Regulatory Design Assessment of Cold Bonded Fasteners

Abstract

An increasing number of Brazilian floating platform units are currently entering a mature age, inducing numerous asset integrity issues. As corrosion damages FPSOs’ hull structures and outfitting, repairs and/or modifications have to be performed in explosive environment. Those features create important operational challenges, both in terms of safety and production continuity, when hot work techniques are to be used. This is the reason why Cold Pad has developed a cold work technique based on a heavy duty, bonded, mechanical fastener called C-CLAW™. On FPSOs, this novel solution allows today to repair primarily corroded outfitting like handrails, pipe supports, cable trays, electrical boxes and the like. Cold Pad and DNV GL are working together on a design philosophy, a regulatory approach, and a validation programme based on the DNVGL-ST-C501 and the so-called load and resistance factor design (LRFD) format. The article focuses on the application of the regulatory approach for the demonstration of the capacity and reliability of these fasteners. The strength of the bondline and steel fastener components, with their multiple failure mechanisms, are addressed and mainly supported by short-term test results. The article details the main challenges of that new design approach throughout the service life of bonded fasteners, and includes results and findings related to e.g. strength, susceptibility to temperature, and allowable short-term mechanical capacities based on regulatory safety factors. It also provides the early conclusions in terms of application on FPSOs and recommendations regarding fire hazards. The novelty of these bonded mechanical fastener lies, firstly in the industrial product itself, and secondly in the application of one of the most recognized offshore standards for composite components to derive its regulatory mechanical rated capacity.