Subsea Pipelines: the Remotely Welded Retrofit Tee for Hot Tap Applications

OMAE2013-10765

Neil

Woodward

Isotek Oil & Gas

Kjell Edvard

Apeland

Statoil ASA

Jan Olav

Berge

Statoil ASA

Richard

Verley

Statoil ASA

Mike

Armstrong

Isotek Oil & Gas

What is a Hot Tap?

Typical Permanent Works

• Retrofit Tee to provide full flexibility & independence when selecting tie-in location

• Cost effectiveness • Utilize spare transport

capacity in pipeline systems

Equipment

• Remote Hot Tap Cutting (through a Valve Module)

• Remote Hot Tap Cutter previously used at 145msw for the Tampen Link project and at 960msw for the Ormen Lange project

Remote Hot TapTechnology

FIRST Retrofit TeeRemote (Diverless)Welding Equipment

•Remote installation of a structural reinforcement clamp containing the branch pipe

•Pressure barrier made by internal weld inside the branch pipe

•Welding system contains all functions for making and monitoring the internal weld

Goals

Reduced cost for future infrastructure development

Increased depth and pressure capability

Åsgard Subsea Compression Project to improve recovery from the Mikkel and Midgard reservoirs by around 280 million barrels of oil equivalents.

Laboratory Pre-Qualification & Qualification Work

•Root Gap Trials

•Low Temperature Trials (4°C) HIGH PROCESS TOLERANCE

•High Humidity Trials (26°C Dew-Point)

•Hydrogen Assisted Cracking Tests (Variable Gap): Tekken Tests, Mock-Up Tests

•Mechanical Property Tests: Macro/Hardness, All-Weld & Cross-Weld Tensile, Charpy V Notch, Fracture Toughness (CTOD)

•Trapped Water / Effect of Salt Water / High Pipe Temperature / Stops & Restarts

•Materials: X65 Mother Pipe, with X65 Branch Insert Pipe with Inconel 625 internal cladding

•Alloy 59 Welding Consumable (CRA)

•Argon Welding Atmosphere: 200 to 300msw

•Lab. Weld Procedure work performed inside a 250bar Pressure Vessel

•2 Years Specific Work for this project

Fjord Trials 2011 & 2012Remote Weld Head

& Retrofit TeeSubsea Testing

Subsea Testing Results 2011: 6-Pass Macros at 265msw

Subsea Test 2012: 6-Pass Macros inside the Retrofit Tee

Acceptance Criteria

•Acceptance based on DNV-OS-F101 and DNV-RP-F113 ‘Pipeline Subsea Repair’, October 2007, and approved by DNV

•Environmental Acceptance Criteria: Humidity / Temperature / Trapped Water

•Torch Target Check Before Welding Each Pass: Dry Run

•Weld QA QC Acceptable

– Electrically: Arc Voltage and Welding Current using a 2s Average

–Average Weld Speed

– Pre- and Post-Dive Wire-Feed Check

–Calculated Heat Input (kJ/mm) using a 4s Average

•Visually Acceptable Weld Bead

•Additional Acceptance Criteria based upon Table D-4 ‘Acceptance criteria for visual examination and surface method testing of welds’ from DNV-OS-F101.

Acceptance Criteria•Weld QA QC ACCEPTANCE CRITERIA defined by Lab. Pre-Qualification Testing

Remote Hot Tap Production Weld Offshore

•Control Cabin •Welding Tool Deployment

•ÅSCP Production Post-Weld Visual Appearance Videos

•Pass 1 & Pass 6

Remote Hot Tap Production Weld Offshore

Remote Hot Tap Production Weld Offshore

•All 6 Passes maintained within ALLOWABLE limits

ÅSCP RHT Production Weld Offshore

•???

•All 6 Passes maintained within ALLOWABLE limits

Remote Hot Tap Production Weld Offshore

•Post-Weld Visual Appearance Video: 6-Pass Completion

•22.4mins Arc-On Time

Conclusions

•Remote Hot-tap technology provides the most flexible tie-in solution avoiding shut

down of pipeline transport systems.

•The paper described the development, subsea test and production application of a 6-

Pass dry hyperbaric GMA weld procedure using Alloy 59 consumable in an Argon

environment.

•Acceptable welding parameters, resultant mech. properties and solidification

cracking behaviour have been achieved under conservative temp. and humidity

conditions in the lab. and in subsea testing at 265 and 350msw.

•The Production Retrofit Tee will be connected with the Åsgard Subsea Compressor

station to extend the gas-field lifetime. This will improve recovery from the Mikkel

and Midgard reservoirs by around 280 million barrels of oil equivalents.

•This milestone represents the world’s first application of diverless dry

hyperbaric GMA welding for a subsea production application.

Acknowledgements

The authors acknowledge the invaluable contribution of all the Åsgard

Subsea Compression project team.

Statoil acknowledge the vital contributions from the main contractors for the

successful Remote Hot Tap testing and operation:

•Technip Offshore Norge (the main marine contractor and PRS operator),

•Imenco (Remote Hot Tap Retrofit Tee design and build supplier),

•Isotek Oil & Gas Ltd (Remote Welding and Cutting Control Systems, Weld-

Head design and build),

•Clear Well Subsea (hot tap cutter tool supplier), and

•Nemo (Gooseneck and Subsea Valve module supplier)