Abstract

Heat resistant Iron-Nickel-Chrome alloys, such as Alloy 800H, are designed to be used at elevated temperatures. At temperatures ranging from 550 to 750°C (1022 to 1380°F) these alloys can be susceptible to stress relaxation cracking (SRC). For these and other high temperature alloys, API Technical Report 942-B provides recommended ranges for material composition, as well as fabrication and heat treatment measures to mitigate Stress Relaxation Cracking. However, it has been shown to be difficult to obtain material that satisfies the API recommended prescriptions. Recommended alloy composition, welding and fabrication steps can become complex for special situations found on projects (i.e. thicker wall piping, dissimilar metal welds, etc.). This paper discusses example applications, and the reasons for selecting Alloy 800H. It also describes the SRC mechanism, the technical justifications for the API 942-B recommendations, and the challenges that have been experienced trying to meet these recommendations.

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