ISO 13628-15:2011

INTERNATIONAL ISO
STANDARD 13628-15
First edition
2011-09-15
Petroleum and natural gas industries —
Design and operation of subsea
production systems —
Part 15:
Subsea structures and manifolds
Industries du pétrole et du gaz naturel — Conception et exploitation des
systèmes de production immergés —
Partie 15: Structures immergées et manifolds

Reference number
©
ISO 2011
©  ISO 2011
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ii © ISO 2011 – All rights reserved

Contents Page
Foreword . v
1  Scope . 1
2  Normative references . 3
3  Terms, abbreviated terms, and definitions . 4
3.1  Terms and definitions . 4
3.2  Abbreviated terms . 7
4  Manifold and template functional considerations . 9
4.1  General . 9
4.2  System requirements . 10
4.3  System Interfaces . 12
4.4  Cluster manifold requirements . 13
4.5  Template system requirements . 13
5  Design considerations . 14
5.1  System design . 14
5.2  Loads . 17
5.3  Piping design . 18
5.4  Structural design . 19
5.5  Foundation design . 22
5.6  Components . 25
6  Verification and validation of design . 26
6.1  Design verification . 26
6.2  Design validation . 28
6.3  Other comments . 30
7  Materials and fabrication requirements to piping systems . 30
7.1  General . 30
7.2  Pipe and pipe fittings . 31
7.3  Forged components . 32
7.4  Chemical composition and weldability . 32
7.5  Test sampling of base materials . 33
7.6  Mechanical and corrosion testing of base materials . 33
7.7  Non-destructive inspection of components . 35
7.8  Fastener materials . 37
7.9  Bending and forming operations . 37
7.10  Overlay welding and buttering of components . 39
7.11  Welding and non-destructive testing of piping systems . 40
8  Fabrication and manufacturing considerations . 49
8.1  External corrosion protection . 49
8.2  Colours . 49
8.3  Material traceability . 49
9  Installation, operation and maintenance considerations . 50
9.1  Installation requirements . 50
9.2  Operations requirements . 50
9.3  Maintenance considerations . 51
9.4  Requirements during installation . 52
10  ROV/ROT aspects . 55
11  Lifting considerations . 56
11.1  Pad eyes . 56
11.2  Other lifting devices .56
12  Equipment marking .56
13  Transportation and storage .57
13.1  General .57
13.2  Storage and preservation procedure .57
13.3  Sea-fastening .57
14  Abandonment provisions .57
14.1  General .57
14.2  Decommissioning .57
14.3  Design .58
14.4  Post-abandonment operation .58
14.5  Structures .58
14.6  Manifolds .58
14.7  Templates .58
Annex A (informative) Typical manifold data sheet .59
Bibliography .61

iv © ISO 2011 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 13628-15 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore
structures for petroleum, petrochemical and natural gas industries, Subcommittee SC 4, Drilling and
production equipment.
ISO 13628 consists of the following parts, under the general title Petroleum and natural gas industries —
Design and operation of subsea production systems:
 Part 1: General requirements and recommendations
 Part 2: Unbonded flexible pipe systems for subsea and marine applications
 Part 3: Through flowline (TFL) systems
 Part 4: Subsea wellhead and tree equipment
 Part 5: Subsea umbilicals
 Part 6: Subsea production control systems
 Part 7: Completion/workover riser systems
 Part 8: Remotely operated tools and interfaces on subsea production systems
 Part 9: Remotely Operated Tool (ROT) intervention systems
 Part 10: Specification for bonded flexible pipe
 Part 11: Flexible pipe systems for subsea and marine applications
 Part 15: Subsea structures and manifolds
A Part 12, dealing with dynamic production risers, a Part 14, dealing with high-integrity pressure protection
systems (HIPPS), a Part 16, dealing with specification for flexible pipe ancillary equipment, and a Part 17,
dealing with recommended practice for flexible pipe ancillary equipment, are under preparation.

