Subsea pipelines | testing
risk of problems caused by installation-related coating and joint damage. The cyclic (fatigue) bend test is ideal to demonstrate
a coating’s theoretical lifespan. The bend test, although a large test that requires a large test rig, normally looks at worst-case scenario. From a polymer point of view, the normal method of cooling samples can cause problems that would not occur in a typical real world situation. Exova belives its new tests may be more suitable for purpose. l Small scale realistic bend tests: Current laboratory bend tests do not take into account the residual strains and stresses which are present in the pipeline coating but are released when samples are produced for testing. In the new proposed test, samples are loaded prior to testing to re-introduce the stress in the coating. l Cyclic full-scale bend test under stress: In order to be realistic, field joints need to be tested within an hour of the joint being produced. Samples need to be put under stress by twisting before bending at a temperature equivalent to the depth when the bend takes place. For S-lay processes the initial bend will be at a higher temperature and should be held while cooling to the
second temperature for the reverse bend. l Crack propagation under pressure: This will deter- mine the effect of damage to the external surface of the pipeline coating system and is based on the principles within ASTM D1693 for environmental stress cracking. Bent notched samples are placed in a holder and exposed to a salt water environment under pressure and temperature. It is likely there are other more suitable tests that
can be developed to better prepare coatings for the harsh environments they are likely to face in the oil and gas industries. Doing this, however, requires the assistance of test institutes in developing a more practical side to the testing.
About the author John Carter is strategic account director within the coatings division of global testing group Exova. The company is at the forefront of oil and gas industry testing via its international network of accredited facilities, from which it provides both testing and advisory services to the oil and pipeline sector. ❙
www.exova.com
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