DEP Fixed Steel Offshore Structures

DEP SPECIFICATION

Copyright Shell Group of Companies. No reproduction or networking permitted without license from Shell. Not for resale

FIXED STEEL OFFSHORE STRUCTURES (AMENDMENTS/SUPPLEMENTS TO ISO 19902:2007)

DEP 37.19.00.30-Gen. February 2011 (DEP Circular 31/12 has been incorporated)

DESIGN AND ENGINEERING PRACTICE

DEM1

© 2011 Shell Group of companies All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, published or transmitted, in any form or by any means, without the prior written permission of the copyright owner or Shell Global Solutions International BV.

This document has been supplied under license by Shell to: Sakhalin Energy Investment Company Ltd (SEIC) [email protected] 09/09/2015 06:36:10

DEP 37.19.00.30-Gen. February 2011 Page 2

PREFACE DEP (Design and Engineering Practice) publications reflect the views, at the time of publication, of Shell Global Solutions International B.V. (Shell GSI) and, in some cases, of other Shell Companies. These views are based on the experience acquired during involvement with the design, construction, operation and maintenance of processing units and facilities. Where deemed appropriate DEPs are based on, or reference international, regional, national and industry standards. The objective is to set the recommended standard for good design and engineering practice to be applied by Shell companies in oil and gas production, oil refining, gas handling, gasification, chemical processing, or any other such facility, and thereby to help achieve maximum technical and economic benefit from standardization. The information set forth in these publications is provided to Shell companies for their consideration and decision to implement. This is of particular importance where DEPs may not cover every requirement or diversity of condition at each locality. The system of DEPs is expected to be sufficiently flexible to allow individual Operating Units to adapt the information set forth in DEPs to their own environment and requirements. When Contractors or Manufacturers/Suppliers use DEPs, they shall be solely responsible for such use, including the quality of their work and the attainment of the required design and engineering standards. In particular, for those requirements not specifically covered, the Principal will typically expect them to follow those design and engineering practices that will achieve at least the same level of integrity as reflected in the DEPs. If in doubt, the Contractor or Manufacturer/Supplier shall, without detracting from his own responsibility, consult the Principal. The right to obtain and to use DEPs is restricted, and is granted by Shell GSI (and in some cases by other Shell Companies) under a Service Agreement or a License Agreement. This right is granted primarily to Shell companies and other companies receiving technical advice and services from Shell GSI or another Shell Company. Consequently, three categories of users of DEPs can be distinguished: 1)

Operating Units having a Service Agreement with Shell GSI or another Shell Company. The use of DEPs by these Operating Units is subject in all respects to the terms and conditions of the relevant Service Agreement.

2)

Other parties who are authorised to use DEPs subject to appropriate contractual arrangements (whether as part of a Service Agreement or otherwise).

3)

Contractors/subcontractors and Manufacturers/Suppliers under a contract with users referred to under 1) or 2) which requires that tenders for projects, materials supplied or - generally - work performed on behalf of the said users comply with the relevant standards.

Subject to any particular terms and conditions as may be set forth in specific agreements with users, Shell GSI disclaims any liability of whatsoever nature for any damage (including injury or death) suffered by any company or person whomsoever as a result of or in connection with the use, application or implementation of any DEP, combination of DEPs or any part thereof, even if it is wholly or partly caused by negligence on the part of Shell GSI or other Shell Company. The benefit of this disclaimer shall inure in all respects to Shell GSI and/or any Shell Company, or companies affiliated to these companies, that may issue DEPs or advise or require the use of DEPs. Without prejudice to any specific terms in respect of confidentiality under relevant contractual arrangements, DEPs shall not, without the prior written consent of Shell GSI, be disclosed by users to any company or person whomsoever and the DEPs shall be used exclusively for the purpose for which they have been provided to the user. They shall be returned after use, including any copies which shall only be made by users with the express prior written consent of Shell GSI. The copyright of DEPs vests in Shell Group of companies. Users shall arrange for DEPs to be held in safe custody and Shell GSI may at any time require information satisfactory to them in order to ascertain how users implement this requirement. All administrative queries should be directed to the DEP Administrator in Shell GSI.


DEP 37.19.00.30-Gen. February 2011 Page 3 TABLE OF CONTENTS PART I 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 2. 2.1 2.2

INTRODUCTION AND GENERAL REQUIREMENTS...............................................4 INTRODUCTION ........................................................................................................4 SCOPE........................................................................................................................4 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS .........4 DEFINITIONS .............................................................................................................4 CROSS-REFERENCES .............................................................................................5 SUMMARY OF CHANGES.........................................................................................5 COMMENTS ON THIS DEP .......................................................................................5 DUAL UNITS...............................................................................................................5 GENERAL REQUIREMENTS.....................................................................................5 GENERAL ...................................................................................................................5 INTERNATIONAL STANDARD ADOPTED FOR USE...............................................5

PART II 3. 5. 6. 8. 9. 10. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 26. ANNEX A ANNEX C ANNEX D ANNEX G

AMENDMENTS/SUPPLEMENTS TO ISO 19902:2007 ............................................6 TERMS AND DEFINITIONS .......................................................................................6 ABBREVIATED TERMS .............................................................................................6 OVERALL CONSIDERATIONS..................................................................................6 ACTIONS FOR PRE-SERVICE AND REMOVAL SITUATION ..................................7 ACTIONS FOR IN-PLACE SITUATION .....................................................................9 ACCIDENTAL SITUATIONS.....................................................................................10 STRUCTURAL MODELLING AND ANALYSIS ........................................................10 STRENGTH OF TUBULAR MEMBERS ...................................................................10 STRENGTH OF TUBULAR JOINTS ........................................................................10 STRENGTH AND FATIGUE RESISTANCE OF OTHER STRUCTURAL COMPONENTS ........................................................................................................11 FATIGUE...................................................................................................................12 FOUNDATION DESIGN ...........................................................................................13 CORROSION CONTROL .........................................................................................18 MATERIALS..............................................................................................................18 WELDING, FABRICATION AND WELD INSPECTION............................................19 QUALITY CONTROL, QUALITY ASSURANCE AND DOCUMENTATION .............20 LOADOUT, TRANSPORTATION AND INSTALLATION..........................................20 IN-SERVICE INSPECTION AND STRUCTURAL INTEGRITY MANAGEMENT .....23 ASSESSMENT OF EXISTING STRUCTURES........................................................23 STANDARD DETAILS ..............................................................................................23 ADDITIONAL INFORMATION AND GUIDANCE .....................................................24 MATERIAL CATEGORY APPROACH .....................................................................29 DESIGN CLASS APPROACH ..................................................................................33 FABRICATION TOLERANCES ................................................................................33

PART III

REFERENCES .........................................................................................................34


DEP 37.19.00.30-Gen. February 2011 Page 4 PART I INTRODUCTION AND GENERAL REQUIREMENTS 1.

INTRODUCTION

1.1

SCOPE This DEP specifies requirements and gives recommendations for the design of fixed steel offshore structures for the petroleum and natural gas industries. It also covers issues relating to planning and construction where these are relevant to design. This DEP is based on ISO 19902:2007. Part II of this DEP amends, supplements and replaces various clauses of ISO 19902:2007. This DEP does not cover design of the topsides structure. In certain situations (e.g. where extensive good historical performance is known), and if approved by the Principal, fixed offshore structures may be designed in accordance with API-WSD instead of ISO 19902:2007 and this DEP. This DEP contains mandatory requirements to mitigate process safety risks in accordance with Design Engineering Manual DEM 1 – Application of Technical Standards This is a revision of the DEP of the same number dated January 2010; see (1.5) regarding the main changes.

1.2

DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS Unless otherwise authorised by Shell GSI, the distribution of this DEP is confined to Shell companies and, where necessary, to Contractors and Manufacturers/Suppliers nominated by them. This DEP is intended for use in offshore exploration and production facilities. This DEP may also be applied in other similar facilities. When DEPs are applied, a Management of Change (MOC) process should be implemented; this is of particular importance when existing facilities are to be modified. If national and/or local regulations exist in which some of the requirements may be more stringent than in this DEP, the Contractor shall determine by careful scrutiny which of the requirements are the more stringent and which combination of requirements will be acceptable with regard to the safety, environmental, economic and legal aspects. In all cases the Contractor shall inform the Principal of any deviation from the requirements of this DEP which is considered to be necessary in order to comply with national and/or local regulations. The Principal may then negotiate with the Authorities concerned, the objective being to obtain agreement to follow this DEP as closely as possible.

1.3

DEFINITIONS The Contractor is the party that carries out all or part of the design, engineering, procurement, construction, commissioning or management of a project or operation of a facility. The Principal may undertake all or part of the duties of the Contractor. The Manufacturer/Supplier is the party that manufactures or supplies equipment and services to perform the duties specified by the Contractor. The Principal is the party that initiates the project and ultimately pays for its design and construction. The Principal will generally specify the technical requirements. The Principal may also include an agent or consultant authorised to act for, and on behalf of, the Principal. The lower-case word shall indicates a requirement. The capitalised term SHALL [PS] indicates a process safety requirement. The word should indicates a recommendation.


