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Remediation and Repair of Offshore Structures
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DOI: 10.1002/9781118476406.emoe409
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Remediation and Repair of Offshore Structures
Nigel W. Nichols and Riaz Khan
PETRONAS Carigali Sdn Bhd (PCSB), Kuala Lumpur, Malaysia
1 Introduction 1
2 Remediation and Repair Techniques 2
3 Recommendations and Conclusions 15
Acknowledgements 15
List of Abbreviations 15
Biographical Sketches 16
Glossary 16
References 17
Further Reading 17
1 INTRODUCTION
Structural integrity management (SIM) is often defined as
the application of qualified standards, by competent people,
using appropriate processes and procedures throughout the
structures life cycle, to ensure that the structures fitness for
purpose (FFP) is maintained. Structural integrity manage-
ment systems (SIMS) are often developed within operators
as a means of managing their structural risk levels for both
their offshore and onshore facilities. Figure 1 provides a
typical risk matrix that is used by operators. These risk
levels are represented in the operator’s risk categorizations
based on corporate expectations and generally presented
in a risk matrix. SIMS often goes hand in hand with the
operators understanding of as low as reasonably practicable
(ALARP) principles, which also outlines FFP criteria for
operating regions. In practice, SIMS ensures that risk levels
Encyclopedia of Maritime and Offshore Engineering, online © 2017 John Wiley & Sons, Ltd.
This article is © 2017 John Wiley & Sons, Ltd.
DOI: 10.1002/9781118476406.emoe409
Also published in the Encyclopedia of Maritime and Offshore Engineering (print edition)
ISBN: 978-1-118-47635-2
are kept within tolerable levels and ensures that mitigation
and remediation processes are deployed to avoid unwanted
structural risk escalation. Strengthening, modification, and
repair (SMR) is one such remediative process that might be
employed.
Prior to implementation of any SMR scheme, it is often
necessary to perform various levels of reassessment or
employ risk reduction measures. Where this is not possible,
or the acceptance criteria for reassessment has not been
met, then some level of SMR work is often required for
FFP. ISO 19902 (2007) Section 24 provides guidance on the
various levels of assessments that may be performed prior to
employing SMR.
1.1 SMR within the SIM process
After an inspection campaign or post-event inspection, there
is a variety of data that is made available to the structural
integrity engineer (SIE). In coming up with a strong strategy,
one must first evaluate this data for the FFP of the structure
and develop the remedial actions. SMR is one such reme-
dial action; however SMR schemes especially for underwater
activities can be costly and at times hazardous if not prop-
erly managed and executed. To formulate an SMR scheme,
it is generally part of the STRATEGY process within SIM
(Figures 2 and 3), and its execution is part of the PROGRAM.
In recent years the growth of computing power and accu-
racy in developing structural models together with a global
acceptance of the benefits of performing ultimate strength
analysis for the substructures (Westlake et al., 2006) have
enhanced the decision-making process to determine whether
it is feasible to perform underwater SMR for particular
defects. For substructures the ultimate strength analysis or
pushover analysis is performed as part of assessment engi-
neering prior to developing the strategy. The basic assump-
tion is that the fixed jacket space frame acts as a system

2 Offshore
L-1
L-2
L-3
Consequence
A B C D E
Likelihood
Increased interval
High
High
Figure 1. Typical risk matrix. (Reproduced with permission from O’Connor et al. (2005). © Society of Petroleum Engineers, 2005.)
Data
Managed system
for archive and
retrieval of SIM
data and other
pertinent records
Evaluation of
structural integrity
and fitness for
purpose;
development of
remedial actions
Overall inspection
philosophy and
strategy and
criteria for in-
service inspection
Detailed work
scopes for
inspection
activities and
offshore execution
to obtain quality
data
Evaluation Strategy Program
Figure 2. The SIM (structural integrity management) process. (Reproduced with permission from API RP2 SIM (2014). © American
Petroleum Institute, 2014.)
of trusses with some members being redundant, depending
on the structural configuration and bracing. In the simplest
of the terms, ultimate strength results (nonlinear analysis)
are generally presented in the form of a reserve strength
ratio (RSR) that is the ratio of lateral load at collapse to the
prescribed reference load. This is compared to the acceptance
criteria for the given operating area. If the RSR is greater
than the acceptance criteria, the jacket structure is generally
considered FFP.
For topside structures, structural elements are generally
assessed on a component level (e.g., members, columns,
joints, etc.). Assessments are generally in the form of linear
static analysis with adherence to acceptance criteria-outlined
design codes and standards. Topside defects should be
assessed on their importance levels, that is, whether they
form part of a (structural) safety critical element (SCE),
in such case remediation may require a more elaborate
SMR scheme development. Typical SCEs include, but are
not limited to, jacket structures, boat landings, helidecks,
primary steel, and fire and blast walls.
Figure 4 provides a simplistic overview of the assessment
process as it relates to determining the necessity of an SMR
scheme. If none of the identified outcomes are economi-
cally feasible in meeting the FFP goal, then ALARP may be
invoked to seek regulatory relief, as an alternative to decom-
missioning and abandonment.
Dier (2004) published the results of a joint industry
project (JIP) on the Assessment of Repair Techniques for
Ageing or Damage Structures. This study provides details
on prescribed SMR techniques, advantages of these options,
and the limitations in using each. This JIP forms the basis
for much of the SMR section of the API RP2 SIM work, and
much of the JIP is referenced in this article due to the compre-
hensiveness of the study. In this article reference is also made
to a host of well-known industry case studies on SMR to
reinforce the concepts and application of particular schemes.
2 REMEDIATION AND REPAIR
TECHNIQUES
2.1 Remediation and SMR
Having completed the evaluation of SIM data, the jacket
or the topsides, the full extent of remediation will be only
determined after the assessment phase of the SIM process.
Initially the main action when considering the SMR options
is to determine whether a local SMR option is viable or if
there is need for a more detailed global SMR action required.
Local SMR options generally tend to be less costly and
less complex to install. Global SMR actions are generally
more costly and complex and may require more than SMR
DOI: 10.1002/9781118476406.emoe409
Also published in the Encyclopedia of Maritime and Offshore Engineering (print edition) ISBN: 978-1-118-47635-2

