NG50-PJ-UFR-TEC-RE-0001

NIGERIA - OML 130
AKPO Field Development Project
AKPO Project Document NG50-PJ-UFR-TEC-RE-0001
AKPO UMBILICALS ENGINEERING and
MANUFACTURING CLOSE-OUT REPORT
Rev.00 16/04/09 Page 1/75
This document is the property of TOTAL and shall not be disclosed to third parties or reproduced without permission of the COMPANY.
Akpo
Project
Remarks:
00 16/04/09 AKPO UMBILICALS ENGINEERING and
FMA YFR/DJO CVU
REV. DATE DESIGNATION Initiator Reviewed by Approved by
Document number revision
NG50-PJ-UFR-TEC-RE-0001 00

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TABLE OF CONTENTS
Added
Modified
1. INTRODUCTION.................................................................................................................... 4
1.1. ABBREVIATIONS..............................................................................................................4
1.2. REFERENCES...................................................................................................................5
1.3. UMBILICAL SYSTEM DESCRIPTION & MAIN INTERFACES....................................................6
1.4. UMBILICAL ANCILLARY EQUIPMENT................................................................................ 10
1.4.1. PULLING HEAD & HANG-OFF FLANGE................................................................ 11
1.4.2. BEND STIFFENER............................................................................................. 11
1.4.3. BUOYANCY MODULES ...................................................................................... 13
1.4.4. SUBSEA UMBILICAL TERMINATIONS and BEND RESTRICTORS............................ 14
1.5. MAIN QUANTITIES & REFERENCES ................................................................................. 15
1.5.1. PRODUCTION UMBILICAL LENGTHS.................................................................. 15
1.5.2. WATER INJECTION UMBILICAL LENGTHS .......................................................... 16
1.5.3. GAS INJECTION UMBILICAL LENGTH................................................................. 16
1.5.4. UMBILICALS IDENTIFICATION & MARKING........................................................ 17
2. DESIGN WORKS & CHARACTERISTICS............................................................................... 18
2.1. MAIN DESIGN WORKS.................................................................................................... 18
2.1.1. UFLEX MODEL & VALIDATION........................................................................... 19
2.2. PRODUCTION UMBILICAL CROSS-SECTION CHARACTERISTICS ........................................ 22
2.3. WATER INJECTION DYNAMIC UMBILICAL CROSS-SECTION CHARACTERISTICS.................. 23
2.4. GAS INJECTION DYNAMIC UMBILICAL CROSS-SECTION CHARACTERISTICS ...................... 24
2.5. WI INFIELD/SHORT INJECTION DYNAMIC UMBILICAL CROSS-SECTION CHARACTERISTICS 25
2.6. FATIGUE DAMAGE ASSESSMENT..................................................................................... 26
2.6.1. FATIGUE DESIGN METHODOLOGY .................................................................... 27
2.7. ACCUMULATED PLASTIC STRAIN (APS) ASSESSMENT....................................................... 32
2.7.1. APS CALCULATION METHODOLOGY .................................................................. 33
2.8. AKPO DESIGN QUALIFICATION PROGRAM....................................................................... 35
2.8.1. PROTOTYPE FLEX FATIGUE TEST...................................................................... 35
2.8.2. PROTOTYPE CRUSH (LATERAL LOAD) / TENSILE & TORQUE TEST ...................... 37
3. MAIN DESIGN ISSUES ........................................................................................................ 39
3.1. AKPO FATIGUE CURVE SELECTION ................................................................................. 39
3.2. AKPO PROTOTYPE FLEX FATIGUE TESTING PROTOCOL.................................................... 40
3.3. AKPO UMBILICAL ELECTRICAL CHARCTERISTICS (QUAD to QUAD CROSS-TALK)................ 41
4. FABRICATION PROCESS ..................................................................................................... 42
4.1. SUPER DUPLEX TUBING FABRICATION............................................................................ 42
4.2. ELECTRICAL CABLES (QUADS) FABRICATION .................................................................. 45
4.3. UMBILICALS LAY-UP ...................................................................................................... 46
4.4. UMBILICALS ARMOURING .............................................................................................. 47

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4.4. UMBILICALS EXTRUSION................................................................................................ 48
4.5. UMBILICALS CUT TO LENGTH & SUTs INTEGRATIONS ..................................................... 49
5. MAIN MANUFACTURING ISSUES........................................................................................ 52
5.1. METALLURGICAL INVESTIGATION on SUPER DUPLEX TUBING (G48 A PITTING CORROSION)
.................................................................................................................................... 52
5.1.1. BACKGROUND ................................................................................................. 52
5.1.2. METALLURGICAL INVESTIGATION..................................................................... 52
5.1.3. INVESTIGATION OUTCOMES ............................................................................ 57
5.1.4. LESSON LEARNT.............................................................................................. 57
5.2. MATERIAL INVESTIGATION (RESIN POTTING) further to AKPO FAT IR TESTING NCR......... 58
5.2.1. BACKGROUND, 17 November 2006 – AKPO Resin Potting Qualification Test.......... 58
5.2.2. BACKGROUND, Umbilicals FAT .......................................................................... 59
5.2.3. BACKGROUND, IR Values Table......................................................................... 60
5.2.4. MATERIAL INVESTIGATION .............................................................................. 61
5.2.5. WAY FORWARD ............................................................................................... 66
5.3. AKPO UMBILICAL BUOYANCY MODULES CRACKS ............................................................. 67
5.3.1. BACKGROUND, SCOPE OF SUPPLY .................................................................... 67
5.3.2. BACKGROUND, FABRICATION PROCESS ............................................................ 68
5.3.3. MANUFACTURING ISSUES (BUOYANCY MODULE CRACKS) .................................. 69
5.3.4. TESTING PROTOCOL & TEST RESULTS.............................................................. 69
5.3.5. ROOT CAUSE ANALYSIS ................................................................................... 71
5.3.6. CORRECTIVE ACTIONS, WAY FORWARD............................................................ 72
5.3.7. LESSON LEARNT.............................................................................................. 73
6. SUBCONTRACTING / COST ELEMENTS............................................................................... 74
7. KEY DATES .......................................................................................................................... 75

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1. INTRODUCTION
1.1. ABBREVIATIONS
APS: Accumulated Plastic Strain
BR: Bend Restrictor
BS: Bend Stiffener
Cameron: SPS Contractor
DHSV: Down hole Safety Valve
DSUT: Distribution Subsea Umbilical Termination
EFL: Electrical Flying Lead
GI: Gas Injection
FACT: Field Assembled Cable Termination
FEM: Finite Element Method
FPSO: Floating Production Storage Offloading (Unit)
HDU: Hydraulic Distribution Unit
HFL: Hydraulic Flying Lead
ISUT: Intermediate Subsea Umbilical Termination
MIT: Maximum Installation Tension
MBR: Minimum Bend Radius
Nexans: Umbilical Manufacturer
RSUT: Relay Subsea Umbilical Termination
Saipem SA: UFR Contractor
SCM: Subsea Control Module
SD: Super Duplex
SUTH: Short Umbilical Termination Head
SUT: Subsea Umbilical Termination
TDP: Touch Down Point
TUT: Topside Umbilical Termination
WI: Water Injection

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1.2. REFERENCES
AKPO umbilicals and equipment are designed, manufactured and tested in accordance with the latest
edition of the documents here in listed:
Project specifications:
“Umbilical design and manufacturing specification”, NG50-3-BE-UMB-PS-AB-000-253
“Umbilicals Installation specification”, NG50-7-OPE-PS-AB-000-006
”Meteocean specification, NG50-1-CO-MET-PS-AB-000-001
“Full scale fatigue testing for weld procedure qualification”, NG50-3-BE-PLR-PS-AB-000-216
“Umbilicals corrosion protection specification”, NG50-3-BE-COR-PS-AB-000-251
“Subsea Temperatures & Pressures”, NG50-7-BE-FAS-CN-000-002
“Subsea Control System Specification” (SUT, Foundations, etc..), NG50-2-BE-UMB-PS-AB-000-504
Company specifications:
“Welding of Super Duplex Stainless Steel Pipe work”, GS PVV 614
“External protection of offshore and equipment by painting”, GS COR 350
“Load-out, sea-fastening, transportation and installation of offshore structures/Load-out of submarine
cables, umbilicals and flexible pipes”, GS STR 401/GS PLR 407
General standards:
“Design and operation of subsea production system/Subsea Control Umbilicals (2002)”, ISO-13628-
1/ISO-13628-5
“DNV Dynamic Risers/DNV Submarine Pipeline Systems”, DNV OS-F101 (2000)/DNV OS-F201 (2001)
“Extruded dielectric insulated power cables of rated voltage from 1kV to 30kV”, IEC 60502

