High pressure long distance transmission gas lines: structural integrity of high strenght steel grade pipeline

摘要

The huge increase in natural gas need, forecast for the next century, even due to the high environmental compatibility, forces to develop new technological solutions for the economical exploitation of gas fields in remote areas. North America, Europe, Russian Asia, in the next century century, will be the main gas consumers; at the same time larger gas producer countries will become available on the international market. This scenario forces to verify the economical attractiveness for natural gas transportation over long-distances with large diameter high pressure pipeline. In order to verify the possible application of high pressure, long distance natural gas transportation, in 1995 E.N.I. sponsored a research program. This activity has been developed by a joint co-operation among SNAM, Centro Sviluppo Materiali (CSM) and ILVA to assess the fracture behaviour of large diameter (up to 1442 mm), heavy wall thickness (up to 30 mm), high steel grade (API 5L X70 and X80) pipes for operating pressure over 15 MPa. Aim of this research was to check the current material criteria, for the avoidance of brittle fracture initiation and long shear ductile fracture propagation for pipes under investigation. The fitness of the DWT Test, to define the ductile to brittle transition temperature, has been validated by comparing laboratory and full scale West Jefferson tests. The validity of the current approach to ductile fracture propagation control, based on the agreement between the Battelle equation predictions and the existing full scale tests data base, has been investigated by means of two full scale propagation tests on X70 and X80 steel pipes, operated at hoop stresses of 408 MPa and 440 MPa respectively.