The 1,166 km Langeled Pipeline was constructed between 2004 and 2006 to carry gas from the Ormen Lange field in the Norwegian Sea.
The system starts from the processing plant at Nyhamna on the mid-Norwegian coast.
The pipeline consists of two sections. The 42 inch diameter northern section carries gas to the Sleipner East field in the North Sea, and became operational in October 2007. The 44 inch diameter southern section of the pipeline runs from the Sleipner East hub to the receiving terminal at Easington on the east coast of England. This part of the pipeline became operational in June 2006.
The Langeled Pipeline is integrated with Norway’s existing gas pipeline system at Sleipner East, and has a capacity of 69.4 MMcm/d.
The UK is Europe’s largest gas consumer. Since Langeled opened in 2006, no less than 41.5 Bcm of gas have flowed from Norway to Easington.
In 2008 alone, just over 15 Bcm were received at the British terminal, representing the UK’s total gas consumption for about two months. Norway ranks today as the world’s second largest gas exporter, closely followed by Canada.
Pipeline challenges
The inspection task posed major difficulties on several accounts. Firstly, the pipeline’s unparalleled length would place great wear-and-tear demands on the inspection tool. Rosen tackled this problem by reducing cup wear through special tool centralisation, based on magnetic forces and a supporting guiding disc.
Secondly, Langeled is a multi-diameter pipeline with 42 and 44 inch sections, and high wall thicknesses of between 23.3 mm and 62 mm. To ensure that the actual inspection tool would be able to pass through the complete length of the pipeline despite its multi-diameter design, the pipeline’s internal features had to be verified prior to the inspection run. For this purpose, a specially designed gauging tool was first sent through the pipeline. This tool featured a gauge and a gauging plate, and was adapted to the multi-diameter configuration of the line to confirm its bend sizes and internal diameter.
Thirdly, the pipeline is characterised by a high flow velocity, the fundamental problem with which is that the inspection tool is propelled through the pipeline too rapidly to allow precise measurements. Although a simple way of dealing with this issue is to reduce the product flow rate, this solution leads to costly throughput losses. Rosen’s response to this challenge consisted of a speed-control unit (SCU), which provided controlled gas by-pass, enabling the inspection run to be conducted at a pre-programmed target tool speed to ensure reliable measurements without the need for a flow rate reduction.
Combined in-line inspection
To meet the objective of gathering accurate corrosion data on the Langeled Pipeline, Rosen designed the RoCorr MFL/SIC, a customised “˜combo’ tool equipped in the front segment with magnetic-flux leakage (MFL) sensors for general corrosion measurement, and in the rear segment with caliper arms equipped with specially-designed sensors for detecting shallow internal corrosion and recording high-resolution geometry measurements.
The RoCorr MFL/SIC in-line inspection tool thus combines the two complementary corrosion measurement methods: MFL and SIC. MFL, which is used for measuring relative wall loss, is a versatile and reliable method for determining the geometry of metal loss in pipelines. In contrast, SIC, an eddy current based technology, enables absolute geometric measurements of internal corrosion defects to be made.
In combination, MFL and SIC permit a close analysis of corrosion defects, and provide an effective tool for monitoring the degradation process. Additionally, the simultaneous application of the two inspection methods ensures an exceptionally high probability of identification of internal and external discrimination, providing high accuracy in depth, length, and width sizing of internal corrosion defects.
Conclusion
The tool passage issues arising from the Langeled Pipeline’s length, multi-diameter design, and high flow rate were overcome by Rosen’s specially-designed RoCorr MFL/SIC inspection tool, which combines MFL and SIC technology. In August 2009, the tool was used to inspect the pipeline – the world’s longest subsea gas pipeline – in a single run. Over a period of 127 hours, the tool covered a surface of 3.83 sq km on which about 450 billion measurements were made, and 374 GB of data were collected. As attested by this unprecedented feat, the RoCorr MFL/SIC combo tool has been shown as not only able to withstand extreme conditions, but also to be highly suitable for monitoring the corrosion process in offshore pipelines.