INTERNATIONAL STANDARD ISO 13628-15:2011(E)

Petroleum and natural gas industries — Design and operation
of subsea production systems —
Part 15:
Subsea structures and manifolds
1 Scope
This part of ISO 13628 addresses recommendations for subsea structures and manifolds, within the
frameworks set forth by recognized and accepted industry specifications and standards. As such, it does not
supersede or eliminate any requirement imposed by any other industry specification.
This part of ISO 13628 covers subsea manifolds and templates utilized for pressure control in both subsea
production of oil and gas, and subsea injection services. See Figure 1 for an example of such a subsea
system.
Equipment within the scope of this part of ISO 13628 is listed below:
a) the following structural components and piping systems of subsea production systems:
 production and injection manifolds,
 modular and integrated single satellite and multiwell templates,
 subsea processing and subsea boosting stations,
 flowline riser bases and export riser bases (FRB, ERB),
 pipeline end manifolds (PLEM),
 pipeline end terminations (PLET),
 T- and Y-connection,
 subsea isolation valve (SSIV);
b) the following structural components of subsea production system:
 subsea controls and distribution structures,
 other subsea structures;
c) protection structures associated with the above.
The following components and their applications are outside the scope of this part of ISO 13628:
 pipeline and manifold valves;
 flowline and tie-in connectors;
 choke valves;
 production control systems.
NOTE General information regarding these topics can be found in additional publications, such as ISO 13628-1 and
API Spec 2C.
Key
A tree
B cluster manifold
C PLEM
D PLET
E inline tee
F multi-phase pump skid
Figure 1 — Example of some typical subsea structures
2 © ISO 2011 – All rights reserved

2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 3183, Petroleum and natural gas industries — Steel pipe for pipeline transportation systems
ISO 3834-2, Quality requirements for fusion welding of metallic materials — Part 2: Comprehensive quality
requirements
ISO 9606 (all parts), Qualification test of welders — Fusion welding
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel — General principles
ISO 10423, Petroleum and natural gas industries — Drilling and production equipment — Wellhead and
christmas tree equipment
ISO 10474, Steel and steel products — Inspection documents
ISO 13628-1:2005, Petroleum and natural gas industries — Design and operation of subsea production
systems — Part 1: General requirements and recommendations
ISO 13628-1:2005/Amd 1:2010, Petroleum and natural gas industries — Design and operation of subsea
production systems — Part 1: General requirements and recommendations — Amendment 1: Revised
Clause 6
ISO 13628-4, Petroleum and natural gas industries — Design and operation of subsea production systems —
Part 4: Subsea wellhead and tree equipment
ISO 13628-8, Petroleum and natural gas industries — Design and operation of subsea production systems —
Part 8: Remotely operated tools and interfaces on subsea production systems
ISO 14731:2006, Welding coordination — Tasks and responsibilities
ISO 15156 (all parts), Petroleum and natural gas industries — Materials for use in H S-containing
environments in oil and gas production
ISO 15590-1, Petroleum and natural gas industries — Induction bends, fittings and flanges for pipeline
transportation systems — Part 1: Induction bends
ISO 15609 (all parts), Specification and qualification of welding procedures for metallic materials — Welding
procedure specification
ISO 15614 (all parts), Specification and qualification of welding procedures for metallic materials — Welding
procedure test
EN 473, Non-destructive testing — Qualification and certification of NDT personnel — General principles
EN 1418, Welding personnel — Approval testing of welding operators for fusion welding and resistance weld
setters for fully mechanized and automatic welding of metallic materials
EN 10228-3, Non-destructive testing of steel forgings — Part 3: Ultrasonic testing of ferritic or martensitic steel
forgings
ASME B31.3, Process Piping
ASME V, 2007, Boiler and Pressure Vessel Code (BPVC), Section V, Nondestructive Examination
ASME VIII, 2007, Boiler and Pressure Vessel Code (BPVC), Section VIII, Rules for Construction of Pressure
Vessels, Div. 1
ASME IX, Boiler and Pressure Vessel Code (BPVC), Section IX, Welding and Brazing Qualifications
ASNT SNT-TC-1A, Recommended Practice No. SNT-TC-1A, Personnel qualification and certification in
nondestructive testing
ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings
ASTM E562, Standard Test Method for Determining Volume Fraction by Systematic Manual Point Count
ASTM G48, Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and
Related Alloys by Use of Ferric Chloride Solution
NS 477, Welding — Rules for qualification of welding inspectors
3 Terms, abbreviated terms, and definitions
For the purposes of this document, the following terms, abbreviated terms and definitions apply.
3.1 Terms and definitions
3.1.1
carbon steel
full range of carbon, carbon-manganese and low-alloy steels used in the construction of conventional oilfield
equipment
3.1.2
corrosion-resistant alloy
CRA
alloy that is intended to be resistant to general and localized corrosion in oilfield environments that are
corrosive to carbon steels
NOTE This definition is in accordance with ISO 15156 (all parts) and is intended to include materials such as
stainless steels and nickel base alloys. Other ISO documents can have other definitions.
3.1.3
driven pile
jetted pile
typically a tall steel cylindrical structure, with or without internal stiffener system, used to support subsea
structures
NOTE Driven piles are usually driven into the sea-floor with impact hammers, while jetted piles rely on jetting the soil
at the lower end of the pile.
3.1.4
inline tee
system of piping and valves used to make a subsea connection at the middle of a pipeline, and generally
integral to the pipeline
NOTE The pipeline may be used to transport produced fluids or to distribute injected fluids.
3.1.5
low-alloy steel
steel containing at least 1 % and less than 5 % of elements deliberately added for the purpose of modifying
properties
4 © ISO 2011 – All rights reserved

