A selected pipeline route is likely to include a number of changes in alignment, grade and elevation.Pipeline designers and constructors have a range of options available to achieve the correct pipeline position. In some sort of logical order; the pipeline string can be “roped” into place, installed withcold-field bends, hot bends or even fittings. The selection of the appropriate mix of measureswould be made on a technical and commercially expedient basis.
Roping the pipeline string into position is limited by the maximum allowable strain of 0.5% (refer AS2885.1 Section 5) which equates to 100% of the specified maximum yield strength (SMYS) for the pipe. At 0.5% strain the equivalent bend radius of the roped pipeline is about 100 times the pipediameter (colloquially 100D). To avoid buckling the pipe and the use of external force, AS2885recommends a minimum radius of 250D for roped bends.
Cold-field bends can be formed from individual coated pipe joints for the pipeline utilisingspecialised field bending machines. Generally, the smallest radius obtainable by cold-field bendingin practice is about 1 ½° of angle deviation per diameter – this is equivalent to a bend radius of about 40D. To ensure suitable results are achievable, trials are conducted to qualify the cold-field bending machines and operators against the range of pipe to be used to construct the pipeline.
Neither of these methods is capable of giving the tight bend radii necessary to place the pipe closeto the alignment intersection point, negotiate tight confines, accommodate difficult terrain or tocope with road and rail crossings and other features - particularly in built-up environments and for larger pipe diameters.
Other than die pressed or forged bends, which may be difficult to obtain and expensive, the onlyalternative is hot bends manufactured by the hot induction bending process. No other hot bendingmethod is explicitly approved by AS2885.1.
Induction bends form an important link in the pipeline chain of delivery. They require careful planning and consideration to deliver high value and high benefit to cost ratio solutions to pipelinerouting problems. In particular, the pipeline can be correctly positioned and the cost of difficult andexpensive excavations may be reduced and environmental impacts minimised through the use of compact hot bends and prefabricated configurations.
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