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1.3. UMBILICAL SYSTEM DESCRIPTION & MAIN INTERFACES
The AKPO Field is located offshore Nigeria, within OML 130, 200km south of Port Harcourt, in water depths
of 1250 to 1480 meters.
AKPO U-system includes 8 dynamic umbilicals, installed through dedicated I-tubes, several subsea infield
umbilicals which control production, WI & GI wells and manifolds through hydraulic and electrical flying
leads.
AKPO umbilicals provides the supply of electrical power and communication signal to SCMs, hydraulic
control lines to operate x-tree valves and DHSV, service lines (Relevant to production umbilicals only) to
prevent the hydrate formation, and chemical lines against corrosion, wax and emulsifiers.
AKPO umbilical network is designed to control 9 production manifolds, 44 subsea Xmas trees.
Phase 1st before first condensate concerns 1st 22 wells (11 Production, 9 WI and 2 GI), which are AKPO
UFR Contractor scope of installation, including associated hydraulic (51-off) and electrical (86-off) flying
leads plus 11 hydraulic bridge jumper and 50-off in-line flying leads.
Fig.: AKPO Field Layout

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The umbilicals ensure the link in between FPSO electro-hydraulic control system and the subsea production and
injection systems for the following functions:
Hydraulic power (LP, HP)
Electrical power and signal communication
Service, e.g. methanol injection
Chemical injection (Production umbilicals only)
The umbilicals are connected to the FPSO through a vertical I-tube. There are three (3) types of umbilical
depending on their location along each umbilical “daisy” chain:
Dynamic umbilical: From FPSO to the first drill centre having a Lazy wave configuration with a buoyancy
module section.
Static or infield umbilical: All sections laid on seabed in between 2 drill centres
Short umbilical: Umbilical static section laid on seabed and branching from a DSUT to control remote WI
wells.
For the umbilicals the battery limits are defined as follows:
Upper battery limit: Topside Umbilical Termination (TUT) on the FPSO
Lower battery limit: Subsea Umbilical Termination (SUT)
The umbilicals, including the pulling head and the bend stiffener assembly for the dynamic sections, are supplied
by Nexans (UFR Subcontractor) and the subsea umbilical terminations are provided by Cameron (SPS Contractor).

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Two (2) umbilicals are located on FPSO portside and six (6) other umbilicals are located on starboard side.
The pulling rig umbilical winch is used to perform the pull-in of the umbilicals. The winch wire is routed from the
top of the umbilical I-tube.
The bottom of the I-tube spool piece (Otherwise called BS Connector Female Part) is located at 6.5 meter under
water assuming a FPSO draft of 8.4m. I-Tube total length is 26360mm, including the spool piece (Nexans supply).
I-Tube vertical angle is 4° at bottom of I-tube.
Fig.: FPSO Side, Umbilicals I-Tubes

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Overall AKPO umbilical dynamic section includes the following lengths:
1 L0 = I-tube length (26m).
2 L1 = I-tube exit to 1st
Buoyancy Module length (Averagely 1405m)
3 L2 = Buoyancy Section (85m for production umbilicals; 62m for WI/GI umbilicals)
4 L3 = Last Buoyancy module to Fixed point (Averagely 170m for prod. Sections, 190m for WI/GI lengths)
In total AKPO umbilical dynamic catenary is approximately 1685m long.

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1.4. UMBILICAL ANCILLARY EQUIPMENT
Here below AKPO umbilical system overview detailing main ancillary equipment:
Fig.: AKPO Umbilical System Overview

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Specific functionality of each umbilical accessory is here below briefly summarized:
1.4.1. PULLING HEAD & HANG-OFF FLANGE
Pulling-Head is used to pull each dynamic umbilical section through its corresponding FPSO slot (I-Tube).
The pulling head has been designed to withstand installation loads without damage to the umbilical components
and to house the topside tubing autoclave connectors and 5m long electrical pigtails.
Fig.: Pulling Head.
The Hang-off flange is used to secure the umbilical to the top of I-tube.
The Hang-off flange is designed to withstand static and dynamic tensile loads associated with FPSO motions and
installation forces and to transfer the maximum tensile loads without damaging umbilical components.
1.4.2. BEND STIFFENER
Umbilical Bend Stiffeners provide a transition in bending stiffness from the umbilical to a rigid attachment.
Fig.: Bend Stiffener.

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They are in the form of a conical mass of polyurethane moulding device surrounding the umbilical, whose
properties and the envelope are designed for AKPO deep-water application.
AKPO dynamic Bend Stiffener (BS) is used to limit the bending stresses imposed on an umbilical when in service,
which are caused by environmental loads.
The BS top flange is located at the I-tube bottom, whereas BS insert (Otherwise called BS male connector) is
interfaced with a designed interference to the internal diameter of I-tube itself, thus providing the resistance to
bending loads:
Fig.: I-Tube Bend Stiffener Interface assembly.
Bend Stiffeners are installed to the I-tube bottom spool (Otherwise called BS Female connector) by means of a
diverless system, using a field proven latching dog arrangement.
There are two types of bend stiffeners: One type (The largest) Bend Stiffener for the dynamic production
umbilicals and the second type for the dynamic water and gas injection umbilicals.
Latching Dogs
Bend Stiffener
BS Insert
BS Spool

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1.4.3. BUOYANCY MODULES
Dynamic Umbilical buoyancy modules are required on the catenary of each dynamic section to provide a lazy wave
configuration, thus avoiding the risk of tubing compression in the umbilicals at the TDP.
Fig.: Buoyancy Modules.
Buoyancy Modules are designed to provide the required uplift to the dynamic sections.
Each module consists of a buoyancy element, split into 2 identical halves, and an integrated clamping system,
made by rubber segments acting as “Compressive springs”, thus allowing for variation in umbilical riser due to lay
and maintaining a constant load during service:
Two (2) types of buoyancy modules are supplied by Nexans, one type for the production dynamic umbilicals and
one type for the water and gas injection dynamic umbilicals.

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1.4.4. SUBSEA UMBILICAL TERMINATIONS and BEND RESTRICTORS
Subsea Umbilical Termination is an assembly which consists of the following items:
Interface flange c/w Bend Restrictor elements (e.g. a series of interlocking metal rings designed to limit the
radius at the umbilical), where welding to umbilical lines is performed and where resin potting ensures
adequate tensile characteristics at installation time.
Subsea termination assembly, where umbilical tubing distribution system is provided and umbilical quads
are terminated in ODI-FACT connectors.
Fig.: SUT Interface Flange c/w Bend Restrictors.
The steel bend restrictors are installed along the umbilical after the SUT to ensure preservation of the umbilical
Minimum Bend Radius (MBR).
The final bend restrictor assembly is an “S” shape. The locking radius of the bending restrictor is 7.5m.
The nominal length is 11,836m, whereas the maximum operating angle is 90 deg..
A Bend Restrictor (BR) element is composed of:
BR-Pipe, mounted on the umbilical, two (2) halves equipped with anode.
BR-Clamp, mounted on the neck of two assembled halves of the BR-Pipe, two halves equipped with anode.
In total 12off BR-elements (Pipe c/w clamp for each item) are installed on each umbilical end:
The assembled Production BR has a total weight of 1500 Kg in air and 1260 Kg in water; the assembled WI or GI
BR has a total weight of 1050 Kg in air and 890 Kg in water.

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1.5. MAIN QUANTITIES & REFERENCES
AKPO U-system comprises 8 dynamic umbilicals, 15 static umbilicals and one spare umbilical.
The lengths, which include a ± 0.3% length tolerance, are below listed.
1.5.1. PRODUCTION UMBILICAL LENGTHS
There are 4off Production Umbilicals daisy chains, each one of them controlling one production loop.
Dynamic umbilicals link the FPSO to the first production drill centres, while static umbilicals link the subsea
production drill centres together in conjunction with the flying leads subsea production system.
The production wells are in a cluster arrangement around the manifold. The umbilicals for each loop are
made of 2 or 3 segments: One (1) dynamic umbilical from the FPSO to the first manifold and one (1) or two
(2) infield umbilicals in between each manifold location. Each subsea end of these umbilicals includes a
subsea SUT.
Distribution from DSUT to the manifold HDU, and then from Manifold HDU to the wells are performed by
flying leads (Hydraulic HFLs and electrical EFLs). All production loops are designed to accommodate three
manifolds.

