Stress Relaxation Cracking, A Misunderstood Problem in the Process Industry

Abstract Many high temperature material failures in pressure equipment in the chemical and refining process industry have been attributed to Stress Relaxation Cracking (SRC) or Reheat Cracking (RC) as it is called in the UK. SRC/RC failures are being reported frequently in the literature [1][2][3][4][5], in spite of construction in accordance with high temperature design codes for pressure equipment. Very few preventive measures have been incorporated in process equipment design codes. Several SRC/RC theories have been proposed [4][7][6]. The mechanism is often described in terms of a degraded microstructural state before damage starts to accumulate. This has not led to predictions on if or when failure occurs, although somewhat successful mitigation strategies [8][9] have been defined, which involve heat treatments of materials and fabricated structures. In this paper, the current understanding of in-service SRC/RC will be summarized with a primary on austenitic stainless steels and Nickel alloys. It will be explained why some mitigation strategies work and what are the practical implications for the process industry. The usefulness of various testing programs for alloy characterization and susceptibility ranking will be briefly discussed, and the paper will highlight the capabilities of the UK nuclear power industry’s R5 “Assessment Procedure for the High Temperature Response of Structures” [10] for the prediction of SRC/RC.