with higher priority than other similar standards NOTE Similar standards may be used as supplements, but not as alternatives to the principal standard shall verbal orm used to indicate requirements strictly to be ollowed in order to conorm to the standard and rom which no deviation is permitted, unless accepted by all involved parties should verbal orm used to indicate that among several possibilities one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course o action is preerred but not necessarily required 3. Abbreviations ALS API BSI CTOD DAF DC DFF DFI DNV EA ECCS FE FEM FLS FPSO HF IMO ISO LF MDS MPI NDT NMD NPD RAO RCS ROV accidental limit state American Petroleum Institute British Standards Institution crack tip opening displacement dynamic ampliication actor design class design atigue actor design, abrication and installation Det Norske Veritas environmental actions European Convention or Constructional Steelwork inite element inite element method atigue limit state loating production storage and oloading high requency International Maritime Organisation International Organisation or Standardisation low requency material data sheet magnetic particle inspection non-destructive testing Norwegian Maritime Directorate Norwegian Petroleum Directorate response amplitude operator Recognised Classiication Society remotely operated vehicle NORSOK standard Page 5 o 64

7 NORSOK standard N-004 Rev. 3, February 013 SDOF SQL SCF TLP ULS WF single degree o reedom steel quality level stress concentration actor tension leg platorm ultimate limit state wave requency 3.3 Symbols A cross sectional area, accidental action, parameter, ull area o the brace/chord intersection A c cross sectional area o composite ring section A e eective area A w cross sectional area o web B hoop buckling actor C rotational stiness, actor C e critical elastic buckling coeicient C h elastic hoop buckling strength actor C m reduction actor C my, C mz reduction actor corresponding to the member y and z axis respectively C 0 actor D outer diameter o chord, cylinder diameter at a conical transition, outside diameter D c diameter to centeroid o composite ring section D e equivalent diameter D j diameter at junction D max maximum measured diameter D min minimum measured diameter D nom nominal diameter D s outer cone diameter E Young s modulus o elasticity, MPa G shear modulus I, I z, I s moment o inertia I c moment o inertia or ring composite section I ch moment o inertia I ct moment o inertia o composite ring section with external hydrostatic pressure and with eective width o lange I e eective moment o inertia I p polar moment o inertia K a actor L length, distance L 1 distance to irst stiening ring in tubular section L c distance to irst stiening ring in cone section along cone axis L r ring spacing M pl,rd design plastic bending moment resistance M Rd design bending moment resistance M red,rd reduced design bending moment resistance due to torsional moment M Sd design bending moment M T,Sd design torsional moment M T,Rd design torsional moment resistance M y,rd design in-plane bending moment resistance M y,sd in-plane design bending moment M z,rd design out-o-plane bending moment resistance M z,sd out-o-plane design bending moment N c,rd design axial compressive resistance N can,rd design axial resistance o can N cg,rd axial compression resistance o a grouted, composite member N cl characteristic local buckling resistance N cl characteristic local buckling resistance N cl,rd design local buckling resistance N E Euler buckling strength N E,dent Euler buckling strength o a dented tubular member, or buckling in-line with the dent elastic Euler buckling load o a grouted, composite member N Eg NORSOK standard Page 6 o 64

8 NORSOK standard N-004 Rev. 3, February 013 N Ey,N Ez N Sd N t,rd N x,rd N x,sd N y,rd N y,sd P Sd Q Q Q g Q u Q yy Q R R d R k S d S k T T c T n V Rd V Sd W Z a a i a m a u b b e c d d 0, d 1, d e c ch,rd cj cl cl,rd clc cle cr d E Epx, Epy Ey, Ez h he hec h,rd k, kx, ky, kp m m,rd m,red mh,rd th,rd y y,b y,c Euler buckling resistance corresponding to the member y and z axis respectively design axial orce design axial tension resistance design axial resistance in x direction design axial orce in x direction design axial resistance in y direction design axial orce in y direction design lateral orce actor chord action actor chord gap actor strength actor angle correction actor geometric actor, tubular joint geometry actor radius, radius o chord, radius o conical transition design resistance characteristic resistance design action eect characteristic action eect thickness o tubular sections, thickness o chord chord-can thickness nominal chord member thickness design shear resistance design shear orce elastic section modulus plastic section modulus stiener length, crack depth, weld throat, actor initial crack depth maximum allowable deect size calculated crack depth at unstable racture actor eective width actor diameter o tubular cross section, brace diameter distance lange eccentricity characteristic axial compressive strength design axial compressive strength in the presence o hydrostatic pressure corresponding tubular or cone characteristic compressive strength characteristic local buckling strength design local buckling strength, design local buckling strength o undamaged cylinder local buckling strength o conical transition characteristic elastic local buckling strength critical buckling strength design yield strength Euler buckling strength Euler buckling strength corresponding to the member y and z axis respectively Euler buckling strength corresponding to the member y and z axis respectively characteristic hoop buckling strength elastic hoop buckling strength or tubular section elastic hoop buckling strength or cone section design hoop buckling strength characteristic buckling strength characteristic bending strength design bending strength reduced bending strength due to torsional moment design bending resistance in the presence o external hydrostatic pressure design axial tensile resistance in the presence o external hydrostatic pressure characteristic yield strength characteristic yield strength o brace characteristic yield strength o chord NORSOK standard Page 7 o 64

