In the exploitation of offshore oilfields, a subsea tubing head might not be used for production immediately after it has been installed at the wellhead. In such circumstances, there is a need to protect the tubing head sealing surfaces against corrosion. Protection against damage or obstruction by falling debris, silt and biological accretions is also required.

The Cap has rubber face seal on the contact area with L-loop hub to minimise loss of preservation fluid from within the L-loop.