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1.5.2. WATER INJECTION UMBILICAL LENGTHS
There are 3off Water Injection umbilicals, each one of them controlling one water injection string (Except
WI10 umbilical which controls both WI10 and WI50 water injection strings). The water injection umbilicals
are in a semi daisy chain configuration. The umbilicals for each string are made of 3 to 6 segments: One (1)
dynamic umbilical, Two (2) infield umbilicals (Daisy chain) and 0 to 3 Short Umbilicals (Star network).
Distribution from the DSUT to the wells located in the vicinity of the DSUT is performed by flying leads
(HFLs and EFLs). Distribution to the remote wells is carried out using short umbilicals.
The short umbilicals are equipped with a SUTH (Short Umbilical Termination Head), otherwise called Cobra
Head, at the connection to the DSUT. The other end is equipped with a relay SUT (RSUT), which supplies
more than one remote well. Exception is made by short umbilical 76-US-W21A, which is provided with an
SUTH on both ends.
1.5.3. GAS INJECTION UMBILICAL LENGTH
Gas Injection umbilical (1off) controlling the single gas injection string. The umbilical includes only one (1)
dynamic/static section terminated with a DSUT for distribution. Distribution from the DSUT to the wells is
carried out by flying leads (HFLs and EFLs).

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1.5.4. UMBILICALS IDENTIFICATION & MARKING
The identification tags of AKPO umbilical lengths are detailed here below:

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2. DESIGN WORKS & CHARACTERISTICS
2.1. MAIN DESIGN WORKS
AKPO System U engineering activities has included following main steps:
UFR Contractor has performed all umbilicals route optimization and final length calculations including
extra lengths required to accommodate the laying corridor and in curves, the seabed undulation, the
SUTs elevation and the installation tolerances at umbilical initiation and abandonment.
This layout study has included all umbilical crossings, whereas the dynamic length comprising the
umbilical catenary from the hang off through the Touch down Point (TDP) until the first DSUT has been
defined by the dynamic analysis dept. of the umbilical manufacturer (Nexans).
Nexans has selected AKPO umbilical riser concept and configuration in terms of a lazy wave catenary on
the basis of their waste deep water experience with steel tube umbilicals:
a) A simple catenary would have featured significantly higher tension dynamics through the riser
configuration with the potential risk of compression at TDP.
b) Nexans in-house software simulation demonstrated the fatigue wear of bending stiffener would have
been much higher with the free-hanging catenary opposite to the proposed lazy wave configuration.
c) The umbilical tension level at the TDP has been lowered due to the “dumping” effect of the buoyancy
section, thus avoiding the need of auxiliary seabed clamp equipment.
d) Interference effects have been avoided using a proper umbilical I-Tube exit angle of 4 deg. opposite
to 13 deg. of the adjacent steel catenary risers.

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2.1.1. UFLEX MODEL & VALIDATION
Nexans has designed AKPO umbilicals to withstand the worst combination of expected loads during
service life.
In-house software called UFLEX has been applied to define each umbilical cross-sectional arrangement:

a) UFLEX uses the Finite Element Method (FEM) to calculate the stresses and strains in the various
umbilical elements due to the applied load cases, which are combination of tension, bending, torsion
and internal tube pressure.
b) UFLEX is able to simulate the effects of internal friction between the umbilical elements. The friction
factors, which are derived according to results from material testing, are incorporated in the FEM
analysis.
c) UFLEX outcomes are the so called “Umbilical Capacity Curve” which defines the umbilical load
envelope, in terms tension/curvature combinations with different utilization factors depending on
different load conditions (Installation versus Operation cases).

Fig.: AKPO PRODUCTION UMBILICAL CAPACITY CURVE

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The UFLEX model has been validated through extensive full-scale umbilical testing. Some of the tests are listed
here below (For more details, please refer to the OTC 17986 Article, presented by Nexans engineering department
during the 2006 Offshore technology conference):
Mechanical behaviour Measurements: For example, the graph of an umbilical under torsion versus the
resulting axial strain, for the case of free torsion (e.g. no displacement controlled), is firstly determined by
UFLEX analysis of a typical cross-sectional arrangement.
Then, following to first preliminary UFLEX outcomes, the mechanical behaviour is checked through
mechanical test to verify the good correlation between UFLEX and the physical trails, carried out in the
UFLEX calibration program onto sample of the typical cross-section:
Considering all mechanical parameters tested, such as in the Fig.2 torsion/axial strain coupling but also axial
and bending stiffness, the mean correlation, between tested and predicted data, was founded by Nexans in
the range (0.95 – 1.10) with a standard deviation in the range of (9-15)%, which is considered acceptable.

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Strain gauge measurements: Strain gauges were used by Nexans for calibration of UFLEX model,
mounting them at regular intervals along the helix path of one tube in the outer-cross section of a
testing “gauged” umbilical sample (See Fig.3 below). Testing sample was 15m long c/w 4m long bell-
mouth at one end (The bell-mouth was divided into 2 equal length sections with curvature radius 150m
and 20m respectively. The umbilical sample was tested by applying a constant tension at one end and a
varying bending angle at the other end.):
Good correlation has been founded in bending stress history, between UFLEX results and strain gauge
outputs:

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2.2. PRODUCTION UMBILICAL CROSS-SECTION CHARACTERISTICS
Here below the main characteristics of the production umbilical cross-sectional arrangement are listed:
High degree of torque balancing, by laying up helically outer layer bundle opposite to inner layer
elements.
Free flooding design, by puncturing HDPE outer sheath every 10m after umbilical extrusion.
5.5mm (Nominal) WT Yellow HDPE outer sheath c/w a black longitudinal stripe, thus monitoring the
presence of twist during spooling and installation operations.
7-off shaped filler elements in the second lay-up pass, thus to achieve a circular consolidated cross-
section arrangement protecting also electrical quads.
All strength members (Tubes) sheathed due to corrosion protection.
6-off 6mm2 (0.6 – 1)V screened electrical cables (Quads)
4-off sheathed steel ropes for ballast purposes.
Outer Diameter: 162 mm (Nominal)
Weight in air (Tube filled): 39.22 kg/m; Weight in water (Umbilical flooded & tubes filled): 20.11 kg/m
Maximum Installation Tension (MHT) (@ 150 bar, 100% usage in tubes): 756 kN
Minimum Bending Radius (MBR) (@ 150 bar, elastic limit, no tension): 6.43m
Maximum clamping force (Per track): 250 kN/m
Fig.: Production Umbilical Cross-Section.

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2.3. WATER INJECTION DYNAMIC UMBILICAL CROSS-SECTION CHARACTERISTICS
Here below the main characteristics of the water injection dynamic umbilical cross-sectional arrangement
are listed:
100% Torque balance balanced design, by means of 2 contra-helically applied armour layers in the lay-
up process.
Free flooding design, by puncturing HDPE outer sheath every 10m after umbilical extrusion.
3.5mm (Nominal) WT Yellow HDPE outer sheath c/w a 10mm wide black longitudinal stripe, thus
monitoring the presence of twist during spooling and installation operations.
2layers of 2x6mm galvanized flat armour wires, applied on a bedding of PP roving, which provides
corrosion resistance properties.
Tubes are sheathed for corrosion protection.
Outer Diameter: 84mm (Nominal)
Fig.: Water Injection Dynamic Umbilical Cross-Section.

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2.4. GAS INJECTION DYNAMIC UMBILICAL CROSS-SECTION CHARACTERISTICS
Here below the main characteristics of the gas injection dynamic umbilical cross-sectional arrangement are
listed:
Design very similar to WI dynamic cross-sectional arrangement, with the exception that 2-off electrical
cables are replaced by 2 hydraulic HP lines 12.7mm ID
Fig.: Gas Injection Dynamic Umbilical Cross-Section.

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2.5. WI INFIELD/SHORT INJECTION DYNAMIC UMBILICAL CROSS-SECTION CHARACTERISTICS
Here below the main characteristics of the gas injection dynamic umbilical cross-sectional arrangement are
listed:
2layers of 2x6mm galvanized flat armour wires, applied on a bedding of PP roving, which provides
corrosion resistance properties.
Outer cover is made by 2 layers of black/yellow PP roving, applied over the armouring and suitable to
ensure intrinsic free-flooding characteristics.
5-off 6mm2 (0.6 – 1)V unscreened electrical cables (Quads): Un-screening quad design is still able to
meet “Quad-to-quad cross-talk” requirements (e.g. -60dB or better @ 12 kHz) by optimizing the lay
length of the different quads, laid inside the WI cross section, e.g. avoiding odd number fractions
between the different lay lengths.
Fig.: WI Infield/Short Umbilical Cross-Section.