Remediation and Repair of Offshore Structures 3
Data
Assessment
Evaluation
Initiator
triggered
No
Yes
Strategy Program
Figure 3. The assessment process within SIM. (Reproduced with permission from API RP2 SIM (2014). © American Petroleum Institute,
2014.)
Input
data
Platform
analysis
Post-process and
code checks
Document
findings
Review findings,
is it worth refining
analysis/checks?
Possible outcome:
Specific inspection
Load reduction
Strengthen/repair
Change operating
procedures
Ok
Not
ok
Yes No
Figure 4. SMR (strengthening, modification, and repair) and the assessment process. (Reproduced with from Dier (2004). Mineral
Management Service/US Government.)
schemes for remediation. Dier (2004) proposed five basic
approaches to SMR work, short of total replacement of the
facility. These include the following:
1. Remove damage (e.g., grinding out of cracks or removal
of bent/bow members)
2. Reduce loadings
3. Local SMR (where no change in the load path of
the structure occurs when used an SMR scheme, e.g.,
employing a clamping mechanism around a joint or
member)
4. Global SMR by provision of new members. (A change
of system load path occurs, e.g., by the addition of a new
member)
5. Total SMR by tying into a new adjacent structure
Figure 5 provides the interrelationship of common defect
scenarios and appropriate SMR schemes that might be
employed. It should be noted that for various component
repair work, it might draw from both the intact structure
SMR and the damaged structure portion of the diagram. The
techniques outlined in Figure 5 will be discussed in more
detail in this section.
2.2 Selection of SMR techniques
When choosing an SMR scheme, it is advisable to review as
many options as possible even though one particular option
may seem to be the obvious choice. It is important to choose
the technique that provides the best scheme based on tech-
nical, operational, and economic considerations. Figure 6
lists all the relevant options of each SMR scheme. Later in
this section each of these will be discussed in more detail.
When making a final decision on the selection of an SMR
scheme, the following data should be considered as part of
the feasibility study to ensure that the SMR scheme chosen
represents the best solution:
DOI: 10.1002/9781118476406.emoe409

4 Offshore
Intact structure Damaged structure
Dented / bowed
member
Corrosion
Fatigue
crack
Non-fatigue
crack
Insufficient
fatigue life
Insufficient
static strength
Member removal
and/or
load reduction
Member removal
and/or
load reduction
Member removal
and/or
load reduction
Local SMR Local SMR Local SMR Local SMRLocal SMR
(2) Weld doubler
plate over dent
(3) Brace the
bowed member,
connect ends of
brace(s) by:
– welding
– clamping
(1) Grout member (1) Remedial
grinding, plus
(2), (3) or (4)
(2) Weld repair
(3) Nodal clamp or
grouted sleeve
(4) Weld doubler
plates
Global SMR
Provide alternate load paths by introducing new members, connect ends by:
– welding
– clamping
(1) Remedial
grinding, plus
(2) or (3)
(2) Nodal clamp or
grouted sleeve
(3) Weld doubler
plates
(1) Grout member
(2) Grouted sleeve
(3) Weld patch
plates
(1) Grout member
and/or joint
(3) Grouted
sleeve
(2) Nodal clamp
(1) Improve weld
– toe grind
– hammer peen
(2) Reduce SCFs
– grout joint
– nodal clamp
Local SMR
Figure 5. Interrelationship between scenarios, SMR schemes, and SMR techniques. (Reproduced with from Dier (2004). Mineral
Management Service/US Government.)
• Technical performance
• Reliability
• Costs
• Depth limitations
• Offshore support requirements
• Existing applications
• Extent of background knowledge
• Timescales for design/fabrication/installation
• Tolerance acceptability
• Post-installation inspection requirements
• Potential problem areas
• Remaining life of installation
• Environmental and other legislative requirements
• Operator preferences
To obtain and make the best use of the data mentioned
above, it is therefore important to develop an SMR database
(methods, experts, and vendors) as part of a decision-making
tool. This type of data must be kept current and up to date by
SIEs and can also be provided with a cost estimation element
that will enable operators to do a proper cost/benefit analysis
prior to undertaking complex and costly SMR work.
2.2.1 Member removal
Member removal is considered as a valid repair technique.
Sometimes to avoid further damage or crack propagation
in a member, it may often be required. In some cases it is
often necessary to remove members to facilitate the instal-
lation of other SMR techniques, for example, underwater
clamping in congested areas. Member removal must have
some basis in logic and engineering as to which member is
selected without compromising the overall integrity of the
system. In many cases full reinstatement of other members
at different locations may be required after the clamps have
been installed. It may also be necessary to remove nonfunc-
tional appurtenances such as spare conductors as a means to
reduce hydrodynamic loadings and to diminish draining of
existing cathodic protection system. The UEG (Underwater
Engineering Group) publication (Thurley and Hollobone,
1981) provides guidance on cutting techniques and cutting
tools that may be used in member removal. Table 1 provides a
brief summary of the various cutting methods, while Figure 7
shows a diamond cutting saw being used in the removal of a
member of a subsea casing stub in the Gulf of Mexico.
DOI: 10.1002/9781118476406.emoe409