9 NORSOK standard N-004 Rev. 3, February 013 g gap h height i radius o gyration i e eective radius o gyration k, k g,k l, k buckling actor l, l L length, element length l e eective length p Sd design hydrostatic pressure r radius, actor t thickness t c cone thickness t e eective thickness o chord and internal pipe o a grouted member coeicient, angle between cylinder and cone geometrical coeicient, actor actor actor BC additional building code material actor partial actor or actions M resulting material actor M0 material actor or use with EN M1 material actor or use with EN M material actor or use with EN and EN actor hoop buckling actor angle c the included angle or the compression brace t the included angle or the tension brace reduced slenderness, column slenderness parameter e reduced equivalent slenderness s reduced slenderness, shell slenderness parameter coeicient, geometric parameter Poisson s ratio rotational stiness actor a,sd design axial stress in member ac,sd design axial stress including the eect o the hydrostatic capped end axial stress at,sd design axial stress in tubular section at junction due to global actions equ,sd equivalent design axial stress within the conical transition h,sd design hoop stress due to the external hydrostatic pressure hc,sd design hoop stress at unstiened tubular-cone junctions due to unbalanced radial line orces hj,sd net design hoop stress at a tubular cone junction j,sd design von Mises equivalent stress m,sd design bending stress mc,sd design bending stress at the section within the cone due to global actions mlc,sd local design bending stress at the cone side o unstiened tubular-cone junctions mlt,sd local design bending stress at the tubular side o unstiened tubular-cone junctions mt,sd design bending stress in tubular section at junction due to global actions my,sd design bending stress due to in-plane bending mz,sd design bending stress due to out-o-plane bending p,sd design hoop stress due to hydrostatic pressure tot,sd total design stress q,sd capped end axial design compression stress due to external hydrostatic pressure T,Sd shear stress due to design torsional moment, x, y actors actor NORSOK standard Page 8 o 64

10 NORSOK standard N-004 Rev. 3, February GENERAL PROVISIONS All relevant ailure modes or the structure shall be identiied and it shall be checked that no corresponding limit state is exceeded. In this NORSOK standard the limit states are grouped into: 1. Serviceability limit states. Ultimate limit states 3. Fatigue limit states 4. Accidental limit states For deinition o the groups o limit states, reerence is made to ISO The dierent groups o limit states are addressed in designated clauses o this NORSOK standard. In general, the design needs to be checked or all groups o limit states. The general saety ormat may be expressed as: Sd R d where S d = Sk R d = R k M Design action eect Design resistance S k = Characteristic action eect = partial actor or actions R k = Characteristic resistance M = Material actor In this NORSOK standard the values o the resulting material actor are given in the respective clauses. General requirements or structures are given in NORSOK N-001. Determination o actions and action eects shall be according to NORSOK N-003. The steel abrication shall be according to the requirements in NORSOK M-101. (4.1) NORSOK standard Page 9 o 64