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2.6. FATIGUE DAMAGE ASSESSMENT
Here the main outcomes of the fatigue analysis, carried out in accordance with the methodology described
in the next paragraph:
Note 1: Sum Damage (D) is derived from Total Fatigue Life (Due to Swell & Wind) as follows:
Total (Fatigue Life): 2740 (1 Year, 34mm ID) -> Total (Fatigue Life): 2740/20 = 137 (20 Year, 34mm ID)
Sum Damage (D) (20 Year, 34mm ID) = 1/Total (Fatigue Life) (20 Year) = 1/137 = 0.0073

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2.6.1. FATIGUE DESIGN METHODOLOGY
Umbilicals are subject to tensile loads as well as variable amplitude loading from wave and current
actions. Fatigue is therefore a critical issue in the design of umbilical components.
Fatigue Damage methodology: Fatigue of AKPO umbilicals have been calculated using 1 hour simulations
and time domain analysis. All singular points have been studied: Bend Stiffener region is the most
critical. Both AKPO Wind Sea and swell sea conditions have been considered. The directional swell sea
scatter diagrams have been investigated using 44 sea-states, whereas Wind Sea is implemented using 1
sea-state only.
Fatigue Damage methodology: The standard linear engineering model, due to typical axial and bending
stresses in the SD tubes as consequence of dynamic umbilical motions, is as follows:
Fatigue Damage methodology: The above model is augmented by one additional term to account for the
friction stress, due to interaction between different tubes within cross-sectional arrangement:
Fatigue Damage methodology: The above model is representative for “Full-slip” conditions, that is when the
curvature variations (C) are large and the strength members (Tubes) slide relative to each other:
Where:
a and b are coefficients for tension (T) and bending (C) respectively
Sxxf is the friction stress amplitude, where ∆Sxxf = 2*Sxxf
It has to be noted that coefficients (a, b) including the friction stress are obtained from UFLEX analyses.

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Graphically the stress model appears as follows:
Fig.: NEXANS Friction Stress Model.
In the fatigue analyses, carried out using RIFLEX, the inputs are the environmental conditions (Sea-states scatter
diagram of swells, wind seas, and currents data) derived from Company Meteocean specification and the outputs
are the tension (T) and curvature (C) variations. The linear stress cycles are first obtained using the conventional
linear stress calculation method (using influential coefficients a, b, and p) and a conventional rain-flow of cycles:
The result from the rain-flow count is presented as histogram of stress cycles (Number of cycles and stress
range). Because these initial stress range values does not include friction, twice the friction stress amplitude value,
as per stress model graphic, is added, so the approach is very conservative since the double of friction effect is
considered, then finally the modified histogram is used to calculate the fatigue damage accounting friction.

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ON AKPO Nexans has estimated max. Friction stress range (Sxxf) by means UFLEX analysis of AKPO umbilical
cross-sectional arrangement, applying rotation of inner bundle versus other bundle as follows, thus simulating the
variation of contact forces between all cross-section elements:
a) 0 deg. (Inner bundle with respect of outer bundle):
b) 30 deg. (Inner bundle versus outer bundle) (Repeated for other angles, 60/90 deg.):
c) Further calculations have been added by rotation of each of larger (34mm ID) tubes within inner bundle in
order to explore all possible contact forces acting on these inner tubes by the compressing forces due to
outer bundle.

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To assess friction effects, the following parameters were taken into account:
16 friction coefficients combinations inputs to UFLEX (Sxxf) calculations (Average/upper bound values
from previous small-scale testing previously carried out in MARINTEK between all AKPO materials
interacting in the umbilical cross section, plus 21 load vs. deformation tests, performed on metals,
polymers, all materials used in cross-section designs. Refer to OTC 17986 for more details.)
Various relative orientations of inner and outer layers.
All elements (Quads, steel ropes, sheathed tubes, fillers) assessed by small-scale testing in terms of their
relative friction coefficients.
To select the friction stress in the fatigue analysis, the worst value found in the attached table here below
was selected (First conservatism): It has been multiplied by 2 (Further conservatism), as the attached
values are single amplitudes
For sake of clarity, worst (Maximum = 3.96 MPa) founded Sxxf value, multiplied by 2 (Further conservatism),
e.g. 7.92 MPa, has been used for the fatigue damage analysis.

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Fatigue Damage Methodology: Fatigue life has been calculated using “MINER-PALGREM” summation
method and applying DNV-RP-C203 SN curve for SD tubes:

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2.7. ACCUMULATED PLASTIC STRAIN (APS) ASSESSMENT
Here below the summary of each APS for each production umbilical type is given, in accordance with strain
history, typically shown in the paragraph below (CPY requirement < 12% Total APS):
Production Umbilical:
Water Injection (Dynamic & Infield) Umbilical:
Gas Injection Umbilical:

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2.7.1. APS CALCULATION METHODOLOGY
During the manufacture of deep water umbilicals, the strength members (Steel tubes) are subject to
curvatures of the manufacture bobbins, the umbilical helical radius, the intermediate chute radius and
transportation reel. All these curvatures induce elastic and plastic strain within the steel tubes, and then
Nexans has developed in-house software suitable to simulate all strain deformation history encountered by
each umbilical section through all manufacturing steps, calculating with accuracy the Accumulated Plastic
Strain (APS), e.g. “The sum of plastic strain increments, irrespective of sign and direction.”
Reference is made, for instance, to AKPO project document, “Stress Analysis Production Umbilical”, NG50-3-
212-REQ-RP-AB-19-1021 (Rev. 05), where APS calculation is conservatively carried out, accounting for 3 re-
welding (which of course increase the total APS, Load step 4/8 of the next table regarding 12.7mm ID
Tube) in addition to pressure testing of tube strings on fabrication reel. A possible re-spool of the tubes,
after extrusion process, is also included (Load step 10/13 of next table regarding 12.7mm ID Tube):
Tab.: APS for Tube 12.7mm ID Tubing (690 bar internal pressure)

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On sketch below an example of summary APS table is given (Relevant to 12.7mm ID and design pressure =
690 Bar), plastic strain values have been calculated using Nexans in-house developed software, where
several points (inner/outer surfaces of tube) are verified; this calculation is the sum of the highest values,
derived by the software.
Strain history is shown as it occurs during manufacturing process here below:
Fig.: Strain History (12.7mm ID and design pressure = 690 Bar).

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2.8. AKPO DESIGN QUALIFICATION PROGRAM
An extensive program of umbilical design qualification has been carried out prior to commencing AKPO umbilical
manufacturing.
2.8.1. PROTOTYPE FLEX FATIGUE TEST
Purpose: To verify that the production umbilical and BR arrangement are capable of withstanding the fatigue
loads during the service life, according to the testing program specified here below.
Production Umbilical prototype c/w BS bolted to the flex rig: Approx. 30m long subject to a fatigue testing
program composed of 2 consecutive batches of curvature and tension stress amplitudes equivalent to more
than 3 times the fatigue damage derived from analysis but no more than 50% of the 0.10 allowed for the
service life, such that actual and representative loads of the actual environmental forces and dynamic motions
are applied to the cross-sectional arrangement and BS equipment.
Fig.: AKPO Flex Fatigue Prototype.

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Flex fatigue (Production umbilical) Outcomes at the dissection (15 November 2006), when the prototype has
completed 55 days of test corresponding to more than 1.2 million of large (Extreme) and small (Fatigue) curvature
cycles:
The dissection results showed no indication of umbilical damage. This result was consistent with the
successful pressure test and electrical functional tests, performed accordingly to test procedures following
completion of flex test.
Conclusion: AKPO production umbilical, including bend stiffener, demonstrated as fit for service at the AKPO
field.
Fig.: Removal of umbilical prototype outer sheath
Fig.: Inspection of outer tape wrapping Fig.: Tubes from the critical section in mid of BS.

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2.8.2. PROTOTYPE CRUSH (LATERAL LOAD) / TENSILE & TORQUE TEST
Purpose: To verify that the umbilical cross-section can withstand lateral loads, from the Tensioner pads during
installation, equal to 250 kN/m/track, checking that required clamping force, either in dry and wet conditions,
are acceptable and do not impair any risk of umbilical slippage (Insufficient squeeze load) or the integrity of
any of the functional elements, e.g. the hydraulic tubes and cables within the umbilical.
Test procedure: tension the lateral load test rig as per testing schematic here below:
Fig.: Test Rig Schematic.
Test no. 11/12/13 and 14 are “Slip tests”. After squeezing to specified clamping force, the umbilical end was
pulled to a value equivalent to Maximum Installation Tension (MIT):
Tab.: Testing program for Production Prototype.

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Here the pictures of Tensioner and test rig arrangement are shown:
Fig.: Tensioner for lateral load test and rig arrangement.
Outcomes: Cross-sectional arrangement showed a crush capacity in excess of umbilical vendor max.
Recommended crush load, e.g. 250 kN/m/track.
At completion of lateral load test, umbilical prototype sample was subject to a tensile/torque test with the
following outcomes:
The elongation measurement resulted in an umbilical axial stiffness of 434MN which well corresponded to
the UFLEX calculated value of 446 MN.
The rotation measured during 4 tension cycles showed a rotation of approximately 10° to 18°, whereas the
theoretical rotation, given in the stress analysis, was around 22°. However, due to friction and big steel
parts included in the test rig set up, it was normal to see deviations like this for the rotation test and
calculations.
After test, dissection of the sample showed no umbilical deformation or damage to the umbilical component.