DEP 37.19.00.30-Gen. February 2011 Page 5 1.4

CROSS-REFERENCES The clause numbering used in Part II of this DEP corresponds with that used in ISO 19902:2007. Other documents referenced by this DEP are listed in (Part III).

1.5

SUMMARY OF CHANGES This is a revision of the DEP of the same number dated January 2010. Content of the previous version that was background information, explanation and tutorial has been removed.

1.6

COMMENTS ON THIS DEP Comments on this DEP may be sent to the Administrator at [email protected], using the DEP Feedback Form. The DEP Feedback Form can be found on the main page of “DEPs on the Web”, available through the Global Technical Standards web portal http://sww.shell.com/standards and on the main page of the DEPs DVD-ROM.

1.7

DUAL UNITS

Amended per Circular 31/12 Dual units have been incorporated throughout this DEP.

This DEP contains both the International System (SI) units, as well as the corresponding US Customary (USC) units, which are given following the SI units in brackets. When agreed by the Principal, the indicated USC values/units may be used.

2.

GENERAL REQUIREMENTS

2.1

GENERAL Part II of this DEP amends, supplements and deletes various clauses/paragraphs of ISO 19902:2007. Wherever reference is made to ISO 19902, it shall be understood to mean ISO 19902:2007 as amended/supplemented by this DEP. For ease of reference, the clause numbering of ISO 19902 has been used throughout Part II of this DEP. Clauses of ISO 19902 that are not mentioned in this DEP shall remain applicable as written.

2.2

INTERNATIONAL STANDARD ADOPTED FOR USE ISO 19902:2007 SHALL [PS] be adopted for use with amendments as described in Part II of this DEP.


DEP 37.19.00.30-Gen. February 2011 Page 6 PART II AMENDMENTS/SUPPLEMENTS TO ISO 19902:2007 3.

TERMS AND DEFINITIONS Add new clauses:

3.57

barge simple floating vessel, normally non-propelled, on which a structure can be transported

3.58

vessel self-propelled ship-shaped unit, on which a structure can be transported.

5.

ABBREVIATED TERMS Add: CoG

centre of gravity

FMEA

failure modes and effects analysis

GRP

glass-reinforced plastic

6.

OVERALL CONSIDERATIONS

6.1

Types of fixed steel offshore structure

6.1.1

General Add: All calculations, dimensions and weights shall be in SI units (see DEP 00.00.20.10-Gen.).

6.1

Service and operational considerations

6.3.3.2

Deck elevation Add: For a structure with exposure level L1 (manned non-evacuated or high consequence, see Table 6.6.1) the abnormal water level should have a return period of 10 000 years and should incorporate the associated storm surge and astronomical tide, in addition to allowances for water depth uncertainty, seabed penetration and subsidence. For a structure with exposure level L2 (manned evacuated or unmanned and medium consequence, see Table 6.6.1) the abnormal water level should have a return period of 1 000 years and should incorporate the associated storm surge and astronomical tide, in addition to allowances for water depth uncertainty, seabed penetration and subsidence. Add to last paragraph: The durability, corrosion protection and fatigue characteristics of such equipment and support members shall also receive detailed attention in design.

6.6.3

Consequence categories Add before last paragraph: A structure with exposure level L1 should achieve a target reliability equivalent to an annual probability of failure of 3x10-5 / year (ref. ISO 19902:2007 A.9.9.3 and EP 97-5050) This target reliability can be achieved by using the 100-year return period environmental actions in conjunction with the action factors given in ISO 19902:2007 Table 9.10.1 and Clause A.9.9.3. A structure with exposure level L2 should achieve a target reliability equivalent to an annual probability of failure of 5x10-4 / year (ISO 19902:2007 A.9.9.3 and EP 97-5050.


DEP 37.19.00.30-Gen. February 2011 Page 7 This target reliability can be achieved by using the 100-year return period environmental actions in conjunction with the action factors given in ISO 19902:2007 Table A.9.9.2. 8.

ACTIONS FOR PRE-SERVICE AND REMOVAL SITUATION

8.3

Actions associated with lifting

8.3.2

Dynamic effects Correction – change list number j) to b) and list number k) to c). Replace a) and b) by the following: a) for lifts in air, performed offshore, in sheltered waters or onshore the DAF is given in Table 8.3-1. Table 8.3-1

DAF for a single crane on a vessel

Gross lift weight [kN]

kDAF Offshore

Lifts in air, onshore or in sheltered waters

Onshore*) Moving

Static

<1000

1.30

1.15

1.15

1.00

1 000 to 10 000

1.20

1.10

1.10

1.00

10 000 to 25 000

1.15

1.05

1.05

1.00

>25 000

1.10

1.05

1.05

1.00

*) Lifts by land based cranes concern marine operations such as loadouts.

Change c) to b). 8.6

Actions associated with transportation

8.6.3

Determination of actions Add: In lieu of a full motion analysis the values given in Table 8.6-1 may be used for design. The partial action factor for environmental, permanent and variable actions may be taken as 1.20.


DEP 37.19.00.30-Gen. February 2011 Page 8 Table 8.6-1

Default values of motion responses for standard transportation analyses Roll Pitch amplitude amplitude

Heave acceleration

degrees

degrees

m/s2 (ft/s2)

Large vessels

LOA ≥ 140 (460) and B ≥ 30 (98)

20

10

0.2 g (0.66g)

Medium vessels

LOA ≥ 76 (250) and B ≥ 23 (75)

20

12.5

0.2 g (0.66g)

LOA <76 (250) or B < 23 (75)

30

15

0.2 g (0.66g)

Large cargo barges

LOA ≥ 76 (250) and B ≥ 23 (75)

20

12.5

0.2 g (0.66g)

Small cargo barges

LOA <76 (250) or B < 23 (75)

25

15

0.2 g (0.66g)

Small vessels

LOA = Length over all, in metres (feet) and B = Breadth, in metres (feet) The default motion criteria shown above should be applied in accordance with the following points. a) The roll and pitch values listed above should be assumed to apply for a 10 s full cycle period of motion for vessels and barges B ≥ 23 m (75 ft). For vessel and barges B < 23 m (75 ft) the roll period can be smaller. b) The roll and pitch axes should be assumed to pass through the centre of floatation. c) The phasing considered should be assumed to combine, as separate load cases, the most severe combinations of: roll and heave; pitch and heave. d) For inland and sheltered water transportation, the greatest effect of the following cases should be taken into account: the static loads caused by an acceleration of 0.1 g applied parallel to the deck in both directions; the static inclination caused by the design wind; the most severe inclination in the one-compartment damage condition. e) The additional heel or trim caused by the design wind should be considered. For many transports, however, it is permissible to omit the effects of direct wind action when calculating the actions on the cargo. f) The direction of the heave component shall be taken to act along the global vertical axis. Therefore components of heave actions parallel to the deck should be added to the roll or pitch loads in the same direction.

Additionally, a maximum allowable angle of heel shall be determined in order to account for structural design limitations of, for instance, topsides modules and the sea fastening. It is clearly irrelevant that the structure may be allowed to heel 15° if the integrity of modules or sea fastening is already compromised at 10°.



9.

ACTIONS FOR IN-PLACE SITUATION

9.2

Permanent actions (G) and variable actions (Q)

9.2.7

Carry down factors Add: The carry down factors for variable actions on open areas may be taken in accordance with the table below. Normal operating actions shall be taken as 100 % fluid content for all analyses. Test weights of pipes and vessels shall not be considered in global structure and foundation design. Test weights do need to be considered in local design.

Area

Local design

Primary topsides structure design

Global design (structure and foundation)

Apply factor given

Apply factor given

Apply factor given

Storage areas

1.0

1.0

1.0

Laydown areas

1.0

f

f

Lifeboat platforms

1.0

1.0

may be ignored

Area between equipment

1.0

f

“

Walkways, staircases and platforms

1.0

f

“

Walkways and staircases for inspection and repair only

1.0

f

“

Roofs, accessible for inspection and repair only

1.0

1.0

“

NOTES:

1. The factor f in the table is the minimum of 1.0 and (0.5 + 3/√A), , where A is the area over which the 2 variable action acts in m .

Add new clause: 9.2.10

Drill cuttings A build-up of drill cuttings on the sea floor adjacent to and on top of the lower level plan bracing may lead to overstressing of members. Where this can occur the lowest plan bracing level shall be designed for potential build up of cuttings including the effects of corrosion or, for example, SRB activity. The problem of drill cuttings affecting the platform installation should also be addressed where template drilling has been carried out prior to installation of the substructure.

9.5

Extreme quasi-static action caused by waves only (Ewe) or by waves and currents (Ewce)

9.5.3

Drag and inertia coefficients Add after last sentence: A minimum increase of 7 % on the Cd shall be applied to account for anodes, unless a lower number can be justified by calculations.

9.10.2

Demonstrating sufficient RSR Add to paragraph at the end:


DEP 37.19.00.30-Gen. February 2011 Page 10 EP 97-5050 provides guidance on determining the RSR value. The RSR is dependent on the probability of failure and the local environmental conditions. 10.