3.1.6
manifold
system of headers, branched piping and valves used to gather produced fluids or to distribute injected fluids in
subsea oil and gas production systems
NOTE A manifold system can also provide for well testing and well servicing. The associated equipment can include
valves, connectors for pipeline and tree interfaces, chokes for flow control and TFL diverters. The manifold system can
also include control system equipment, such as a distribution system for hydraulic and electrical functions, as well as
providing interface connections to control modules. All or part of the manifold can be integral with the template or can be
installed separately at a later date if desired. Manifold headers can include lines for water or chemical injection, gas lift and
well control.
3.1.6.1
cluster manifold
structure used to support a manifold for produced or injected fluids
NOTE There are no wells on a cluster manifold.
3.1.7
mudmat
typically a shallow structure used to support a subsea structure by distributing the load to the seabed via a
structural plate or shallow skirt
3.1.8
pipeline end manifold
PLEM
system of headers, piping and valves used to gather produced fluids or to distribute injected fluids in subsea
production systems, generally integral to the pipeline and having more than one subsea connection
3.1.9
pipeline end termination
PLET
system of piping and valves, generally integral to the pipeline, used to make a subsea connection at the end
of a pipeline
NOTE 1 Typically, a PLET has only one subsea connection.
NOTE 2 The pipeline can be used to transport produced fluids or to distribute injected fluids.
3.1.10
pitting resistance equivalent number
PREN
index that exists in several variations and usually based on observed resistance to pitting of corrosion-
resistant alloys in the presence of chlorides and oxygen, e.g. as found in seawater
NOTE Though useful, these indices are not directly indicative of the resistance to produced oil and gas environments.
The most common examples are given in Equations (1) and (2):
f  w  3,3w  16w (1)
PREN Cr Mo N
f  w  3,3(w  0,5w )  16w (2)
PREN Cr Mo W N
where
w is the mass fraction of chromium in the alloy, expressed as a percentage of the total composition;
Cr
w is the mass fraction of molybdenum in the alloy, expressed as a percentage of the total composition;
Mo
w is the mass fraction of tungsten in the alloy, expressed as a percentage of the total composition;
W
w is the mass fraction of nitrogen in the alloy, expressed as a percentage of the total composition.
N
3.1.11
protection structure
independent structure that protects subsea equipment against damage from dropped objects, fishing gear and
other relevant accidental loads
3.1.12
riser base
structure that supports a marine production riser or loading terminal, and that serves as a structure through
which to react to loads on the riser throughout its service life
NOTE A riser base can also include a pipeline connection capability.
3.1.13
sealine
subsea flowline
3.1.14
sour service
service in H S-containing fluids
NOTE In this part of ISO 13628, “sour service” refers to conditions where the H S content is such that restrictions as
specified in ISO 15156 (all parts) or NACE MR 0175 apply.
3.1.15
suction pile
typically a tall steel cylindrical structure, open at the bottom and normally closed at the top, with or without an
internal stiffener system and used to support subsea structures
NOTE A suction pile is installed by first lowering it into the soil to self-penetration depth (i.e. penetration due to
submerged pile weight). The remainder of the required penetration is achieved by pumping out the water trapped inside
the suction pile.
3.1.16
sweet service
service in H S-free fluids
3.1.17
template
seabed structure that provides guidance and support for drilling and includes production/injection piping
NOTE 1 A template typically comprises a structure that provides a guide for drilling and/or support for other equipment,
and provisions for establishing a foundation (piled or gravity-based), and is typically used to group several subsea wells
(modular manifold) at a single seabed location.
NOTE 2 Production from the templates can flow to floating production systems, platforms, shore or other remote
facilities.
NOTE 3 Templates can be of a unitized or modular design.
3.1.17.1
modular template
template installed as one unit or as modules assembled around a base structure (often the first well)
NOTE If installed as one unit, the template is of a cantilevered design. If installed as modules, these modules can be
of cantilevered design.
3.1.17.2
drilling template
multi-well template used as a drilling guide to predrill wells prior to installing a surface facility
6 © ISO 2011 – All rights reserved

