For many process industries, the ability to minimise or avoid downtime, particularly unscheduled downtime, is a key element in successful asset management. It is in this respect that advanced carbon fibre composites technology, once seen as the domain of industries such as aerospace and motor racing, is increasingly being recognised across industries from oil and gas to chemical, petrochemical, power, mining and process industries generally.
This is a technology that offers permanent asset repair and rehabilitation, where often the only alternative would be to cut and replace at high cost, offering substantial savings.
Primarily the growing interest in composite repair technology arises from the ability to restore full pressure integrity and structural strength to corroded, damaged or weakened plant, permanently and, importantly, while plant operation continues as normal and uninterrupted. As such, it holds high value for industrial plant operators.
Moreover, while repairs are usually completed on-line, the work can of course be undertaken during a planned plant shutdown, and still generate valuable savings by not having to purge the lines or implement other safety requirements, since no hotwork is required – in itself an important benefit.
Further, the resulting repair is 10 times as strong as steel, at less than a quarter the density, and is corrosion-resistant.

Design and application

Application of composites repairs involves layers of carbon fibre impregnated with epoxy resin being built up to the specified requirements in terms of thickness, overlap onto good metal, fibre orientation, gradient at the ends or edges of the repair and so on, in line with the repair design specifications. The repairs are highly engineered, and must be bespoke-designed to the application requirements for long term high performance and reliability.
The repair design takes a number of critical factors into account, from the size of the repair, the geometry, pressures and temperatures, and pipeline or vessel material, to whether there is sufficient good pipe onto which to overlap the repair, and the
load-bearing contribution of the substrate.
Whether or not there is a through-wall defect will have implications on the repair design (where there is no through-wall damage the repair material will largely be subjected to membrane forces and the thickness reduces to one of load share between the repair laminate and underlying substrate), as will the shape of any defect. A crack, for instance, will require different design calculations to a hole, while a defect extending round the circumference of a pipe involves different design considerations again.
In terms of application, the first stage is to prepare the surface (a vital requirement since this will enable the necessary bond and therefore strength of repair to be achieved), followed by a glass fibre tie-coat which provides a good quality interface between repair and substrate. The epoxy resin-impregnated carbon fibre plies are then applied, followed by a final peel-ply layer, which removes excess resin and provides a textured finish, and is removed once the repair is cured. Installation is undertaken by qualified technicians, being a skilled process given the need to ensure correct fibre orientation, thickness, overlap and taper - all of which are critical to strength and reliability.

Proven benefits

Industrial application of this relatively new technology is increasingly widespread in the region. Petronas Gas Bhd, for example, selected advanced composites technology from Furmanite Malaysia to provide permanent repairs to a critical 10 inch feed condensate liquid line near the Gas Processing Plants (GPP) 5 and 6 at Kerteh, Terengganu in Malaysia, to avoid shutdown to cut and replace sections of the line, representing significant savings. Some 22metres of the line, on which internal corrosion had been identified, were repaired at 20 different remote locations over a stretch of some 7km along the line, while production continued uninterrupted. The repairs were designed against a design pressure of 153barg and temperature of 40°C (well within the reaches of Furmanite’s composites technology which can extend beyond 200barg and up to 200°C) and required just 13mm thickness of carbon to provide the required pressure and structural integrity.
This particular project also illustrated a further benefit of the technology. The light weight and flexibility of the materials (carbon fibre and epoxy resin), requiring no pre-fabrication, makes them easy to handle and readily transportable, which provided a significant advantage in this instance given the remote locations and awkward access to some of the repairs.
Another project undertaken at a Malaysian refinery also illustrates the benefits, in this case by being engineered to accommodate complex geometries including nozzles, elbows, tees and flanges, whereas some composite repair technologies can only cater for straight lengths. Internal corrosion and excessive wall-thinning had been discovered on two 3-inch carbon steel nozzles on two process vessels and downstream pipework, containing a mixture of light hydrocarbons and sour water. Traditionally this would have required shutdown of the plant, drainage of the vessels and removal and re-welding of the nozzles and pipework – at considerable cost given that the next scheduled shutdown was not due until some three years’ time. Composites technology, however, enabled this to be avoided, providing a repair that could be applied with no disruption to operation.
Further, while this technology is increasingly being recognised for the repair of pipes and pipelines, advanced composite repair technology from Furmanite can also restore pressure integrity and structural strengthening to structures requiring more challenging engineering, such as tanks and pressure vessels. In one example at a pharmaceutical plant, composite repairs to the carbon steel jackets of a glass-lined chemical reactor vessel avoided the need for revalidation of the process that replacement of the vessel would have entailed. In another case, at an alumina refinery, composite repair technology was successfully used to repair corrosion damage to a 21metre tall caustic soda storage tank.
Additionally, the ability to overcome issues of awkward and confined access is often a further valuable advantage, particularly on congested plants. Where repairs are required to asset components situated in confined or awkward access areas, the materials' flexibility and light weight often makes a repair possible where other techniques are not, and overcomes the logistical difficulties that are encountered if cutting and replacing, as well as avoiding the need for costly craneage and specialist equipment. In one instance at an ore mine, access to carry out a composite repair could only be gained by reaching over and under existing pipework, but was successfully achieved, facilitating repairs to a cooling water system without needing to stop production in the smelter furnaces (whereas to isolate the line to effect any other type of repair would have meant shutting down to cut and replace, or weld a patch, at a massive potential cost).

Permanency

The design life of a composite repair is itself a key feature of the technology. The repairs can be designed for the lifetime required – from just a couple of years, to permanent (25 years plus), thus offering either a means to avoid shutting down until the next scheduled outage, or indeed providing a full rehabilitation and removing the need to undertake any further work to the repaired component or section. A repair to three metres of corroded pipe on a 28km fuel line at a nickel refinery, for example, was undertaken in just two days, while operation continued uninterrupted, providing a permanent repair with a 20 year design life.
Moreover, the repairs require minimal maintenance or attention during their lifetime. Importantly, in situations where the cause of the wall-thinning or through-wall defect has been internal corrosion, composite repairs can be engineered to cater for continuing corrosion and indeed total loss of the substrate without in any way compromising the strength or pressure integrity of the repair for the duration of its design life. In the case of external corrosion the composites will prevent further corrosion damage.

Extending use

Given the extensive use of carbon steel in the construction of industrial plant, and its susceptibility to corrosion, the value of advanced composites technology is high, as a means of undertaking necessary repairs, typically with a permanent solution, with no need for hotwork and typically while plant operation continues as normal. Moreover, the resulting repair offers strength, durability and low maintenance among other benefits, further contributing to the high value of this technology. Not surprisingly it is attracting growing interest in the Asia Pacific region, and as the many advantages are repeatedly proven and industry confidence grows, composites repair and strengthening technology is increasingly being embraced – a trend that looks set to continue.

Colin Bickerstaff is Furmanite Asia Pacific general manager. For more information, www.furmanite.com