Oil States tests giant Nord Stream subsea clamps

Offshore staff

SHEFFIELD, UK – Sheffield Forgemasters International (SFI) has delivered two repair clamp bodies for use on the 1,224-km (760-mi) Nord Stream gas pipeline system in the Baltic Sea.

The hydro-clamps, designed by Oil States in Houston, provide risk mitigation in the event of a breach in one of Nord Stream’s two subsea pipelines.

George Brown, group projects director at SFI, said: “The Nord Stream clamps are hydraulically operated repair mechanisms, designed to reinforce the Nord Stream pipeline at any required point along the Baltic Sea floor.

“The size of the forging exceeded the known parameters for the designated material selection and required a new engineering solution to make it possible.”

The clamp comprises two matched halves that can be locked around the pipeline to halt a leakage. In order to ensure matched pairs of half-clamps, the forging was produced as a single piece before being cut longitudinally to produce the two halves.

“To achieve this, we worked close to the limits of capable production,” Brown said. “Starting with a 120-in. diameter ingot, a singular form for the whole clamp was forged, rough machine and heat treated.

“This provided a safe envelope for the finished shape which was then cut along its 22-ft [6.7-m] length to produce two forgings which could be independently machined to the tight tolerances required before being finally reassembled and pressure tested.

“With a forged weight of over 200 metric tons [220 tons], no subsea clamp of this size has ever been produced before and if required, can restore full structural and pressure integrity to the Nord Stream pipeline in the event of a leak or identified weakness.”

The clamps are currently undergoing testing in Houston and will then be shipped to Nord Stream for emergency back-up use.


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Forgemasters’ forgings for the Nord Stream gas pipeline in the Baltic Sea
Forgemasters’ forgings for the Nord Stream pipeline. (Photo courtesy Sheffield Forgemasters International Ltd.)

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