Following a planned inline inspection pigging program of its 32-inch gas export pipeline (GEP) on the Bongkot platform in the Gulf of Thailand, PTT Exploration and Production Public Company Limited (PTTEP) discovered that the line’s primary shutdown valve (SDV), last manual isolation valve, and one of the two isolation valves for the line’s pig trap were defective. The issues were creating unacceptable internal passing rates and external leakage to the atmosphere. In addition, the line had severe corrosion at the surface of a 5D bend underneath the deck sealing block. The situation mandated valve repair, removal and replacement operations, while the corroded bend necessitated treatment with composite fiber wrap.
PTTEP planned for their shutdown and maintenance for over a year and it was to take place in April 2014. Faced with two options for safe and reliable isolation of its gas export line, PTTEP could either bleed down the entire line — a protracted and very costly option, or it could pressure isolate the line downstream of the valves and just bleed down the section back to the pig launcher. PTTEP chose SmartPlug pressure isolation with the remote-controlled plugging technology engineered by T.D. Williamson (TDW).
With the export line securely isolated, the SDV and manually operated valves were replaced. Following the replacement of the valves, a hydrotest was carried out against the SmartPlug tool’s third plugging module to verify the integrity of the repair work.
This paper describes the challenges of such an offshore pressure isolation, as well as the steps taken from planning, to site visit and engineering, to safely and successfully executing the isolation.