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3. MAIN DESIGN ISSUES
3.1. AKPO FATIGUE CURVE SELECTION
CPY Specification B1 curve (Free corrosion in seawater) was superseded given the fact this curve would have lead
to a Bend Stiffener size out of maximum operational limit for spooling on reel.
In addition, Nexans stipulated the B1 free corrosion curve (Orange curve in the Fig. below) is based on crack
growth and fracture mechanism rather than on data obtained from fatigue tests on umbilical super duplex tube
samples as the curve finally applied by the manufacturer, DNV-RP-C203 (Red curve in the Fig. below):
Fig.: S/N Curves comparison.

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3.2. AKPO PROTOTYPE FLEX FATIGUE TESTING PROTOCOL
The definition of an adequate testing protocol for the Umbilical prototype flex fatigue test. Below testing program
was opted with the objective of inducing a total damage really “representative and realistic” of the expected
fatigue loads as calculated in the dynamic analysis, e.g. applying 3 times the fatigue calculated damage given by
the Fatigue analysis:
Tab.: AKPO Production Umbilical Prototype Fatigue Testing Program.

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3.3. AKPO UMBILICAL ELECTRICAL CHARCTERISTICS (QUAD to QUAD CROSS-TALK)
The achievement of some key umbilical electrical characteristics in accordance SPS requirement in terms of SPS
electrical communication:
Focus was made to cross-talk parameter for the infield umbilicals where electrical cables (Quads) had not been
designed with screens as the original CPY umbilical spec. did not call for screening, being “The quad-to-quad
crosstalk” as the most important requirement related to the need for electrical screening.
Nexans sorted out the issue thanks to their experienced cable design skill based on selecting the most appropriate
lay length of the different quads, thus suitable to minimize the effective electro/magnetic coupling length in
between the neighboring quads.
Reference is made to Nexans internal Memo here below copied:

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4. FABRICATION PROCESS
4.1. SUPER DUPLEX TUBING FABRICATION
Seamless UNS 32750 (SAF 2507) SD tubes were produced by Sandvik Chomutov SCPT factory (CHZ), according to
the following sizes and length ranges:
OD WT Length Range
15.30mm ± 0.13mm 1.30mm ± 10% 30m in average
(33m max. length)
(33m max. length)
(33m max. length)
Following main technological processes were applied for the production of seamless lengths:
Melting and extrusion of base material, e.g. hollows preparation
Cold pilgering process, where tubes are cold-rolled to their requested dimensions (Ratio 1:7)
Heat treatment (1050 – 1120 deg.) through annealed solution, followed by a rapid fast quenching (Average
minimal 200 deg./min from 1000 to 500 deg.) To ensure a proper micro-structure and thereby the corrosion
and mechanical properties required by CPY specifications.
Prior to the commencement of the heat treatment process, the tolerance set on the key-annealing parameters was
verified to give adequate annealing conditions. The following main annealing parameters were measured and
recorded continuously during the complete heat treatment:
a) Temperature in all 5-off annealing zones.
b) Inlet and outlet temperature in cooling water and gas
c) Speed of the tubes throughout the annealing and cooling zones.
All SD lengths successfully passed through NDT examination (Sigma phase detection, ultrasonic testing for
dimensional controls (OD, WT)), mechanical tests (Tensile, Hardness Tests; Flaring and Flattening tests), Pitting
corrosion G48 A tests and Ferrite Content analysis, are released for delivery to umbilical vendor, then grouped in
batches per size and shipped to Norway via railway.

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On umbilical site prior to start the welding of umbilical tubes, POLYSOUDE GTAW orbital welding machine was set
up as far as the essential variables (Current I, Tension V and welding speed v) ensuring that, as required by CPY
general specification GS PVV 614, production welding parameters (A2) were within range defined by approved
WPS (Welding Procedure Specifications), derived from a specific program of welding qualification trials WPQR:
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All SD lengths were butt welded and spooled on production reel (Diameter: 2.3m), then run though sheathing
process prior to umbilical lay-up. Exception was made for largest 34mm ID tubes, which were firstly spooled
outside the welding shop onto a dedicated turntable and then loaded out to reel after extrusion process:
Fig.: AKPO Umbilical Tubing Production line

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Each and every weld were level 2 NDT examined by the use of a real time x-ray station prior to spooling onto
production reel/turntable.
In addition, following tests were performed during production welding:
a) 100% level 3 NDT check of all level 2 images
b) G48A test, one sample from each welding line per day
c) Ferrite content measurement
d) Micro-examination
Fig.: Tubes storage prior welding Fig.: Tube orbital welding
Hydro-test of all tubes (1.5 x DP) was performed prior to umbilical lay-up, in accordance with project specification
NG50-3-212-REQ-SP-AB-19-1102.
Fig.: Tubes spooling.

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4.2. ELECTRICAL CABLES (QUADS) FABRICATION
AKPO quads were fabricated at Rognan, Nexans factory located in the north of Norway, where all electrical
elements are produced.
Following are the main fabrication steps:
Conductor cores assembly, made by high conductivity circular plain copper wire strands to IEC 60228 class 2
Core insulation by means of medium density Polyethylene (MDPE)
Cores lay-up: SZ stranding of 4 conductors to form a diagonal star quad, e.g. composing an electrical circuit
equivalent to 4 symmetrically balanced capacitive elements, around PE centre filler, with 4 PE fillers in the
lay-up interstices. The assembly was filled with petroleum jelly in all interstices to prevent longitudinal
transport of water, and then it was wrapped with polyester tape.
Inner sheath: Black MDPE was applied over the laid-up conductors to provide a barrier against water ingress.
Armouring: Aramid Yarn was applied over the inner sheath to provide longitudinal strength.
Radial protection (Not applicable for unscreened quads): Two layers of galvanized steel tapes were applied
for radial protection, they also constituted screening layers.
Fig.: Quad cross-sectional arrangement.
Fig.: Quad assembly, S-Z stranding. Fig.: Quad reeling.

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4.3. UMBILICALS LAY-UP
All umbilical functional elements (SD tubes of proper sizes and required number, electrical cables and needed
fillers, etc.., all spooled on production reels) were assembled by means of a vertical lay-up machine:
A unique Nexans patented assembling system, whereby the components to be bundled together were
continuously rotated onto a turntable around the vertical axis of the umbilical product such that the elements were
incorporated in the form of continuous helixes.
Fig.: NEXANS Vertical Lay-up Machine.
To be noted that all strength members (Tubes) and functional elements (Quads) bobbins were turning in the
direction opposite to turntable, thus ensuring that those components were torque balanced within the cross-
sectional arrangement.
Fig.: Prod umbilical 1st pass/2nd
pass assembly through closing eye.

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4.4. UMBILICALS ARMOURING
Armouring was applicable to WI and GI umbilicals only: Laid-up bundles were made passing through armouring
machines where 2 layers of contra-helically galvanized flat steel wires were applied surrounding the laid-up
functional components of injection umbilicals. Armour layers provided mechanical strength, protection and ballast
for the umbilical bundle.
Fig.: Armouring Machine schematic.
The process was carefully monitored, by adjusting from a control room the armouring speed:
During AKPO umbilical fabrication, this speed was kept in between approximately 5.5 to 7.5 m/min, whereas max.
Allowable speed is 15 m/min, thus ensuring further application of bedding tapes occurred properly over
uninterrupted and uniform armour coverage:
Fig.: AKPO Armouring Machine.

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4.4. UMBILICALS EXTRUSION
Outer sheath was applied by means of an extruder, where following parameters were measured and recorded:
Extruder barrel/Head Temperatures
Melt temperature
Sheathing speed
Fig.: Umbilical outer sheath extruder
The insulation thickness was measured and the outside diameter was measured continuously at 4 positions 90°
apart and recorded continuously through a computerized system.
10mm wide longitudinal stripe was frequently inspected during trans-spooling activities for any evidence of twist in
the umbilicals.

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4.5. UMBILICALS CUT TO LENGTH & SUTs INTEGRATIONS
Following overall umbilical lengths were manufactured in continuity by Nexans for AKPO project:
31.766 meters of production umbilical (Including 4km of installation & service spare sections)
11851 meters of WI dynamic umbilical
5717 meters of GI umbilical
23607 meters of infield/short umbilical
Above extruded lengths were then transferred on the outside carousel HH524 near to the concrete key-side for
the further trans-spooling operation, where each umbilical section, as per AKPO field layout were cut to the
required length and loaded onto dedicated 9.2m diameter (or 10.6m diameter) reels:
Fig.: AKPO Turntable HH524 Fig.: NEXANS Umbilical reels key-side
Here below a schematic of the overall umbilical path from lay-up machine until termination works area, where
umbilical integration to SUTs (Cameron supply) was carried out:
Fig.: Termination Works Schematic.

