A leader in subsea isolation

Plug for launch on platform. Image supplied by STATS Group.

Offshore Sarawak was the location for STATS Group latest project, which marked the first subsea isolation and largest piggable isolation in Malaysia for the company.

STATS supplied a 38-inch Remote Tecno Plug® and contingency subsea encapsulation clamp for the 75-bar gas pipeline to facilitate the safe repair of a leaking flange.

STATS Group Regional Manager Asia Pacific Gareth Campbell said this challenging project marked a significant milestone in the region.

“The successful completion of our first and largest subsea isolation in Malaysia provided a leak-tight isolation for seven weeks allowing divers to carry out essential repair works safely,” he said.

“In addition, we provided our largest subsea repair clamp, a 38-inch class 900 encapsulation clamp which although not required, will be kept in storage by the client to be used as an emergency response should an unplanned issue arise in the future.

The 38in Subsea Clamp provided by STATS Group. Image supplied by STATS Group.
The 38in Subsea Clamp provided by STATS Group. Image supplied by STATS Group.

“The provision of emergency pipeline repair equipment can provide rapid and safe repair ensuring pipeline production can be resumed as soon as possible, minimising environmental and commercial impact.”

STATS DNV type approved 38-inch Remote Tecno Plug was deployed from the platform and pigged for 4.1km to the set location on the seabed.

The high integrity isolation provided safe breaking of containment conditions for the divers in compliance with subsea isolation guidelines.

The Remote Tecno Plug also included a separate test plug module which was used to conduct a reinstatement test of the pipeline following the repair activities.

This project marked the first subsea isolation and largest piggable isolation in Malaysia for the company. Image supplied by STATS Group.
This project marked the first subsea isolation and largest piggable isolation in Malaysia for the company. Image supplied by STATS Group.

Engineering and testing

ILI data supplied by the client was analysed and a site survey was conducted on the platform to gather critical information for the successful deployment and pigging of the Remote Tecno Plug.

Prior to deployment of the isolation equipment to Malaysia a full factory acceptance test (FAT) was performed in a purpose-built test-fixture. Upon successful completion and independent witnessing of all FAT operations the equipment was mobilised to the port at Johor Bahru in Malaysia.

Final pre-deployment checks and an equipment demonstration was conducted and witnessed by local teams prior to mobilising equipment to the platform and Diver Support Vessel (DSV).

Deployment

Once on the platform, and the pig launcher was drained, vented and nitrogen purged to allow the isolation plug to be loaded into the launcher.

Communication with the Remote Tecno Plug is achieved using an extremely low frequency inductive system which is used to track, set, and monitor the Tecno Plug throughout the work scope.

The DSV was used to position subsea tracking and communication systems at various positions along the pipeline and at the final isolation location.

With the tracking system positioned and function checked, the pigging was commenced and the Tecno Plug travelled through the topsides pipework and subsea to the isolation location.

The high integrity isolation provided safe breaking of containment conditions for the divers in compliance with subsea isolation guidelines. Image supplied by STATS Group.
The high integrity isolation provided safe breaking of containment conditions for the divers in compliance with subsea isolation guidelines. Image supplied by STATS Group.

Pipeline isolation

Pigging was halted once the Tecno Plug reached the exact isolation location and the plug was hydraulically activated to engage the locks and dual seals against the pipe wall.

As part of the isolation barrier proving sequence, each seal was tested independently with full pipeline pressure in the direction of the expected pressure differential, proving both seals of the double block isolation were leak tight.

The annulus between the Remote Tecno Plug seals was then vented to subsea ambient to create a zero-energy zone. With the pipeline vented to subsea ambient (11 bar) behind the Tecno Plug an isolation certificate was then issued to the client.

Flange replacement

Once the isolation was in place divers could enter the water, break the flanged joint and safely recover a section of pipeline to inspect the flange face.

A repair of the flange was conducted on the deck of the DSV, and the spool was replaced. In total the isolation was maintained for 49 days, providing leak-tight double block and monitor isolation.

With repair activities completed, prior to un-setting and recovering the Tecno Plug, a reinstatement test of the pipeline was conducted to leak-test the pipeline at 115 bar.

The test plug was set using a second control module and a test boundary was created to perform a reinstatement leak-test of the replaced pipe spool and flange.

This was achieved by raising the pipeline pressure on the launcher side against the seal on the test plug, creating a test boundary to confirm the integrity pipeline back to the platform.

Isolation plug recovery

On completion of the reinstatement test, the test plug was unset and the pressure behind the isolation plug back to the platform was equalised and the Tecno Plug was hydraulically unset, retracting the locks and seals from the pipe wall.

Pressure in the pipeline was then vented from the platform launcher causing the Tecno Plug to pig back to the platform. Controlled venting was conducted until the Tecno Plug was tracked back into the launcher.

For more information, visit statsgroup.com.

This article featured in the January edition of The Australian Pipeliner. 

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