11 NORSOK standard N-004 Rev. 3, February STEEL MATERIAL SELECTION AND REQUIREMENTS FOR NON-DESTRUCTIVE TESTING 5.1 Design class Selection o steel quality and requirements or inspection o welds shall be based on a systematic classiication o welded joints according to the structural signiicance and complexity o joints. The main criterion or decision o DC o welded joints is the signiicance with respect to consequences o ailure o the joint. In addition the geometrical complexity o the joint will inluence the DC selection. The selection o joint design class shall be in compliance with Table 5-1 or all permanent structural elements. A similar classiication may also be used or temporary structures. Table 5-1 Classiication o structural joints and components Design Class 1) Joint complexity ) Consequences o ailure DC1 DC DC3 DC4 DC5 High Low High Low Any Applicable or joints and members where ailure will have substantial consequences 3) and the structure possesses limited residual strength. 4). Applicable or joints and members where ailure will be without substantial consequences 3) due to residual strength. 4). Applicable or joints and members where ailure will be without substantial consequences. 3) Notes: 1) Guidance or classiication can be ound in Annex K, L, M and N. ) High joint complexity means joints where the geometry o connected elements and weld type leads to high restraint and to triaxial stress pattern. E.g., typically multiplanar plated connections with ull penetration welds. 3) Substantial consequences in this context means that ailure o the joint or member will entail - danger o loss o human lie; - signiicant pollution; - major inancial consequences. 4) Residual strength means that the structure meets requirements corresponding to the damaged condition in the check or accidental damage limit states, with ailure in the actual joint or component as the deined damage. See Clause Steel quality level Selection o steel quality level or a structural component shall normally be based on the most stringent DC o joints involving the component. Through-thickness stresses shall be assessed. The minimum requirements or selection o steel material are ound in Table 5-. Selection o a better steel quality than the minimum required in design shall not lead to more stringent requirements in abrication. The principal standard or speciication o steels is NORSOK M-10, Material data sheets or rolled structural steel. Material selection in compliance with NORSOK M-10 assures toughness and weldability or structures with an operating temperature down to -14 C. Cast and orged steels shall be in accordance with recognised standards. I steels o higher speciied minimum yield strength than 500 MPa or greater thickness than 150 mm are selected, the easibility o such a selection shall be assessed in each case. Traceability o materials shall be in accordance with NORSOK Z-001. NORSOK standard Page 10 o 64

12 NORSOK standard N-004 Rev. 3, February 013 Table 5- Correlation between design classes and steel quality level Design Class Steel Quality Level I II III IV DC1 X DC (X) X DC3 (X) X DC4 (X) X DC5 X (X) = Selection where the joint strength is based on transerence o tensile stresses in the through thickness direction o the plate. See Clause Welding and non-destructive testing (NDT) The required racture toughness level shall be determined at the design stage or joints with plate thickness above 50 mm when or joints in design class DC1, DC or DC3. The extent o non-destructive examination during abrication o structural joints shall be in compliance with the inspection category. The selection o inspection category or each welded joint shall be in accordance with Table 5-3 and Table 5-4 or joints with low and high atigue utilisation respectively. Welds in joints below 150 m water depth should be assumed inaccessible or in-service inspection. The principal standard or welder and welding qualiication, welding perormance and non-destructive testing is NORSOK M-101. Table 5-3 Determination o inspection category or details with low atigue utilisation 1) Design Class DC1 and DC DC3 and DC4 DC5 Type o and level o stress and direction in relation to welded joint. Inspection category ) Welds subjected to high tensile stresses transverse to the weld. 6) A Welds with moderate tensile stresses transverse to the 7) weld and/or high shear stresses. 3) B Welds with low tensile stresses transverse to the weld 8) and/or moderate shear stress. 4) C Welds subjected to high tensile stresses transverse to the 6) weld. 3) B Welds with moderate tensile stresses transverse to the 7) weld and/or high shear stresses. 4) C Welds with low tensile stresses transverse to the weld 8) and/or moderate shear stress. 5) D All load bearing connections. Non load bearing connections. Notes: 1) Low atigue utilisation means connections with calculated atigue lie longer than 3 times the required atigue lie (design atigue lie multiplied with the DFF). ) It is recommended that areas o the welds where stress concentrations occur be marked as mandatory inspection areas or B, C and D categories as applicable. 3) Welds or parts o welds with no access or in-service inspection and repair should be assigned inspection category A. 4) Welds or parts o welds with no access or in-service inspection and repair should be assigned inspection category B. 5) Welds or parts o welds with no access or in-service inspection and repair should be assigned inspection category C. 6) High tensile stresses mean ULS tensile stresses in excess o 0.85 o design stress. 7) Moderate tensile stresses mean ULS tensile stresses between 0.6 and 0.85 o design stress. 8) Low tensile stresses mean ULS tensile stresses less than 0.6 o design stress. D E NORSOK standard Page 11 o 64

13 NORSOK standard N-004 Rev. 3, February 013 Table 5-4 Determination o inspection category or details with high atigue utilisation 1) Design Class DC1 and DC DC3 and DC4 Direction o dominating principal stress Inspection category 3) Welds with the direction o the dominating dynamic principal stress transverse to the weld ( between 45and 135) Welds with the direction o the dominating dynamic principal stress in the direction o the weld ( between - 45and 45) Welds with the direction o the dominating dynamic principal stress transverse to the weld ( between 45and 135) Welds with the direction o the dominating dynamic principal stress in the direction o the weld ( between - 45and 45) A ) B 4) B 4) C 5) DC5 Welds with the direction o the dominating dynamic principal stress transverse to the weld ( between 45and 135) Welds with the direction o the dominating dynamic principal stress in the direction o the weld ( between - 45and 45) Notes: 1) High atigue utilisation means connections with calculated atigue lie less than 3 times the required atigue lie (design atigue lie multiplied with the DFF). ) Butt welds with high atigue utilisation and SCF less than 1.3 need stricter NDT acceptance criteria. Such criteria need to be developed in each case. 3) For joints in inspection categories B, C or D, the hot spot regions (regions with highest stress range) at welds or areas o welds o special concern shall be addressed with individual notations as mandatory or selected NDT methods. 4) Welds or parts o welds with no access or in-service inspection and repair should be assigned inspection category A. 5) Welds or parts o welds with no access or in-service inspection and repair should be assigned inspection category B. D E NORSOK standard Page 1 o 64