ACCIDENTAL SITUATIONS

10.1.6.2 Assesment of structures following damage Add after last paragraph: A push-over analysis to confirm the residual strength after damage and to determine any reduction of the intact RSR is mandatory for L1 structures. 10.2

Vessel collisions

10.2.2

Collision events Add after last paragraph: Risers and conductors SHALL [PS] be positioned to minimise exposure to accidental damage. Sufficient clearance SHALL [PS] be provided in the impact zone to alleviate contact forces from deforming structural elements.

10.3

Dropped objects Add before first paragraph: A dropped objects study SHALL [PS] be undertaken to evaluate the impact energy and potential damage caused by objects dropped, based on crane usage and objects lifted during rig workover and platform activities. Resistance to dropped objects should be provided by indirect means, such as using redundant framing patterns and materials with sufficient ductility and toughness in vulnerable areas.

12.

STRUCTURAL MODELLING AND ANALYSIS

12.4

Analysis requirements

12.4.4.6 Analysis for reserve strength Correction - the last sentence of b) does not belong to b) and should become a new paragraph: b)

where foundation failure occurs before structural failure, structural failure should be determined by assuming a foundation capacity based on upper bound estimates of soil properties.

The upper bound approach, b) above, provides an assessment of the steel structure strength. 13.

STRENGTH OF TUBULAR MEMBERS

13.2

Tubular members subjected to tension, compression, bending, shear or hydrostatic pressure

13.2.6.2 Hoop buckling Correction - Equation (13.2-28) should read: Ch = 0,44 t/D + 0,21 (D/t)3/µ4

for 0,825 D/t ≤ µ < 1,6 D/t

14.

STRENGTH OF TUBULAR JOINTS

14.2

Design considerations

14.2.5

Detailing practice

(13.2-28)

5th paragraph, replace the first sentence with: The nominal gap (i.e. excluding weld toes) between adjacent braces, whether in-plane or out-of-plane, should not be less than 75 mm (3 in). Alternatively the joint gap may be taken as 50 mm (2 in) between weld toes.


DEP 37.19.00.30-Gen. February 2011 Page 11 5th paragraph; add the following sentence at the end of the paragraph: Partially overlapped braces are not allowed in the ship impact zone. Figure 14.2-4: Correction - The two requirements for details on the left referring to the lower brace should read: ≥ d2 and ≥ 600; ≥ d2/4 and ≥ 150

Add new clause: 14.11

Bolted connections Bolted connections are permitted, but should only be used for the attachment of non-primary items where use of bolted connections is either more cost-effective or offers operational advantages (e.g. post-installed risers) over welded connections. Particular attention should be paid to the following:

15.

-

avoidance of corrosion in bolted assemblies;

-

interaction of bolting material with the CP system (e.g. potential for hydrogen embrittlement)

-

methods for tensioning bolts (if required) and clearances for tensioning tools;

-

avoidance of secondary stresses (e.g. bending due to non-parallel flanges).

STRENGTH AND FATIGUE RESISTANCE OF OTHER STRUCTURAL COMPONENTS Add new clause:

15.4

Conductors

15.4.1

General Forced displacements and any consequent actions on the conductor due to the relative movement between the structure and a drilling jack-up, where applicable, shall be considered in an Ultimate Limit State (ULS) check. Deterioration of surface soil strength can result from conductor/casing cementing operations. Such effects shall be considered in the foundation design of conductors. Details of top hole construction practice are defined in the DEP supplement to A.15.4.1. Welded or threaded conductors may be used as foundation piles provided a rigorous technical analysis of the static strength and fatigue endurance due to driving stresses and in-situ axial and lateral actions is performed to demonstrate robustness and long-term integrity. It is important that at the design stage all expected actions on the conductor are well defined. In all cases, the conductor shall be able to support its own weight plus the weight of any equipment to be placed on top of it and/or casings to be hung off it. A partial action factor of 1.3 shall be applied. The axial capacity of the conductor shall be calculated using the methods described in Clause 17 and a partial resistance factor of 1.5 shall be applied to the representative value of the axial capacity of the conductor. No end bearing on the conductor shall be allowed. The conductor tip should preferably be located in a cohesive soil rather than in a non-cohesive soil such as sand or silt.

15.4.2

Conductor guides The conductor guide stubs and stub support members shall be included in the respective analysis models. They shall be checked for both extreme and abnormal in-place actions,


DEP 37.19.00.30-Gen. February 2011 Page 12 and for fatigue repetitive actions. In addition to this the conductor guides shall be checked (manually) for the highest reaction from wave actions and for fatigue endurance. The top conductor guide shall also be checked for accidental setting of a conductor on the edge of a guide; this case is an accidental design situation where permanent deformation of the cone is allowed. Forced displacements and any consequent actions on the conductor guides due to the relative movement between the structure and a drilling jack-up, where applicable, shall be considered in a ULS check. The minimum clearance between conductor and conductor guide is 25 mm (1 in) on radius. Conductor guide geometry may be included in the structural model in the following manner: conductor guide connected to framing by cantilever stub; conductor guide connected to surrounding framing by vertical plates (8 equi-spaced around the perimeter); conductor guide connected to framing by horizontal plate (not preferred). The following minimum requirements apply to the conductor guide and cantilever stub design: the guide shall have a cone at both the top and the bottom of the guide, or a cone at the top and a ring stiffener at the bottom; Add new clause: 15.5

Caissons Causes of caisson failure should be considered in the design of caissons to ensure longterm structural integrity and robustness. Deterioration of the integrity of seawater lift caissons, which are critical to platform safety, can occur due to a number of factors: Mechanical abrasion due to the pump string orbiting during operation and/or the caisson moving against the pump under the action of wave loads and current; Stray current corrosion as a result of metallic contact between electrical anti-fouling systems and the caisson wall; Localised galvanic corrosion due to dissimilar metal reaction either from pump strainers or the pump column material; Corrosion fatigue.

16.

FATIGUE

16.4

Performing the global stress analyses

16.4.2

Actions caused by waves Replace the second sentence of the last paragraph with: The drag coefficient shall be taken as Cd=0.65 for smooth tubulars and Cd=0.80 for rough tubulars.

16.8

Determining the long-term stress range distribution by deterministic analysis

16.8.1

General Correction - the cross-references in the last line of the 2nd paragraph should read: Guidance on dynamically responding structures is given in 16.4.4 and 16.6.4.



Geometrical stress ranges

16.10.2.2 Unstiffened tubular joints Add paragraph at the end: The fatigue endurance for butt welds with and without thickness transitions shall be assessed in the following way: internally flush connection shall be assessed using the S-N curve D for single and double sided shop welds; externally flush connections shall be assessed using the S-N curve D for double sided shop welds and the S-N curve F2 for single sided shop welds; an SCF shall be applied to the nominal stress using the SCF formulation given in A.16.10.2.2.6. 17.

FOUNDATION DESIGN

17.3.4

Foundation capacity Modify the first sentence of a) as follows: a) Pile strength The pile strength shall be verified using the steel tubular strength checking equations given in 13.3 or 13.4 for conditions of combined axial and lateral force and bending. b) Pile axial resistance Add after last sentence: The above pile resistance factors apply for the design of foundations comprising isolated piles and for groups of closely spaced piles designed to the methods detailed in the ISO document main text. Where alternative methods are used, further guidance is given in Reference A.17.4-25. For pile groups, φPE and φPO apply to the overall capacity of the group, determined in accordance with the ISO document. For individual piles within a group, φPE and φPO may be taken as 1.0, providing it can be shown that loads can be redistributed to other piles within the cluster if the individual pile is overloaded.

17.4.1

General Replace the second paragraph with: Further to the introductory discussion in 17.1.2, pile capacities are commonly determined using the simplified calculation model described in 17.4.2; the parameters that are used in this model are determined in accordance with 17.4.3 to 17.4.5. This simplified model has been developed and applied in many years of offshore practice and represents the current industry standard, but the methods given in 17.4.3 to 17.4.5 are based on poor physical models. The procedures developed by Imperial College (Ref. 1 in Part III) [A.17.4-25] are based on a more realistic physical model and provide more reliable and accurate design methods when compared with the available pile load tests. The ICP procedures are the default pile design method for soil conditions encountered in the North Sea and in regions with similar soil conditions. The methods described in Clauses 17.4.3 and 17.4.4 may still be used when the soil data needed for more recent and reliable methods are unavailable and cannot be economically collected. The model in 17.4.2 does not provide any information about axial pile displacements which are important for serviceability requirements, especially in non-extreme conditions for actions due to permanent, variable and operating environmental actions that are generally well below the design actions. Axial pile behaviour aimed at meeting service requirements is referred to as axial pile performance and is discussed in 17.6. Methods for determining pile performance are described in A.17.6.2 and A.17.6.3.


