MANCHESTER, UK -- During the planning stage of the Tampen Link Project, Statoil's engineers determined that subsea bolted connectors with an angular misalignment capability would be required to accommodate fabrication tolerances for the spools and positional tolerances for the pipelay. Taper-Lok flanges were chosen.
Four sizes of Taper-Lok flanges were required with the same pressure rating: 32 in. (81cm), 12 in. (30 cm), and 10 in. (25 cm) 172 bar.
The Welding Units-designed Taper-Lok flange features a pressure-energized seal that assists the design by keeping bolt tensions low during load application.
The Taper-Lok's angular misalignment capability is achieved by a 'ball & socket' sealing mechanism. One side of the connector has a male nose that fits into a female pocket. This male nose has a spherical radius included to provide the ball and socket.
Statoil tested the 32-in. (81-cm) 172 bar weld neck to swivel joint. The test involved temperature cycles from –10°C to +55°C while under full pressure, half pressure, and zero pressure. The joint was constantly monitored by sniffer probes to detect any leakage of the 2% helium / 98% nitrogen gas mixture. Zero leakage was confirmed at the end of the test.
The joint was disassembled and 6-m (conversion) pipe lengths were welded onto each connector to allow bending while the joint was under pressure. The connector was subsequently assembled and the cavity pressurized to full operating pressure of 172 bar. A minimum bending moment of 3.125 MNm (equal to the design bending moment of 90% pipe capacity) was applied to the joint by pushing the pipe ends down and pivoting the assembly on positioned lugs, forming an arch with the joint in the middle. Monitoring of internal pressure during the bending moment load application revealed no leakage.
On resumption of the testing, pressure was taken up to 172 bar, and then an undetermined bending moment load was applied with the intent of subjecting the joint to failure. A .250 MNm load application was reached without failure, but the test was terminated in the interests of health and safety. After load retraction the joint recovered to its original condition and was still considered fit for purpose.