<p>Hydrogen Manufacturing Units which have a Pre-reformer often have large diameter, thick-wall stainless steel (SS) piping operating at 540-650°C (1000-1200°F). At numerous units, welds on this piping have experienced failures due to stress relaxation cracking (SRC). &nbsp;Similarly, SRC has been reported in SS piping operating at this&nbsp;temperature range in hydroprocessing and olefin units. This paper will give a description of the in-service SRC mechanism and describe some case histories of the cracking. It will define how the risk varies depending on the process conditions, pipe size and thickness, fabrication steps and more. The paper will also briefly list the pros and cons of different material choices for this piping based on various possible conditions, and rank the materials for their SRC resistance. Various other damage mechanisms also need to be considered and affect the optimum materials choice. The paper will provide some recommended steps for minimizing the risk of SRC on SS piping when SS is determined to be the preferred material choice. One of the key steps for providing resistance to in-service SRC is postweld heat treatment of the welds, but this has led to cases of reheat cracking during the fabrication stage. Guidelines for predicting and minimizing this risk are also reported.</p>

Stress Relaxation Cracking of Thick-Wall Stainless Steel Piping in Various Refining Units

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

ASME 2021 Pressure Vessels & Piping Conference (PVP2021)

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