DEP 37.19.00.30-Gen. February 2011 Page 14 17.4.3

Skin friction and end bearing in cohesive soils Replace the first paragraph with: There are a number of methods for calculating the skin friction and end bearing in cohesive soils and it is important in layered soils that the shaft friction at any point along the pile is calculated using a method consistent with that used for shaft friction in sand. The method described below has been developed and applied over many years and is the current industry standard. However, caution should be exercised in its application as there are many more variables which affect pile capacity, apart from those included in the design equations. This matter is discussed below and in A.17.4.3. The procedure developed by Imperial College for cohesive soils [A.17.4-25] is the default for the North Sea and regions with similar soil conditions. Elsewhere, and when the soil data needed for more recent and reliable methods are unavailable and cannot be economically collected, the unit skin friction, f, in stress units, at any point along the pile, can be calculated using Equation (17.4-2): Add to second paragraph: For the unit shaft friction derived by α methods:•

An upper limit of f = 250 kPa (36.3psi) is recommended. Justification of higher values will require verified supporting evidence;

•

The equations 17.4-2 to 17.4-4 are applicable for flush tubular piles. If an internal driving shoe is applied to reduce the driving resistance, the effect of the internal driving shoe on the ultimate internal skin friction shall be considered;

Replace first sentence of end bearing paragraph with: For piles with end bearing in cohesive soils, the unit end bearing, q in stress units, shall be determined consistently with the method used to determine the skin friction, f. The end bearing, q in stress units, shall be computed for the α method using Equation (17.4-5): Replace first sentence of next paragraph with: Advice on combining shaft friction and end bearing for the ICP method is given in part V of [A.17.4-25]. Shaft friction is considered to act only on the external pile surface. The shaft friction, f, in α methods is considered to act on both the inside and outside of the pile. Replace first sentence of layered soil paragraph with: For layered soils, advice on the development of shaft friction and end bearing for the ICP method is given in part V of [A.17.4-25]. The shaft friction values, f, in α methods shall be as given in Equations (17.4.2) to (17.4.4). 17.4.4

Skin friction and end bearing in cohesionless soils Replace the first paragraph with: This clause describes a simple method for assessing pile capacity in cohesionless soils, but it is unreliable. Simplified versions of other, recent and more accurate methods for predicting pile capacity in cohesionless siliceous soils are presented in A.17.4.4. These other methods are based on direct correlations of pile unit friction and end bearing data with Cone Penetration Test (CPT) results. CPT-based methods are considered to be fundamentally better and have shown statistically closer predictions of pile load test results than the simple method described in this clause. The CPT-based methods cover a wider range of cohesionless siliceous soils and the ICP method also comes with a complementary method for cohesive soils. However, of the CPT methods, only ICP has established its credentials, having been used to design the foundations for offshore structures in the North Sea. The full version of the ICP method, as given in A17,4-25, should be the default method for routine design in cohesionless siliceous soils and replaces the simple method presented herein and the simplified methods given in A.17.4.4.


DEP 37.19.00.30-Gen. February 2011 Page 15 Replace first sentence of second paragraph with: For tubular piles in cohesionless siliceous soils where no CPT data exists, and it is uneconomic to obtain it, the unit skin friction at a given depth, f, in stress units, can be calculated by Equation (17.4-6): Replace first sentence of fourth paragraph with: For tubular piles in cohesionless soils, the unit end bearing, q in stress units, shall be determined consistently with the method used to determine the skin friction, f. Advice on determining end bearing for the ICP method is given in A17.4-25. Where no suitable in situ penetrometer data exists, the unit end bearing, q, may be computed using Equation (17.4-7). Add to seventh paragraph: Available data suggest that driven piles in these soils may have substantially lower design strength than given in Table 17.4-1. Factors of importance for assessment of limiting unit end bearing and skin friction values are, among others, the degree of cementation, grain crushability, relative density, compressive strength and carbonate content. Drilled and grouted piles in calcareous sand have a significantly higher capacity than driven piles. The characteristics of calcareous sand are highly variable and local experience should dictate the design parameters and pile type selected. Amend the ninth paragraph to read: For layered soils, advice on the development of shaft friction and end bearing for the ICP method is given in Reference A17.4-25. Where no CPT data exists, skin friction values, f, in the siliceous cohesionless layers shall be as given in Table 17.4-1. End bearing values for piles tipped in cohesionless layers with adjacent soft layers should also be taken from Table 17.4-1, provided that a) the pile achieves a penetration of two to three diameters or more into the cohesionless layer, and b) the tip is approximately three diameters or more above the bottom of the layer to preclude punch-through. Where these distances are not achieved, verification of the validity of the tabulated values should be performed. 17.5

Pile capacity for axial tension Amend the fifth paragraph to read: The ultimate pile pullout capacity is less than or equal to, but shall not exceed, Qf, the total skin friction resistance. In computing the tensile design action on the pile, the weight of the pile may be considered; the weight of the soil plug shall be ignored: For cohesive soils, f shall be the same as stated in 17.4.3. For cohesionless soils, f shall be computed according to 17.4.4. For rock, f shall be the same as stated in 17.4.5.

17.7.2

Axial shear transfer t-z curves Amend the last paragraph to read: The value of tres/tmax for clays can range from 0.70 to 1.00. Laboratory, in situ or model pile tests can provide valuable information for determining values of tres/tmax and zres for various soils.

17.8

Soil reaction for piles under lateral actions

17.8.2

Representative lateral capacity for soft clay Correction - Equation (17.8-1) should read: pr = 3⋅cu⋅D + p0′⋅D + J⋅cu⋅X

17.9.2

(17.8-1)

Axial behaviour Add:


DEP 37.19.00.30-Gen. February 2011 Page 16 For piles acting in a group the axial bearing capacity of the pile group is considered to be the lesser of the: •

Sum of the capacities of the isolated piles, or

•

Capacity of the 'equivalent pier', where the pier forms an envelope around all piles.

The axial bearing capacity of the pile group consists of skin friction along the outer perimeter of the pile group plus end bearing of the pier. Unit skin friction values, f, shall be calculated for the stress and friction conditions that will exist on the relevant failure surfaces. The end bearing capacity of the pier may be calculated using the same equations as for individual piles. It should be noted that these equations are applicable for small size footings in uniform soils. In estimating the end bearing capacity of the pile group, the following shall especially be taken into account :

17.10

•

size effect of the footing;

•

allowable displacement;

•

the presence of weak layers within a distance of 1.5 to 2 times the equivalent pier diameter from the tip of the foundation.

Pile wall thickness

17.10.5 Stresses during driving Add to the first paragraph: The fatigue damage during driving shall be assessed based on the expected blow count. Stress concentration factors shall be treated in a similar way as for butt welds in structural members. The fatigue damage design factor (see 16.2.2) shall be based on failure critical components and the non-inspectable joint category. The fatigue analysis for the pile butt welds shall be done in accordance with ISO clauses 16.10.2.2 and A.16.10.2.2.6. Insert the following paragraph after the first paragraph: The effects of weld beads on a grouted skirt pile shall be assessed based on an appropriate S-N curve based on weld qualification; the SCF shall be taken as 1.0 in combination with the ISO E S-N Curve. 17.10.6 Minimum wall thickness Add to the end: The maximum D/t ratio at the pile tip shall be limited to 40 to avoid pile tip damage. The following minimum length of the pile tip section should be: Pile diameter

Length of pile tip section

< 150 cm (59 in)

150 cm (59 in)

≥ 150 cm (59 in)

> one pile diameter

17.10.7 Allowance for underdrive and overdrive Add: The possibility of underdrive and overdrive should also be considered when determining the required length of the piles and when determining the position and extent of shear keys in grouted pile sleeve connections.


DEP 37.19.00.30-Gen. February 2011 Page 17 17.10.8 Driving shoe 1st paragraph, replace 1st sentence by: The purpose of driving shoes is : 1) to reduce the driving stresses at the pile tip when driving into hard (cemented) layers or 2)

to reduce internal driving resistance in cohesive soils

2nd paragraph, replace last sentence by: External shoes should not be used, as they will reduce the skin friction along the length of the pile above them. 3rd paragraph; add at the end: A driving shoe shall have a minimum additional wall thickness of 13 mm (1/2 in) and have a length of at least one diameter. 17.10.9 Driving Head Add to the end of the sentence: (e.g. pile lifting tools, hammers, followers, levelling tools, etc.)

Add new clause: 17.12.3 Mudmat design A gravity load factor of 1.1 shall be used for checking bearing capacity and 0.9 for sliding and uplift. The unpiled structure shall also be checked for the still water condition using a gravity load factor of 1.3. The structural design of mudmat components and connections should normally satisfy the strength and stability requirements in Sections 13 and 14. However, some relaxations in strength requirements may be permitted (e.g. allowing local yielding in mudmat components) if it can be shown that bearing and sliding resistances of the mudmats are not impaired and the components are not required for the long-term performance of the structure. Alternative materials to steel, such as aluminium or wood, shall be considered and used if cost benefits can be shown. Add new clause: 17.13

Pile spudcan interaction

17.13.1 Spudcan induced pile stresses As a general rule a clearance of at least one spudcan diameter should be maintained between the perimeter of the embedded section of the spudcan and the nearest structure foundation pile. Where this cannot be achieved, the effect of the spudcan actions on the structure’s foundation pile stresses shall be evaluated. Spudcan diameter is defined by the area of contact between the soil and the bottom of the spudcan. 17.13.2 Effect of jetting during spudcan retrieval Jetting beneath the spudcans shall not be permitted within a distance of 2 spudcan diameters of the platform piles during leg penetration. Temporary pumping of water beneath the spudcans may be performed to break the suction force when retracting the legs.


