The vast state of Western Australia stands largely arid and sparsely populated. Although Perth, in the southwest, functions as the business and service centre for WA’s energy industry, it’s actually the state’s north-west coastal and desert areas that house the majority of oil and gas infrastructure. Pipeline operators working in the largely isolated north-west must be well prepared for every eventuality, meaning they rely heavily on pipeline service companies to provide a wide range of services, including offshore line isolation, hot tapping and plugging, in-line inspection, cleaning and batching, and emergency response.
In June 2013, T.D. Williamson (TDW) was asked to replace a leaking pipeline valve, located at the end of a line. It had to be fully functional in order to operate a pig trap. To make the request especially challenging, the operator informed TDW that, in addition to an arduous trek to the desert jobsite, technicians would encounter a transmission pipeline with an operating pressure of approximately 1,480 psi, which had to be maintained throughout the valve replacement. A fully-rated STOPPLE® Train line isolation at this pressure would be the highest in company history, as well as an exciting challenge for TDW engineers and technicians.
The operator chose STOPPLE® Train technology for two reasons. First, it has been designed to plug live pipelines, meaning that the operator doesn’t bleed down or evacuate more than a few meters of the line. This avoids a significant investment in time, as well as a loss of revenue resulting from reduced throughput. The operator’s second reason was safety. With every hot tap into a pipeline there is inherent risk – cutting into a pressurised pipe filled with highly flammable material. In addition, once the line is isolated, workers downstream must then perform maintenance. Traditional plugging methods could allow for product to seep past the single seal, the seal could fail entirely, and sparks from welding or cutting could come in contact with product.
The STOPPLE® Train system addresses both of these concerns as it employs double block and bleed technology. The tool, which has two linked plugging heads, is designed to enter a pipeline through a single opening, eliminating the need for multiple hot taps. Once the tool is set in the line, the pressure is bled, all product is drained from the pig trap and the space between the two plugging heads is depressurised. This method of having one hole, two sealing units and a zone of zero energy in between is one of the safest line isolation methods available.
To avoid the midday heat, the operator and TDW caravan began the early morning trek to the remote compressor station. Once at the site, the TDW team used a pressure-balanced tapping machine to hot tap the 406 mm pipeline and the specially-engineered STOPPLE® Train system to plug it. For two days, the affected section of the pipeline was isolated while the valve was replaced. The entire operation was completed in seven days and without disrupting throughput.
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