Strengthening/modification/repair techniques
Welding
Dry welding
Wet welding
Other welding
– Stitch
– Stud
(Friction,
drawn arc)
– Explosive
– Laser
(1) Atmospheric
– Above water
– Cofferdam
– Chamber
(2) Hyperbaric
– Habitat
– Shroud
Weld
improvement
Weld toe
removal
– Grinding
– Abrasive
Water jet
Remedial
grinding
Peening
Dressing
– Unstressed
– Stressed
– Unstressed
– Stressed
– Full
– Partial
– Annuli
– By fluid
pressure
Explosives
– By
– GTA (TIG)
– Plama Arc
Post weld heat
treatment
Mechanical
clamp
Grouted clamp
or sleeve
Neoprene
clamp
Members
Joints
– Hammer
– Needle
– Shot
– Ultrasonic
Clamp
technology
Grout filling
Bolted
connections
Member
removal
Diamond wire
cutting
Swaging
Mechanical
connectors
Adhesives Cold forming Composites
Figure 6. Overview of commonly used SMR techniques. (Reproduced with permission from API RP2 SIM (2014). © American Petroleum
Institute, 2014.)
Figure 7. Deployment of diamond cutting saw for member cutting and removal. (Reproduced with from Dier (2004). Mineral Management
Service/US Government.)
2.2.2 Welding
One of the best SMR techniques that can be used is welding.
The key challenge is when the welding process migrates
to underwater, and there are difficulties in replicating the
suitable environment to maintain good quality welding with
the right performance. For SMR, there are three major types
of welding techniques that are generally used. They are the
following:
• Dry Welding at One Atmosphere. This is generally used
topside and around the splash zone areas and includes
the use of a cofferdam (Figure 8) or pressure-resistant
chamber to maintain a similar environment as
DOI: 10.1002/9781118476406.emoe409

6 Offshore
Table 1. Summary of methods for making underwater cuts.
Method Type Cutting Technique Steel Thickness Range (mm) Water Depth Limit Comment
Mechanical Cutter 2–60 Used for weld preparation
Wire saw Closing of crack due to platform
movement can be troublesome
Abrasive water jet 2–230 Safety hazard
Diamond wire
Thermal Oxy-acetylene 10–40 6 m Decomposes under pressure
Oxy-hydrogen 10–40 1500 m
Oxy-arc 10–40 Electric shock hazard
Thermic and ultra-thermic lance Used to cut grout-filled members
Plasma arc
Pyronol Custom made “firework” operating
on thermic reaction
Explosives Primer cord 2–6 May be wrapped around thin
tubular sections and used as a
cutter without main charge
Shaped charges 20–120 >7 Tailor-made charges in a soft metal
casing with “V” notch
Eletro-chemical Spark corrosion
Assisted grinding
Reproduced with permission from Dier (1996). © Society of Petroleum Engineers, 1996.
Figure 8. Cofferdam in position and welder working within cofferdam. (Reproduced with permission from Harris (1986). © Springer,
1986.)
atmospheric. All normal welding processes can be used
including gas metal arc welding (GMAW), shielded
metal arc welding (SMAW), flux-cored arc welding
(FCAW).
• Dry Welding Using Hyperbaric Chambers. The chamber
is typically open to the sea at its base, allowing diver
access and capturing a bubble of compressed gas at
ambient pressure. The main process are GMAW and
SMAW although other processes may also be used.
Gas composition in the chamber must be controlled
to limit the partial pressure of oxygen, nitrogen, and
hydrogen. Dry welding in chambers/cofferdams is gener-
ally restricted to depths up to 50 ft (15 m). Deeper repairs
are technically feasible but become much more costly
due to the need for saturation diving. Robotic welding
has been used to splice deepwater pipelines, but its use
on structures is discouraged by geometric complexity.
• Wet Welding. For practical purposes only the SMAW
process is suitable (Figure 9). In this process, the arc is
operated in direct contact with the water. It has the advan-
tage of not having to use a cofferdam or chamber. It has
the disadvantage of possibly creating a poorer quality
DOI: 10.1002/9781118476406.emoe409

Figure 9. Wet welding. (Reproduced with from Dier (2004).
Mineral Management Service/US Government.)
weld, even with special electrodes and qualified diver
welders. Wet welding is depth sensitive, and it is chal-
lenging to maintain desirable metallurgical properties in
the presence of rapid cooling of oxygen and hydrogen
from the wet environment. Repairs with low-restraint
fillet welds are most likely to be successful.
Reference should be made to AWS D3.6M that provides
guidance on the all welding techniques for both dry and wet
welding.
Figure 8 shows the welding for a jacket brace repair to
a shallow water platform on the Dutch continental shelf of
the North Sea, using a cofferdam. The extent of damage
to an underwater brace from vessel impact required the
replacement of the entire brace member. The SMR work
was performed within 8 days inclusive of cofferdam deploy-
ment, repair, and cofferdam retrieval. The repair was not
affected by adverse weather, and a good quality weld was
also achieved.
2.2.3 Weld improvement
The main purpose of employing a weld improvement tech-
nique is to improve fatigue life and provide no assistance in
the improvement in static strength. Fatigue lives are gener-
ally improved by the removal of the welding imperfection,
local improvement of the weld profile, and introduction
of compressive residual stresses in the surface layer, thus
replacing tensile residual stresses and changing the orienta-
tion and the shape of the welding and other defects. The two
most popular types of weld improvement techniques used are
toe grinding and peening.
Toe Grinding. This is the purposeful removal of weld and
parent material from the toes of the welded connection. The
operation is generally undertaken by a grinding tool. The
major techniques for grinding include disc grinding (use
with caution) and rotary blur grinding (preferred). The main
purpose is to introduce a circular groove into the weld profile
and parent material, thus reducing the stress concentrations
that lead to poor fatigue lives. The cut dimensions X and Y
(Figure 10) must be limited to ensure that the removal of
any parent material is limited. If toe grinding is employed,
it is advisable that after the process, NDE (nondestructive
examination) methods of the completed weld be undertaken
to ensure that defects have been appropriately removed.
Shot, Needle Hammer, and Ultrasonic Peening. A cold
work process in which the surface layer is plastically
deformed. This is possible through a high velocity shot
(shot peening) or by using a tool (needle, hammer, or
ultrasonic peening). A plastic zone is created under impact
from each shot or tool strike, with the material outside
this zone being elastically deformed in compression. As
the process continues the adjacent material will impose
further compressive stresses within the plastically deformed
zone. Finally the whole surface layer will contain compres-
sive residual stresses. The compressive residual stresses
contribute to lower fatigue. Also during peening, work
hardening occurs in the plastically deformed zone. The
work hardening increases the yield strength, thus also
contributing to improved fatigue lives. Peening techniques
should be subjected to strict quality control measures,
and improved fatigue lives are generally dependent on
the care and attention that is placed on the peening
process. Shot peening is generally not used underwater
as water slows the shot down and the technique becomes
ineffective.
From an inspection of a mobile exploration and drilling
platform in 1992 (Figure 11), it was found that there were
fatigue cracks at the pontoon. The crack was found near a
gusset plate at the corner of a pontoon column. To rectify the
defect, toe grinding was performed to remove the toe weld
defects, using a high speed blur grinder. A successful repair
scheme requires approximately 1 month to execute. AWS
D3.6M (1999) and ISO 19902 (2007) also provides good
guidance on weld improvement techniques and the benefits
of each technique.
2.2.4 Clamp technology
Clamping techniques have proven to be a very versatile SMR
technique. In many cases clamps can be used for member
clamping (damaged or member with insufficient strength),
nodal clamping (damaged or joint with insufficient strength),
connecting a new structure to an existing one, providing
DOI: 10.1002/9781118476406.emoe409