DEP 37.19.00.30-Gen. February 2011 Page 18 Add new clause: 17.14

Suction caissons The use of suction caissons is permitted, subject to detailed technical analysis of the soilstructure interaction and evaluation of long-term performance.

18.

CORROSION CONTROL Replace this clause by: Cathodic protection design shall be in accordance with DEP 30.10.73.10-Gen. and DEP 37.19.30.30-Gen. Coating design shall be in accordance with DEP 70.48.11.30-Gen.

19.

MATERIALS

19.6

Cement grout for pile-to-sleeve connections and grouted repairs

19.6.1

Grout materials Add to first paragraph: Typical grout types are Oilwell Class B or G, Eucellite B. Alternative grout mixes may be used subject to approval of the Principal and if supporting test data on their characteristic compressive strength and other mechanical properties are provided. Add new clause:

19.7

Other materials

19.7.1

Timber Where timber is used for structural purposes, for example skid beams, launch runners or mudmats, a specification should be prepared taking account of locally available timber types and locally applied standards relating to timber materials. The specification should detail the strength requirements, the grading and moisture content applicable and should define requirements for testing and storage of the timber prior to use. Dimensional tolerances and constraints on timber arrangement should be specified and requirements for coating, sealing, lubrication and fastening of the timber should be defined. The stiffness of the timber should be specified if this is important for the design. Glue laminated beams may be considered for launch runners. The adhesives used should be suitable for marine applications and the intended orientation of the lamination planes relative to the applied actions should be defined. The following list is indicative of the types of hardwood timber that may be used: -

greenheart;

-

ekki;

-

opepe;

-

iroko.

Hardwood timber shall be specified in accordance with BS 5756, and BS 5268 shall apply for strength and design criteria. All hardwood used shall carry a FSC (Forest Stewardship Council) label. 19.7.2

Fibre reinforced composites and glass reinforced plastic (GRP) Fibre reinforced composites or GRP can be produced with a wide range of properties, including high strength. A wide range of resin binders and fibres are employed and the technology is developing rapidly. The cost of high performance composite is generally high but can be offset by low or zero maintenance costs.


DEP 37.19.00.30-Gen. February 2011 Page 19 Due to the large variation in material properties there are very few design codes for the use of these materials and their suitability is usually determined by type testing to meet performance criteria. Fibre reinforced composites may be considered for caissons and other structural applications where a life cycle cost benefit and structural integrity can be demonstrated. Design criteria for GRP items shall be agreed with the Principal. 19.7.3

Novel materials Where a new material, not previously employed for a particular function or application, is considered to be beneficial, it shall be carefully screened, validated and supported by the provision of material qualification records, certification and test data. The following is a list of issues that shall be considered: -

strength, toughness, stiffness, fatigue, temperatures;

durability

-

resistance to chemical attack and corrosion;

-

resistance to environmental exposure: weathering, moisture and ultraviolet (UV);

-

electrochemical reaction with other materials, including crevice corrosion;

-

maintenance and inspection requirements;

-

weight and life cycle costs;

-

quality control complying with recognized standards.

20.

WELDING, FABRICATION AND WELD INSPECTION

20.2

Welding

20.2.1

Selected generic welding and fabrication standards

and

behaviour

at

elevated

Correction - the list numbering should be corrected as follows: -

change list number s) to number h);

-

change s) 9) to h) 1) and s) 10) to h) 2);

-

change list numbers t) through cc) to i) through r).

20.2.2.4.2

Additional essential variables

Correction - change the list numbers dd), ee) and ff) to b), c) and d), respectively. Add new clause: 20.5

Closure welds NOTE: This clause does not apply to brace-to-can welds in point-to-point fabrication.

During fit-up of single-sided closure welds, the quality of the weld preparation shall be optimized by making appropriate use of pipe end re-rolling and templates. Pup-pieces and temporary access man-ways should not be generally used to facilitate welding. Welding processes and techniques (e.g. non-metallic backing strips) which have greater tolerance to fit-up, may be used for the root pass, subject to the approval of the Principal. The root finish shall be visually inspected during welding by means of fibrescope or boroscope techniques and suitable light sources. Access shall be via the remaining temporary root gap and not through windows purposely cut in the tube wall. For tube wall thicknesses over 30 mm, interstage inspection of the weld using double-wall single image radiography and dry MPI may be applied after about one-third of the wall thickness has been completed. Interstage inspection shall only be carried out where preheat temperatures can be maintained. Ultrasonic inspection of such single-sided welds shall be in accordance with EN 1714 and ISO 5817 Quality Level B.


DEP 37.19.00.30-Gen. February 2011 Page 20 21.

QUALITY CONTROL, QUALITY ASSURANCE AND DOCUMENTATION

21.7

Documentation

21.7.1

General Add to Table 21.7.1:

21.8

Structural design report

X

X

X

FEM model

X

X

X

Drawing and specifications Correction - change the list numbers gg) until ll) to b) until g).

22.

LOADOUT, TRANSPORTATION AND INSTALLATION

22.2

Loadout and transportation

22.2.6

Buoyancy and flooding systems

22.2.6.1 General Add: For the upending and installation of self-floating and launched steel structures, the following should be considered: Intact and damage conditions should take into account the most severe combination of tolerances on structure weight, CoG, buoyancy, centre of buoyancy and water density. A FMEA (failure modes and effects analysis) or similar study should be carried out on the ballast and buoyancy systems to ensure that no single failure of a component or system can lead to an unsafe condition either during or after marine operations. Reserve buoyancy, meaning remaining buoyancy that can be mobilized before flooding can occur, should not be less than that shown in Table 22.2-1, based on nominal total intact buoyancy. The minimum GM (metacentric height) after launch and during upending should not be less than that shown in Table 22.2-2. Reserve buoyancy, Br, in percentage of the total available buoyancy, is calculated using the following equation : Br=((Bo-Wo)/Bo)*100 % where Br is the reserve buoyancy in percentage Bo is the total available buoyancy of the structure in kN Wo is the weight in air of the structure in kN.


DEP 37.19.00.30-Gen. February 2011 Page 21 Table 22.2-1 Recommended reserve buoyancy based on nominal total intact buoyancy Case Structure after launch During upending by ballasting; without crane assistance

Intact (%)

Damage (%)

10

5

Sufficient to maintain required bottom clearance

The damage case shall be based on accidental flooding of any one buoyant compartment, for instance due to tearing/breakage of rubber diaphragms on skirt pile sleeves. The extent of flooding of a compartment should be based on the hydrostatic pressure balance, i.e. it is not required to fully flood compartments, where vent valves prevent full flooding of a compartment. Table 22.2-2 Recommended minimum GM after launch and during upending Case

Intact, m (ft)

Damage, m (ft)

After launch, transverse and longitudinal

1.0 (3.3)

0.2 (0.66)

During upending, transverse

1.0 (3.3)

0.2 (0.66)

During upending, longitudinal

greater than zero

greater than zero

(see NOTE)

(see NOTE)

1.0 (3.3)

0.2 (0.66)

After upending, before final positioning, both directions

NOTE: A limited period during upending, when the steel structure is metastable or unstable longitudinally, can be acceptable, provided the behaviour has been investigated and all interested parties are aware of it. Practical problems that can be encountered with attending vessels, or rigging and handling lines, should be resolved.

Documents should be prepared by the Contractor to show the calculations of the minimum GM after launch and during upending with the top of the steel structure immersed, if applicable. As it is not practical to provide either damage stability or reinforcement against collision over the full range of waterlines, planning and risk assessment should also include: a clear statement of the draughts, times, durations, and operational sequences when damage stability is not available, or the reinforcement cannot be carried out; and a procedure to return to a waterline that is reinforced against collision should the installation operation be aborted. 22.5

Pile installation

22.5.1

General Add to the end of the 1st sentence: …without damage or early refusal.

22.5.2

Stabbing guides Replace “stabbing guides” by “stabbing points” Replace part of the last sentence by:


DEP 37.19.00.30-Gen. February 2011 Page 22 … safely supporting the full weight of the add-on pile section and stabbing loads prior to welding. 22.5.5

Driveability studies Amend and add to the last sentence of the 4th paragraph: …, in particular when delays are necessary for welding add-on pile sections or due to breakdowns, waiting on weather or standby time.

