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Structural integrity assured for Liverpool Bay

Back to Pre-1998 Articles Adhesive technology demonstration centre Aged samples lend added credence to safety codes Arc welding Demonstration Centre shows best practice in action Boiler takes the heat in comfort Conductive adhesive for ultrasound catheter cracking-risk-in-steel-pipelines-from-external-hard-zones Engineering critical assessment of pipeline welds Far East fitness-for-purpose check First UK Research Council contract for TWI Friction stir welding of titanium Help with adhesives training Joining demonstration centres in industry Joining Forces success in Belfast Joints take 10 seconds in the microwave LIVEMAN - Advanced joining processes for lightweight vehicle manufacture Making calculations easier 'Mildly sour' environment project saves half a million pounds New standard for weld fracture toughness testing Novel method joins plastic pipes Plastics fume - new findings released Project saves time and money for Amerada Hess Small firms seize no-cost reviews and low-cost trials South East Asia ACFM course Space Shuttle technology transferred to power generation industry Spot the evidence Structural integrity assured for Liverpool Bay Supporting technology on the Indian sub-continent Technology demonstrators show best practice in action Thermomechanical material processing by friction [friction pillar processing] 'Tubestress' measures residual stresses in parts that other equipment cannot reach TWI enhances on-stream inspection service Underwater welding work expands at TWI North Wider recognition for welding inspectors

Connect, no.74, February/March 1996, p.1

The Douglas Platform complex in the Liverpool Bay / Irish Sea showing the Accommodation Platform on the right. (Courtesy BHP Petroleum)
The Douglas Platform complex in the Liverpool Bay / Irish Sea showing the Accommodation Platform on the right. (Courtesy BHP Petroleum)

When crack-like flaws are discovered in welded structures an assessment on the necessity of repair is needed as soon as possible. TWI engineers were called in to address just this situation in an accommodation rig being built for the Liverpool Bay Development Company.

Flaws had been detected in rack welds on the Morecambe Flame Jack-up Rig (now called the Douglas Accommodation Platform) during refurbishment. These were old fabrication flaws discovered while non-destructive testing the side plates which join the racks to the legs. Cracking had occurred at the weld toe of each rack.

The racks were fabricated from thick section high strength steel, so by trying to repair the old cracking more problems might be induced. TWI needed to assess the situation - could structural integrity be maintained if nothing was done?

Engineers at TWI studied the stress data supplied and the results from special shallow crack fracture mechanics tests (conducted on test samples taken from the racks). By carrying out an engineering critical assessment they were able to show that the flaws would remain stable with respect to failure by fatigue and fracture over the next 30 years (the design life of the platform).

Structural integrity was assured without repair.

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