8 Offshore
Chord T
Root
Single sided
Brace
y
x
Toe of weld
But weld
Figure 10. Typical toe grinding application. (Reproduced with from Dier (2004). Mineral Management Service/US Government.)
(a) (b)
Figure 11. Weld repair using toe grinding. (a) Mobile exploration and drilling platform. (b) Column–pontoon corner. (Reproduced with
permission from ABS Consulting (2004). © ABS Consulting, 2004.)
a length adjustment to a new or existing member, and
providing a means to connect or support a new appurtenance
guide. At its simplest level clamping involves the bolting
of two plates connected by bolts. In many respects they
are similar but the essential differences in clamps involve
the load transfer capability of each, for example, existing
steel with clamp steel and grout or neoprene or whether the
interface is prestressed by clamp bolts. Great care must be
taken in the design of clamps. It is recommended prior to
design a metrology survey be done to ensure the dimensions
of the tubulars (members/joints) subjected to any ovaliza-
tion due to hydrostatic forces are taken into consideration.
The general terminology for clamp technology is provided
in Figure 12.
The main clamping mechanisms include the following:
• Stressed Mechanical (Friction) Clamps. The strength of a
mechanical connection is obtained from the steel-to-steel
friction that is developed by means of the external
studbolt loads that lead to compressive forces normal
to the tubular/clamp saddle interface. These clamps for
all purposes should be avoided if the repair is a perma-
nent solution or requires close monitoring to ensure that
the clamp maintains its prestress and functionality over
time.
• Unstressed Grouted Clamps/Sleeve Connections. An
unstressed grouted clamp or sleeve connection comprises
sleeves, which are placed around a tubular member or
DOI: 10.1002/9781118476406.emoe409

Cap plate
Curved saddle plate
Stiffener
Flange
Side plate
Split
Stiffener
Flange
(a) (b)
Studbolt (typ.)
Figure 12. Clamp terminology. (a) Continuous flange, (b) discontinuous flange. (Reproduced with from Dier (2004). Mineral Management
Service/US Government.)
Figure 13. Post-hurricane Lilli platform stabilization in the Gulf of Mexico. (Reproduced with permission from ABS Consulting (2004).
© ABS Consulting, 2004.)
joint with the annular space so created filled with grout.
The bond and interlock between the grout/steel interface
provides the means of load transfer between the tubular
member and the clamp. Unstressed grouted clamps and
connections offer a versatile means for strengthening or
repair of tubular joints and members since they require
less accurate offshore surveys than do the mechanical
clamps.
• Stressed Grouted Clamps. This form of clamp is a hybrid
between a stressed mechanical clamp and an unstressed
grouted clamp. The strength of a stressed grouted clamp
is obtained from a combination of “plain-pipe” bond and
grout/steel friction developed as a result of compressive
radial stresses at the grout/tubular member interface. This
is quite a popular and effective clamping mechanism. The
effects of compressive hoop stress in the base member
should be considered.
• Stressed Elastomer-Lined Clamps. Stressed
elastomer-lined clamps are very similar to stressed
mechanical clamps, except that an elastomer lining is
bonded to the inside faces of the clamp saddle plates, for
example, to accommodate irregularities in the existing
tube surface.
Figure 13 shows part of the damage to a drilling platform
located at 68 m depth in the Gulf of Mexico and the stress
grouted clamp attached with sleeves to new piles as part of
the SMR scheme. Post-hurricane inspection revealed that a
pile was exposed and severed about 6 m below the mudline.
The repair work involved the installation of stress grouted
clamps at the existing piles. The clamp was connected to
pile sleeves for new pile installation. Several repair options
were considered at the concept stage including guy wires to
piles and props attached to undamaged platform. Structural
DOI: 10.1002/9781118476406.emoe409