NOTE The wells are typically tied back to the surface facility during completion. The wells can also be completed
subsea, with individual risers back to the surface.
3.1.18
type 316
austenitic stainless steel alloy
EXAMPLES UNS S31600/S31603.
3.1.19
type 6Mo
austenitic stainless steel alloy having PREN  40 mass fraction and Mo alloying  6,0 % mass fraction, and
nickel alloy having a Mo content in the range 6 % mass fraction to 8 % mass fraction
3.1.20
type 22Cr duplex
ferritic/austenitic stainless steel alloy with 30  PREN ≤ 40 and Mo  1,5 % mass fraction
EXAMPLES UNS S31803 and S32205 steels.
3.1.21
type 25Cr duplex
ferritic/austenitic stainless steel alloys with 40  PREN  45
EXAMPLES S32750 and UNS S32760 steels.
3.1.22
verification
confirmation that specified design requirements have been fulfilled, through the provision of objective
evidence
NOTE Typically verification is achieved by calculations, design reviews, and hydrostatic testing.
3.1.23
validation
confirmation that the operational requirements for a specific use or application have been fulfilled, through the
provision of objective evidence
NOTE Typically validation is achieved by qualification testing and/or system integration testing.
3.2 Abbreviated terms
ACCP ASNT Central Certification Program
API American Petroleum Institute
ASME American Society of Mechanical Engineers
ASTM American Society for Testing and Materials
ASNT American Society of Nondestructive Testing
AWS American Welding Society
BOP blowout preventer
BPVC Boiler and Pressure Vessel Code
CE carbon equivalent, based on the International Institute of Welding equation
IIW
CE carbon equivalent, based on the chemical portion of the Ito-Bessyo carbon equivalent equation
Pcm
CRA corrosion-resistant alloy
DAC distance amplitude curve
DNV Det Norske Veritas
EWF European Federation for Welding, Joining and Cutting
EN European Norm
FBH flat-bottom hole
FIV flow-induced vibration
FL fusion line
GMAW gas metal arc welding
GTAW gas tungsten arc welding
HAZ heat-affected zone
HAZOP hazard and operability analysis
H diffusible hydrogen, expressed as ml/100 g deposited metal
D
HIP hot isostatic pressed
IDS interface data sheet
IIW International Institute of Welding
IWE International Welding Engineer
LP liquid penetrant
MAG metal-active gas
MDT minimum design temperature
MEG monoethylene glycol
MIG metal-inert gas
NDT non-destructive testing
NORSOK Norsk Sokkels
NS Standards Norway
O-ROV observation/inspection-class remote operated vehicle
P&ID process and instrumentation diagram
PLEM pipeline end manifold
8 © ISO 2011 – All rights reserved

