DEP SPECIFICATION

OFFSHORE TOPSIDES STRUCTURES

(ADOPTION OF IOGP S-631-04,
Copyright Shell Group of Companies. No reproduction or networking permitted without license from Shell. Not for resale

AMENDMENTS/SUPPLEMENTS TO ISO 19901-3: 2014)

DEP 37.19.00.12-Gen.

February 2021

DESIGN AND ENGINEERING PRACTICE

DEM1

© 2021 Shell Group of companies

All rights reserved. No part of this document 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.

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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 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 typically 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.
The DEP Specification-With-Informative provides the main rationale for certain requirements and recommendations in the
companion DEP Specification with the same number. DEP Specification-With-Informatives are intended for internal use by
the Principal.

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TABLE OF CONTENTS
PART I. INTRODUCTION ........................................................................................... 4
1.1 SCOPE ......................................................................................................... 4
1.2 RISKS AND CONTROLS............................................................................... 4
1.3 DISTRIBUTION, INTENDED USE AND REGULATORY
CONSIDERATIONS ...................................................................................... 5
1.4 DEFINITIONS................................................................................................ 5
1.5 CROSS-REFERENCES ................................................................................ 5
1.6 SUMMARY OF MAIN CHANGES .................................................................. 6
1.7 COMMENTS ON THIS DEP .......................................................................... 6
1.8 DUAL UNITS ................................................................................................. 6
1.9 NON NORMATIVE TEXT (COMMENTARY) .................................................. 6
PART II. GENERAL REQUIREMENTS ........................................................................ 7
PART III. Supplementary Specification for Offshore Topside Structure .......................... 8
1. Scope ............................................................................................................ 8
2. Normative References ................................................................................... 8
3. Supplementary Requirements for Topside Structures .................................... 8
4 Symbols and Abbreviated Terms ................................................................... 8
6 Design requirements...................................................................................... 9
7 Actions .......................................................................................................... 9
8 Strength and resistance of structural components ........................................ 13
9 Structural systems ....................................................................................... 14
10 Materials ..................................................................................................... 16
11 Fabrication, quality control, quality assurance and documentation................ 17
13 Loadout, transportation and installation ........................................................ 17
15 Assessment of existing topsides structures .................................................. 17
Bibliography .................................................................................................................... 17
PART IV. REFERENCES ............................................................................................ 19

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PART I. INTRODUCTION
1.1 SCOPE
This DEP specifies requirements and gives recommendations for the structural design,
fabrication, installation, modification and structural integrity management of offshore
topsides structures for the petroleum and natural gas industries.
This DEP is based on ISO 19901-3:2014.
Part III of this DEP replicates IOGP S-631-04, that amends, supplements and deletes
various clauses of ISO 19901-3:2014, and follows the numbering of ISO 19901-3 for easy
reference.
All clauses of ISO 19901-3 not modified by this DEP remain valid as written.
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 September 2019; see (Part I, 1.6)
regarding the changes.
1.2 RISKS AND CONTROLS
Risks and controls have been added to this DEP to provide support for the requirements.
Risks and scenarios are associated with the DEP requirements in the database such that
they can be scaled by the project.
Risk Description: Unplanned event leads to damage or loss of structural integrity in the
event of a fire or explosion. The structure needs sufficient robustness and redundancy in
the design to be able to survive at least long enough to support the temporary refuge and
allow evacuation of personnel and making the process systems safe.
DEP Control: NLFEA to demonstrate robustness (arguable if there are other
equivalent or equally valid means of analysis)
DEP Control: Redundancy checks
DEP Control: Blast, fire and defining event scenarios available from safety case
analysis – location, extent of damage, escape scenario and survival time.
DEP Control: Passive Fire Protection to maintain structural integrity for defined
period
DEP Control: Minimum requirements for bolting
DEP Control: Minimum requirements for materials
Risk Description: Environmental factors or machinery causing cyclic loading, resulting in
fatigue failure and loss of structural integrity.
DEP Control: Fatigue Endurance analysis using FLS or other method
Risk Description: Clash with other structures or vessels leads to structural damage. This
can be triggered by seismic or environmental as well as system/human error.
DEP Control: Assessment of possible scenarios and minimum safety controls
Risk Description: Operability and Decommissioning incidents leading to failure and loss of
integrity.
DEP Control: Design for removal of temporary connections
Risk Description: Loss of system due to transient conditions during construction or
maintenance
DEP Control: Assessment and design to consider temporary conditions