10 Offshore
assessments indicated that more than one template was
required in addition to severed leg replacement to provide
sufficient torsional resistance against potential hurricane
wave loads. The final SMR scheme included two templates,
a stress grouted clamp and five piles. This case study has
been published on the BOEMRE (Bureau of Ocean Energy
Management, Regulation, and Enforcement) website (2011)
as part of an ABS Consulting publication (2004) on Hurri-
cane Lilli impacts on Fixed Platforms.
2.2.5 Grout filling
For local buckling of tubular sections and growth of dents
in damaged tubular sections, the process of grout filling
provides a good repair solution. In many cases grout filling
not only restores the damaged member to original perfor-
mance but also improves it. Grouting a member may also
be part of the preparatory process to another SMR scheme
such as clamping. A grout-filled joint is one where the chord
is filled with a cementitious grout material (Figure 14a). The
chord may be completely filled or, in the case of the piled
leg, the annulus between the tubulars is filled (Figure 14b),
double-skinned joint. Grout filling enhances the strength of
joints and tubular members as it reinforces the chord and
restricts local shell bending and section ovalization. Grouting
is a well-established technique used in the offshore industry
and is relatively easy to employ. It is highly effective and rela-
tively cheap compared to other options. Great care should be
taken when employing grout filling to avoid the formation of
voids that may be formed in the joints or members. Addi-
tionally, when employing a grouting SMR, one must also
consider what this means to the overall global response of the
structure. Grout filling might introduce new stiffer sections
that attract loads to unstiffened sections in the vicinity. ISO
19902 (2007) provides good guidance on the performance of
grout-filled joints and sections.
2.2.6 Bolted connections
Bolted connections have been used extensively on topside
repair and modifications to existing structures (Figure 15).
While used as a modification technique in its own right,
it is also a key component in clamping systems. Bolting
is a proven system with key advantages including quick
application, no delay time being required to achieve full
strength, easy to fabricate, and readily available key compo-
nents. Design is available in existing codes and standards and
provides great flexibility in it use, including easy removal.
There are in fact some limitations in using bolting systems
in the splash zone area and underwater. Due to the high
corrosion environment offshore, it is often required to seek
specialist advice when designing bolts for the splash zone
repair techniques or use in underwater schemes. Dier (2004)
noted that most popular materials for bolting in subsea
work are L7 and B7 (11∕4% chromium–molybdenum steels)
and have proved themselves with a substantial track record.
Macalloy bar was formerly specified in clamp applications
but has fallen out of favor following a number of hydrogen
embrittlement failures.
2.2.7 Adhesives
There are a number of structural resins that are used in SMR
work including acrylic, cyanoacrylic, and urethane products,
with epoxy resins being the most commonly used as they
cure in the wet. The use of adhesives has had considerable
success in the aerospace industry, but their use in the offshore
industry has already been treated with caution. The main
source of suspicion is that the design of adhesives is not
included in codes and standards so its applicability often
requires additional research or working together with the
manufacturers to better understand their performance. Bond
strength can be adversely affected by contaminants (e.g.,
flash oxidation) and by variable thickness due to a poor fit.
Adhesives potentially offer a series of advantages, including
their use to joint different types of materials, their application
in areas where there is limited access, and their properties
largely independent of depth. When selecting a resin the
following are generally considered:
• Curing period.
• Preparation requirements for the substrates.
• Quality assurance to ensure that the required bond has
been achieved.
• Inspectability of joint during service.
• Ability to remove the joint if the scheme proves to be
inadequate.
• For topside applications consideration should be given to
heat and fire resistance.
2.2.8 Cold forming
Using mechanical connectors and swaging techniques in
SMR work relies on cold forming the steel tubulars. Though
not generally popular as SMR schemes, mechanical connec-
tors and swaging can provide many advantages, in particular
repair/strengthening situations. Mechanical connectors
involve the use of grab, twist, and/or gripping devices
to achieve the mechanical locking of two steel tubulars.
Swaging involves forming a structural connection by the
hydraulic expansion of a steel liner to create an interface
lock joint with another tubular.
Caisson repairs have been performed on many North
Sea platforms due to perforations resulting from internal
DOI: 10.1002/9781118476406.emoe409

Brace
Grout Chord
Pile Leg
Brace
Grouted annulus
(a) (b)
Figure 14. (a) Grout-filled joints and (b) double-skinned grout-filled joints. (Reproduced with permission from Dier (1996). © Society of
Petroleum Engineers, 1996.)
Figure 15. Typical bolting connections for modification work at topsides. (Reproduced with permission from Dier (1996). © Society of
Petroleum Engineers, 1996.)
and external corrosion/erosion and fatigue stress cracking.
External access to the damaged regions of caissons is often
restricted so an alternative solution is provided using the
swaging technique. A liner tube, lowered from the topside
to bridge the damaged section, is plastically deformed above
and below the defect area to form a connection between
the liner and existing caisson reinstating its structural
integrity. The solution provides a cheaper, diverless solution
to employing external clamps (Figure 16).
2.2.9 Composites
Generally composites are used in SMR as a mate-
rial of choice for the replacement of structural access
members including railings, stairways, and handrails. The
fiber-reinforced polymers (FRP) have become a popular
composite here. Composites are also used as a containment
formwork as in the case of repair work to corroded conduc-
tors. In some cases composites are used as a reinforcing
plate to bond existing steelwork, for example, strengthening
of beam and column flanges, the reinforcement of webs and
deck plating, and repairs to conductor and riser casings, cais-
sons tanks, and pipework. There are a variety of suppliers
available in the market on a variety of composites for various
areas of SMR work.
Figure 17 shows the application of the Syntho-Glass XP, a
high strength fiberglass composite wrap on a 32 inch heavily
corroded riser on a platform in the South China Sea. The
application took less than 36 h to complete compared to
member removal or replacement that can take a few days, and
costs were considerable less compared to member replace-
ment. In addition, member removal and replacement require
DOI: 10.1002/9781118476406.emoe409

12 Offshore
Corrosion
damage to
caisson
Liner connected to caisson
bridging the damaged area
Figure 16. Caisson repair using swaged connection in the North Sea. (Reproduced with permission from Oil States Industries (2011). ©
Oil States Industries, Inc.)
(a) (b)
Figure 17. Repair on a 32 inch riser using a composite. (a) Condition before repair, (b) pipe being coated with Syntho-Subsea LV and
Syntho-Glass XT. (Reproduced with permission from Neptune Research, Inc. © 2016.)
the use and mobilization of heavy equipment, which is
avoided here, through the use of this composite. Hand lay-up
of chopped fiberglass in an epoxy matrix has been used for
corrosion protection in the splash zone since the 1960s.
2.2.10 Summary of SMR methods
Dier (2004), through an extensive JIP study on the Assess-
ment of Repair Techniques for Ageing or Damage Structures,
catalogued each repair scheme and its applicability to various
defects. Table 2 summarizes the SMR technique as well as its
performance against known defects.
It must be noted that Table 2 provides reasonable guid-
ance to the SIE when selecting a preferred SMR scheme.
However, other criteria may have to be taken into considera-
tion as well including the availability of technical expertise,
vessels and equipment, fabrication yards, costs, and so on in
the region/area the SMR work is to be undertaken, prior to
making a final decision. Moreover, the SMR schemes, espe-
cially specialist work as clamp design, require using skilled
consultants in that area of work (Table 3). Additionally, the
JIP also provides a list of advantages and disadvantages
on proposed SMR schemes, and these are provided within
Table 4.
DOI: 10.1002/9781118476406.emoe409

