Ultrasonic Inline Inspection of the Moomba to Sydney Pipeline

For the majority of Australian gas pipelines it is not practical to remove them from service for extended periods of time. This rules out hydrostatic testing as a means of confirming the integrity of older pipelines including those that may contain Stress Corrosion Cracking (SCC). The Moomba to Sydney pipeline (MSP) at 864 mm (34 inch) nominal bore and 1299 km (807 miles) in length is the largest diameter onshore gas transmission pipeline in Australia. Commissioned in 1976, it has a history of susceptibility to SCC and, in 1982, six years after commissioning, suffered a SCC initiated rupture. Since this time the pipeline owners have operated and maintained the pipeline to ensure no further SCC initiated failures. Maintenance for SCC has included a targeted excavation program which, between 2000 and 2004, found significant SCC colonies. This created the need to develop a more comprehensive approach to locate and identify every significant SCC colony in the pipeline. Several options were considered but the one that was selected as best meeting the performance criteria was the use of an ultrasonic intelligent pig running in a liquid medium. This pigging operation had to be carried out while the pipeline continued in operation with minimal disruption to gas transmission operation. This had never been done before in Australia. The initial intelligent pigging program of the first 162 km (101 miles) of the pipeline was conducted in early 2005 with an additional 292 km (181 miles) pigged in early 2006. This paper provides information on the approach taken to overcome the many technical, operational and commercial challenges of this operation. Water was chosen as the liquid medium and a major issue was the introduction and removal of water from the pipeline while it remained in operation. This could not have been achieved without the co-operation of producers, shippers, network owners, network operators, technical regulators and contractors. The paper also looks at the how the results obtained from the pigging will be used to enable the SCC to be managed in a safe and efficient manner and confirming the safety and fitness for purpose of the MSP now and into the future.