Intergranular susceptibility in failures of high pressure tubes

Two competing crack growth mechanisms in very high pressures tubes

“…The diameter of each curve is around 2.4 m; the length of the tract up to the thread is of 4.2 m. Within the tubes ethylene circulates in a polymerization stage. These fatigue failures follow other failures in the same reactor, but of an intergranular type, concentrated in the curved tracts, between 2002 and 2005 [1]. These failures involve unexpected plant stops, production losses and maintenance costs.…”

“…These last failures prompted a study to determine the weaknesses of the material that eventually favored the occurrence of such failures, in order to define and implement effective mitigation measures. These studies are presented in a previous article by the authors [5]. Transgranular Tempered Martensite Embrittlement (TME) was detected at test temperatures close to the ductile-brittle transition temperature.…”

Experimental assessment of thermal grain boundary embrittlement after tubeplate failure in a petrochemical heat exchanger

“…The phenomenon is already detectable with less than 5% plastic strains, while maintaining temperatures between 250°C and 400°C for even few hours. Since this mechanism is frequent in the tempering processes, it is usually called temper embrittlement [14]. Temperatures higher than 500°C do not weaken the deformed structure, so the manufacturer specified tempering at 720°C should not have embrittled the tubeplate.…”