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1.3 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. Any authorised access to DEPs does not for that reason constitute an
authorization to any documents, data or information to which the DEPs may refer.
This DEP is intended for use in facilities related to offshore oil and gas production. This
DEP may also be applied in other similar facilities.
When DEPs are applied, a Management of Change (MOC) process shall 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 could 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 regards 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.
1.4 DEFINITIONS
1.4.1 General 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 it. The Principal
may also include an agent or consultant authorised to act for, and on behalf of, the
Principal.
The word shall indicates a requirement.
The capitalised term SHALL [PS] indicates a process safety requirement.
The word should indicates a recommendation.
The word may indicates a permitted option.
1.5 CROSS-REFERENCES
Where cross-references to other parts of this DEP are made, the referenced section
number is shown in brackets ( ). Other documents referenced by this DEP are listed in
(Part IV).

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1.6 SUMMARY OF MAIN CHANGES

This is a revision of the DEP of the same number dated February 2019. The following are
the main, non-editorial changes for this revision.

Section/Clause Change

All Full adoption of IOGP S-631-04

Part I, 1.2 Application of Risk and Control structure to assist with

application of the DEP

Part III, 7.10.1, SHALL [PS] clauses retained but reworded to clarify source
Item 1 and Item 2 definitions in ISO 19900

Part III, 9.12, SHALL [PS] clauses retained in the IOGP context, wording
Item 1 unchanged

1.7 COMMENTS ON THIS DEP

Comments on this DEP may be submitted to the Administrator using one of the following
options:

Shell DEPs Online Enter the Shell DEPs Online system at

(Users with access to https://www.shelldeps.com
Shell DEPs Online) Select a DEP and then go to the details screen for
that DEP.
Click on the “Give feedback” link, fill in the online
form and submit.
DEP Feedback System Enter comments directly in the DEP Feedback
(Users with access to System which is accessible from the Technical
Standards Portal http://sww.shell.com/standards.
Shell Wide Web)
Select “Submit DEP Feedback”, fill in the online form
and submit.
DEP Standard Form Use Standard Form 00.00.05.80-Gen. to record
(other users) feedback and email the form to the Administrator at
standards@shell.com.

Feedback that has been registered in the DEP Feedback System by using one of the above
options will be reviewed by the DEP Custodian for potential improvements to the DEP.
1.8 DUAL UNITS
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.
1.9 NON NORMATIVE TEXT (COMMENTARY)
Text shown in italic style in this DEP indicates text that is non-normative and is provided as
explanation or background information only.
Non-normative text is normally indented slightly to the right of the relevant DEP
clause.

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PART II. GENERAL REQUIREMENTS

Part III of this DEP is a replication of IOGP Specification S-631-04. The IOGP S-631-04 in
turn supplements ISO 19901-3: 2014. The purpose of replication is to prevent the need for
a Shell layer on top of the IOGP S-631-04 layer over ISO 19901-3: 2014. The copyright for
IOGP S-631-04 rests with the International Association of Oil & Gas Producers. IOGP
permits reproduction of the report provided the copyright and sources are acknowledged.
For ease of reference, the clause numbering of ISO 19901-3 has been used throughout
(PART III) of this DEP.
Clauses in ISO 19901-3: 2014 which are not mentioned in this DEP shall remain valid as
written.

