High temperature stainless steels and nickel alloys are successfully used in many areas of ethylene cracking furnaces. Although resistant to various types of corrosion e.g. high temperature oxidation or creep, under certain conditions those materials are susceptible to stress corrosion cracking phenomenon. The following paper reviews failures of tubes and supporting piping, made of austenitic stainless steel ASTM(1) A312-TP321H and nickel alloy 800H (ASTM B407, UNS(2) N08810), that have occurred in ethylene furnaces. Damages of bent ethane inlet coils (pig-tail type) made of ASTM A312-TP321H and "pressure gauge tapping” lines made of alloy 800H have been investigated. All failed elements were located outside the firebox with operating temperature below 700°C. Metallurgical analysis revealed stress-assisted corrosion as a major damage mechanism. Residual stress originated either from design or fabrication process, accompanied by severe carburization was recognized as a driving force responsible for observed failures.

Subject
Carburization, Materials, Valves, Nickel based alloys, Stress cracking, Lead, Intergranular cracking, Furnaces, Ethylene, Creep, Hardness, Cracks, Samples
Keywords:
ethylene furnaces, stress relaxation cracking, carburization, ASTM A312 - 321H, alloy 800H
Government work published by the Association for Materials Protection and Performance (AMPP) with permission of the author(s). Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2014
GOV
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