A diver-assisted TIG welding system has been successfully employed for pipeline repair and tie-in in the North Sea for the last 20 years. Known as the ‘Pipeline Repair System’, it is operated in water depths down to 180msw. For the last ten years, research and development has been performed in the laboratory, investigating and establishing the capability of the Gas Metal Arc hyperbaric welding process for operation beyond water depths of 180msw (the diver-assisted limit) and down to 2,500msw for remote welding pipeline repair and hot tapping applications. Hyperbaric weld procedures have been qualified down to 1,000msw. After an extensive equipment design, development, build and test programme the Remote Welding System (RWS) has recently been tested offshore at 310 and 940msw. The Remote Welding System is based upon similar operating principles to the diver-assisted equipment spread: a Habitat, to be deployed around the pipe, to facilitate the creation of a suitably dry fully inert welding environment, and a recoverable Power and Control Module (known as the POCO) to dock onto the Habitat and deploy the remote welding equipment. The offshore test included full operational sequences of the anticipated pipeline repair scenario: deploying the Remote Welding Habitat (RWH) around the pipe; creating a dry welding environment; deploying the Remote Welding POCO (RWP) and Remote Welding Tool (RWT); entering the Habitat; pre-heating the pipe; multi-pass hyperbaric positional GMA welding and post-weld review; post-weld heating; recovering the Remote Welding Tool and POCO and re-deploying when necessary during the operation; and finally recovering the Remote Welding Habitat after completion of the welding sequence. In order to qualify the remote welding technology, with the approval of DNV GL, and demonstrate that the offshore equipment is fully capable of producing acceptable welds comparable with those qualified in the laboratory, the 310 and 940msw root and multi-pass welds were subject to Visual, NDT and basic mechanical property testing. The results represent the world’s first acceptable hyperbaric GMA offshore welding operation in the 1,000msw range facilitating the successful capability for pipeline repair applications beyond diver depths.

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Neil Woodward
Subsea Hyperbaric Welding Trials for
Pipeline Repair Applications
Neil Woodward B. Eng, PhD, FWeldI, C.Eng
njw@isotek.co.uk
Isotek & Oil Gas Ltd
www.isotek.co.uk
EuroJoin 9, 21st May 2015

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Neil Woodward
Content
1. Application
2. Technology Background
3. Repair Method
4. Remote Welding System
5. Subsea Hyperbaric Weld Results
6. Conclusions
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Neil Woodward
APPLICATION:
Pipe Damage to be repaired by
new pipe section (Spool Piece)
>180msw Diver Depth Limit
>30” Pipeline Diameter
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Neil Woodward
Hyperbaric Welding Qualification
performed in Pressure Chambers
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250bar & 400bar Hyperbaric
Welding Chambers
>10 Years Understanding Mechanical
Properties (CTOD, Sour Service
Corrosion etc.), Heating Level & Cooling
Rate, Humidity Levels, Hydrogen
Assisted Cracking, Consumables,
Parameters etc. Welding Parameters to
2,500msw, Qualification to 1,000msw

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Neil Woodward
Welded Sleeve: Joint Design
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 Spool side 1-Atm welded during onshore
fabrication
 Pipe inserted into sleeve subsea
 Pipe side dry hyperbaric weld subsea
 Tolerance to ovality and misalignment

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Remote Welding System
Main modules
 Remote Welding Habitat
 Remote Welding Power and Control (POCO)
 Remote Welding Tool
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Remote Welding Habitat
 Providing a dry, gas filled habitat for
the welding operation
 Support and stabilise the pipes by a
claw system
 Based on seawater hydraulics
 Direct vertical landing interface of
Remote Welding POCO
 Remote Welding POCO recovery
possible without flooding the habitat
 Dry weight 90ton
 Launch and recovery by vessel crane
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 Contains the most critical systems most likely
to fail during operation
 Gas filled container: 0.4 bar overpressure
 Permanent umbilical connection
 Easy launch and recovery from vessel using
module handling tower through moon pool or
by A-frame over vessel side
 Welding & Pre-Heat Power Sources
 Dry weight 25ton
 Provide a dry transfer «garage» for the
Remote Welding Tool
Remote Welding POCO

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Remote Welding Tool
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Contains all functions for subsea welding:
 Welding head
 Torch tip changer
 Welding consumable (bulk storage)
 Pre- and Post-Heating Sleeve & Pipe Coils
 Survey head
 Service head
Extensive 1-Atm
Robustness Testing

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1-Atm Welding Tests
Post-Weld Inspect, Service Head Cutter, Close Inspect
Service Head CuttingRoot Weld Review Sensor Head Close Inspect

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Deep Water Test October 2014
REM OCEAN Vessel
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Deep Water Test October 2014:
Habitat Deployment
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Vessel Crane Over-Boarding
Argon Purge, Blow-Down, IR Heating,
De-humidify for Welding Atmosphere

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Deep Water Test October 2014:
Remote POCO Launch & Recovery via Vessel Moon Pool
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Argon Purge on Deck prior to Launch

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Deep Water Test October 2014:
Remote POCO Dock at 400 and 1,000msw
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Remote Welding System
Hyperbaric MIG welding process4
8 Hours Arc-On Time at Depth, 60kW Heating Power Used Subsea
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Weld QA QC Summary
400msw: Arc Voltage & Welding Current

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Remote Welding System
Hyperbaric MIG Welding Results
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1,000msw
Hyperbaric MIG Welds
 Visual Appearance at
1:30 and 6 o’clock
Acceptable:
 Visual & NDT
 Multiple Macros
 HV10 Hardness
 All-Weld Tensile
 Charpy V Notch

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Remote Welding System
Hyperbaric MIG Welding Results
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Mechanical Properties at 1,000msw:
 Acceptable Visual & NDT, Multiple Macros
 Checks for H.A.C. (High Restraint, Moisture), Chemical Analysis, Oxygen Content
HV10 Hardness
 Peak HV10 Hardness is 276HV10 (Pipe Cap HAZ) and 260 HV10 (Pipe Cap HAZ)
All-Weld Tensile
 564MPa 0.2% PS, 632MPa UTS 27.5% El.
 563MPa 0.2% PS, 626MPa UTS, 27.6% El.
Charpy V Notch (Full Set at -20⁰C)
 FL+5: >Capacity of Machine
 FL+2: 316J Minimum
 Fusion Line: 173J Minimum
 Weld Metal: 123J Minimum

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Chemical Analyses
 Weld Metal Oxygen Levels comparable with Lab. results

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The future….
STATUS OF TECHNOLOGY
 Remote welded sleeve repair method is implemented for the large diameter pipelines
in deep waters; 30” to 42” in water depths 180-1,300meters
 Remote Welding System is qualified and approved by DNV-GL and in accordance
with Statoil corporate requirements
 Technology is available via Pipeline Repair and Subsea Intervention (PRSI) Pool
FUTURE DEVELOPMENT
 Extend pipeline dimension range downwards to 10” – 30” pipelines
 Extend depth range to 3,000meters
 Develop method for bi-metallic materials like clad and lined pipelines
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