Table 2. Applicability of SMR techniques.
Technique Defect
Fatigue crack Non-fatigue crack Dent Corrosion Inadequate static strength Inadequate fatigue strength
Member Joint High loads Fabr. fault
Dry welding Yesa Yes Yesc Yesc Yesa Yesa No Yes
Wet welding Nob
Yes Yesc
Yesc
Yesa
Yesa
No Yes
Toe grinding No No No No No No Yes No
Remedial grinding Yes Yesa
No No No No No No
Hammer peening No No No No No No Yes No
Stressed mechanical clamp Yes Yes No Yes Yes No Yes Yes
Unstressed grouted clamp Yes Yes Yes Yes Yes Yes Yes Yes
Stressed grouted clamp Yes Yes Yes Yes Yes Yes Yes Yes
Neoprene-lined clamp No Yes No Yes No No No No
Grout filling of members No No Yes Yes Yes Yesd Yesd No
Grout filling of joints No No Yes No Yes Yesd
Yesd
No
Bolting No Yes No No No No No No
Member removal Yese
Yese
Yese
Yese
No No Yese
Yese
Composites Yes Yes Yes Yes Yes Yes Yes Yes
a
Usually in conjunction with additional strengthening measures.
bExcept to apply weld beads in unstressed grouted connection/clamp repairs.
cTo apply patch plates.
dApplicability depends on type and sense of loading.
eIf member is redundant (otherwise replace it).
Yes, applicable; no, not applicable.
Reproduced with from Dier (2004). Mineral Management Service/US Government.
Table 3. Comparison of SMR techniques.
Technique Design Background Equipment
Needs
Offshore
Installation
Timescales
Onshore
Fabrication
Costs
Load Penalties
Static Strength Fatigue Strength Weight Wave Load
Dry welding Yes Yes Heavy Very slow High (for habitat) None None
Wet welding Yes Yes Moderate Quick None None None
Toe grinding N/A Yes Low Moderate None None None
Remedial grinding Yes Yes Low Moderate None None None
Hammer peening N/A Yes Low Quick None None None
Stressed mechanical clamps Yesa Yesa Moderate Quick High Moderate High
Unstressed grouted clamps Yesa Yesa Moderate Moderate Moderate Moderate Moderate
Stressed grouted clamps Yesa Yesa Moderate slow High Moderate High
Neoprene-lined clamps Yesa Yesa Moderate Moderate High Moderate High
Grout filling Yesa Yesa Low Quick Low High None
Bolting Yes Yes Low Moderate Low Low Low
Member removal N/A N/A Moderate Quick None None None
Composites Yesa Yesa Low Quick Moderate Low Low
aMSL has proprietary information.
Italic, bad; bold italic, poor; underline, ok; bold, good.
2.3 Inspection, maintenance, and monitoring
As with all SMR techniques, there must be rigorous
procedures in place to monitor the performance of these
schemes over time. Inspection techniques must be agreed
upon by the operator and certifying body (if required)
up front. Once installed/executed, the SMR needs to
be monitored as part of the SIMS process. This would
mean including the inspection/monitoring techniques
in the operator’s in-service inspection plans (ISIPs) as
part of their risk-based underwater inspection or other
routine inspections to assess the performance of the SMR
scheme. This performance can be used as lesson learnt
to understand the limitations of particular schemes and to
ensure that they are addressed when choosing future SMR
schemes.
DOI: 10.1002/9781118476406.emoe409

14 Offshore
Table 4. Advantages and disadvantages of SMR schemes.
Technique Advantages Disadvantages
Dry welding Universally accepted from a technical standpoint Hot work permit required. Below the waterline
requires the construction of either cofferdam
or hyperbaric habitat—both being time
consuming and expensive. The cofferdam, in
particular, will attract high wave loading
Wet welding Proven technique. Relatively quick method Not accepted in all parts of the world. Weld
properties not as good as dry welds, although
this can be accounted for in the design
Toe grinding Doubles fatigue life Only applicable for fatigue life extension
Remedial grinding Proven technique. Relatively quick method for
arresting fatigue cracks
Static strength needs to be assessed
Hammer peening Very effective method for increasing fatigue life Only applicable for fatigue life extension
Stressed mechanical clamp Proven technique. Immediate capacity realized
on tensioning studbolts. Can be used as an
end connection to introduce new members
into the structure
Poor tolerance acceptability precludes use
around nodal joints or over girth joints
between tubular cans. Welds and other
protuberances have to be ground flush or
otherwise accommodated in depressions
machined in saddle plate
Unstressed grouted clamp Proven technique. High tolerance acceptability.
Can be used as an end connection to introduce
new members into the structure
Clamps are relatively long unless they, and the
clamped member, are provided with weld
beads
Stressed grouted clamp Proven technique. High tolerance acceptability.
Clamps are relatively short. Can be used as an
into the structure
There is a requirement to allow the grout to cure
sufficiently before returning to tension the
studbolts
Neoprene-lined clamp Some tolerance acceptability. Can be used as an
into the structure
Friction coefficient is lower than generally
realized. Neoprene introduces flexibility,
thereby compromising its ability to take up
load if alternate load paths exist
Grout filling of member Proven technique. Relatively quick method Weight penalty, especially poor in seismic
regions. Complete grout filling may be
difficult to achieve
Grout filling of joints Proven technique. Relatively quick method.
Good for improving both static and fatigue
strengths
Weight penalty, especially poor in seismic
regions. Joints with expanded cans, or internal
ring stiffening, are more difficult to grout fill
Bolting Good for topsides SMR Limited use below water
Member removal Proven technique. Relatively quick method Safety issue if member springs when final
ligament severed
Composites Lightweight strengthening and repairs are
possible. No hot work
Longevity for underwater use is not yet proven
Nichols and Md Harif (2014) advocated using an online
monitoring (OLM) process to monitor the effectiveness of
an SMR scheme. Upon performing underwater inspections
on a platform, it was found that one member was severed
and partially detached from one of the jacket legs. Other
members were damaged above and below sea level, together
with impact damage at the joints. A total of five members
were found to be partially damaged. The repairs to the plat-
form would involve the installation of two new members
and the installation of three specially designed and fabricated
clamps to connect the new members and reenforce the weak-
ened joints (Figure 18). The clamps and members would
then be grouted with an ultra high performance cementitious
material to stabilize the structure. An OLM instrumenta-
tion system installed at deck level was used to continuously
monitor the structural response of the platform (e.g., natural
frequencies and mode shapes) before, during, and after the
repair process.
The observed changes in structural response provide
evidence of the improvement in the structural integrity of
the platform. Further confidence in the effectiveness of the
repairs can be gained by comparing the changes in structural
response with those predicted using finite element structural
analysis (FESA).
DOI: 10.1002/9781118476406.emoe409

