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Deepwater risers require inspection assurance

Connect, no. 107, July/August 2000, p.7

Automated UT equipment Courtesy RD Tech
Automated UT equipment Courtesy RD Tech

A GSP investigating the capability of the automated ultrasonic inspection systems (including multi probe and phased array equipment) for root defects in single sided girth welds is being carried out at TWI. It is supported by a total of 12 sponsors including oil companies, manufacturers, inspection and construction contractors and a regulatory body. The budget is £420k.

Deepwater steel catenary risers are being developed in many parts of the world for future oil extraction. The welded joints in these structures, and similar joints in tendon legs and some structural joints, are manufactured using welding processes applied from the outside of the pipe only.

Fatigue studies at TWI have shown that root defects are the primary cause of early failure in these joints. For the risers in particular periodic inspection of the welds is not envisaged and the emphasis is therefore being put on the initial manufacturing inspection to ensure the fatigue life.

Deep water riser
Deep water riser

It is anticipated that the inspection will be carried out by high speed ultrasonic methods recently developed for pipeline weld inspection during laying. Detection of the root defects in the fatigue sensitive areas is much more stringent than the normal pipeline inspection and it is therefore necessary to be sure that this inspection capability available is sufficient for the new application.

More information may be obtained from John Rudlin. E-mail:

For more information please email: