The biggest users of bolts are the auto and aerospace industries. In the oil and gas industry bolted connections are often used for high integrity systems and are thus vital for the long term performance of (the given structure) e.g. structural components, pressurised vessels and piping. It is therefore of paramount importance that bolted connections can be designed and installed to provide the required service life for the various exposure and service conditions. Bolting can fail for a number of reasons (e.g. overload, fatigue or corrosion). The materials selection and manufacturing, bolt fabrication, applied protective coating and the final bolt installation are all factors which need to executed adequately to ensure that a long service performance. The actual service conditions and the external environment impact and maintenance will subsequently determine the service life of the bolting. To improve the reliability of bolted connections, a joint industry project” “Corrosion protection and maintenance of bolting and fasteners” was initiated by DNV in 2001. The initial part of the project will be to provide a summary of the best practice for corrosion protection of bolted connections for offshore application. Here bolted connection embrace materials selection of bolts, corrosion protection of bolts and performance of bolts on flanges and other mechanical connections (e.g. cranes). The main part of the project is a 10 year testing program of pretensioned stud bolts. The exposure program will be performed in the marine atmospheric zone, splash zone and submerged zone. This will be performed at the DNV seawater laboratories in Bergen and at the LaQue Center, North Carolina, US.

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