22.5.8

Pile refusal remedial measures Correction - change list number mm) to b), and list number b) to c). 1) Plug removal, 2nd paragraph Delete last sentence 2) Soil removal below the pile tip 1st paragraph Replace first sentence by: Soil below the pile tip may be removed, either by drilling an undersized hole or by jetting and possibly airlifting. 2nd Paragraph Replace sentence by: Considering the uncertainties with respect to the pile axial capacity, uncemented soils below the pile tip shall not be removed by any means to reduce the pile driving resistance. 5th paragraph Delete from last part of this sentence: ..., unless this zone has been grouted. Delete last sentence

22.5.12 Grouting pile-to-sleeve connections and grouted repairs Add: Each sleeve to be grouted shall have primary and secondary grout supplies. Each supply line shall terminate at a ring manifold offering at least four entry ports into the pile sleeve. A tertiary grout supply to the sleeve shall be provided for a diver back-up system. The secondary and tertiary grout supplies may be used to complete grouting a pile sleeve in cases where the primary supply line has been used to set a 'grout plug'. A grout plug shall be required to seal the bottom of the sleeve if the inflatable packer system becomes damaged. Grout monitoring equipment, either permanent or temporary (diver or ROV manipulated), shall be provided at the top of each sleeve. Packer inflation lines shall also be provided with a back up inlet to the packer. All lines for grouting, packer inflation and monitoring shall be clearly marked and shall terminate in appropriate control manifolds/panels at the top bracing elevation of the fixed structure or another convenient and easily accessible location. Flexible hoses may be used for all grout supply lines, if it can be shown that they cannot sustain damage during installation and that this option is more cost effective than running hard lines down the structure’s leg. 22.5.13 Pile installation records Add in 1st sentence: Throughout the driving of piles (main piles, skirt piles, docking piles, TLP piles, conductors, etc.), comprehensive… 22.5.14 Use of hydraulic hammers 1st paragraph, add at the end:


DEP 37.19.00.30-Gen. February 2011 Page 23 This is why it is important to study the free length behaviour of piles during their installation. For instance how are the piles supported, what loads can the piles support (wind, wave, top loads such as hammers, etc.). Commonly this is done by performing a pile free-length study during the design/engineering phase. 2nd paragraph, include in the 1st sentence: … to maintain a fairly low blow count (usually between 8 and 20 blows per 0.25 m [10 in]). 22.6

Installation of conductors Add after paragraph 5 and before the list: The procedures described in A.22.6 shall be used as a guide to determine conductor setting depth with respect to hydraulic fracture of the soil and minimum spacing between conductors and foundation piles. Either a safety factor of 1.1 should be applied to the calculated mud or cement density or a suitable allowance should be made for suspended cuttings load. A.22.6 gives minimum horizontal centre-to-centre spacing between conductors and piles for both sand and clay strata. It should be noted that the spacing criterion for sandy soils is much more severe than for clay soils. Wherever possible, conductor tips should be set in a clay stratum. Where this is not possible, conductor installation procedures should be arranged so as to minimize the possibility of wash-out around the conductor tips. In all cases a minimum vertical separation between conductor setting depth and pile tip of 5 m (16 ft) shall be maintained. Add to b): Driving alone is the method least likely to prove detrimental to the capacity of adjacent conductors or piles. However, where it is not possible to achieve the desired conductor setting depth using the driving method, a drill-drive solution may be used. With this method, the soil plug inside the conductor is drilled out and, where necessary, a pilot hole is drilled ahead of the conductor. A method of predicting driving behaviour during drill-drive installation is given in A.22.6. The option of drilling an open hole and placing the conductor inside increases the possibility of wash-out of the soil and therefore should not be used. This could lead to subsequent grouting problems and degradation of the soil bearing strength around the foundation piles. This technique shall not be used where sand formations have to be penetrated.

23.

IN-SERVICE INSPECTION AND STRUCTURAL INTEGRITY MANAGEMENT

23.4

Inspection strategy

23.4.3

Inspection types Correction - renumber the list under a) to 1), 2) and 3).

23.4.4

Factors to consider in determining strategy Correction - change the list numbers nn), oo) and pp) to b), c) and d).

24.

ASSESSMENT OF EXISTING STRUCTURES

24.2

Assessment process Correction - change list number g) 3) to item h). Add new clause:

26.

STANDARD DETAILS

26.1

General In the absence of specific standard drawings for a particular operating unit or a particular project, the minimum requirements in 26.1 to 26.5 are applicable.



Handrails Handrail geometry and design shall as a minimum comply with ISO 14122-3 and the following amendments. The design action shall be taken as 0.75 kN/m (51.4 lb/ft) for normal handrails and 1.5 kN/m (102.8 lb/ft) for handrails around muster areas and laydown areas. If the handrails around laydown areas are used to stop swinging loads, the design shall take this into account.

26.3

Ladders Ladders shall comply with ISO 14122-1 and ISO 14122-4. Sidestep ladders are the preferred solution.

26.4

Stairs Stairs shall as a minimum comply with ISO 14122-1 and ISO 14122-3 and the following amendments. The stair angle should normally not exceed 38°. The Principal's approval is required for stairs with an angle between 38° and 45°. The stair angle shall be the same throughout a complete platform. Access stairs to the fixed structure may be single flight stairs. Maximum step size shall be 220 mm (8-5/8 in) instead of 250 mm (10 in). The minimum width of stairs shall be 1000 mm (40 in), except for stairs that are part of a main escape route where the width shall be 1200 mm (48 in) minimum.

26.5

Working platforms and flooring Working platforms and flooring shall comply with ISO 14122-1 and ISO 14122-2.

26.6

Self closing gates Gates shall have at least a handrail and a knee rail to the relevant requirements of ISO 14122-3. A gate shall be self-closing inward from a platform deck.

ANNEX A

ADDITIONAL INFORMATION AND GUIDANCE

A.7

General design requirements

A.7.12

Structural reliability analysis Replace “No guidance is offered” with: Guidance can be found in EP 97-5050.

A.8

Actions for pre-service and removal situations

A.8.3

Actions associated with lifting

A.8.3.3

Effect of tolerances Add to second bullet: A possible method to analyze this in a finite element package is to use a temperature increase on the sling to obtain the required length increase.

A.9

Actions for in-place situations

A.9.4

Extreme quasi-static action due to wind, waves and current (Ee)

A.9.4.5

Vortex induced vibrations Replace “No guidance is offered” with: Calculations of VIV due to waves and current should be carried out in accordance with EP 93-0455, calculations of VIV due to wind should be carried out in accordance with OTH 92-379.


DEP 37.19.00.30-Gen. February 2011 Page 25 A.9.8

Equivalent quasi-static action representing dynamic response caused by extreme wave conditions

A.9.8.3.2 Dynamic analysis methods Replace “No guidance is offered” with: Guidance can be found in EP 87-0170 and EP 93-2525. A.9.9

Factored actions

A.9.9.3.3 Partial action factor, γf,E Add to the end of the last paragraph: Further guidance can be found in EP 97-5050 A.9.10

Design situations

A.9.10.2 Demonstrating sufficient RSR under environmental actions Replace “No guidance is offered” with: Guidance can be found in EP 97-5050 A.10

Accidental situations

A.10.1

General Add new clause:

A.10.1.6.1

Requirements for damage tolerance

There should be no impairment of performance standards for low energy impacts. Only minor repairs should be subsequently required. The follow up requirements to demonstrate short term integrity should be outlined in terms of damage survey and analysis. A summary of post-impact requirements for various regions are listed in Table A.10.1-1. This data may be overridden by local or project requirements. Table A.10.1-1 Damage tolerance criteria Area

High energy impact

Low energy impact

Southern North Sea

No progressive collapse in 10 yr storm condition

No impairment

Northern North Sea


No impairment

Malaysia


No impairment

Brunei

TBA

NA

Nigeria


No impairment

A.10.2.2 Collision events Add to last paragraph: High energy impact velocities in m/s may be taken as half the numerical value of the significant wave height in metres of operating sea state, with a maximum of 2.0 m/s. The following table gives the typical vessel weight and speed to be taken into account in the Shell regions. This data may be overridden by local or project requirements.


DEP 37.19.00.30-Gen. February 2011 Page 26 Table A.10.2-1 Impact energy requirements Vessel size

Area

A.10.3

Accidental velocity

Impact energy, broadside, MJ

MT

m/s

ft/s

Low energy

High energy

Southern North Sea

3000

2.0

6.6

0.50

8.40

Northern North Sea

5000

2.0

6.6

0.50

14.00

Malaysia

3200

1.25

4.1

0.50

3.50

Brunei

1750

1.00

3.3

NA

1.23

Nigeria

3000

1.00

3.3

0.50

2.10

Dropped objects Replace “No guidance is offered” with: Guidance on methods for design against dropped objects is provided in EP 89-0230 and NORSOK N-004.

A.14

Strength of tubular joints Add new clause:

A.14.11 Bolted connections No guidance is offered. A.15

Strength and fatigue resistance of other structural components Add new clause:

A.15.4

Conductors

A.15.4.1 General No comments A.15.4.2 Conductor guides No guidance is offered A.15.5

Caissons No guidance is offered

A.16

Fatigue

A.16.3

Description of the long-term wave environment

A.16.3.7 Long-term distribution of individual wave heights Correction - in the line between Equations (A.16.3-1) and (A.16.3-2), the cumulative probability should read P(H > H*) instead of p(H > H*). A.16.10 Geometrical stress ranges A.16.10.2.2.5

Tubular joints welded from one side

Add after last paragraph:


DEP 37.19.00.30-Gen. February 2011 Page 27 A detailed fatigue analysis of the weld root is only required when weld improvement techniques are employed or when there is a regulatory requirement for analysing weld root fatigue. A.16.10.2.2.6

Tubular thickness transitions.