PLET pipeline end termination
PQR procedure qualification record
PREN pitting resistance equivalent number
PSL product specification level
PWHT post-weld heat treatment
ROT remotely operated tool
ROV remotely operated vehicle
SAFOP safety and operability analysis
SCM subsea control module
SMYS specified minimum yield strength
SSIV subsea isolation valve structures
TFL through-flow loop
UNS Unified Numbering System
UT ultrasonic testing
VIV vortex induced vibration
WM weld metal
WPS welding procedure specification
WPQR weld procedure qualification record
W-ROV work-class remotely operated vehicle
XT christmas tree
4 Manifold and template functional considerations
4.1 General
4.1.1 Manifold system design typically fulfils the following functions:
a) gather production or distribute water or gas from or to multiple production, water, or gas injection wells;
b) direct flow of fluids through manifold headers;
c) contain one or more headers;
d) allow isolation of individual well slots from header;
e) incorporate flowline connections between manifolds and appropriate flowlines and/or test lines;
f) allow continuity of pigging of flowline system.
4.1.2 The end user should define or approve the following performance and configuration requirements,
including
 maximum dimensions and target weight;
 pressure and temperature ratings;
 equipment interfaces;
 process and instrumentation diagrams (P&IDs);
 materials requirements;
 water depth;
 design life;
 geotechnical and geophysical data;
 metocean data;
 dropped-objects protection requirements;
 over-trawling requirements including special fishing gear loads (snag loads) for the geographic region.
4.1.3 All equipment should
 comply with the latest revision of end user's product requirements;
 be designed to the pressure and temperature ratings;
 be compatible (dimensions and mass) with handling and installation capabilities of the installation vessel;
 be functional and fit for purpose for specified operating environment.
Subsea production or injection manifolds should be located in proximity to production or injection wells of field
development.
4.1.4 Material selection for individual components, including all seal materials, should meet the
requirements of ISO 13628-1 concerning
 production, injection fluids, and completion fluids for wetted areas;
 exposure to chemical injection and service fluids. This applies equally to seal materials.
NOTE For the purposes of this provision, ANSI/API RP 17A is equivalent to ISO 13628-1.
Manifolds typically provide termination points for flowlines.
Subsea tree tie-ins may be directed to flow product into or out of a flowline system by remotely or manually
functioning valves on a manifold.
4.2 System requirements
The flexibility to meet various production scenarios (e.g. “retrofit” installation of pumps, separators and other
modules) and possible future expansions should be considered. For each design, potential future
requirements should be addressed, and it should be clearly explained how the manifold system is prepared for
implementing the identified functions.
10 © ISO 2011 – All rights reserved

The following considerations related to structures and modules should be addressed:
 transportation, lifting, installation (inclusive of potential levelling), abandonment;
 flowline pull-in, connection and testing;
 well drilling, completion, workover and XT installation;
 precommissioning and commissioning;
 production/injection start-up and production/injection;
 injection of chemicals, such as emulsion, scale, wax and corrosion inhibitors;
 methanol or MEG injection for hydrate control;
 thermal performance;
 annulus bleed operations;
 well testing;
 barrier testing;
 planned and emergency shutdowns of wells and manifold;
 pressurization and depressurization of piping system;
 pigging of flowlines, such as for gauge and cleaning operations;
 ROV/ROT inspections and interventions, inclusive of module replacement;
 sand/pig detection facilities inspection;
 well interventions;
 potential hook-up of retrofit-installed modules and components;
 seawater ingress during tie-in operations;
 corrosion protection;
 erosion protection;
 wall thickness measurement;
 fluid flow rate;
 pressure drop through piping system;
 fluid composition;
 fluid flow regimes (slugging).
4.3 System Interfaces
4.3.1 The system interfaces should maintain integrity and functionality in the service conditions and take
into account the following:
 internal and external pressure;
 simultaneous expansion and contraction on the same structure, whether the structure is an XT, a module,
a template or a manifold;
 zero external leakage and seawater ingress;
 tolerance loops for interface make-up;
 internal and external temperature variations;
 structure for protection against dropped objects and fishing gear;
 impact from dropped objects and fishing gear;
 short- and long-term structure settlement;
 marine growth;
 corrosion and erosion;
 scaling on subsea mate-able surfaces;
 potential formation of hydrate;
 installation loads;
 pull-in and connection loads;
 projected product lifespan;
 serviceability;
 protection from ROV impact loads;
 subsea controls connection systems;
 chemical injection requirements.
4.3.2 Interface data sheets and outlined installation procedures for critical external interface areas should
be provided. The data sheets, when implemented, should clearly describe design limitations, weights and
dimensions as applicable. Areas that, as a minimum, should be covered are
 interfaces towards the well system, including maximum conductor angle, hang-off weights, lengths of
conductor, BOP envelopes, sequential requirements (sequence and number of wells that can be drilled
before design load capacity is achieved), limitation on mud pressure/flow during drilling out the conductor,
cement/grouting strength, well growth, wellhead design, etc.;
 interfaces towards marine contractor (equipment mass and size, lifting height, deck space, load capacity
of tie-in points and structures, installation limitations, sea states, etc.);
 interfaces towards flowline jumpers and well jumpers, controls flying leads.
12 © ISO 2011 – All rights reserved

