Solution & Implementation
Furmanite was called in to undertake the work, including the design and manufacture of the specialist machinery required. Under most circumstances Furmanite pipeline intervention techniques can be applied on-line, whilst production continues. However, in this instance work was being carried out as part of a planned shutdown and, as such, timing was critical. To ensure the time allowed was accurate an onshore trial was undertaken and successfully performed at Furmanite’s Aberdeen workshop prior to offshore mobilisation.
Cutting at a 45 degree angle is not straightforward as the change of angle means that the depth of metal being cut varies and the coupon being removed becomes oval. Extended pilot drills and cutters are required to accommodate this. Furthermore, because of the angle at which the pilot drill and the cutter contact the pipe, deflection of the pilot drill and cutter assembly is a considerable problem. To overcome this a pad providing a face perpendicular to the pilot drill axis was welded to the pipe prior to the branch being welded, enabling the pilot drill to maintain its central alignment.
The Furmanite hot tapping technique employs a branch connection attached to the line (either welded or mechanical) with a full bore gate or ball valve installed. A pressure tight drilling machine is used to commission new connections to existing piping, tanks or vessels. The valve acts as an isolation valve for the new connection and allows the drilling machine to be removed after cutting, while the welded or bolted branch connection contains the system pressure.