Published: Jan 1994
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This case study shows the importance of considering welding flaws in pipelines that may be subjected to cyclic pressures. The case study will demonstrate that the ASTM specifications currently used to purchase welded pipe do not ensure adequate safety for cyclic loading.
A piping system was installed using Specification for Seamless and Welded Austenitic Stainless Steel Pipe (ASTM A 312) welded pipe. Longitudinal welds are made without the addition of filler metal by resistance welding from both sides of the pipe wall. This process frequently results in lack of fusion (LOF) flaws in the pipe. Hydrostatic testing used to demonstrate conformance with ASTM standards does not detect flaws that will grow in service.
An example of a failed pipeline system is presented. Pressure loading histories were obtained during normal operation of the piping system. Crack growth materials data were available for a fracture mechanics analysis of the system. A discussion of the ASTM standards as they relate to this problem are included.
fatigue failues, design codes, lack of fusion (LOF) flaws
University of Illinois at Urbana-Champaign, Urbana, IL
U.S. Army, Construction Engineering Research Laboratory, Champaign, IL