14 NORSOK standard N-004 Rev. 3, February ULTIMATE LIMIT STATES 6.1 General This clause gives provisions or checking o ULSs or typical structural elements used in oshore steel structures, where ordinary building codes lack relevant recommendations. Such elements are tubular members, tubular joints, conical transitions and some load situations or plates and stiened plates. For other types o structural elements NS-EN or member design and NS-EN or other joints than tubular joints apply. See also sub clause and 6.7. The material actor is 1.15 or ULSs unless noted otherwise. The material actors according to Table 6-1 shall be used i NS-EN and NS-EN are used or calculation o structural resistance: Table 6-1 Material actors Type o calculation Material actor 1) Value Resistance o Class 1, or 3 cross-sections M Resistance o Class 4 cross-sections M Resistance o member to buckling M Resistance o net section at bolt holes M 1.3 Resistance o illet and partial penetration welds M 1.3 Resistance o bolted connections M 1.3 1) Symbols according to NS-EN and NS-EN For resistance check where other material actors are used than given in Table 6-1 the recommended material actor in NS-EN , NS-EN and NS-EN should be multiplied by an additional building code material actor BC =1.05 The ultimate strength o structural elements and systems should be evaluated by using a rational, justiiable engineering approach. The structural analysis may be carried out as linear elastic, simpliied rigid plastic, or elastic-plastic analyses. Both irst order or second order analyses may be applied. In all cases, the structural detailing with respect to strength and ductility requirements shall conorm to the assumption made or the analysis. When plastic or elastic-plastic analyses are used or structures exposed to cyclic loading (e.g. wave loads) checks shall be carried out to veriy that the structure will shake down without excessive plastic deormations or racture due to repeated yielding. A characteristic or design cyclic load history needs to be deined in such a way that the structural reliability in case o cyclic loading (e.g. storm loading) is not less than the structural reliability or ULSs or non-cyclic actions. It should be checked as a minimum that the structure will carry all loads throughout the entire storm comprising the ULS environmental condition. In case o linear global beam analysis combined with the resistance ormulations set down in this NORSOK standard, shakedown can be assumed without urther checks. 6. Ductility It is a undamental requirement that all ailure modes are suiciently ductile such that the structural behaviour will be in accordance with the anticipated model used or determination o the responses. In general all design procedures, regardless o analysis method, will not capture the true structural behaviour. Ductile ailure modes will allow the structure to redistribute orces in accordance with the presupposed static model. Brittle ailure modes shall thereore be avoided or shall be veriied to have excess resistance compared to ductile modes, and in this way protect the structure rom brittle ailure. The ollowing sources or brittle structural behaviour may need to be considered or a steel structure: 1. Unstable racture caused by a combination o the ollowing actors: - brittle material; NORSOK standard Page 13 o 64