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PART III. Supplementary Specification for Offshore Topside Structure

1. Scope
This specification provides supplementary requirements and recommendations to
ISO 19901-3: 2014.
2. Normative References
The following normative references shall apply:
API Spec. 2SC Manufacture of Structural Steel Castings for Primary Offshore Applications
ASTM A307 Standard Specification for Carbon Steel Bolts, Studs and Threaded Rod
60000 PSI Tensile Strength
ASTM F1136/F1136M Standard Specification for Zinc/Aluminum Corrosion Protective
Coatings for Fasteners
ASTM F2329/F2329M Standard Specification for Zinc Coating, Hot-Dip, Requirements for
Application to Carbon and Alloy Steel Bolts, Screws, Washers, Nuts, and Special Threaded
Fasteners
ASTM F2833 Standard Specification for Corrosion Protective Fastener Coatings with Zinc
Rich Base Coat and Aluminum Organic/Inorganic Type
ASTM F3125/F3125M Standard Specification for High Strength Structural Bolts and
Assemblies, Steel and Alloy Steel, Heat Treated, Inch Dimensions 120 ksi and 150 ksi
Minimum Tensile Strength, and Metric Dimensions 830 Mpa and 1040 Mpa Minimum
Tensile Strength
CAP 437 Standards for offshore helicopter landing areas
EEMUA PUB NO 176 Specification for structural castings for use offshore
ISO 19901-3: 2014 Petroleum and natural gas industries -- Specific requirements for
offshore structures -- Part 3: Topsides structure
ISO 19901-5 Petroleum and natural gas industries — Specific requirements for offshore
structures — Part 5: Weight control during engineering and construction
ISO 23693 Determination of the resistance to gas explosions of passive fire protection
materials
ISO 898-1 Mechanical properties of fasteners made of carbon steel and alloy steel – Part 1:
Bolts, screws and studs with specified property classes – Coarse thread and fine pitch
thread
3. Supplementary Requirements for Topside Structures
Requirements for topsides offshore structures shall be in accordance with ISO 19901-3:
2014 and the following amendments to the referenced clauses in ISO 19901-3: 2014.
NOTE: ANSI/API RP 2TOP:2019 is a modified adopt-back of ISO 19901-3:2010.

Amend the following referenced Clauses in ISO 19901-3: 2014:

4 Symbols and Abbreviated Terms

4.2 Abbreviated terms
Add the following terms:
CoG Centre of Gravity
FRP Fibre Reinforced Polymer

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6 Design requirements
6.7 Design for fatigue limit states (FLS)
Add at the end of the last sentence of the first paragraph:
… or other suitable standards shall apply (see Clause A.6.7).
A.6.7 Design for fatigue limit states (FLS)
Substitute the existing text with:
A suitable code for design for fatigue limit states in cases where the support structure
standard does not provide adequate fatigue guidance for a topsides structure is
DNVGL-RP-C203.
6.9 Robustness
Substitute the first paragraph with:
Robustness is defined and discussed in ISO 19900.
7 Actions
7.1 General
Delete from the penultimate bullet point:
o , and
Strikethrough added to clarify that this is deleted in S631-04
Add before the last bullet point:
o Damage and survival conditions, and
Add at the end of the second-last paragraph:
Specific variable loads requirements are reported in each relevant Clause. General
guidance on variable loads on deck areas are reported in ISO 19904-1 (A.7.3 Variable
actions (Q)).
Add before the last paragraph:
Design of topsides structure shall make use of Not-to-exceed weights (see 19901-5) and
CoG envelopes.
7.4 Vortex-induced vibrations
Substitute the last paragraph with:
Wind induced fatigue analysis and vortex shedding analysis shall be performed on lattice
structures (e.g. flare booms and drilling derricks) and exposed pipework.
7.10 Accidental situations
7.10.1 General
Add the following to the list of the second paragraph:
g) Clashes between jack-up and topsides during seismic and metocean events. However,
jack-up clashes with topsides primary steelwork and potentially manned areas (e.g. LQ,
muster areas, emergency escape routes) shall not be permitted.

