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T.D. Williamson has completed a subsea hot tap intervention operation to facilitate the successful tie-in of a new gas pipeline to an existing pipeline


The new pipeline forms part of the Burullus Gas Company’s West Delta Deep Marine (WDDM) Phase VII development project in the Mediterranean Sea.

The operation was carried out for Technip Norge on behalf of the Burullus Gas Company, which required a tie-in of the new 36-inch gas export pipeline to an existing 26-inch gas export pipeline. TDW’s primary objective was to facilitate the tie-in program without shutting down production.

TDW completed two traditional 16-inch hot tap operations on the 26-inch gas export pipeline. In addition, an innovative 20-inch hot tap on the 36-inch line was executed on a blind weld-neck “tappable flange” made of duplex stainless steel. To prepare for the hot tap operations that would take place in depths to 95 meters, TDW carried out extensive engineering, design and preliminary testing at its facility in Nivelles, Belgium. A special hot tap tool known as a “cutter” that would effectively cut the duplex plate was customized for the operation. This special cutter, which is more rigid than the standard tool, is vibration-free and features a specially manufactured removable cutting teeth system for use on specific duplex tools.

Hot taps

For approximately three weeks TDW worked from Technip’s dive support vessel Wellservicer to carry out all three hot taps. The innovative hot tap on the duplex tappable flange required just six days to complete. Throughout the process, a prevailing pressure of 100 bar was successfully maintained in the 26-inch gas export pipeline.

In spite of the fact that the hot tap intervention was carried out subsea, which makes it more complicated to mobilise and install equipment than for projects conducted onshore, the operation went to plan. According to TDW, the company’s extensive experience in executing subsea hot tap operations and dedication to planning and pre-operational equipment trials and testing are the reasons for its success. “In co-operation with the Technip team, we worked hard to ensure that the operation would proceed like clock-work, and that the customised cutting tool would operate effectively on duplex stainless steel,” said Michel Courbat, Offshore Project Manager for TDW. “As a result, our joint efforts paid off and the WDDM hot tap tie-in programme was achieved, safely and efficiently,” he added.

Although this is the first time that TDW has delivered offshore hot tap services for the Burullus Gas Company, in 2009 TDW provided similar services on portions of the onshore pipeline system that form part of the WDDM in Egypt.