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WA - 2016 - September Technical Meeting

Structural Composite Repairs in Challenging Environments

West Australian Branch Meeting

12 September 2016

Structural Composite Repairs in Challenging Environments

Jason LeCoultre, Business Development Manager, IAS Group

L to R: Jason LeCoultre, Steve Algie

Jason LeCoultre graduated with a degree in materials engineering from UWA, where his interest in composite materials first developed. He has been involved with the oil & gas industry for most of his professional career and his work with IAS Group combines both interests. Jason explained that IAS Group has grown over the past 20 years to employ around 70 staff engaged in what it describes as innovative brownfield maintenance solutions, with a focus on the offshore oil & gas industry. The two major aspects of their technologies are ultra-high water jet cleaning and cutting, and repairs using composite materials. As well as undertaking the maintenance work, the company develops specialised technology and tooling used in the work.

The great advantage of composite materials is that they avoid the need for hot work, and so can be used on live plant. The main product used is Technowrap™, for which IAS Group acts as agent through another company, IC Integrity. Technowrap is a fibre reinforced composite available in pre-cured, pre-preg and wet lay-up (2-part epoxy) forms, along with primer systems for adhesion to steel. The materials used by IAS are approved for helicopter transport to off-shore operations.

The challenges involved in composite repair, include not only the corrosive marine environment, but the demand of the oil & gas industry for proven solutions. Jason went on to explain how IAS Group demonstrates to clients the suitability of proposed repairs. The approach taken is to work as far as possible with accepted standards. For repairs to corroded steel the relevant standard is ISO 24817, for composite repairs to pipework. When the repair has a structural function, the standard is DNV-RP-C301 for bonded repair of steel structures. More complex repairs can have aspects relevant to both standards, for example, when a repair to a pipe is made with the prospect of the remaining steel corroding away completely.

IAS uses a hierarchy of steps to validate repair designs to meet standards. This starts with materials specification and testing as the baseline, with third-party validation. The next step involves finite element analysis of specification samples, followed by testing of actual samples to validate the mathematical modelling. Evidence is also provided by service in the field. Through such validations IAS has assembled a ‘toolbox’ of useful materials. These are preferred, because “it is a big job to add to the toolbox”.

Jason took questions throughout his presentation, and at this point confirmed that in finite element modelling, the bond-line between the steel and composite is a critical factor. Bond strength is only classified for specific surfaces and surface conditions, and as with the repair materials, a lot of work is needed to extend the range of approved surfaces. He also made the point that sometimes a composite repair might be justified by the absence of other options.

He also ran through methods of monitoring and inspecting the remaining steel under a composite repair. Fire resistance was also questioned; intumescent coatings such as Chartek® can be used over composites. Fire rating considerations with composites are different from those used for steel; for example, softening is a concern with composite gratings and walkways. Maximum service temperature is 240ºC, with the design limit being 220ºC.

Jason then turned to structural repairs, in which designs have to take into account such considerations as whether the remaining steel is to be redundant, or still providing strength and stiffness in the repaired structure. Failure modes also need to be considered; for example, a structural repair to a pipe might require design against buckling, which is not a concern in a simpler leak repair. The codes set the maximum life for repairs as twenty years, and this is the normal design life. However, another option is to design for, say, five years, with inspection at that time and possible extension.

Modelling of connections made from composites can be very complex, and in some cases it is more practical to use new steel connectors in conjunction with the composite material. Matching stiffness is often a major consideration, and this can lead to more composite material than might otherwise be needed.

Jason concluded some examples of major repairs on offshore structures, including a radio tower repair, and structural replacement of a caisson section, made with the aid of purpose-designed tooling for cleaning and inspection.