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Add before the sixth paragraph ("In addition, the protection of the asset and the costs of
failure should be considered with respect to importance to the owner and to the relevant
national authorities."):
The risk shall be estimated for adjacent structures collapsing onto and significantly
damaging the Temporary Refuge (TR) or its systems, or obstructing escape and evacuation
routes.
Adjacent structures can include derricks, flare towers, cranes, jack-up etc.
Shell adds the following to the end of the fourth paragraph of this clause:
1. For a structure with exposure level L1 as defined in ISO 19900, clause 7.3.2,
Non-linear Finite Element Analysis (NLFEA) SHALL [PS] be performed to assist in
demonstrating adequate robustness and redundancy to mitigate the effects of
accidental events.
L1 is characterised in ISO 19900 with the example of manned, non-evacuated
structures and high environmental consequence platforms.
Shell considers this to be a DEM1 requirement in addition to industry base
standards.
Add the following reference at the end of the last paragraph, after “ISO 19902”:
… and ISO 19904-1.
Shell adds the following to last paragraph of this clause:
2. For a structure with exposure level L1 as defined in ISO 19900, clause 7.3.2,
Non-linear Finite Element Analysis (NLFEA) SHALL [PS] be performed to confirm a
structure’s residual strength after accidental damage and its resistance to
environmental actions.
L1 is characterised in ISO 19900 with the example of manned, non-evacuated
structures and high environmental consequence platforms.
Shell considers this to be a DEM1 requirement in addition to industry base
standards.
7.10.2 Evaluation of accidental situations
7.10.2.3 Risk assessment

7.10.2.3.1 General

Substitute the last paragraph with:

Accidental events for platforms with risk levels 2 and 3 shall be considered as load cases
for structural design.
7.10.3 Hydrocarbon incidents

Add as the last bullet point:

- prevention of escalation of a hazardous event.

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7.10.4 Explosion

Delete the last sentence of the second paragraph:

The explosion overpressure at the limit of significant probability, often taken as a probability
of 10−4 per year, should be the minimum value used for design explosion overpressure.
Strikethrough added to clarify that this is deleted in S631-04
Add after the second paragraph:
Structural components subject to blast load and required for business risk and/or life-safety
risk shall have sufficient blast capacity to achieve the business risk performance objective
and the life-safety performance objectives.
The business risk performance objective typically requires little or no repair costs when the
structural component is exposed to loading with annual probability of exceedance of 10-2.
This can be achieved by requiring the structural component to remain elastic (or only
localised regions with limited peak stress above material yield) under SLB (strength level
blast) loading, where SLB loading is the blast load with an annual probability of exceedance
of 10-2. A less frequent event for SLB loading may be adopted based on the business
consequences of the facilities (e.g. annual probability of exceedance of 10-3).
The life-safety risk performance objective typically requires no escalation of the blast or fire
event when the structural component is exposed to loading with annual probability of
exceedance of 10-4. This can be achieved by requiring the structural component not to
fracture or collapse under DLB (ductility level blast) loading, where DLB loading is the blast
load with an annual probability of exceedance of 10-4. A less frequent event for DLB loading
may be adopted based on the life-safety consequences (e.g. annual probability of
exceedance of 10-5) for catastrophic events where life-safety by evacuation cannot be
demonstrated).
Plastic design may be used for the DLB loading with fracture prevented by limiting the
magnitude of plastic strain (typical limit plastic strain is 5% for welds).
A.7.10.4 Explosion

A.7.10.4.3 Method of analysis

A.7.10.4.3.1 General

Delete the second paragraph, i.e.:

Structures can be designed to respond elastically (i.e. in the elastic deflection range) or
plastically, in response to explosion pressures. In the latter case, structures will be found to
have resistance to higher levels of explosion. In design this can be accounted for by
specifying two different explosion levels:
— elastic design: a strength level explosion (SLB), being an explosion with a
probability of exceedance of around 10−2 per year;
— plastic design (no fracture or collapse): a ductility level explosion (DLB), being an
explosion with a probability of exceedance of around 10−4 per year.
Strikethrough added to clarify that this is deleted in S631-04

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7.10.6 Explosion and fire interaction

