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Pipeline Technology Journal 2-2015

Latest developments and news from the pipeline industry

RESEARCH / DEVELOPMENT / TECHNOLOGY Possiblesolutionswhenexistingpipelineexceedstheexpectedlifetime The integrity test is a specially modified stresstest where controlled hydrostatic overloading of pipeline up to yield point is monitored by a very precise measurement system. This test proves the real level of integral elasticity limit of the pipeline and verifies the real safety factor. Pressure overloading blocks the fatigue growth of under-critical cracks existing in the pipeline wall for many years of future operation and therefore extend its operational lifetime. The cracks of the over-critical size burst safely during the test and are cut out and repaired. Integrity test of pipeline material was mod- elled on a test vessel manufactured from a pipe taken from the pipeline section (see Figure 1). The parameters of the test were specified based on the results of material properties testing. During the integrity test the following measurements and monitoring were car- ried out and recorded continuously: • Measuring of test pressure depend- ence on added water volume, • Monitoring of the crack growth using the acoustic emission, • Measuring of local deformations and microdefects. Completed material tests proved the high quality of steel material of the oil pipeline section. After more than forty-year period of operation there were no signs of degra- dation of pipe material. Acoustic emission showed that a reduction of internal stress- es in the pipe material and a stabilization of defects occurred during the test. Based on the results of all the tests, the maximum allowed test pressure and the maximum allowed value of plastic circum- ferential deformation for on-site integrity test of the pipeline were determined. Figure 1: Pipe test vessel Figure 2: Cyclic fatigue test - part of p-t chart PIPELINE TECHNOLOGY JOURNAL 19

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