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Pipeline Technology Journal 2-2015

Latest developments and news from the pipeline industry

RESEARCH / DEVELOPMENT / TECHNOLOGY In the reassessment of detected defects that were evaluated by TFI provider by standard way, CEPS chose the following approach: • Dents, laminations and certain weld defects were not repaired - the strength of pipeline in these spots should be checked during the integ- rity test, • Material loss defects were recalculat- ed according to: ANSI/ASMEB31.G modified and RSTRENG and DNV – Code. INTEGRITY TEST OF THE PIPELINE SECTION The special pressure test method was de- signed for the test of integrity of the pipe- line section after the internal inspection. CEPS used such a modified pressure tests for steel pipelines after a long period of operation. This integrity test is a modified stresstest that evaluates the real integral yield strength of the pipeline section, and therefore its real safety against the oper- ating pressure. The principle of this test is overloading of the tested pipeline section by high pressure water up to integral elas- ticity limit in the pipeline wall (calculated in advance) respective to stress approaching the elasticity limit. The result of the integrity test, except ver- ification of current technical condition of the pipeline, is improving conditions for its future safe and reliable operation by remov- ing a large and critical defects and the long- term blocking (stabilization) of the further development of subcritical defects caused by fatigue processes. DESTRUCTION DURING THE INTEGRITY TEST One destruction of the testing section occurred during the integrity test. In the course of destruction the pressure in the pipeline decreased to 0 bar during 1 second. It represents a water leakage of about 10 m3. The damaged part of the pipe was cut out and investigated. A longitudinal crack in the middle of the longitudinal weld on the external pipe wall caused the destruction. We found that the pipeline bitumen coating penetrated on the fracture surface up to the depth of 7 mm while the total thickness of the longitudinal weld was about 11 mm (see Figure 7). This area at the outer surface with incoherently black coating was about 150 mm long, but the total length of crack reached a length of up to 250 mm. Maximum and Minimum Tool Velocity Specification Distance [m] Velocity[m/s] Figure 6: Tool velocity chart Defects description Defects recommended to repair by TFI provider Defects repaired based on CEPS reassessment Dents with an another types of defect 9 - Dents located in/near a weld 9 - Metal loss (internal and external) 16 6 Anomaly of a circumferential weld 85 1 Anomaly of a longitudinal/spiral weld 26 - Inadmissible design elements and illegal hot taps 17 12 Total 162 19 Table 1: Defect assessment by provider vs reassessment detemined by CEPS Figure 7: Fracture surface 22 PIPELINE TECHNOLOGY JOURNAL Metal loss (internal and external) 166 Anomaly of a circumferential weld 851 1712 Total 16219

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