4.4 Cluster manifold requirements
4.4.1 General
The cluster manifold consists of a framework that supports other equipment, such as piping, pipeline pull-in
and connection equipment, and protective framing. The cluster manifold commingles flow from a number of
subsea wells into one or more headers. The cluster manifold provides a foundation to sufficiently transfer
design loads into the seabed. The cluster manifold may include the following components; see Figure 2:
 subsea control module;
 subsea distribution unit;
 electrical distribution unit.
4.4.2 Alignment
The cluster manifold should provide alignment capability for proper physical interfaces with other subsystems,
such as connectors and foundations.
4.4.3 Guidance system
The cluster manifold should provide for a guidance system to support operations through the life of the
installation. If guidelines are used, the cluster manifold should provide proper spacing and installation/
maintenance capability for the guide posts. If guideline-less methods are used, the cluster manifold should
provide sufficient space and passive guidance capability to successfully install key equipment items.

Figure 2 — Typical cluster manifold
4.5 Template system requirements
4.5.1 General
The framework of a template supports equipment such as manifolds, risers, drilling and completion equipment,
pipeline pull-in and connection equipment and protective framing (template and protective framing are often
built as one integrated structure). The template should provide a foundation to sufficiently transfer design
loads into the seabed. See Figure 3.
4.5.2 Drilling and completion interface
If wells will be drilled through the template, it should provide a guide for drilling, landing/latching capability for
the first casing string, and sufficient space for running and landing a BOP stack. If subsea trees will be
installed, the template should provide proper mechanical positioning and alignment for the trees and sufficient
clearance for running operations.
4.5.3 Alignment
The template should provide alignment capability for proper physical interfaces among subsystems, such as
wellhead/tree, tree/manifold and manifold/flowlines.
4.5.4 Guidance system
The template should provide for a guidance system to support operations through the life of the installation. If
guidelines are used, the template should provide proper spacing and installation/maintenance capability for
the guide posts. If guideline-less methods are used, the template should provide sufficient space and passive
guidance capability to successfully install key equipment items.

Figure 3 — Typical template system
5 Design considerations
5.1 System design
5.1.1 Number of wells
If wells are incorporated into the template or cluster manifold, the number of wells will vary depending on the
site-specific application, and will greatly influence template size and manifold design. The addition of spare
well slots should be considered for contingencies such as changes in reservoir depletion plan, dry holes,
drilling problems and other unforeseen production requirements.
14 © ISO 2011 – All rights reserved

