Handling the heat subsea

Subsea hot tapping specialist TD Williamson has been called upon lately to assist with a number of Southeast Asian gas line tie-ins without recourse to costly and disruptive production shutdowns. TDW's Bancha Pitayagulsarn and Ray Foster discuss the planning and successful execution of these jobs.

Subsea hot tapping has been employed offshore Thailand and Indonesia in recent months to facilitate complex tie-ins of major gas pipelines to new platforms and pipeline infrastructure without shutting down production.

In the Gulf of Thailand 400km offshore, TD Williamson (TDW) was called in by EPC contractor Hyundai Heavy Industries to assist with subsea hot tapping services during the expansion of PTT's offshore gas spur line project. 

The expansion would be achieved by extending two gas transmission pipeline systems from an offshore supply point to PTT's third transmission pipeline and then on to distribution terminals located onshore Thailand. The two pipelines from the Platong Gas II and Greater Bongkot South fields would be connected via subsea tie-in points created by TDW on the third transmission pipeline.

The first subsea hot tap took place in mid-summer 2011 on the Platong Gas II project. In preparation, TDW designed and built a full-size mock-up of the 28in diameter pipe in order to simulate the hot tap operation, confirm the integrity of the equipment, and familiarize the technicians and divers.

Following successful completion of the hot tap simulation, the subsea operation was carried out from the HD 2500 dive support vessel in approximately 70m of water.

TDW technicians monitored the divers continuously via live images transmitted from cameras attached to the divers' helmets and fixed on an ROV. The crew also monitored the hot tap area for gas bubbles, which would have signalled a potential leak in the system. The offshore operation took place over nine days, with the subsea hot tap carried out in one day. Gas flowed and a safe operating pressure of 1926psig at 55°C was maintained throughout. The point will be used to facilitate tie-in of the new 48km pipeline from a point on the third transmission pipeline, which runs between PTT's riser platform and Rayong, to the new Platong Central Processing 2 platform.

Similar results were achieved with the second hot tap six weeks later, with the tap again completed in a day. This operation was required to prepare for the tie-in of a 38km pipeline that will eventually extend from the new Greater Bongkot South PPS platform and terminate at a point on the third transmission pipeline, which stretches from JDA A-18 to the Arthit pipeline end manifold.

Both operations were completed as planned, and Robert Morris, Far East Asia Pacific director for TD Williamson Asia Pacific observed afterwards: ‘By opting to create tie-in points via hot tap, PTT avoided the daunting – and costly – task of removing product from the producing lines in order that the tie-in points could be prepared. In essence, they would have been shut down, causing considerable expense and disruption. Instead, gas flowed throughout the process and the new lines have since been tied-in, providing access to neighboring fields.'

Meanwhile, offshore Indonesia TDW also provided hot tapping services to PT Saipem Indonesia on Premier Oil's Gajah Baru gas field. To facilitate tie-in of a new 16in diameter gas export line extending from the Gajah Baru export riser to the Anoa expansion tee tie-in point on the West Natuna transportation system, a hot tap was made through a special flange that had been installed during the construction of the pipeline, obviating the need to install a fitting on the pipeline to prepare for the tie-in. The operation proceeded smoothly, allowing gas to flow uninterrupted through the line. Operating pressure was maintained at 2030psig at 50°C.

A second operation was carried out for PT Timas Suplindo on behalf of Kangean Energy Indonesia in the Java Sea. Under phase one of the Terang Sirasun Batur development, a tie-in was required on the East Java gas pipeline. This would later enable a new platform in the nearby Kangean gas field to be connected at a fraction of the cost of laying a new line.

Custom subsea clamp

To facilitate completion of this subsea hot tap operation, TDW designed and custom built a 10t clamp, with a 16in branch flange for installation on the 28in diameter East Java gas pipeline. The clamp was necessary to secure the content of the pipeline during the tap and to provide the connection point for the tie-in.

Extensive testing, including an onshore integrated mock-up of the hot tap, was carried out at the TDW facility in Singapore prior to taking the integrated equipment spread – including clamp, isolation valve and hot tap machine – offshore. Over the course of seven days last September, TDW performed the subsea operation from a DSV, providing guidance and round-the-clock monitoring of all subsea activity. The hot tap itself was completed in one day in 91m of water. The clamp contributed to the success of the operation by allowing the hot tap and tie-in to be conducted safely while flow through the East Java gas pipeline remained uninterrupted. Operating pressure was safely maintained at 2000 psig at 49°C. OE

Bancha Pitayagulsarn, country manager for TD Williamson (Thailand), is a graduate of Chulalongkorn University with a BSc in Electrical Engineering.

Ray Foster, TDW's country manager for Indonesia, holds a Master of Business Administration degree in marketing from Eastern New Mexico University.