15 NORSOK standard N-004 Rev. 3, February a design resulting in high local stresses; - the possibilities or weld deects.. Structural details where ultimate resistance is reached with plastic deormations only in limited areas, making the global behaviour brittle, e.g. partial butt weld loaded transverse to the weld with ailure in the weld. 3. Shell buckling. 4. Buckling where interaction between local and global buckling modes occur. In general a steel structure will be o adequate ductility i the ollowing is satisied: 5. Material toughness requirements are met, and the design avoids a combination o high local stresses with possibilities o undetected weld deects. 6. Details are designed to develop a certain plastic delection e.g. partial butt welds subjected to stresses transverse to the weld is designed with excess resistance compared with adjoining plates. 7. Member geometry is selected such that the resistance does not show a sudden drop in capacity when the member is subjected to deormation beyond maximum resistance. An unstiened shell in crosssection class 4 is an example o a member that may show such an unavourable resistance deormation relationship. For deinition o cross-section class see NS-EN Local and global buckling interaction eects are avoided. 6.3 Tubular members General The structural strength and stability requirements or steel tubular members are speciied in this section. The requirements given in this section apply to un stiened and ring stiened tubulars having a thickness t 6 mm, D/t < 10 and material meeting the general requirements in Clause 5. In cases where hydrostatic pressure are present, the structural analysis may proceed on the basis that stresses due to the capped-end orces arising rom hydrostatic pressure are either included in or excluded rom the analysis. This aspect is discussed in Clause 1. In the ollowing subclauses, y and z are used to deine the in-plane and out-o-plane axes o a tubular member, respectively. The requirements assume the tubular is constructed in accordance with the abrication tolerances given in NORSOK M-101. The requirements are ormulated or an isolated beam column. This ormulation may also be used to check the resistance o rames and trusses, provided that each member is checked or the member orces and moments combined with a representative eective length. The eective length may in lieu o special analyses be determined according to the requirements given in this chapter. Alternatively the ULSs or rames or trusses may be determined on basis o non-linear analyses taking into account second order eects. The use o these analyses requires that the assumptions made are ulilled and justiied. Tubular members subjected solely to axial tension, axial compression, bending, shear, or hydrostatic pressure should be designed to satisy the strength and stability requirements speciied in 6.3. to Tubular members subjected to combined loads without hydrostatic pressure should be designed to satisy the strength and stability requirements speciied in Tubular members subjected to combined loads with hydrostatic pressure should be designed to satisy the strength and stability requirements speciied in The equations in this section are not using an unique sign convention. Deinitions are given in each paragraph Axial tension Tubular members subjected to axial tensile loads should be designed to satisy the ollowing condition: N Sd where N t,rd A M y (6.1) NORSOK standard Page 14 o 64

16 NORSOK standard N-004 Rev. 3, February 013 N Sd = design axial orce (tension positive) y = characteristic yield strength A = cross sectional area M = Axial compression Tubular members subjected to axial compressive loads should be designed to satisy the ollowing condition: N Sd N c,rd A M c (6.) where N Sd = design axial orce (compression positive) c = characteristic axial compressive strength M = see In the absence o hydrostatic pressure the characteristic axial compressive strength or tubular members shall be the smaller o the in-plane or out-o-plane buckling strength determined rom the ollowing equations: c c [ ] 0.9 cl E cl kl i cl E cl or 1.34 or 1.34 where cl = characteristic local buckling strength = column slenderness parameter E = smaller Euler buckling strength in y or z direction E = Young s modulus o elasticity, MPa k = eective length actor, see l = longer unbraced length in y or z direction i = radius o gyration The characteristic local buckling strength should be determined rom: y c l y or y c l c le or y c l y or y cle c le and cle C E e t D cle cle (6.3) (6.4) (6.5) (6.6) (6.7) (6.8) NORSOK standard Page 15 o 64

17 NORSOK standard N-004 Rev. 3, February 013 where cle = characteristic elastic local buckling strength C e = critical elastic buckling coeicient = 0.3 D = outside diameter t = wall thickness y For c le the tubular is a class 4 cross section and may behave as a shell. Shell structures may have a brittle structure ailure mode. Reerence is made to 6.. For class 4 cross sections increased M values shall be used according to Equation (6.) Bending Tubular members subjected to bending loads should be designed to satisy the ollowing condition: M Sd M Rd mw M where M Sd = design bending moment m = characteristic bending strength W = elastic section modulus M = see section The characteristic bending strength or tubular members should be determined rom: Z yd m y or W Et D Z Et W y y m y m yd Et Z W where W = elastic section modulus 4 4 D (D t) = 3 D Z = plastic section modulus y cle = D (D t) 6 y D Et yd y Et E (6.9) (6.10) (6.11) (6.1) For the tubular is a class 4 cross section and may behave as a shell. Shell structures may have a brittle structure ailure mode. Reerence is made to 6.. For class 4 cross sections increased M values shall be used according to Equation (6.) Shear Tubular members subjected to beam shear orces should be designed to satisy the ollowing condition: NORSOK standard Page 16 o 64

18 NORSOK standard N-004 Rev. 3, February 013 V Sd V Rd A y 3 M (6.13) where V Sd = design shear orce y = yield strength A = cross sectional area M = 1.15 Tubular members subjected to shear rom torsional moment should be designed to satisy the ollowing condition: M T,Sd M T,Rd I p y D 3 where M T,Sd = design torsional moment M 4 4 I p = polar moment o inertia = D (D t) Hydrostatic pressure 3 (6.14) Hoop buckling Tubular members subjected to external pressure should be designed to satisy the ollowing condition: p,sd p, Sd h,rd p Sd D t h M (6.15) (6.16) where h = characteristic hoop buckling strength p, Sd = design hoop stress due to hydrostatic pressure (compression positive) p Sd = design hydrostatic pressure M = see I out-o-roundness tolerances do not meet the requirements given in NORSOK M-101, guidance on calculating reduced strength is given in Clause 1. h y, 0.4 he h 0.7 y or.44 y he 0.55 y y h he, or.44 (6.17) he he y y (6.18) or 0.55 (6.19) The elastic hoop buckling strength, he, is determined rom the ollowing equation: he C h E t D where C h = 0.44 t/dor 1.6D/t = 0.44 t/d (D/t) 3 / 4 or 0.85D/t < 1.6D/t = 0.737/( ) or 1.5 < 0.85D/t (6.0) NORSOK standard Page 17 o 64

