Clamping down on downtime
6 Jan 2004
Furmanite International has recently been involved in two piping repair projects that have saved millions of pounds for its customers by avoiding costly unplanned shutdowns.
At ExxonMobil's Mossmorran petrochemical complex in Scotland, a specialist, semi-permanent, on-line clamp designed and installed by Furmanite saved an estimated £10 million following discovery of leakage on a tee section of a critical steam line.
A small crack had developed at the junction of a 16in pipe and the 20in header and, though the leak was not deemed immediately dangerous, the operating pressures of up to 84barg and temperatures of 480 degrees C clearly dictated a repair, with shutdown being thought of as the only option.
Already contracted for on-site leak sealing and other core maintenance at Mossmorran, Furmanite developed the idea of using a restraint clamp to relieve the stress in the pipework, thus avoiding an unscheduled shutdown. The company's engineering manager, Mark Burton, explains: 'the specialist assembly - comprising a saddle clamp attached to the vertical 20in clamp and two gripper clamps linked by pre-tensioned tie-bars fixed to the horizontal 16in pipe - is designed to exert a tensile load of around 100tonnes, forcing the pipes together and removing the axial crack opening stress.'
To fit the clamp assembly, a temporary by-pass line was installed so the plant could continue in operation while the repair was effected. But time was critically important, as the by-pass could not cope with fluctuations in plant throughput, which in this situation could have led to flaring of excess gas.
With the plant switched to by-pass in the early morning, there was no time to wait for the pipe surfaces to cool down. So Furmanite technicians donned Kevlar gloves to fit the clamp, getting the entire assembly in place and pre-tensioned by mid-afternoon.
Steam was then gradually reintroduced and the technicians worked through the night to adjust the pretension as the assembly was brought back to normal operating pressure and temperature.
The repair is expected to last until 2006 when a full shutdown of the complex is planned and the line can be replaced.
More recently, Furmanite has designed and installed a self-sealing clamp on a 36in 180 degree return line carrying crude oil at a major UK refinery. The line was suffering from wall thinning caused by internal corrosion, but again would have necessitated shutting down production of the associated oil field for it to be replaced.
Furmanite's solution was a bespoke six-part repair clamp mitred to match the pipe geometry.
Fluoroelastomer was used to make a high integrity seal and, once fitted, the enclosure was injected with resin to provide the defective pipeline with support. The enclosure was engineered to the 20bar pipeline design pressure and is seen as a long-term solution to the problem of internal corrosion and erosion.
