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Composites Provide Strong and Speedy Repair

  • Friday, 20th August 2004
  • Reading time: about 4 minutes

Damage to a 24in crude oil line elbow was repaired at Shell Stanlow by Furmanite with a cost-effective permanent solution using DML composites technology.

The primary requirement to cater for structural loads over and above pressure meant high level engineering expertise was needed to provide a reliable repair. Fretting damage had occurred on the 45-degree elbow on the carbon steel crude line at the support due to movement caused by thermal expansion, causing a wear groove.

A design study to assess the effect of the defect showed that the elbow was overstressed and required repair and strengthening. The loads on the pipe due to thermal expansion were significant.

A composites solution was engineered that optimised the fibre orientation to carry the necessary loads (using qualified materials), minimising the thickness and maximising the effectiveness of the repair, in a truly bespoke design to meet the application demands efficiently and cost-effectively. Alternative options to cut and replace the damaged section would have been more troublesome and more costly.

The composites route from Furmanite was preferred, providing a permanent repair that could be achieved quickly, and with minimum supervision.

Given that this was not a simple repair to restore pressure integrity, but required bending loads to be catered for, standard composite designs allowing for hoop loads only were not suitable. Moreover, the geometry of the piece requires more sophisticated engineering and installation skills than are needed for a straight length of pipe.

The repair was designed to support an axial force of 250kN, bending moment of over 300kNm, shear force of 5kN and torsion of almost 0.8kNm, as well as catering for line pressures to 50bar(g) and temperatures to 35C.

By tailoring the orientation of the reinforcing carbon fibres so that the repair hoop and axial capacities were equally utilised the repair was engineered to provide maximum efficiency minimising the number of epoxy resin-impregnated carbon layers, thus also keeping materials cost and installation time to a minimum. Two different carbon types were used, and a total thickness of just 14.5mm was needed.

The resulting repair is designed to support all the required loads without contribution from the existing steel, over a 25 year lifetime.

Skilled application was crucial, particularly given the critical importance of correct orientation of the carbon fibres especially difficult to achieve on a complex geometry in addition to ensuring correct surface preparation (abrasive blasting), required area of overlap, taper and so on. In this instance installation was undertaken with no flow in the line, and to reduce the time required, a low temperature post-cure was used, enabling this to be completed in 48 hours.

Furmanite Composites Business Manager Paul Smith pointed out that “”Furmanite, using DML technology, is the only company with the experience and engineering expertise to provide a repair that would meet the challenging demands that the structural strengthening requirement and complex geometry presented here””, moreover, we were able to do so cost-efficiently, by designing a repair that not only met all the requirements but kept the materials and installation time to a minimum””.

Earlier this year Furmanite held a number of seminars in Aberdeen, UK to promote best practice in repair management, looking at ways of preventing dangers caused during repairs.

“Recent tragic events have brought issues surrounding temporary repairs, their safety and effectiveness, into sharp focus in the industry,” explains Furmanite offshore business manager Graham McKay. “We have got together with the OCA to set up these seminars, in recognition of an industry need for a better understanding of the issues and requirements surrounding these repairs, so that operators and contractors can use the technologies available with confidence, and ensure they gain a reliable repair and maintain effective process integrity.”

Given by Furmanite engineering manager Dr Mark Burton and FD Alliance technical manager Dr Paul Hill, the seminars are open to project engineers, contractors, integrity managers and HSE representatives, and will look at the repair technologies available, the design and methodology behind them, and give advice and guidance on best engineering practices in applying them. The focus will be on leak sealing and advanced composites technology, drawing in both cases on Furmanite’s and FD Alliance’s experience and expertise in these fields. Flange repairs, pipe repairs, valve gland repairs, sealing compounds, and composites repairs will all be covered in detail.

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