Add:
The structural design or assessment shall include the consequences of blast and fire
scenarios with either event occurring first. Refer to API RP 2FB and ANSI/API RP 2TOP for
more guidance.
a) The endurance period to allow a controlled evacuation from the TR (or LQ) shall
be demonstrated for a blast event followed by a fire event. Performance of the
structure in a fire event followed by a blast event shall be demonstrated for credible
scenarios. The return periods may be taken from the Fire Hazard Analysis and
Explosion Hazard Analysis or using the UK’s HSE Guidance on TR Integrity.
b) Following a blast event, PFP applied to a blast wall or primary structure shall
remain functional in order to achieve the required fire endurance period in a
subsequent fire event. ISO 23693 provides requirements for barriers and structural
elements.
c) Where plastic strains are incurred under the design blast, fire, or sequence
blast/fire event, the post-accident integrity of the damaged structure shall be
demonstrated under permanent and environmental loads (for a 1-year return period).
A.7.10.6 Explosion and fire interaction

A.7.10.6.1 General

Delete the last sentence of the second paragraph:

Fire and explosion assessments should demonstrate that the escape routes and safe areas
survive the fire and explosion scenarios.
Strikethrough added to clarify that this is deleted in S631-04
A.7.10.6.3 Explosion and fire walls

Delete the point:

a) fire protection should be able to maintain integrity at the required strain,
Strikethrough added to clarify that this is deleted in S631-04
7.11 Other actions
7.11.2 Conductors

Add before the second-last sentence:

Where drilling is performed from a derrick cantilevered from a jack-up through a platform
conductor, the ULS check shall include forced displacements and any consequent actions
on the conductor and its supports due to the relative movement between the structure and
the drilling jack-up.
7.11.6 Bridge supports

Add at the end of potential action b):

When active or passive motion compensated gangways are used for transfer of personnel or
goods from floating support vessels to a topsides structure the designer shall use data from
the gangway vendor to determine the design actions on the topsides during installation and
operation of the gangway.

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8 Strength and resistance of structural components

8.4 Connections
8.4.3 Bolted connections

Add before the bulleted list:

Bolts in conformance with ISO 898 Gr 4.6 or ASTM A307 shall not be used.
Higher strength bolt designations than ISO 898 Gr. 10.9 or ASTM F3125 A490 Type 1 shall
not be used.
Note: Higher strength bolt designations can cause hydrogen embrittlement in sea
environment.

Substitute the existing bulleted list with:

— For preloaded bolts, the effective length of the bolt (between the underside of the head
and the nut) shall be sufficiently long to minimize the consequence of creep in reducing the
tension in the bolt. Preloaded bolts should have a minimum effective length of L/D > 5 or
collars should be added.
— A 2nd re-tightening of the bolts shall be performed at a minimum of 40mins after the
initial tightening.
— A reduction in pretension over the life of the bolted connection (20 to 50 years) due to
creep of 20% shall be assumed for bolts with any protective coating applied to the bolt
surface.
— Bolt hole edges shall be rounded and the connection shall be sealed with a durable
sealant, or a durable paint system, or both.
— Washers shall be used beneath both bolt heads and nuts to minimise coating damage.
Loose washers (plain or spring) should not be used.
— The nut should be prevented from loosening under vibration by chemical bonding (e.g.
loctite) of the nut to the bolt thread. The nut may be prevented from loosening under
vibration by wedge-locking using corrosion resistant alloy washers surface hardened via a
low temperature carbon diffusion process.
— Corrosion protection of bolted connections shall be assured by the adoption of corrosion
resistant alloy or high durability coating or metallizing. All surfaces that are in contact or
inaccessible after assembly should be coated in aluminium spray. ISO 898 Gr 8.8 and
ASTM F3125 A325 type 1 bolts shall be hot dip spun galvanised (HDSG) in conformance
to ASTM F2329. ISO 898 Gr 10.9 and ASTM F3125 A490 type 1 bolts shall be coated with
a liquid applied Zn/Al based coating system in conformance with ASTM F1136 Gr3 or
ASTM F2833 Gr1. After final assembly, accessible parts of the bolts shall be overcoated
with an organic coating system to match the surrounding structure. Cadmium-plated bolts
shall not be used as they can emit a lethal toxic fume when heated.
— Regular inspection of bolted connections should be specified.
— Structural bolts should be tensioned using one of the following:
o Proprietary bolt tensioning devices (e.g. Hydratight)
o Turn of nut procedures
o Direct tension indicating devices or bolts (e.g. rotabolts)
o Bench calibrated wrench
— Bolt holes shall not be drilled in any members that are classified as DC 1 or 2, with
reference to Table 7.
— For repair clamps using grout or an elastomer liner, additional losses due to long-term
effects shall be accounted for in deriving the residual bolt tension.

