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Attwater

Novel Resin Simplifies Composites Repairs Outdoors

22 April 2004

A new product by FD Alliance claims to remove the problems that can be associated with composites repairs in wet or humid environments - namely logistical issues, delays and high costs.

This development allows FD Alliance to carry out repairs in conditions where achieving a permanent, effective repair would not previously have been possible. It is estimated to benefit some 80% of composites repairs executed in outdoor conditions within the UK by removing the need for environmental protection that has to date been required to enable repairs to be undertaken.

The new resin system performs effectively in wet conditions, yet is still of sufficiently low viscosity to be usable for laminating purposes. Water-activated resin systems can already be applied in wet conditions, although the pipe surface must be dry at time of application if they are to develop their full bond strength but they are also hydrophilic (being water-cured) and so continue to absorb water with a resulting reduction in mechanical properties.

Eventually this can result in the failure of the adhesive bond with the substrate being repaired. While these can be used for temporary repairs, a permanent repair had not previously been available in wet conditions.

This latest advance by FD Alliance therefore opens up a further breadth of applications in which permanent composites repairs are possible and viable.

""Previously, attempting to achieve adhesive bonding on a wet surface meant having to displace the water to create the adhesion, but this required such a viscous resin that it was impracticable to use"", FD Alliance Technical Manager Dr Paul Hill explains. The challenge has been to find a low-viscosity resin (so that it's practical) but that still displaces the water which means it has to do so chemically rather than physically. Moreover, it's the first step towards achieving an effective subsea composites repair system"".

FD Alliance's new resin system may well open up new opportunities in which weather protection would have been required to enable the job to go ahead. Measures to counter condensation have, until now, have added cost and caused disruption, Hill points out:

""Where there was condensation usually as a result of a cold pipe content in a humid, higher ambient temperature environment this has, to date, meant either doing the work at night when the ambient temperature drops, or using tenting (requiring scaffolders or riggers to erect it) coupled with either dehumidification equipment, forced-ventilation of the area, or locally heating the pipe to stop the condensation forming. These required additional time and cost easily equal to, if not more than, the price of the composite work itself. But this is now a thing of the past"".

The new moisture-tolerant resin system developed by FD Alliance overcomes the problems highlighted by Hill. Composites can now be applied to repair and strengthen in wet weather conditions, splash zones, and where condensation has previously been an issue.

Permanent repairs at pressures up to 100bar and temperatures up to 70C can be achieved using the new resin system, provided there is no through-wall defect.

Although all FD Alliance composites repairs are waterproof once applied and fully cured, it is the ability to apply them in wet conditions that now makes the difference. Extensive testing has of course been carried out to prove that repairs using the new resin system still satisfy the validation requirements of the Industry Workgroup and ASME specifications.