Test Behavior of Low-Toughness Pipe Affected by Corrosion Defects

The general rule of thumb for a carbon steel material at a temperature more than 60°F below its fracture propagation transition temperature (FPTT) is that it may be susceptible to failing in a brittle manner. Such a material, if it contains a sharp flaw and if it is subjected to a tensile stress, even a stress level within the normal operating range, may exhibit a failure. This type of failure is often termed a “low-stress brittle fracture”. Historical occurrences of such failures in various structural applications have raised concerns regarding the application of traditional corrosion analysis methods to “old brittle pipe”, despite the fact that few such failures are known to have occurred in thousands of miles of older pipe in service. Testing of tubular products as described herein has demonstrated that pipe materials operating at much larger temperature shifts below their transition temperatures are capable of exhibiting ductile fracture initiation in the presence of metal loss flaws and in the absence of other embrittlement mechanisms.