High-quality failure analysis and good engineering judgment can turn plant shutdowns resulting from methanol reformer tube failures into an opportunity to improve the future performance of the reformer furnace. The plant down time can be used to evaluate remaining tube life and provide some insight into the effect of tube operating history, especially tube metal temperature on tube performance. The results can be used to minimize potential future failures and economic losses because of reformer shutdowns. In this article, the failure mechanism of a ruptured reformer tube is determined and an assessment of the remaining life of non-ruptured tubes in the reformer is discussed. Two assessment methods are reviewed (1) metallographic examination of ex-service material to characterize microstructure and creep damage and (2) modeling of creep damage accumulation using special-purpose finite-element software (WinTUBE TM ).
There are more than 2.5 million miles of oil and gas pipelines in the United States. Approximately 900 failures occurred on hazardous liquid pipelines from 2002 to 2003, and 9% of these failures were attributed to damages due to natural force, which included lightning strikes, among other naturally occurring events. This paper provides a case history in which failure analysis was applied to determine the metallurgical cause of a failure involving a polyethylene-coated hydrocarbon pipeline that leaked as a result of a lightning strike.
The static accuracy and zero offset meet the Association for the Advancement of Medical Instrumentation (AAMI) BP22:1994 standard. The zero drift is judged to be acceptable for arterial pressure measurement because a change of 3 mmHg is not clinically significant. The 15% bandwidth is judged to be adequate for fluid-filled pressure monitoring systems. It will be advantageous to couple the disposable dome to the reusable transducer when the disposable dome has a positive pressure.
There are more than 2.5 million miles of oil and gas pipelines in the United States, totaling over 330 million girth welds below ground. During construction, girth welds are susceptible to the formation of various defects, one of which is hydrogen-assisted cracks. The synergistic impact of tensile stress, a susceptible microstructure, and atomic hydrogen can lead to hydrogen embrittlement and the formation of hydrogen cracks. This paper reviews hydrogen cracking of girth welds in carbon steel pipelines made during new construction and provides examples involving hydrogen cracking in which failure analysis techniques were used to establish the metallurgical cause of failure.
The types of defects that have caused in-service failures and hydrostatic test failures of natural gas and hazardous liquid pipelines comprised of electric resistance welded (ERW) or flash-welded seams were revealed by a study of 569 seam failure incidents that occurred over a period from the 1940s through the present. This study confirmed that ERW and flash-welded seam manufacturing defects, such as cold welds (lack of fusion) and hook cracks, are frequent causes of hydrostatic test failures. Causes of in-service failures included cold welds, hook cracks enlarged by fatigue, other manufacturing defects enlarged by fatigue, selective seam weld corrosion, hydrogen stress cracking, sulfide stress cracking, and stress corrosion cracking (SCC). An important finding with respect to low-frequency-welded ERW and flash-welded materials was that defects in the bond lines of such materials (e.g., cold welds, selective seam weld corrosion) sometimes failed at much lower stress levels than one would predict based on the toughness of the parent metal. This fact complicates seam integrity assessment by means of in line inspection (ILI) because toughness is needed to prioritize anomalies for examination, and the toughnesses of the bond lines of most pipelines are not known. The findings suggest that conservative assumptions may have to be made in order for a pipeline operator to have confidence in a seam integrity assessment by means of ILI even if the ILI technology accurately characterizes the anomalies.
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