Explosion at the hydrogen unit of a refinery

A pipe rupture occurred in a steam methane reformer (SMR) producing hydrogen and steam. The component affected was a 24-inch diameter stainless steel pipe used at startup, allowing the process gas to bypass the high-temperature shift converter during start-up. Due to the rupture, the process gas contained in pipe upstream and downstream of the break vented into the SMR plant yard area. The vented process gas was a mixture of hydrogen, carbon monoxide, carbon dioxide, steam, and methane at 550 psig (38 bar) and 650 F (345 C).
The escaping high-pressure gas caused an explosion and a subsequent fire. The fire was confined within the SMR plant, but equipment located near the pipe failure was damaged. The SMR plant distributed control system worked as designed and automatically shut down the process. Thid action limited the amount of process gas escaped.

Emergency response services were provided on the scene by the local county fire department within minutes of the incident and the fire was extinguished within 10 minutes.

Metallurgical examination revealed that the INITIATING CASUE was a crack starting from pipe interior, due to stress corrosion cracking (SCC) caused by the of presence of potassium hydroxide.
The most likely source of the caustic was small amounts of potassium promoter normally present in the SMR catalyst. During normal operation, the section of the bypass pipe where the rupture occurred was cool and without flow. Its layout allowed water and potassium hydroxide condensed from the process gas stream to collect in a low point. The stainless steel, material of construction of the bypass piping was susceptible to SCC from the concentrated caustic solution collecting in the bypass piping.
It is possible that this problem could not be foreseen during plant design. Nevertheless, it should have been possible to detect material degradation during inspection. Therefore, a possible ROOT CAUSE could be identified in inadequate inspection and maintenance procedures.

high-temperature shift converter

A high-temperature shift converter is a part of the Steam Methane Reforming.
It is the first step in the shift conversion section, reducing It is a reactor unit converting CO and water into H2 and CO2.

Its role is to increase the hydrogen yield and minimising CO concentration.
It operates at temperature of 310–450°C , and uses normally a iron-chromium catalyst F𝑒3𝑂4/𝐶𝑟2𝑂3

The sources provide conflicting values for the injuries. H2TOOLS claim no injuries, EPA and the only news report 2 injuries. It is probable that the discrepancy is due to different criteria for injuries.
No releases of acutely hazardous materials covered by the Risk Management Prevention Plan (RMPP), EPA CERCLA, and SARA Title III regulations.

The stainless steel 24-inch pipe that failed was replaced with a 1-1/4 Cr 1/2 Mo low alloy steel pipe, that is corrosion-resistant to stress corrosion cracking.
A revised bypass piping layout was installed on the High-Temperature Shift Converter, to prevent the hazardous conditions that lead to the failure.
A detailed hazard review and evaluation of all construction materials in the hydrogen plant process gas system led to preventively changing several other pieces of pipes and equipment items in the SMR process to 1-1/4 Cr 1/2 Mo stainless steel.