Add at the end: The SCF for tubular butt welds with and without thickness transition (see DNV-RP-C203) is given by the following equations.

Cbw = 1 +

6δ tot ⋅ t

1 ⎛T ⎞ 1+ ⎜ ⎟ ⎝t⎠

2,5

⋅ e −α

δ tot = δ t − δ 0

if there is a thickness transition (see figure below)

δ tot = δ m − δ 0

if there is no thickness transition (see figure below)

δ 0 = 0,1t

α=

1,82 L ⋅ Dt

1 ⎛T ⎞ 1+ ⎜ ⎟ ⎝t⎠

2,5

where

Cbw

is the stress concentration factor for butt welds with or without thickness transition;

δ

is the misalignment;

δ0

is the misalignment inherent in the S-N data;

T

is the thickness of the thicker part (see figure below);

t

is the thickness of the thinner part (see figure below);

L

is the length of the thickness transition (see figure below);

D

is the diameter of the tubular member.



A.16.10.2.3 Internally ring stiffened tubular joints Add: Ring stiffened joints made from one side should be assessed using the SCF ratio for the brace to chord intersection as derived in Reference [A.16.10-19]. The following S-N curves should be used: F S-N curve for brace to ring intersection points; TJ S-N curve for other points at the brace to chord intersection; D S-N curve for the ring stiffener inner edge. The fatigue damage design factor should be selected based on the fact that the joint is not inspectable and that the members connected at the joint are failure critical components. A.17

Foundation design

A.17.4

Pile capacity for axial compression

A.17.4.4.2.1 General Amend third paragraph Since the friction component, Qf, involves numerical integration, results are sensitive to the depth increment used, particularly for CPT-based methods. As guidance, depth increments for CPT-based methods should be in the order of 1/50 of the pile length with shorter increments used close to the pile tip. Correction - the definition of pa in Equation (A.17.4-4) should read: pa

is the atmospheric pressure, in stress units, pa = 100 kPa (14.5 psi).

A.17.4.4.2.2 Method 1 a) Friction In Paragraph 2 replace "larger resistance factors" with "appropriate resistance factors".

Add new clauses: A.17.13 Pile spudcan interaction No guidance is offered A.17.14 Suction caissons No guidance is offered A.18

Corrosion control Delete the text of this clause.

A.19

Materials Add new clause:


DEP 37.19.00.30-Gen. February 2011 Page 29 A.19.7

Other materials No guidance is offered

A.20

Welding, fabrication and weld inspection

A.20.1

General Replace “No guidance is offered” with: Clause 20, Clause A.20, Annex B, Annex E, Annex F and Annex G may be substituted by EEMUA 158 [A.20.2-1] as stand-alone specification for welding, fabrication and weld inspection specification. EEMUA 197 or another approved fabrication specification may be used for non-primary steelwork fabrication.

A.20.2.1. Selected generic welding and fabrication standards Add before the last paragraph: EEMUA 158[A.20.2-1] under a) is the preferred standard. A.22

Loadout, transportation and installation

A.22.6

Installation of conductors Replace “No guidance is offered” with: The recommendations of EP 52510 should be used for general guidance. Calculation of hydrofracture should make use of Ref. 2 and Ref. 3 (Part III). Prediction of drill-drive installation should make use of Ref. 4 (Part III).

A.23

In-service inspection and structural integrity management Add after the clause title and before A.23.1: Additional guidance is provided in DEP 37.19.60.10-Gen.

ANNEX C C.3

MATERIAL CATEGORY APPROACH

Specific steel selection Add after the second paragraph: The steel grades listed in Tables C.2, C.3, C.4, and the steel grades in the added Tables C.5, C.6 and C.7, may be used if the first natural period of the structure is below 2.5 seconds in areas where: LAST (lowest anticipated service temperature) is above +10 °C (+50 °F). In all other areas, DEP 37.19.10.30-Gen. SHALL [PS] be used for material specification; material selection SHALL [PS] remain in accordance with ISO 19902:2007 (Material Category MC1). The tables below are copies of the design class tables from with ISO, with some minor adjustments (additional grades for CV2 class). However the tables have not been updated to reflect the higher allowable test temperature based on LAST +10 °C (+50 °F). Grades with higher test temperatures (e.g. –10 °C [+14 °F] for CV2 ISO –40 °C (40 °F)) may be selected if approved by the Principal.


DEP 37.19.00.30-Gen. February 2011 Page 30 Table C.5

Correlation of steel group and toughness class for steel plates to European specifications

Steel group

Toughness class

Specification

Grade MPa

kpsi

I

NT

EN 10025[D.1]

S275JR / S235JRG2

275 / 235

39.9 / 34.1

II

NT

EN 10025[D.1]

CV1

S355J0

355

51.5

S355N/M

355

51.5

[D.2]

S355J2G3

355

51.5

Option 5; PCE≤0.43, PP≤0.025 ; PS≤0.025, longitudinal Charpy ≥ 40J

[D.2]

S355K2G3

355

51.5

Option 5; PCE≤0.43, PS≤0.025, PP≤0.025

EN 10025

EN 10225 CV2

EN 10225[D.2]

S355G7N/M or S355G9N/M

355

51.5

Options 6, 12 and 18

CV2Z/ZX

EN 10225[D.2]

S355G8N/M or S355G10N/M

355

51.5

Options 6, 12, 13 and 18

CV1

EN 10025[D.1]

S420NL/ML

420

60.9

CV2

[D.2]

S420G1Q/G1M

420

60.9


[D.2]

S420G2Q/G2M

420

60.9

Options 6, 9, 12, 13 and 18

[D.2]

S460G1Q/G1M

460

66.7


[D.2]

S460G2Q/G2M

460

66.7

Options 6, 9, 12, 13 and 18

CV2Z/ZX IV

CV2 CV2Z/ZX

V

Comment

[D.1]

EN 10225

III

SMYS

EN 10225

EN 10225 EN 10225

EN 10225

CV2

NORSOK M-120

S460G1Q/G1M modified

500

72.5


CV2Z/ZX

NORSOK M-120

S460G2Q/G2M modified

500

72.5

Options 6, 9, 12, 13 and 18

[D.3]

[D.3]

For CV2, CV2Z and CV2ZX materials, base material information, documentation and results of weldability tests according to EN [D.2] should be established prior to delivery. The documentation of base material should include a strain aging test for group V 10225 steels, typical tensile tests and weldability tests for plates within each of the following thickness ranges, relevant for the order: 25 mm to 40 mm, 40 mm to 63 mm, 63 mm to 100 mm and 100 mm to 150 mm, for both the AW and PWHT conditions. CTOD testing shall be included for thicknesses above 40 mm and shall meet the requirements of a minimum 0.20 for PWHT and 0.25 mm for AW conditions.


DEP 37.19.00.30-Gen. February 2011 Page 31 Table C.6

Correlation of steel group and toughness class for steel sections to European specifications

Steel group

Toughness class

Specification

Grade MPa

Kpsi

I

NT

EN 10025[D.1]

S275JR / S235JRG2

275 / 235

39.9 / 34.1

II

NT

EN 10225[D.2]

CV1

S355J0

355

51.5

S355N/M

355

51.5

[D.2]

S355J2G3/G4

355

51.5

Option 5; PCE≤0.43, PP≤0.025 ; PS≤0.025, longitudinal Charpy ≥ 40J

[D.2]

S355K2G3/G4

355

51.5

Option 5; PCE≤0.43, PS≤0.025, PP≤0.025

EN 10025

EN 10225

CV2Z/ZX III

S355G11N/M

355

51.5

Options 9 and 18

[D.2]

S355G12N/M

355

51.5

Options 9, 13, 18 and 21, class 2.1

S420NL/ML

420

60.9

EN 10225

EN 10025[D.1]

CV2

[D.2]

S420G3M

420

60.9

Options 9 and 18

[D.2]

EN 10225

S420G4M

420

60.9


EN 10225[D.2]

S460G3M

460

66.7

Options 9 and 18

[D.2]

S460G4M

460

66.7


CV2 CV2Z/ZX

V

EN 10225[D.2]

CV1

CV2Z/ZX IV

Comment

[D.1]

EN 10225

CV2

SMYS

EN 10225

EN 10225

CV2

NORSOK M-120 [D.3]

S460G3M modified

500

72.5

Options 9 and 18

CV2Z/ZX

NORSOK M-120 [D.3]

S460G4M modified

500

72.5


For CV2, CV2Z and CV2ZX materials, base material information, documentation and results of weldability tests according to EN [D.2] should be established prior to delivery. The documentation of base material should include a strain aging test for group V 10225 steels, typical tensile tests and weldability tests for sections within each of the following thickness ranges, relevant for the order: 25 mm to 40 mm, 40 mm to 63 mm, 63 mm to 100 mm and 100 mm to 150 mm, for both the AW and PWHT conditions. CTOD testing shall be included for thicknesses above 40 mm and shall meet the requirements of a minimum 0.25 mm for AW condition.