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8.5 Castings

Add to the end of the Clause:

The manufacture and testing of castings, including qualification of welding shall be in
accordance with EEMUA 176 or API Spec. 2SC, unless company requirements indicate
otherwise.
9 Structural systems
9.1 Topsides design
Add as a new sub Clause:

9.1.4 Equipment and equipment supports

Equipment supports that are subject to uplift shall be mounted directly on the supporting
steelwork and not on deck plate or grating.
Deck plate or deck grating shall incorporate cut-outs to permit attachment to the supporting
steelwork.
9.2 Topsides structure design models
9.2.1 General

Substitute the first paragraph with:

Internal forces in structural components shall be derived using an indeterminate, three-
dimensional structural analysis methodology.
9.2.2 Support structure model for topsides design

Add at the end of the Clause:

During Front End Engineering Design (FEED) and detail design, primary steel joint
eccentricities shall be modelled with additional nodes to reflect the true eccentricities in
order to account for shear transfer through the chord.
9.2.4 Modelling for design of equipment and piping supports

Add at the end of the Clause:

Equipment skids or packages shall be modelled such that the mass is lumped at the local
vertical CoG for conditions subject to lateral accelerations.
Dummy members shall not add stiffness to the model.
9.4 Flare towers, booms, vents and similar structures

Add before the last paragraph:

The designed support of the access platform at the top of the flare tower/boom shall take
into account the potential expansion of the platform in relation to the primary steelwork due
to thermal radiation.
Flare design shall account for the effects of the flare header filling with liquid.

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9.5.3 Design actions and resistances

9.5.3.3 Helicopter emergency landing situation

a) Helicopter dynamic actions (undercarriage local actions)

Substitute point a) with the following:

The dynamic helicopter landing action shall be calculated based on CAP 437.
9.6 Crane support structure
9.6.1 General

Add at the end of the Clause:

For the design condition, deflections and accelerations at the top of the crane
pedestal/crane cab shall be evaluated and reviewed by operations personnel and the crane
manufacturer.
If the crane pedestal is used for storage, design actions and internal corrosion protection
shall be based on the nature of the liquid to be stored and the maximum levels and
pressures under normal operating, test or failure of level control conditions.
Note: Under certain circumstances, it could be advantageous to use crane pedestals for
diesel or water storage.

9.8 Bridges
Add after the first paragraph:
Bridge primary steelwork and supports should be evaluated for fatigue due to the
transmission of wave loading through the supporting substructures.
9.12 Fire protection systems
Add after the second paragraph:
Where the PFP can be wetted, the PFP shall be sealed to prevent water ingress and
corrosion of the substrate.
Where protection from jet fires is required, PFP products shall be specified that have been
successfully tested to ISO 22899-1.
Coat back lengths for secondary members attached to PFP protected primary members
shall be determined to avoid potential system weaknesses.
Shell adds the following after the second paragraph:
1. Proprietary fire protection systems SHALL [PS] be submitted to the Principal for
approval.
As defined in DEP 34.19.20.11‑Gen., a proprietary material is a material developed
and protected by exclusive right under a specific name by a specific Manufacturer/
Supplier.
Shell considers this to be a DEM1 requirement in addition to industry base
standards.

