December 2011, Vol. 238 No. 12

Projects

T.D. Williamson Performs First Subsea STOPPLE® Train Isolation

T.D. Williamson Inc. recently completed the first-ever subsea STOPPLE® Train isolation.

The patented STOPPLE® Train plugging system links two plugging heads into a “train” capable of providing the added assurance of double block at each isolation point. The double isolation was performed in about 60 feet of water in the Gulf of Mexico to facilitate abandonment and decommissioning of an old platform.

In the past, pipeline operators used different methods to achieve double block functionality. These methods typically required more than one hot tap and fitting to achieve a double block, but the STOPPLE® Train plugging system requires one tap and fitting. Its linked plugging heads can be inserted into a line through just one opening. A single hot tap and fitting yield the double block benefit of two separate inline plugs.

Double block was critical in this case. A platform was being abandoned, requiring the removal and replacement of a section of pipeline. The pipeline section came up as a riser, crossed the platform and returned down as a riser before continuing. Both of the risers and the platform section of the line needed to be removed.

The line was bled down to 0 psi, then two 12-inch STOPPLE® Train systems were inserted – one on each side of the section to be removed – to prevent seawater, sand and organic debris from entering the 100-mile line when the section of the pipeline was cut out.
Once the new piping was installed, the seawater between the two plugging systems was evacuated and replaced with warm nitrogen to absorb and remove moisture. Following removal of the plugging heads, the pipeline was re-energized and placed back into service.