Composites Provide Cost-Effective Pipe Repair

25 June 2004

Advanced composites technology from FD Alliance has been used to restore some 11m of a 16in hydrocarbon line to full structural and pressure integrity at an Azerbaijan oil terminal while the plant remained online.

The project is one of a growing number undertaken by Furmanite in the Caspian region. The fuel gas line operating at pressures and temperatures of 1.38bar(g) and 82C, was suffering from wall loss due to internal corrosion.

This had reduced the thickness to as little as 6mm in some areas (a loss of 3.5mm). FD Alliance was therefore called in to provide a repair solution that would restore full integrity and extend the life of the line for a further five years, until the next shutdown when a replacement section of pipe could be fitted.

Moreover, the repair was designed to accommodate any through-wall defects in the substrate that may be caused by the corrosion within the five-year design life of the repair, allowing for potential defects up to 27mm diameter to appear without compromising the structural or pressure integrity of the line, at the design pressure of 6.9bar(g).

The repair was installed in line with ASME draft standard guidelines (in which the alliance has been a key driver) by FD Alliance's highly skilled and qualified technicians (expert installation being critical to a successful repair) while the line remained fully operational.

It was designed to restore full structural strength and pressure integrity to the design pressure (6.9bar) and a maximum operating temperature of 100C (well within the current upper reaches that have been achieved by FD Alliance of 209bar and 200C).

Epoxy resin-impregnated carbon fibre layers were applied to achieve this, adding just 5mm thickness to the line.

Furthermore, the design calculations and specified application procedures allowed for the high ambient temperatures and humidity in which the installation was carried out. Given these conditions and the relatively high operating temperature of the line, the repair was post-cured at a temperature of 120C for 4h, further enhancing the strength and quality of the repair and extending the temperature at which it can be expected to operate successfully.

Such post-curing, required for any repair designed to operate at over 40C, overcomes any potential problems caused by changes in the resin's mechanical properties at high temperatures (when the glass transition temperature is reached) which could otherwise affect the integrity of the repair, and is critical to long-term performance. The repair was carried out within nine days, is fully validated, and carries a one-year warranty.

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