19 NORSOK standard N-004 Rev. 3, February 013 = 0.80 or < 1.5 and where the geometric parameter,, is deined as: L L D D t and = length o tubular between stiening rings, diaphragms, or end connections Ring stiener design The circumerential stiening ring size may be selected on the ollowing approximate basis: I c he tl rd 8E (6.1) where I c = required moment o inertia or ring composite section L r = ring spacing D = diameter (see Note or external rings) Notes: 1. Equation (6.1) assumes that the yield strength o the stiening ring is equal to or greater than that o the tubular.. For external rings, D in Equation (6.1) should be taken to the centroid o the composite ring. 3. An eective width o shell equal to 1.1 D t may be assumed as the lange or the composite ring section. 4. Where out-o-roundness in excess o tolerances given in NORSOK M-101 is permitted, larger stieners may be required. The bending due to out-o-roundness should be specially investigated. Local buckling o ring stieners with langes may be excluded as a possible ailure mode provided that the ollowing requirements are ulilled: h 1.1 t E w y and b t 0.3 E y where h = web height t w = web thickness b = hal the width o lange o T-stieners t = thickness o lange Local buckling o ring stieners without langes may be excluded as a possible ailure mode provided that: h t 0.4 E w y Torsional buckling o ring stieners with langes may be excluded as a possible ailure mode provided that: 3.5 h b h E 10 r y Check or torsional buckling o the stiener shall be made according to DNV RP-C0 /13/ Material actor The material actor, M, is given as: NORSOK standard Page 18 o 64

20 NORSOK standard N-004 Rev. 3, February 013 M M M s or or 0.5 or s s 0.5 s (6.) where s c,sd cl c p,sd h h (6.3) where cl is calculated rom Equation (6.6) or Equation (6.7) whichever is appropriate and h rom Equation (6.17), Equation (6.18), or Equation (6.19) whichever is appropriate. y (6.4) y c,and h cle he cle and he is obtained rom Equation (6.8), and Equation (6.0) respectively. p,sd is obtained rom Equation (6.16) and c,sd NSd A M y,sd M W N Sd is negative i in tension. z,sd (6.5) Tubular members subjected to combined loads without hydrostatic pressure Axial tension and bending Tubular members subjected to combined axial tension and bending loads should be designed to satisy the ollowing condition at all cross sections along their length: N N Sd t,rd where 1.75 M y,sd M M Rd z,sd 1.0 M y,sd = design bending moment about member y-axis (in-plane) M z, Sd = design bending moment about member z-axis (out-o-plane) N Sd = design axial tensile orce (6.6) I shear or torsion is o importance, the bending capacity M Rd needs to be substituted with M Red,Rd calculated according to subclause or Axial compression and bending Tubular members subjected to combined axial compression and bending should be designed to satisy the ollowing condition accounting or possible variations in cross-section, axial load and bending moment according to appropriate engineering principles: N N Sd c,rd 1 M Rd C mym N 1 N y,sd Sd Ey C mzm N 1 N and at all cross sections along their length: z,sd Sd Ez (6.7) NORSOK standard Page 19 o 64