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During trans-spooling operations, umbilical reels were put on “Reel-on condition”, e.g. 2-off reel flanges rest on
foundation cradles with spool-on rollers (Dolly bases), and 2 rollers each flange:
Fig.: Typical arrangement for umbilical section transpooling.
Finally umbilical integration to SUTs was carried out, being the assembly composed of the following main
activities:
Welding of umbilical tubes to SUT adapters
Moulding (Resin potting) of each termination housing (Interface flange to each SUT unit)
Electrical quads soldering to ODI/FACT (Field Assembly) connectors
Fig.: SUT resin potting. Fig.: Tubes welding to SUT adapters.

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Fig.: G41 DSUT lift.

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5. MAIN MANUFACTURING ISSUES
5.1. METALLURGICAL INVESTIGATION on SUPER DUPLEX TUBING (G48 A PITTING CORROSION)
5.1.1. BACKGROUND
In the course of AKPO umbilical qualification program, one (1) SANDVIK Super Duplex (SD) tube failed the
corrosion test (ASTM G48 Method A) with irregularities in the base material macrostructure.
The investigations were initiated solely between SANDVIK and NEXANS for almost three months after the
detection of the tube defect and the enquiry remained in this period at a basic step, stipulating the “Poor manual
tube cleaning” as the pre-supposed hypothesis rather than focusing on a deeper and fully exhaustive investigation
with the purpose of screening all potential causes.
The preliminary explanation, given by tubing manufacturer (SANDVIK), was that Chromium Carbides (CrC) might
have formed as a result of an improper cleaning after pilgering. It was envisaged that carbon from the oil diffused
into the material during final heat treatment and formed chromium carbides, which created a depletion of
chromium in the surrounding SD matrix.
UFR CPY considered that a systematic technical approach, fully exploring the nature of this non-conformity, should
have been adopted by UFR CTR with the objective of establishing, with the highest degree of accuracy, the types
of precipitates (CrC instead of sigma phase formations) found in the metal and origin of the pitting corrosion.
In this respect UFR CPY required a detailed metallurgical investigation capable of stipulating whether or not the
supposed phenomenon of carbides precipitates was effectively behind the reduction of the corrosion resistance of
the Super Duplex tube.
BUREAU VERITAS (BV) was called by Saipem SA (UFR CTR) to investigate on this preliminary explanation as an
independent Third Party Organisation.
Saipem SA provided a sample of the failed SD tube (GRADE SD UNS S32750), identified by N. 657459 / A.
5.1.2. METALLURGICAL INVESTIGATION
The scope of this investigation was split as follows:
Visual examination
Chemical analysis
Metallurgical examination
Glow Discharge Emission Spectrometry (GDAES)

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VISUAL EXAMINATION
Visual examinations on the tube sample showed, after longitudinal cutting, some strained areas on the Internal
Diameter (ID) surface:
CHEMISTRY ANALYSIS
BV performed a chemical analysis on tube N. 657459 / A:
Element UNS S32750 Measured Method
Carbon ≤ 0.030 0.016 ± 0.002 Infra Red Combustion (IRC)
Silicon ≤ 0.80 0.33 ± 0.01 Optical Emission Spectrometry (OES)
Manganese ≤ 1.0 0.39 ± 0.01 OES
Phosphorus ≤ 0.030 0.019 ± 0.002 OES
Sulphur ≤ 0.020 0.001 ± 0.0005 OES
Chromium 24.0 – 26.0 25.36 ± 0.25 IRC
Nickel 6.0 – 8.0 6.39 ± 0.10 OES
Molybdenum 2.50 – 3.50 3.25 ± 0.05 OES
Nitrogen 0.24 – 0.32 0.29 ± 0.01 Reducing Melting Thermal Conductivity (RMTC)
Samples were taken at mid-thickness so the results confirmed only that base (Bulk) material chemistry of the tube
under investigation was within the requirements of UNS S32750.

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MICROSTRUCTURAL EXAMINATION
Examination of the material in the “As received” State:
BV performed metallurgical examinations by Scanning Electron Microscopy (SEM) on different sections
polished and electrolytically etched with a 40% NAOH solution.
The following outcomes were given:
a) The microstructure of the Super Duplex is composed of a balanced mixture of Ferrite (Dark) and
Austenite (White). However, near the ID surface of the tube the Austenite phase (White) was observed
in somehow larger quantity:
b) Some precipitates were observed locally in the austenite (White) phase at austenite/ferrite grain
boundaries, near to the ID surface of the tube:

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c) The observed precipitates were small (i.e. far below the smallest image resolution corresponding to
5000x magnification) so a direct individual characterisation by X-ray Spectroscopy was not feasible to
detect the type of precipitates:
Examination of the material after deliberate greasing and heat-treating:
Some bearing grease was then deliberately spread on the ID surface of a SD tube sample, which then
was subject to annealing process (900°C for 30 min. then air cooling).
At the completion of the heat treatment, some metallurgical examinations were carried out by SEM
technique on the ID surface in question.
Again the sample surface was polished and etched with a 40% NAOH solution. Due to the change of
contrast and brightness, this time austenite appeared in dark, whereas ferrite in white.
The following main features were observed:
a) Near the surface of the sample, the microstructure was almost full austenitic (Dark section now)
b) Near the surface, a large concentration of fine precipitates was seen at grain boundaries

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GLOW DISCHARGE ATOMIC EMISSION SPECTROMETRY (GDAES)
This method of characterisation is based on Plasma Arc Analysis, where the metal surface is vaporised using an
electric arc and a flow of argon. The ions, released by the metal surface vapour, are captured by an analyzer
which is able to identify different chemical elements like Carbon and to determine their percentage in the SD
material on the basis of different thickness of HV photon rays:

Analyses were performed by using this method. The results are shown in the Fig. here below and can be
summarized as follows:
On the Outer Diameter (OD) of the tube and more generally in the bulk of the material (Mid thickness), the
measured carbon concentration was similar to the nominal carbon content of the SD material, e.g.
approximately 0.016%.
Near the ID of the sample, significant carbon enrichment was measured (Along 40µm from the surface).
This enrichment was in the order of 7 times (Approximately 0.13%) higher than the content of the bulk.

The carbon enrichment, measured by GDAES instrument, near and on the ID surface is coherent with both a
predominant austenitic structure (Being carbon an austenitic stabilizer) and the presence of CrC precipitates
(Being higher carbon content a promoter of carbides precipitation).

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5.1.3. INVESTIGATION OUTCOMES
In light of the results from the analyses performed on the SD tube, supplied by Saipem SA, the following main
conclusion could be drawn:
Direct measurements on the “As received” sample gave evidence of important carbon enrichment from the
Internal Diameter (ID) surface.
Micro-structural examinations of the “As received” sample confirmed the local presence of carbides
precipitates near the ID surface, which is consistent with a material surface greased and heat treated
(Annealing).

5.1.4. LESSON LEARNT
To ensure with the support of a CPY inspection program that both SD qualification phase and SD tubing
fabrication are carried out in accordance with tube manufacturer common practice, e.g. only automatic
cleaning process is admitted whereas SD tubing manual cleanliness after pilgering and prior annealing is
forbidden.
To reiterate the importance of the SD cleaning process and quality control, either in the early phase of the
qualification program and throughout all umbilicals tubing manufacturing campaign, for example calling for
a specific quality audit, where all parties have to attend with the supervision of a certifying authority
(Example DNV).

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5.2. MATERIAL INVESTIGATION (RESIN POTTING) further to AKPO FAT IR TESTING NCR

5.2.1. BACKGROUND, 17 November 2006 – AKPO Resin Potting Qualification Test
A resin potting within a dummy subsea termination head was arranged on Friday morning (17th
November 2006)
under attendance of CPY representatives. Hardener and araldite were mixed and filled within termination housing
in accordance with the same filling procedure detailed below (2 batches waiting 12 hours for curing each. Max. 6
buckets (10+ 2kg) per batch) before being filled within termination chamber:
Thermocouple was set up for the purpose of measuring temperature variations versus time during curing period:
Max. Temperature reached during curing was 53/55 deg.:

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5.2.2. BACKGROUND, Umbilicals FAT
AKPO umbilicals FAT testing program included IR (Insulation Resistance) measurements to be carried out, Ref.
UFR project document NG50-3-212-REQ-SP-AB-19-1102 “Acceptance Test Specification – Umbilicals”, after
spooling and molding of termination housings but prior to assembly of the ODI connectors.
The acceptance criteria established the minimum (IR) value to be measured, when a DC voltage of 1000V is
applied between cores in each quad using a calibrated meg-ohmmeter, thus proving the integrity of the conductor
insulation material:
On week N.34 (August 2007), Nexans testing engineers performed (IR) measurements on the following umbilical
ends, after that resin potting in the respective termination housings was completed:
Umbilical 30-US-P43, end: DSUT 30-DS-P45, 6 quads (Q1, Q2, Q3, Q4, Q5, Q6) tested
Umbilical 30-UD-P41, end: DSUT 30-DS-P41, 6 quads (Q1, Q2, Q3, Q4, Q5, Q6) tested
Umbilical 30-UD-P31, end: DSUT 30-DS-P31, 6 quads (Q1, Q2, Q3, Q4, Q5, Q6) tested.
Several recorded values were below the minimum requirement (5 GΩ km @ 1000V DC), but these abnormal
values were circumscribed to following quads, as specified here below:
DSUT 30-DS-P45: 2 quads failed IR test (Q3, Q5)
DSUT 30-DS-P41: 3 quads failed IR test (Q1, Q3, Q5)
DSUT 30-DS-P31: 3 quads failed IR test (Q1, Q2, Q6)
Since the non conformance results were recorded (Week N.34), Nexans started an investigation, involving resin
supplier in conjunction with their own testing laboratory.

