On bending and breaking: Cost-optimized construction of subsea pipelines

Mitsui Babcock, of Glasgow in Scotland, is a global leader in the validation and testing of subsea oil pipelines. This guarantees optimum pipeline construction, as well as safe laying even in deep sea. To derive the maximum possible benefit from their tests, they decided to use linear strain gages from HBM’s standard product program, the MGCplus amplifier system and the data analysis software catman.

Ensuring integrity under load …

A common method used in pipeline construction is to fit an enclosed stainless steel coating into the external carbon steel pipe by hydraulic widening. When the pipelines are laid, they are exposed to bending moments and transverse forces, whereas later on, they must withstand temperatures and pressures,
for example, that must not be allowed to impair their function.

It is particularly important to test the loading capacity of the pipelines, to prevent subsequent damage that could have far greater effects on production and the environment.

"One reason for using HBM’s MGCplus amplifier system is that it gives us access to significantly more measurement channels than were previously available for determining stress levels." Albert Holt, principal test engineer at Mitsui Babcock

… with HBM strain gages, MGCplus and catman to 35 MPa.

Pipeline sections up to 12 m in length are tested on a four-point bending rig designed by Mitsui Babcock. The duration of the tests varies, depending on the complexity of the test program. The latest technology is used to optimize the information obtained from the tests. For example, extremely high resolution cameras are inserted into the body of the pipe to provide visual evidence of possible structural damage, such as that occurring at the onset of buckling. The largest pipe tested by Mitsui Babcock was 660 mm in diameter.

"HBM was a great help, as they developed a customized interface just for us. It allowed our engineers to see for themselves the effects of a pipeline bending under load. catman is the perfect tool for this." Albert Holt

Most of the tests are static, it is only when testing to destruction with compression, tensile force and burst testing that dynamic tests are performed. Strain gages are used to determine the levels of strain that for static tests is 3% above nominal strain. The pipes are exposed to temperatures up to 165 °C and pressures up to 35 MPa.

"HBM’s equipment is quickly configured and we can connect vast numbers of transducers. This clearly represents the best value for money." Albert Holt

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