by Phillip E. Prueter, P.E. / May 01, 2019

High-temperature hydrogen attack (HTHA) is a damage mechanism that can detrimentally affect the service life of carbon steel and low-chrome pressure equipment in the petroleum refining and related industries. HTHA involves the diffusion of hydrogen into steel, where it chemically reacts with free carbon at high temperatures to produce methane. This methane then gets trapped inside small cavities and other material defects. Over time, the rising methane pressure in these cavities can cause damage at the material grain boundaries. To this end, long-term exposure to high-temperature hydrogen environments can lead to volumetric damage that can diminish the load-carrying capability of pressure equipment and accelerate the propagation of crack-like flaws. There have been several known industry failures attributed to HTHA damage as well.

This article summarizes a case study of a detailed analytical evaluation of potential HTHA damage in a vintage C-0.5Mo hydrotreater reactor. The goal of this study is to quantify the severity of HTHA damage using methods developed as part of an ongoing, multi-year Joint Industry Project (JIP) to justify continued operation of the reactor until the earliest practical replacement opportunity. HTHA damage and crack growth predictions are carried out based on documented historical operating conditions. Additionally, sensitivity in predicted remaining life to anticipated future operating temperatures is considered. Furthermore, based on state-of-the-art non-destructive examination (NDE) methods, fracture mechanics-based minimum pressurization temperature (MPT) envelopes are generated to help guide start-up and shutdown procedures that mitigate the risk for brittle fracture. Practical recommendations are also provided to facilitate the interpretation of NDE findings and to implement ongoing failure mitigation and risk management strategies, including the development of Integrity Operating Windows (IOWs), for the reactor until planned replacement.

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