Study On Safety Assessment Methods Of The Penstock Of The High Head Hydropower Station

The penstock, which bears a large internal water pressure and weight of the penstock and water, is an important part of the High head hydropower station. Besides, the penstock has an important impact on the safe operation of the whole plant. During the pressure test, suddenly the spherical vale on the bottom of the third deviated hole was cracked and the water blew out from the damaged areas of the spherical vale. Several minutes later, the pipe close on the top of the third deviated hole was thrust aside by the huge air burst.The accident never happened in the process of installing the penstock. In order to check the possible damage of the penstock made by the accident, based on the finite element analysis, the general mechanical property tests and the CTOD (crack tip opening displacement) test of the penstock in the third deviated hole, the GB/T19624-2004, that is the criterion of safety assessment for in-service pressure vessels containing defects suggested by China, is applied to assess the five weld defects in the penstock, which experienced the failure of the pressure test. The assessment results indicate that1#defect and5#defect could be accepted, while the other defects should be repaired. According to the assessment results, the defects over criterion in the penstock must be repaired. After the penstock was repaired, it was checked by the ultrasonic flaw detection again. And the results indicate that all weld joints including circumferential and longitudinal weld joints in the penstock around the pipe close in the third deviated hole are acceptable, what provides a scientific basis for the second pressure test and the safe operation of the High head hydropower station.