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9.13 Penetrations
Add after first paragraph:
Where penetrations are required through a safety critical barrier, penetrations shall be
designed such that the performance objectives of the barrier are not impaired.
Detailing at penetrations shall minimise stress concentrations and corrosion development.
9.16 Actions due to drilling operations
Add after the first paragraph:
Coincident drilling weights for Storm and Operating conditions shall be in conformance
with ISO 19901-5 Annex - Weight management during operations.
9.19 Muster areas and lifeboat stations
Add after the last paragraph:
Dynamic impact factor applied to the loaded weight of the lifeboat shall comply with
regulatory requirements.
10 Materials
10.5 Fibre-reinforced composites
Add after the third paragraph:
FRP shall be considered as an alternative to steel for floor grating, hand railing and
ladders, lightweight fire and explosion-resistant panels.
Specific design requirements shall be included in assessing and selecting FRP elements.
For example, for a floor grating, as a minimum, the following design requirements shall be:
a) layout requirements;
b) spacing between load bearing bars;
c) uniformly distributed loads and concentrated loads, including trolley wheel loads
and wave uplift loads;
d) span of grating and deflection limits;
e) impact resistance;
f) fire performance, including fire endurance, flame spread, smoke and toxic gas
emissions, and residual strength following the exposure;
g) skid resistance and durability of anti-slip surface;
h) ultra-violet protection;
i) chemical resistance;
j) static electricity discharge;
k) grating fixing details;
l) cut-outs and penetrations.
Similarly, assessments shall be made for other product types (handrails, etc.).
For locations where FRP does not meet all the performance requirements, a suitable steel
grating shall be specified.
Add at the end of the Clause:
Primary escape routes shall not contain fibre-reinforced composites grating.

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11 Fabrication, quality control, quality assurance and documentation

11.2 Welding
Add to the list of additional considerations:
d) n general, DC 1, 2 and 3 steel member splices, connections to other members, and joints
shall be full penetration welds.
e) All partial penetration and fillet welds shall be designed and verified.
f) Full penetration weld of a thicker member to a thinner member shall be avoided, e.g. by
tapering at 1:4 or lower.
13 Loadout, transportation and installation
Add at the end of the Clause:
Installation aid structures that are planned to be removed shall be designed taking safe and
easy removal into account.
Removal requirements of temporary attachments are provided in Clause 11.1.4.
Verification of the deformation induced forces during loadout shall account for the stiffness
and relative displacements of the structure being loaded out, the grillage structure, the
trailers or skid beams, the barge and the quay soil.
Differential deflections of the topsides structure during pre-service (fabrication, loadout,
transportation and installation operations) shall be evaluated to verify equipment and piping
serviceability and structures strength as required in Clauses 7.9.2, 9.2.3 and 9.2.4.
15 Assessment of existing topsides structures
Shell adds the following to this section:
Triggers for performing structural assessments to provide assurance of technical integrity
are specified in ISO 19901-9.
1. In order to extend the operating life of an offshore topside structure beyond the original
design life, assurance for extended life-cycle service SHALL [PS] be provided by:
a) performing a review of the integrity condition of the installation;
b) identifying any integrity gaps requiring reassessment and inspection.
Shell considers this to be a DEM1 requirement in addition to industry base
standards.
Bibliography
API RP 2FB Recommended Practice for the Design of Offshore Facilities
Against Fire and Blast Loading

ANSI/API RP ISO 19901-3:2010 (Modified), Petroleum and natural gas

2TOP industries — Specific requirements for offshore structures —
Part 3: Topsides structure

DNVGL-RP- Fatigue design of offshore steel structures

C203

ISO 19900 Petroleum and natural gas industries -- General requirements for
offshore structures

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ISO 19904-1 Petroleum and natural gas industries — Floating offshore

structures — Part 1: Ship-shaped, semi-submersible, spar and
shallow-draught cylindrical structures

ISO 22899-1 Determination of the resistance to jet fires of passive fire

protection materials – Part 1: General requirements

UK HSE Hazardous Installations Directorate (HID) Inspection Guide

Offshore – Inspection of Temporary Refuge Integrity

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PART IV.REFERENCES
In this DEP, reference is made to the following publications:
Unless specifically designated by date, the latest edition of each publication shall be used,
together with any amendments/supplements/revisions thereto.
SHELL STANDARDS

DEP 00.00.05.80-Gen. DEP feedback form

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