5.1.2 Well spacing
Well spacing may be governed by the type and size of drilling and production equipment used, the functional
requirements of the manifold, and subsequent maintenance and inspection requirements. Consideration
should be given to providing space for such items as flowline and wellhead connections and their running
tools, and adjacent BOP and production tree clearances. Access should also be provided for inspection and
maintenance tools.
5.1.3 Maintenance
Maintenance is a key factor in system design, and the maintenance approach should be considered early in
the design of a template/manifold system.
Some factors to consider are
 diver-assisted or remote maintenance methods;
 the requirement that components be retrievable;
 clear access space for divers, ROVs or other maintenance equipment;
 clear markings to allow distinguishing similar components;
 height above seabed for adequate visibility;
 system safety with components removed;
 fault detection to identify failed components.
5.1.4 Barrier philosophy
See ISO 13628-1:2005, Annex J for additional information on barrier philosophy.
Permanent isolation requirements against external leakage for pressurized systems should be provided by
double, pressure-containing barriers in all applicable external connection points, and in particular
a) un-utilized end connections or prior to hook-up of XT in combination with pressurized manifold piping:
two pressure barriers are required, one isolation valve and one pressure plug or cap or two isolation
valves;
b) prior to hook-up of XT in combination with non-pressurized manifold piping:
one pressure barrier, in combination with a protection device that retains inhibited fluids to protect the
environmental side of the isolation valve in order to avoid seawater-imposed corrosion of and fouling on
the valve, is required; the pressure barrier can be provided by the manifold branch valve, while the
protection device can be provided by a pressure cap on the hub towards the XT;
c) for diver-mated connections:
It is recommended to have two pressure barriers with a block-and-bleed function.
For temporary, time-limited operations, it can be acceptable to use only one valve for isolating a manifold
pressurized towards the environment. The valve should be checked to ensure it is holding pressure prior to
releasing the outboard barrier, in combination with an overall safety assessment for the activity.
The closure element of a valve (gate, ball) shall not be permanently exposed to the environment, i.e. an
inhibited volume is required on the environmental side of the isolation valve in order to avoid seawater-
imposed corrosion of and fouling on the valve.
It is recommended that all hubs be provided with high-pressure caps at delivery. Generally, they are required
for testing prior to installation and operation.
NOTE For the purposes of these provisions, ANSI/API RP 17A is equivalent to ISO 13628-1.
5.1.5 Safety
It is important that safety risks be considered for all phases and uses of the manifold system, including:
fabrication, testing, transportation, installation, operation and recovery. See the section on design criteria
safety and hazards of ISO 13628-1.
NOTE For the purposes of this provision, ANSI/API RP 17A is equivalent to ISO 13628-1.
5.1.6 External corrosion protection design
External corrosion control can be provided by appropriate materials selection, coating systems and cathodic
protection. A corrosion control programme should be developed during the design phase and incorporated
into the design of the system.
5.1.7 Templates
5.1.7.1 General
The template design may be based on an integrated or modular system layout. Selection of the template
concept should consider the following parameters:
 field development strategy, including future expansion;
 reuse of exploration wells and predrilling of wells;
 field development schedule (including marine operations and rig schedule);
 field infrastructure;
 onshore facilities and infrastructure;
 installation vessel availability;
 reuse of tools.
Shock absorbers or any soft landing devices may be included, as required, in order to allow for specified
maximum landing velocity.
5.1.7.2 Integrated template
An integrated template concept may include bottom structure, manifold and protection structure in one unit,
depending on the application and requirements for protection against fishing gear and dropped objects.
5.1.7.3 Modular template
A modular template concept may consist of separately installable/replaceable modules and structures. If
applicable, an additional requirement for moon-pool installable size may be applied.
The manifold can be designed for installation both together with the template and as a separate module.
16 © ISO 2011 – All rights reserved

5.2 Loads
5.2.1 External loads
5.2.1.1 Design loads
All applicable loads that can affect the subsea production system during all phases, such as fabrication,
storing, testing, transportation, installation, drilling/completion, operation and removal, should be defined and
form the basis for the design. Accidental loads are project-specific and should be verified by a special risk
analysis for the actual application. Accidental loads can include dropped objects, snag loads (fishing gear,
anchors), abnormal environmental loads (earthquake), etc. The data sheet in Annex A may be used to define
applicable loads.
5.2.1.2 Snag loads
Design of subsea structures for protection against trawl loads and dropped objects should be based on the
requirements in ISO 13628-1, and NORSOK U-001 as a basis.
However, due to the fact that fishing gear, in general, has changed in design and increased in size/mass
during recent years, increased trawl-loads protection can be necessary fo
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