21 NORSOK standard N-004 Rev. 3, February 013 N N Sd cl,rd M y,sd M M Rd z,sd 1.0 (6.8) where N N Sd = design axial compression orce C my, C mz = reduction actors corresponding to the member y and z axes, respectively N Ey, N Ez = Euler buckling strengths corresponding to the member y and z axes, respectively cl,rd c A l M design axial local buckling resistance N Ey EA kl i y (6.9) N Ez EA kl i z (6.30) k in Equation (6.9) and Equation (6.30) relate to buckling in the y and z directions, respectively. These actors can be determined using a rational analysis that includes joint lexibility and side-sway. In lieu o such a rational analysis, values o eective length actors, k, and moment reduction actors, C m, may be taken rom Table 6-. All lengths are measured centreline to centreline. Table 6- Eective length and moment reduction actors or member strength checking Structural element k (1) C m Superstructure legs - Braced 1.0 (a) - Portal (unbraced) k () (a) Jacket legs and piling - Grouted composite section 1.0 (c) - Ungrouted jacket legs 1.0 (c) - Ungrouted piling between shim points 1.0 (b) Jacket braces - Primary diagonals and horizontals 0.7 (b) or (c) -K-braces (3) 0.7 (c) - Longer segment length o X-braces (3) 0.8 (c) Secondary horizontals 0.7 (c) Notes: 1. C m values or the cases deined in Table 6- are as ollows: (a) 0.85 (b) or members with no transverse loading, C m = M 1,Sd/M,Sd, where M 1,Sd/M,Sd is the ratio o smaller to larger moments at the ends o that portion o the member unbraced in the plane o bending under consideration. M 1,Sd/M,Sd is positive when the number is bent in reverse curvature, negative when bent in single curvature. (c) or members with transverse loading, C m = N Sd/N E, or 0.85, whichever is less, and N E = N Ey or N Ez as appropriate.. Use eective length alignment chart in Clause At least one pair o members raming into the a K- or X-joint shall be in tension i the joint is not braced out-o-plane. For X-braces, when all members are in compression, the k-actor should be determined using the procedures given in Clause The eective length and C m actors given in Table 6- do not apply to cantilever members and the member ends are assumed to be rotationally restrained in both planes o bending. NORSOK standard Page 0 o 64

22 NORSOK standard N-004 Rev. 3, February Interaction shear and bending moment Tubular members subjected to beam shear orce and bending moment should be designed to satisy the ollowing condition provided that the direction o the shear orce and the moment vectors are orthogonal within 0: M M V Sd Sd Sd 1.4 or 0. 4 Rd VRd VRd V (6.31) M Sd VSd 1.0 or 0. 4 M V Rd Rd (6.3) Interaction shear, bending moment and torsional moment Tubular members subjected to beam shear orce, bending moment and torsion should be designed to satisy the ollowing condition provided that the direction o the shear orce and the moment vectors are orthogonal within 0: M M M Sd Red,Rd M Sd Red,Rd where V 1.4 V Sd Rd VSd or 0. 4 V VSd 1.0 or 0. 4 V M Red,Rd = m,red = T,Sd = d = W m,red M m 1 3 M R y M T,Sd t T,Sd d R = radius o tubular member M = see Rd Rd (6.33) Tubular members subjected to combined loads with hydrostatic pressure The design provisions in this section are divided into two categories. In Method A it is assumed that the capped-end compressive orces due to the external hydrostatic pressure are not included in the structural analysis. Alternatively, the design provisions in Method B assume that such orces are included in the analysis as external nodal orces. Dependent upon the method used in the analysis, the interaction equations in either Method A or Method B should be satisied at all cross sections along their length. It should be noted that the equations in this section are not applicable unless Equation (6.15) is irst satisied. For guidance on signiicance o hydrostatic pressure, see Clause 1. NORSOK standard Page 1 o 64

23 NORSOK standard N-004 Rev. 3, February Axial tension, bending, and hydrostatic pressure Tubular members subjected to combined axial tension, bending, and hydrostatic pressure should be designed to satisy the ollowing equations in either Method A or Method B at all cross sections along their length. Method A ( a,sd is in tension) In this method, the calculated value o member axial stress, a,sd, should not include the eect o the hydrostatic capped-end axial stress. The capped-end axial compression due to external hydrostatic pressure, q,sd, can be taken as 0.5 p, Sd. This implies that, the tubular member takes the entire capped-end orce arising rom external hydrostatic pressure. In reality, the stresses in the member due to this orce depend on the restraint provided by the rest o the structure on the member. The stress computed rom a more rigorous analysis may be substituted or 0.5. (a) For a,sd q,sd (net axial tension condition) p, Sd a,sd where th, Rd mh, Rd th,rd q,sd my,sd mh, Rd mz,sd 1.0 (6.34) a,sd = design axial stress that excludes the eect o capped-end axial compression arising rom external hydrostatic pressure (tension positive) q,sd = capped-end design axial compression stress due to external hydrostatic pressure (= 0.5 ) (compression positive) p,sd my,sd = design in plane bending stress mz,sd = design out o plane bending stress th,rd = design axial tensile resistance in the presence o external hydrostatic pressure which is given by Equation (6.35): y M [ B B 0.3B] (6.35) mh,rd = design bending resistance in the presence o external hydrostatic pressure which is given by Equation (6.36): m M [ B M = see and Equation (6.37): B p,sd h,rd, 5 4 h y B 1.0 B 0.3B] (b) For a,sd < q,sd (net axial compression condition) a,sd cl,rd q,sd my,sd mh, Rd mz,sd 1.0 (6.36) (6.37) (6.38) (6.39) NORSOK standard Page o 64

