05.07.2009

Pipelines will be an integral part of our energy distribution systems for the foreseeable future with tens of billions of dollars being invested in pipeline infrastructure, due in part to the increase use worldwide of combined cycle power generation plant using natural gas a fuel. The need to construct large diameter pipelines over long distances has led to an increased demand to improve the productivity of pipeline girth welding. In a number of cases, the cost of exporting the energy will have a dominating influence on the viability of the upstream production facilities. These facilities will progress only if the industry can substantially reduce capital expenditure and improve design for pipeline integrity. Whether the application is an onshore gas transmission line or a deepwater pipeline, there is a need to constantly improve the productivity, quality, integrity, and reliability of pipeline girth welds to reduce construction costs. There is also a need for improved technologies suitable for the higher strength steels currently being developed. Different types of welding procedures exist such as one-shot welding and power beam processes. Currently, innovative hybrid laser/arc welding techniques, such as GMAW are the dominant pipe girth welding technique. They best assure weld soundness, material properties, geometric profile, and offer the best chance of developing high integrity welding processes

This involves the testing of valves and the removal of surface impediments to pipeline inspection

Oil that contains less than 1% sediments and is clean enough to transmit in the pipeline

Signs on the surface above natural gas pipelines indicate the presence of underground pipelines to the public, to reduce the chance of any interference with the pipeline.

The main inspection methods that are used are MFL (Magnetic Flux Leakage) and UT (Ultrasonics). MFL is an inferred method where a strong magnetic flux is induced into the pipeline wall. Sensors then pick up any leakage of this flux and the extent of this leakage indicates a flaw in the pipe wall. For instance, internal material loss in the line will cause flux leakage that will be picked up by the sensors. Defect libraries are built up to distinguish one defect from another. Ultrasonic inspection is a direct measurement of the thickness of the pipe wall. A transducer emits a pulse of ultrasonic sound that travels at a known speed. The time taken for the echo to return to the sensor is a measurement of the thickness of the pipe wall. The technique needs a liquid through which the pulse can travel. The presence of any gas will affect the output.

The competitive edge of LNG over pipeline gas grows in direct proportion with the distance between the source of the natural gas and the market. LNG is more competitive when distances are greater than 1,500 km at sea and is more competitive over non-mountainous land when distances are greater than 1,800 km. When the distance is greater than 4,000 the topography no longer plays a role and LNG is always the most economic choice.

Gas under enough pressure to enter the high-pressure gas lines of a purchaser; gas in which enough liquid hydrocarbons have been removed so that such liquids will not condense in the transmission lines

Gas consumed in the operation of pipelines, primarily in compressors

Lifting cradle for pipeline as it is being laid