Table C.7

Correlation of steel group and toughness class for steel tubulars to European specifications

Steel group

Toughness class

Specification

I

NT

EN 10210[D.4]

II

S275J0H / S235JRH

275 / 235

39.9 / 34.1

Hot finished

EN 10219[D.5]

S275J0H / S235JRH

275 / 235

39.9 / 34.1

Cold formed

EN 10210[D.4]

S355J0H

355

51.5

Hot finished

[D.5]

S355J2H

355

51.5

Cold formed

[D.2]

S355G1N

355

51.5

Hot finished

S355NH

355

51.5

Hot finished, option 1.4; PCE≤0.43

EN 10219

[D.5]

S355MLH

355

51.5

Cold formed, option 1.4, PS≤0.025, PP≤0.025

CV2

EN 10225[D.2]

S355G14 Q/N

355

51.5

Options 6, PP≤0.016

CV2Z/ZX

EN 10225[D.2]

S355G15 Q/N

355

51.5

Options 6, 7, 13, 18 and 22; PC≤0.16

CV1

EN 10219[D.5]

S420MLH

420

60.9

Cold formed, PS≤0.015, Charpy ≤ 50J

CV2

EN 10225[D.2]

S420G6Q modified

420

60.9

Options 6 and 18

CV2Z/ZX

EN 10225[D.2]

S420G6Q modified

420

60.9


CV2

EN 10225[D.2]

S460G6Q modified

460

66.7

Options 6 and 18

CV2Z/ZX

EN 10225[D.2]

S460G6Q modified

460

66.7


CV2

NORSOK M-120 [D.3]

S460G6Q modified

500

72.5

Options 9, 12 and 18

CV2Z/ZX

NORSOK M-120 [D.3]

S460G6Q modified

500

72.5

Options 9, 12, 13, 18 and 22

NT

EN 10225

EN 10210[D.4]

V

Comment kpsi

CV1

IV

SMYS MPa

EN 10219

III

Grade

7

and

18;

PCE≤0.39, PP≤0.025;

For CV2, CV2Z and CV2ZX materials, base material information, documentation and results of weldability tests according to EN [D.2] should be established prior to delivery. The documentation of base material should include a strain aging test for 10225 group V steels, typical tensile tests and weldability tests for tubulars within each of the following thickness ranges, relevant for the order: 25 mm to 40 mm, 40 mm to 63 mm, 63 mm to 100 mm and 100 mm to 150 mm, for both the AW and PWHT conditions. CTOD testing shall be included for thicknesses above 40 mm and shall meet the requirements of a minimum 0.25 mm for AW conditions.



ANNEX D D.2

DESIGN CLASS APPROACH

Specific steel selection Add after the second paragraph: Tables D.4, D.5 and D.6 may be used if the first natural period of the structure is below 2.5 seconds in areas where: LAST is above +10 °C (+50 °F). In all other areas DEP 37.19.10.30-Gen. SHALL [PS] be used for material specification; material selection SHALL [PS] remain in accordance with ISO 19902:2007.

ANNEX G

FABRICATION TOLERANCES

Add new clause: G.14

Other tolerances Tolerances in G.1 to G.13 should be supplemented by tolerances given EEMUA 158[A.20.2-1] or, if approved by the Principal, another fabrication specification.


in

DEP 37.19.00.30-Gen. February 2011 Page 34 PART III REFERENCES In this DEP, reference is made to requirements in following publications: NOTES:

1. Unless specifically designated by date, the latest edition of each publication shall be used, together with any amendments/supplements/revisions thereto. 2. The DEPs and most referenced external standards are available to Shell staff on the SWW (Shell Wide Web) at http://sww.shell.com/standards/.

SHELL STANDARDS The use of SI quantities and units (endorsement of ISO 31, ISO 1000 and ISO 80000)

DEP 00.00.20.10-Gen.

Cathodic protection

DEP 30.10.73.10-Gen.

Weldable structural steels for fixed offshore structures (amendments/supplements to EN 10225 and EN 10025)

DEP 37.19.10.30-Gen.

Design of cathodic protection systems for new fixed offshore steel structures (amendments/supplements to DNV RP B401)

DEP 37.19.30.30-Gen.

Structural inspection of offshore installations

DEP 37.19.60.10-Gen.

Protective coatings for offshore facilities

DEP 70.48.11.30-Gen.

Conductor design and installation manual for offshore platforms (formerly published as EP 2314, 1980)

EP 52510

Practice for the analysis and design of marine conductors

EP 87-0160

Practice for the dynamic analysis of fixed offshore platforms for extreme storm conditions. A review of available methods and guidelines for their application

EP 87-170

Design guidance for offshore steel structures exposed to accidental loads, VERITEC

EP 89-0230

Practice for the assessment of vortex-induced vibrations of structural members

EP 93-0455

Practice for calculation of an extreme inertial load for steel substructures for fixed offshore platforms

EP 93-2525

Reliability based design and re-assessment of fixed steel platforms

EP 97-5050

AMERICAN STANDARDS Recommended practice for planning, designing and constructing fixed offshore platforms – Working stress design

API RP 2A-WSD

Issued by: American Petroleum Institute Publications and Distribution Section 1220 L Street Northwest Washington DC 20005 USA

BRITISH STANDARDS Structural use of timber

BS 5268

Visual grading of hardwood – Specification

BS 5756


DEP 37.19.00.30-Gen. February 2011 Page 35 Issued by: British Standards Institution 389 Chiswick High Road London W4 4AL, UK

Construction specification for fixed offshore structures in the North Sea

EEMUA 158

Specification for the fabrication of non-primary structural steelwork for offshore installations

EEMUA 197

Issued by: Engineering Equipment and Materials Users’ Association (EEMUA) 10-12 Lovat Lane, London EC3R 8DN, UK

A criterion for assessing wind induced crossflow vortex vibrations in wind sensitive structures

OTH 92-379

Issued by: The Health and Safety Executive Rose Court 2 Southwark Bridge London SE1 9HS UK

EUROPEAN STANDARDS Non-destructive examination of welds – Ultrasonic examination of welded joints

EN 1714

Hot finished structural hollow sections of non-alloy and fine grain steels

EN 10210

Cold formed welded structural hollow sections of non-alloy and fine grain steels

EN 10219

Weldable structural steels for fixed offshore structures – Technical delivery conditions

EN 10225

Issued by: CEN Rue de Stassart 36 B-1050 Brussels Belgium Copies can also be obtained from national standards organizations

INTERNATIONAL STANDARDS Welding – Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) – Quality levels for imperfections

ISO 5817

Safety of machinery – Permanent means of access to machinery, Part 1: Choice of fixed means of access between two levels

ISO 14122-1

Safety of machinery – Permanent means of access to machinery, Part 2: Working platforms and walkways

ISO 14122-2

Safety of machinery – Permanent means of access to machinery, Part 3: Stairs, stepladders and guard-rails

ISO 14122-3

Safety of machinery – Permanent means of access to machinery, Part 4: Fixed ladders

ISO 14122-4


DEP 37.19.00.30-Gen. February 2011 Page 36 Petroleum and natural gas industries – Fixed steel offshore structures

ISO 19902:2007

Issued by: ISO Central Secretariat 1, ch. de la Voie-Creuse Case postale 56 CH-1211 Genève 20, Switzerland Copies can also be obtained from national standards organizations.

NORWEGIAN STANDARDS Fatigue design of offshore steel structures

DNV-RP-C203

Issued by: Det Norske Veritas Industri Norge AS Veritasveien 1 1322 Høvik Norway

Material data sheets for structural steel

NORSOK M-120

Design of steel structures

NORSOK N-004

Issued by: Standards Norway (Standard Norge) P.O. Box 242 NO-1326 Lysaker Norway

OTHER REFERENCED DOCUMENTS Ref. 1

Jardine, R., Chow, F., Overy, R., and Standing, J. (2005) ICP Design Methods for Driven Piles in Sands and Clays, – Imperial College, Thomas Telford Publishing, London

ICP Design

Ref. 2

Overy, R.F. and Dean, A.R. (1986) "Hydraulic Fracture Testing of Cohesive Soil"

OTC 5226

Issued by: Offshore Technology Conference 222 Palisades Creek Drive Richardson, TX 75080-2040 USA

Ref. 3

Overy, R and Sayer, P (2007) The Use of ICP Design Methods as a Predictor of Conductor Drill-Drive Installation, Proceedings of the 6th International OSIG Conference, September 2007 Issued by: Society for Underwater Technology 80 Coleman Street London EC2R 5BJ UK

Ref. 4

Schotman, G.J.M. and Hospers, B (1992) An Improved Method for Conductor Setting Depths in Sand, Proc. Conf. on Behaviour of Offshore Structures, BOSS 1992


DEP Fixed Steel Offshore Structures

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