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Pipeline Technology Journal 2-2015

Latest developments and news from the pipeline industry

CYCLIC FATIGUE TEST – EXPERIMENTAL MODEL The test of resistance to cyclic fatigue and the crack growth caused by the fatigue mechanism was performed by high cycle loading (see Figure 2) on the same test vessel as the integrity test. The fatigue test was performed under these conditions: • Pressure amplitudes were from 5 bar to MAOP, • 15 000 of cycles simulated 30 years of the future pipeline life. During the fatigue test, no development of dangerous defects was detected by acoustic emission. Simulation of the long-term operation by cyclic pressure loading verified the considerable life-time exten- sion which was achieved by the integrity test. DESTRUCTION OF THE TEST VESSEL The test vessel was pressured up to the ultimate strength limit Rm of the pipe material. When pressure achieved the value of in advance calculated pressure of ultimate strength, the destruction of the longi- tudinal weld occurred (see Figures 3). INTERNAL INSPECTION OF THE PIPELINE SECTION As it is well known, on pipelines of that age there are almost always manufacturing defects, then defects caused during construction of the pipeline (welding, laying),defects initiated by the service load, corrosion defects and defects caused by third parties. For this reason, the pipeline operator required an internal inspection of a short pipe- line section, whose main objective was to detect and locate defects that would certainly not withstand the test pressure during the sub- sequent integrity test. In 2000 the MFL and UT internal inspection of the pipeline was carried out. After subsequent shut down of the pipeline it was not expected further development of fatigue defects (particularly the cre- ation and growth of cracks caused by changing pressures in the oil pipeline. Based on this fact the pipeline operator decided to carry out the internal inspection using TFI tool before the integrity test. The section was not equipped with launching and receiving traps and therefore CEPS designed a manufactured the temporary traps for the inspection tool run (see Figures 3 and 4). The pipeline remained empty after chemical cleaning and subse- quent preservation and it was necessary to ensure a steady move- ment of the inspection tool by a substitute medium. CEPS propelled the TFI tool through the pipeline by water in this case. PROPELLING OF THE INSPECTION TOOL THROUGH THE PIPELINE SECTION In accordance with the requirements of the TFI provider, the inspec- tion tool had to be driven through the pipeline with a speed at least 0.5 m/s (see Figure 3). It meant pumping of 685 m3/h of water into the pipeline during the run. In total we pumped in about 3,100 m3 of water during 4.5 hours. For illustration - this amount of water would be enough for the supply of all fountains in the gardens of Versailles for one hour. Figure 3: Destruction of the test vessel RESEARCH / DEVELOPMENT / TECHNOLOGY 20 PIPELINE TECHNOLOGY JOURNAL • 15000 of cycles simulated 30 years of the future pipeline life.

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