24 NORSOK standard N-004 Rev. 3, February 013 cl,rd cl M (6.40) where cl is ound rom Equation (6.6) and Equation (6.7). he When c,sd 0.5 and cle 0.5 he M, Equation (6.41) should also be satisied: c,sd cle M 0.5 he 0.5 he M M he M p,sd 1.0 (6.41) in which c, Sd m,sd q,sd a, Sd ; c,sd should relect the maximum combined compressive stress. m,sd M z,sd M W y,sd M = see Method B ( ac,sd is in tension) In this method, the calculated member axial stress, ac,sd, includes the eect o the hydrostatic capped-end axial stress. Only Equation (6.4) needs to be satisied: ac,sd th,rd where my,sd mh, Rd mz,sd 1.0 (6.4) ac,sd = design axial stress that includes the eect o the capped-end compression arising rom external hydrostatic pressure (tension positive) Axial compression, bending, and hydrostatic pressure Tubular members subjected to combined compression, bending, and hydrostatic pressure should be proportioned to satisy the ollowing requirements at all cross sections along their length. Method A ( a,sd is in compression) a,sd ch,rd a,sd where 1 cl,rd mh,rd q,sd C my 1 my,sd my,sd a,sd Ey mh, Rd mz,sd C mz mz,sd a,sd Ez (6.43) (6.44) a,sd = design axial stress that excludes the eect o capped-end axial compression arising rom external hydrostatic pressure (compression positive) NORSOK standard Page 3 o 64

25 NORSOK standard N-004 Rev. 3, February 013 Ey E kl i y (6.45) Ez E kl i z (6.46) ch,rd = design axial compression strength in the presence o external hydrostatic pressure which is given by the ollowing equations: ch,rd 1 cl M [ q,sd cl 1.1 q,sd cl ] or 1.34 (1 cl q,sd ) 1 (6.47) and ch,rd where 0.9 cl M When 0.5 also be satisied., he c,sd and he M M = see Method B ( ac,sd is in compression) (a) or ac,sd > q,sd ac,sd cl,rd When ac,sd satisied. ch,rd q,sd 1 my,sd mh,rd mh, Rd or 1.34 (1 cl cle 0.5, Equation (6.41), in which c, Sd m,sd q,sd a, Sd C 1 mz,sd my my,sd ac,sd 1.0 Ey q,sd C 1 mz mz,sd ac,sd Ez q,sd q,sd ) 1 (6.48) (6.49), should (6.50) (6.51) ac,sd = design axial stress that includes the eect o capped-end axial compression arising rom external hydrostatic pressure (compression positive) 0.5 he c,sd and M cle he 0.5, Equation (6.41), in which c, Sd m,sd ac, Sd M M, should also be NORSOK standard Page 4 o 64

26 NORSOK standard N-004 Rev. 3, February 013 (b) or ac,sd q,sd For ac,sd q,sd, Equation (6.51) should be satisied. When satisied. 0.5 he c,sd and M M = see cle M he 0.5, Equation (6.41), in which c, Sd m,sd ac, Sd M, should also be 6.4 Tubular joints General The ollowing provisions apply to the design o tubular joints ormed by the connection o two or more members. Terminology or simple joints is deined in Figure 6-1. Figure 6-1 also gives some design requirements with respect to joint geometry. The gap or simple K-joints should be larger than 50 mm and less than D. Minimum distances or chord cans and brace stubs should not include thickness tapers. Figure 6-1 Detail o simple joint Reductions in secondary (delection induced) bending moments or inelastic relaxation through use o joint elastic stiness may be considered. In certain instances, hydrostatic pressure eects may be signiicant Joint classiication Joint classiication is the process whereby the axial orce in a given brace is subdivided into K, X and Y components o actions, corresponding to the three joint types or which resistance equations exist. Such subdivision normally considers all o the members in one plane at a joint. For purposes o this provision, brace planes within ±15º o each other may be considered as being in a common plane. Each brace in the plane can have a unique classiication that could vary with action condition. The classiication can be a NORSOK standard Page 5 o 64

27 NORSOK standard N-004 Rev. 3, February 013 mixture between the above three joint types. Once the breakdown into axial components is established, the resistance o the joint can be estimated using the procedures in Figure 6- provides some simple examples o joint classiication. For a brace to be considered as K-joint classiication, the axial orce in the brace should be balanced to within 10 % by orces in other braces in the same plane and on the same side o the joint. For Y-joint classiication, the axial orce in the brace is reacted as beam shear in the chord. For X-joint classiication, the axial orce in the brace is carried through the chord to braces on the opposite side. Additional explanation o joint-classiication is ound in Clause 1. NORSOK standard Page 6 o 64