Figure 18. Platform A strengthened joints and member computer model and as-built photo. (Reproduced with permission from Nichols
and Md Harif (2014). © Society of Petroleum Engineers, 2014.)
2.4 SMR data within SIM database
Due to the variety of options and varying levels of
complexity for the SMR for both topsides and substruc-
tures, Nichols et al. (2015) proposed the development of
an SMR database/toolkit with a cost estimation module,
which can be part of the operators SIM database. Global
case studies on SMR can reside within the SIM database,
making it easier to access them and aid the decision-making
process prior to selecting an SMR option, and the feasibility
of particular options based on accessibility and availability
of resources and competencies can be based on operating
region requirements.
3 RECOMMENDATIONS AND
CONCLUSIONS
The following are recommended when developing SMR
schemes or managing a fleet of aging structures that require
SMR work:
• SMR can be a very costly and complex undertaking,
especially for underwater repairs. It is critical to find out
initially whether SMR is required in the first place by
ensuring that a proper evaluation of the defect/damage
is performed or some form of assessment engineering is
also done to determine the extent of SMR.
• Once SMR has been decided upon, it is highly recom-
mended to consider the feasibility of more than one
option depending on operational, regional, resources, and
technical competency on designing and executing the
options.
• It is also recommended to develop a database of SMR
options from global and regional studies to aid the
decision-making process, prior to final scheme selection.
• Include inspection/monitoring techniques in operator’s
ISIPs to ensure that the performance of SMR schemes
over time. Modern technology such as OLM has proven
quite effective in monitoring the structural behavior and
performance of jacket structures in the implementation
of an SMR scheme.
ACKNOWLEDGEMENTS
The authors would like to thank the publishers of the EMOE
for their encouragement to present this article.
LIST OF ABBREVIATIONS
ALARP (human risk) as low as reasonably
practicable
API American Petroleum Institute
BOEMRE Bureau of Ocean Energy Management,
Regulation, and Enforcement
FCAW flux-cored arc welding
FFP fitness for purpose
FESA finite element structural analysis
FRP fiber-reinforced polymer
ISIP in-service and inspection plan
ISO International Standards Organization
JIP joint industry project
NDE nondestructive examination
RSR reserve strength ratio
SCE (structural) safety critical element
DOI: 10.1002/9781118476406.emoe409

16 Offshore
SIE structural integrity engineer
SIM structural integrity management
SIMS structural integrity management system
SMAW shielded metal arc welding
SMR strengthening, modification, and repair
OLM online monitoring
UEG Underwater Engineering Group
BIOGRAPHICAL SKETCHES
Nigel Wayne Nichols is a custodian of Structural Integrity at
PETRONAS Carigali Sdn Bhd (PCSB), with over 30 years of
experience in offshore engineering. He has a master’s degree
from Cranfield University. He started his career in 1982 with
Heerema Engineering responsible for structural design and
installation of lift facilities required for topside modules and
jacket structures (i.e., tandem lift 14,000 tonnes, Morecambe
Bay). He then joined Lloyd’s Register of Shipping in 1984
where he was responsible for the certification of offshore
jacket structures and development of class rules for strength
and fatigue. He continued his career in 1990 with the Depart-
ment of Energy responsible for managing a large portfolio
of offshore structural related projects for developing guid-
ance including the HSE background document for fatigue.
His last employment from 1997 to 2000 before joining PCSB
in 2001 was MSL Engineering Group where he was project
manager and principal for a number of advanced structural
engineering projects and JIP projects.
He is an internationally known technical authority in
fatigue/strength of structural components and integrity
assessments of existing facilities. Nigel is a serving/voting
member of the API SC2 Offshore Committee and Tech-
nical Panel Leader of the ISO 19902 fixed steel structures
WG3, being involved in the development of API standards
(in particular the new API RP2SIM code for managing
existing structures) and most recently participating in
the development of the new ISO 19901-9 SIMS, which
is now being embarked upon. He has been the author
and coauthor of over 20 technical papers related to the
structural integrity assessment of offshore jacket struc-
tures. Email: nigel_waynenichols@petronas.com.my Tele:
+60129308424 (m).
Dr Riaz Khan is a chartered engineer and a principal of
structural integrity at PCSB, with over 20 years of experi-
ence in the civil engineering discipline. He has particular
expertise in the structural integrity management of fixed
and floating offshore structures and has assumed respon-
sible positions on a variety of projects ranging from major
offshore and onshore field developments. He has devel-
oped particular expertise in the area of lifecycle integrity
management for energy related facilities. His experience
also includes conceptual field development studies, detailed
design, and analyses of both onshore and offshore structures
including fatigue, seismic, vessel impact, decommissioning,
and ultimate strength considerations in a variety of operating
regions including the Gulf of Mexico, North Sea, Latin
America, Asia, and the Far East. He also serves as a task
group leader and member of the OGP (ISO 19901-9) Code
Committee for the structural integrity management of fixed
offshore structures. Email: riaz.khan@petronas.com.my
Tele: +60132802162 (m).
GLOSSARY
Database Historical data is a cornerstone of
informed structural integrity
assurance and a suitable system for
referencing and archiving documents
relating to the SIMS process shall be
established and maintained.
Fitness for
purpose
Each offshore facility is maintained
safely for its designed purpose or an
alternative purpose.
Mitigation Mitigation is defined as modifications or
operational procedures that reduce the
consequence in the event of structural
failure or reduce the likelihood of
structural failure.
Monitoring Structural integrity monitoring is
considered to be the process whereby
response characteristics of a fixed
offshore jacket structure are measured
(either continuously or at regular
intervals) with a view to comparing
the measured characteristics with a
previously measured baseline or trend.
Risk assessment Risk assessment is the analytical process
that determines the types of adverse
events or conditions that might impact
the structural integrity, the likelihood
that those events or conditions will
lead to a loss of integrity, and the
nature and severity of the
consequences that might occur
following a failure.
Strengthening,
modification,
and repair
(SMR)
The technique of restoring an offshore
structure that has severe damage and
is borderline with regard to fitness for
purpose. SMR can involve grouting
members, replacing full sections and
repair to members, and/or
appurtenances.
DOI: 10.1002/9781118476406.emoe409