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5.2.3. BACKGROUND, IR Values Table
All production umbilical sections were spooled on their own reels. Then all reeled umbilical sections were (IR)
tested. Abnormal values were founded only at the 3 previously named termination ends (DSUT P45/P41/P31),
already subject to resin potting. Here below, IR table of umbilical 30-UD-P41 (DSUT 30-DS-P41) is copied:
30‐UD‐P41

Length:

3402m

Potted end:
30‐DS‐P41
Quad

Colour

Read [MΩ]
2 minutes
Corrected value
2 minutes
[GΩ * km]
BLUE 189 0.64
RED 232 0.79
GREEN 165 0.56
Q1
(Out of spec.)

WHITE 236 0.80
BLUE 10500 35.72
RED 9400 31.98
GREEN 10000 34.02
Q2

WHITE 10500 35.72
BLUE 69 0.23
RED 131 0.45
GREEN 61 0.21
Q3
(Out of spec.)

WHITE 89 0.30
BLUE 8400 28.58
RED 9700 33.00
GREEN 8800 29.94
Q4

WHITE 8900 30.28
BLUE 96.5 0.33
RED 126 0.43
GREEN 89 0.30
Q5
(Out of spec.)

WHITE 100 0.34
BLUE 11100 37.76
RED 12600 42.87
GREEN 12200 41.50
Q6

WHITE 12400 42.18

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5.2.4. MATERIAL INVESTIGATION
An external company came to site, performing some diagnostic tests: 50m electrical pigtails were jointed to
electrical ends thus it allows the location of IR faults be determined with accuracy:
All analyses showed IR anomalies are in the termination housing (T.H.) section only, where resin curing occurred.

Since week N.34/35 Nexans started their own in house analyses:
Lab. tests week N.34/35 (August 2007): They prepared 2 cans, whose volume was equivalent to the termination
Housing volume, where 3 electrical quads were inserted leaving ends free for IR measurements:
1st
can was filled with araldite/hardener used for old WI integration works (Where no IR abnormal values
occurred),
2nd
can was filled with last batch of araldite/hardener used for last prod SUT (P45/P41/P31, where IR values
were out of spec.).
Both cans were moulded using the same filling procedure described in the project procedure, as follows:
a) Mix 1st
batch of araldite (Product: RENCAST CW 2215: 10 Kg) with Hardener (Product: REN HY 5160: 2Kg);
Max. filling volume per batch (6 buckets: 10Kg + 2 Kg) to avoid high temperature during curing; Use
thermocouple to log temperature during curing, wait 12 hours allowing the resin to set.
b) Repeat same steps for 2nd
batch of araldite + hardener: Again max. Number of buckets is 6.
c) Finally resin top up in termination housing.
Temperature monitoring was performed: 2nd
can batch developed quicker reaction, reaching early max.
Temperature. Value recorded by thermocouple, for both cans, were the followings:
a) 1st
Can: Max. Temperature around 99 deg.
b) 2nd
Can: Max. Temperature around 120 deg.
To be noted that qualification test, carried out last year (Nov. 2006), resulted in an exothermic reaction with
temperature well below recorded values, e.g. 55 deg, See “BACKGROUND 17 November 2006 AKPO Resin
Potting Qualification Test”. However, the evidence of a temperature, developed by 1st
can where
araldite/hardener were supposed as per the normal composition, higher than value of qualification questioned
weather or not the qualification trial was performed under the same operating conditions, which were
reproduced during these lab. Tests.

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Tests week N.36 (September 2009): On Tuesday afternoon (04/09/’07), Termination Housing was cut-off from
umbilical section 30-UD-P31. Then IR measurements were taken from umbilical end. Results were in accordance
with specification (Min. 5GOhm.km @ 1000V DC), confirming the previous third party trail, e.g. insulation quads
damage is locally circumscribed to (T.H.), where resin was poured:
30‐UD‐P31

Length: 4239m

Potted end: 30‐DS‐P31

Quad

Colour

Recorded values [GΩ * km]
Acceptance criteria: Min. 5 GΩ * km
BLUE 12.2
RED 11.4
GREEN 11.1
Q1

WHITE 10.3
BLUE 12.8
RED 10.2
GREEN 10.1
Q2

WHITE 9.4
BLUE 11.7
RED 10.8
GREEN 11.7
Q3

WHITE 11.3
BLUE 10.4
RED 10.1
GREEN 10.2
Q4

WHITE 15.8
BLUE 14.0
RED 14.5
GREEN 15.0
Q5

WHITE 14.3
BLUE 12.6
RED 11.2
GREEN 11.3
Q6

WHITE 12.3

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On Friday (05/09/’07), NXS completed the break of the resin and then the dissection of umbilical section (DSUT
P31), which was within resin compound in the termination housing of P31, 3 quads (Q1, Q2 and Q6), which failed
IR values, were founded with their 4 cores insulation sheaths (Identified by colours red/blue green/white)
"melted" each other and to the cables’ internal fillers:
Fig.: Production Umbilical cross-sectional view, Q1, Q2 and Q6 found melted.

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Conference call arranged by Nexans with supplier (Week 36, September 2007):
They recognized from available info, taken from week N.34/35 tests in NXS laboratory, that temperature rise in
curing was steeper than expected. All araldite batches, resulting in abnormal curing, were returned back to
supplier for chemical analyses with the purpose of assessing whether or not an undue change in resin chemical
composition occurred, thus affecting the speed of reaction.
Supplier proposed 2 mitigation measures for keeping the temperature during curing under control:
Storage of araldite/hardener in “cold” environment, thus reducing the temperature at the beginning of the
curing (13 deg. rather than typical 20 deg.)
Use a specific additive, suitable for limiting the temperature increase in the exothermic reaction (NXS has
provided the following name: DT082 Powder.
Tests week N.37:
Following week N.36 conference call, Nexans kept on preceding some laboratory tests, according to the corrective
measures proposed by the resin supplier:
They prepared 2 testing cans filled with araldite + hardener (New batch, supposed “unaffected” and normal
received from resin supplier) as per specified mixing ratio (10 Kg Araldite/2 Kg Hardener):
a) 1st
can filled with 2 tins of araldite/hardener (20Kg/4Kg) plus the addition of DT082 recommended powder.
b) 2nd
can filled with 2 tins of araldite/hardener (20Kg/4Kg) with no powder.
On both cases, araldite has been stored in "cold" environment before filling thus helping to reduce the
temperature at the start of curing (13 deg. rather than 20 deg.). Both curing period (12 hours) have been
monitored, giving the following outcomes:
a) 1st
Can (Powder): Max. Temperature around 71 deg.
b) 2nd
Can (No powder): Max. Temperature around 97 deg.
Once again the recorded values diverged significantly with the outcome of 2006 qualification test (See next
paragraph: Max. temperature 55 degrees), whose validity and conformance to the current operating conditions
could be challenged.

