Cracks in ships' structure are traditionally repaired by welding; however, the application of fibre reinforced polymer patches can often save considerable time and expense. Patching technology was originally investigated at Rosyth in the 1980s. More recently QinetiQ personnel have applied patches to a number of warships and also to FPSOs (Floating Production Storage and Offloading vessels) operating in the North Sea. QinetiQ is currently providing underpinning work to achieve qualification of composite patching as a method for crack repair. A test programme has been conducted in which un-patched and patched plates containing cracks have been subjected to a cyclic load of ±100 MPa. These tests have demonstrated that patches can control crack growth and extend ship life. An ACPD (alternating current potential drop) technique has been shown to successfully characterise crack growth in laboratory patched specimens. This inspection method has also been used on warship repairs.
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