Structural
integrity
management
system (SIMS)
A continuous integrity process applied
throughout the design, operations,
maintenance, and decommissioning of
a platform to ensure a platform is
safely managed and is fit for its
individual purposes.
Structural risk The cornerstone to successful
implementation of SIM is the ability
to effectively manage the structural
risks associated with the platform
operations is the adoption of a
risk-based approach to managing the
structural integrity for existing
offshore structures. Within this
context, structural risk is defined as
the combination of the likelihood of
some event occurring during a time
period of interest and the
consequences (generally negative)
associated with the event. In
mathematical terms, risk can be
expressed as
Risk = Likelihood × Consequence
Structural safety
critical
elements
(SCEs)
These are structural members within the
platform that, if are severely damaged
or damage goes unmitigated, can lead
to a reduction in the performance of
the structure and may lead to eventual
collapse.
Ultimate strength
analysis
Also called a “pushover analysis,” is a
nonlinear measure of the reserve
strength ratio (RSR) of the jacket
structure. It is based on truss action
and system strength rather than
component strength.
REFERENCES
ABS Consulting (2004) Hurricanes Lili Impacts on Fixed Platform.
https://www.boem.gov/ (accessed June 2011).
API RP2 SIM (2014) Recommended Practice for the Structural
Integrity Management of Fixed Offshore Structures, 1st edn, Amer-
ican Petroleum Institute, Washington, DC.
AWS D3.6M (1999) Specification for Underwater Welding, Amer-
ican Welding Society, Miami, FL.
Dier, A.F. (1996) Background to New Design Manual for Plat-
form Strengthening, Modification and Repair. Paper OTC 8079
presented at the Offshore Technology Conference, Houston, May
1996.
Dier, A.F. (2004) Mineral Management Service (MMS). JIP on the
Assessment of Repair Techniques for Ageing or Damage Struc-
tures. MSL Engineering Ltd. DOC REF C357R001 Rev 1. Nov
2004.
Harris, G. (1986) The Use of Cofferdams for Welded Repair to
Offshore Structures, Comex Houlder Diving Ltd, Aberdeen.
ISO 19902 (2007) Fixed Steel Offshore Structures, 1st edn, British
Standards International, London.
Nichols, N.W. and Md Harif, H. (2014) Use of Platform Response
Measurements from On-Line Monitoring (OLM) System to verify
the Effectiveness of Structural Repairs & Managing On-going
Structural Integrity. OTC Asia Paper 24947-MS.
Nichols N.W., Khan, R., Ng, S.M., Lee, L.A., and PETRONAS Cari-
gali Sdn Bhd (2015) A Strengthening, Modification and Repair
(SMR) Toolkit for Structural Integrity Management of Ageing
Offshore Structures. SPE Conference, Bali 2015.
O’Connor, P.E., Bucknell, J.R., DeFrance, S.J., Westlake, H.S., and
Westlake, F.J. (2005) Structural Integrity Management (SIM) of
Offshore Facilities. Paper OTC 17545. Offshore Technological
Conference.
Oil States Industries (2011) Case Study: Hydra Lok Swaging System.
http://www.oilstates.com/fw/main/Hydra-LokCAE-Swaging-
Systems-227.html (accessed June 2011).
Thurley, L.S. and Hollobone, T.A. (1981) Handbook of Underwater
Tools. CIRIA/UEG UR18, CIRIA, London.
Westlake H, Puskar, F.J., O’Connor, P.E., and Bucknell, J.R. (2006)
The Role of Ultimate Strength Assessments in the Structural
Integrity Management (SIM) of Offshore Structures. OTC 18331.
FURTHER READING
API RP2A (2000) API Recommended Practice for the “Planning,
Designing and Constructing Fixed Offshore Platforms”, 21st edn,
American Petroleum Institute, Washington, DC.
Dier, A.F. (2003) Mineral Management Service (MMS). JIP on the
Definition and Reporting of Significant Damage for Offshore Plat-
forms. MSL Engineering Ltd. DOC REF CH161R001 Rev 1. Jan
2003.
Nichols, N.W., Petronas Carigali Sdn Bhd, and Goh, T.K. (2006)
Managing Structural Integrity for Aging Platform. Proceedings for
the Society of Petroleum Engineers (SPE), Adelaide, Australia.
Puskar, F., DeFranco, S., O’Connor, P., Bucknell, J., and Digre,
K. (2010) API RP 2SIM: Recommended Practice for Structural
Integrity Management. Proceedings of the Offshore Technological
Conference (OTC) 20675.
Society of Petroleum Engineers (1998) New Technologies in the
Reassessment, Strengthening and Repair of Offshore Steel Struc-
tures. Proceedings for the Society of Petroleum Engineers (SPE),
International Petroleum Conference and Exhibition in Mexico.
DOI: 10.1002/9781118476406.emoe409
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