INTRODUCTION

A considerable external load application was specified by Statoil for all connectors therefore, our ASME VIII design analysis of the flanges had to consider and accommodate these additional loads. In addition to the theoretical analysis, Statoil requested a full size test to be performed on a 32” NB joint to further qualify the design.

Statoil required all flanges to have a ±0.7° misalignment capability due to possible alignment limitations during installation and so the Taper-Lok flange was the natural choice due to the male nose / female pocket sealing arrangement. The misalignment requirement posed no problems with the 10” and 12” flange but the 16” and 32” design required a spherical male nose and corresponding gasket seal face in order to comfortably achieve the full ±0.7° of misalignment. The drawing below shows an exaggerated concept of the spherical nose detail.

THE TESTING

This test consisted of two parts:

1 - API 6A PR2 Testing (Gas & Temperature Test)

This test was performed on a full size Weld Neck to Swivel Ring joint after being assembled to our specified pre-tension using 100% hydraulic tensioner coverage. The test involved many temperature changes from –10° to +55° whilst 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 resulting in a first class pass. The pictures below show some of the pretest engineering work and the actual components under test.

2 - Pressure & Bend Test

The joint having successfully passed the gas and temperature test, was disassembled after which, 6 metre, 32” NB pipe lengths were welded onto each connector to allow a bending moment to be applied whist the joint was under pressure. The connectors were subsequently assembled to our specified pre-tension values then, the cavity pressurised to full operating pressure at 172Bar. A minimum bending moment equal to the design bending moment value was then applied to the joint by pushing the pipe ends down and pivoting the assembly on accurately positioned lugs. Monitoring of internal pressure during the bending moment load application revealed no leakage and a secondary visual check of the joint also provided confirmation - the joint had successfully passed the 2ND and final test.

 

Having completed the testing to client requirements and proving a leak-free joint, it was decided to take the joint through a further pressure / bend test to establish its ultimate capacity i.e. the point of failure. On resumption of the testing, pressure was taken up to 172Bar, at which point an undetermined bending moment load was applied with the intent of subjecting the joint to failure. An amazing 4,250,000Nm load application was reached at which point 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.

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