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A meeting was organized on 13th
of September 2007, involving all parties.
Here below listed are the main outcomes of the meeting:
Resin chemical composition analysis was not completed by that time the meeting was held: Saipem estimated
resin batch, which gave origin to abnormal potting (DSUT P45/P41/P31), was altered in some ingredients; No
clear and firm statement was made by resin supplier so far.
Both araldite and hardener, part of the defective batch, were put under investigation.
Hardener data sheet was found identical to that one used for AKPO qualification trial (Nov 2006), however the
chemical composition is not usually checked per batch by the resin supplier, being different batches part of a
large industrial production volume.
Outcome of NXS lab tests, carried out on weeks 34/35/36, seemed concurring to the hypothesis defective resin
batch had a different mix of chemical ingredients when compared to resin (Araldite + hardener) applied on
both AKPO and Ehra qualification programs:
a) Ehra project: Max. Temperature ~ 60 deg. with 8 buckets per each batch.
b) AKPO qualification (See attachment): Max. Temperature ~ 55 deg. with 8 buckets per each batch.
c) NXS lab. Tests (Week N.34): Max. Temperature ~ 120 deg. using 6 buckets per batch.
Following initial lab. Tests results (Max. Temp. During curing significantly higher than previous qualifications)
and further to conference call with resin supplier (Where corrective measure were proposed:
a) Storage in cold environment prior to potting, thus reducing temp. Level at the beginning of potting (13/15
deg. rather than 20/23 deg.)
b) Use of retardant powder (DT082), NEXANS focused on finding out a new mixing procedure, which will be
subject to a re-qualification program:
a) Araldite/Hardener ratio: 10/2 kg (Not varied)
b) Step by step filling (No more 8 or 6 buckets per batch):
- Production umbilical T.H.: 2 buckets max. Each time (Even 3 buckets are sufficient to induce a
high temperature during curing.)
- Short umbilical T.H.: 1 bucket each time
Note: Week N.37 lab tests have given these outcomes
a) 2 buckets of araldite/hardener with no DT082 powder and storage, prior potting, in cold ambient: Max.
Temp. Around 95 deg.
b) 2 buckets of araldite/hardener with no DT082 powder and storage, prior potting, in cold ambient: Max.
Temp. Around 70 deg.
AKPO Quads had been qualified to withstand until 120 deg. with no loss of functionality.

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Following Way forward to resume potting on AKPO termination works was agreed in between UFR CPY and
CTR:
a) Nexans to carry out mechanical tests (Tensile, tubing/resin adhesion, etc..) with the purpose of
characterize and qualify the resin with the revised mix procedure (2 buckets/cold environment/Use of
powder eventually if mech. Characteristics are still adequate)
b) Chemical analysis of resin batches by a third party.
c) (Preventive action during potting): Temperature recording for each T.H.
5.2.5. WAY FORWARD
SUT Termination works were resumed. Indeed a revised mixing (Araldite/Hardener) procedure was applied by
Nexans c/w the systematic use of thermocouple during each resin moulding operation.
However since September 2007 UFR CPY is waiting a summary/memo from UFR CTR/Nexans
detailing all pending features (Testing program carried out, Root cause analysis, new mixing
procedure) on this subject.

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5.3. AKPO UMBILICAL BUOYANCY MODULES CRACKS
5.3.1. BACKGROUND, SCOPE OF SUPPLY
The scope of supply for AKPO Umbilicals included the fabrication of buoyancy modules as per quantity here below
specified:
No. 272 BM halves of 800mm diameter c/w rubber clamp having following characteristics (Prod. Umbilicals):
Target weight of shell + macro-spheres: 51.2 Kg ± 1.5 Kg
Final cured weight: 106 Kg ± 4.2 Kg (4%); Final assembled weight: 112 Kg
Uplift in water: 89.9 Kg ± 3.6 Kg (4%); Operating depth: 1350 WD
No. 224 BM halves of 610mm diameter c/w rubber clamp having following characteristics (WI/GI Umbilicals):
Target weight of shell + macro-spheres: 27.32 Kg ± 0.75 Kg
Final cured weight: 55 Kg ± 2.2 Kg (4%); Final assembled weight: 59.3 Kg
Uplift in water: 43.8 Kg ± 1.2 Kg (4%); Operating depth: 1350 WD
All modules were manufactured by a subcontractor (Phoenix Ltd.) of the main U-system supplier (Nexans).

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5.3.2. BACKGROUND, FABRICATION PROCESS
The outer shells of the BMs (Buoyancy Modules) were manufactured by a sub-vendor using a rotational moulding
process using Poly-Ethylene base material procured by Phoenix Int. Ltd.
Phoenix fabrication process followed the following manufacturing steps:
Macro-spheres were produced by progressive coating of low density starter spheres, which are rotated in a
“Tumbler” where mixed epoxy resin and glass are added; a series of coatings, until the required wall
thickness, equivalent to the pressure resistance required for AKPO project (1350 m WD) is reached.
Fig.1: Micro-spheres were not included on AKPO Modules.
The procured BM PE shells were then filled with these coated macro-spheres and vibrated until the spheres
settled and the shells adequately full. Then the epoxy matrix was prepared to form the basic syntactic foam,
and further de-gassed under a vacuum to remove any trapped air, which could weaken the matrix
compound.
The syntactic foam was then poured into shell and then left in a warm location until fully cured, and finally
cooled slowly to prevent stress build-up in the module.
Each half, filled by epoxy matrix subject to curing process was finally weighted and examined and the fill
ports sealed. Each module as manufactured was then ready for shipment.

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5.3.3. MANUFACTURING ISSUES (BUOYANCY MODULE CRACKS)
On week 39/07 (End of September 2007), it was found that approximately 30 halves of both types developed
cracks along the Poly-Ethylene outer shells, while stored in an outside area at the umbilical vendors factory.
According to Phoenix production schedule, all Buoyancy Modules were completed EXW (Ex-works) during January
2007. Once shipped to Halden (Nexans factory) they remained stored in an outside area for all of 2007 until the
cracks were discovered.
Phoenix Lead engineer visited first Nexans factory during week 41/07. All damaged shells were segregated and
investigation of the cause of the problem commenced. A further survey by was also completed at Nexans plant on
Monday 12th
of November, during this survey further WI buoyancies were founded damaged with cracks on outer
shells.
Nexans/Saipem then rejected all supplied modules.
5.3.4. TESTING PROTOCOL & TEST RESULTS
Following testing program was implemented on samples of the cracked BMs.
Tests were carried out primarily on samples of “Damaged” shells. Visual inspections were then carried out further
c/w weight measurement to be compared with value before testing, checking water absorption in the interface
between PE openings and syntactic foam.
a) Clamping test: 2 Damaged halves were pulled face to face at a distance corresponding to the installation
condition using bolts tensioned until the installation gap (20mm nominal) between 2 halves is reached:
Modules were left under compression, in order to test residual fragility, if any, in the PE sheath material.
Acceptance criteria: To verify there was no crack development under installation condition.

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Clamping test Outcomes: Test was carried out on 08 November 2007. It was noted that cracks did not travel
further on tensioning 2 halves until installation gap was reached (20mm nominal):
b) Hyperbaric test: Damaged assembled buoy, 2 halves compressed with 20mm nominal gap, were immersed into
a hyperbaric chamber, where installation speed was simulated increasing pressure from 0 bars to design depth
(140 bars) in approximately 2 hours. Then modules were kept under hydrostatic pressure for few days, prior to
being taken off testing chamber.
Visual inspections were then carried out further c/w weight measurement to be compared with value before
testing, checking water absorption in the interface between PE openings and syntactic foam.
Acceptance criteria: To verify that foam of the damaged modules was still able to withstand design pressure with
no crush due to squeeze loads.
Hyperbaric Test Outcomes: WI/GI Type and Production Type modules were left for a few days, Thursday 22nd
to
Monday 26th
November 2006, in the hyperbaric chamber under the hydrostatic pressure.
Outcome of test resulted in a very high water absorption for injection modules (9/10 Kg), out of minimum
requirement (<2% weight increase at operating pressure).

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5.3.5. ROOT CAUSE ANALYSIS
During fabrication process, epoxy matrix was mixed up from its component materials and non-reactive hardener
was added, forming the pure syntactic mixture, which was then poured into BM shell (Shells previously
manufactured by rotational molding):
The syntactic foam flooded the remaining spaces between the macro-spheres, which filled before the shell;
Filled shell was then left in a furnace until fully cured.
Hardening process occurred by means of an endothermic reaction, where heat was provided by oven for activating
the reaction and then developed during the curing of syntactic foam. It was envisaged that temperature reached
during curing exceeds typical value of 70/75 deg. for some buoyancy elements (Phoenix was not able to provide
temperature logging and to detail how long they estimate hardening differed from usual temperature range. It has
to be noted that Phoenix oven was not equipped with a temperature monitoring system c/w alarm should the
temperature exceeded a typical trip level.), thus causing an abnormal expansion of foam against the inner wall of
shell. Then all cured assembly was likely not let cooling slowly, preventing stress build-up but hurriedly located
outside in a very cold environment (Wintry season in Aberdeen).
The consequent thermal shock might give origin to the fragility of modules, prior to further developments of large
cracks, once stored outside in Halden (Umbilical vendor factory).
In addition, Phoenix was not been able to determine whether or not PE shells, which were fabricated by a sub-
contractor to Phoenix ( e.g. 3rd
level of sub-contracting from EPCI-C contractor Saipem) and experienced these
cracks, were affected by important manufacturing defects, prior to foam filling, like trapped air and void formation
inside the PE sheath. As standard practice, Phoenix did perform visual inspection/dimensional inspection of shells.

NG50-PJ-UFR-TEC-RE-0001

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