Pipeline out-of-roundness issues resolved

With potential for widespread application where such problems exist, the value of this solution has already been successfully demonstrated on a pipeline being constructed in one of the most inhospitable regions of the world.

Difficulties can arise when automated welding is used for speed of pipeline construction if the pipe is not fully round, as this can make it impossible to achieve a sound root weld, resulting in defects and potential failure. When such a situation arose on one 40 km gas pipeline construction project, running from drilling rigs to central processing facilities, Furmanite was called in to help.

A solution involving counter-boring the inside of the pipe-ends in-situ was developed to produce identical dimensions for a perfect match, and machining a weld prep enabled the automated welding to be undertaken successfully. Each pipe end was surveyed by Furmanite before and after the machining work, logging the as-found and final dimensions to ensure that all pipe specifications were met – including a circular bore and, critically, that the required minimum wall thickness was retained.

Purpose-developed pipe cutting and bevelling equipment was built for the project, based on modified existing machines fitted with special boring attachments. Because the pipeline was being constructed in an inhospitable desert environment in this instance, modifications included enabling the machines to withstand the onerous conditions, including extreme temperatures of up to 55°C and sub-zero, as well as regular sandstorms that could cause problems with bearings and lubrication systems. Further, the fact that the lines were an exotic material also had to be accounted for, and this involved modifying the contact pad materials used to avoid any cross-contamination.

The machines used were aluminium and lightweight, enabling them to be manually mounted, eliminating the need for cranage or lifting equipment. In trials, an externally-mounted machine design, consisting of a round bearing clamped to the outside of the pipe around which it rotated, proved to be the more versatile. This provided the flexibility required both to undertake the dimension logging and for maximum speed of metal removal. Importantly, the high level of adjustability – allowing the machine to be off-set where required rather than necessarily central to the pipe – enabled the ovality of the pipe ends to be rectified with minimum material removal, achieving the surface finish required in this instance – between 1.6 µmRa and 3.2 µmRa.

At the start of the process, the out-of-roundness discrepancy between the circular machine bearing and pipe was logged at eight points around the pipe circumference, using a dial test indicator attachment on the machine. The same equipment also confirmed that sufficient circularity had been achieved while retaining critical wall thickness, after machining was completed.

Workshop trials to confirm speed, accuracy and repeatability were followed by trial runs on site, undertaking the work to the pipe ends alongside the pipe trench, after which the automated welding was resumed – this time producing 100 per cent success rates in the welding process. Following this proven success, the remaining pipe ends were modified in the same way. In all, Furmanite technicians machined more than 12,000 pipe ends.

Furmanite also provided a full maintenance package on-site allowing the machines to be rotated daily so that those not in use could be serviced. This ensured continuity of work with no loss of time and maximum progress.

Commenting on the success of the project, Furmanite Australia sales manager David Arnold said “Furmanite was able to apply its on-site machining expertise and experience to this project to design a solution that solved the problem without having to involve replacement with the high cost, time and logistical issues that would have raised, representing a high value contribution.

“Moreover, this was not a unique situation, and the solution can now be applied elsewhere, particularly where long distances of pipeline are being constructed requiring automated welding processes, and therefore needing to ensure perfect roundness to enable the welding machines to operate effectively. There have already been further enquiries for similar work in other regions.”

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