A pipe rupture occurred in a steam methane reformer (SMR) process that produces hydrogen and export steam. The rupture occurred in a 24-inch diameter stainless steel (SS) pipe used to allow the process gas flow to bypass the high-temperature shift converter (HTS) during start-up. When the pipe ruptured, process gas contained in process equipment located 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 and 650 deg F. The escaping high-pressure gas caused an energy release and 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 (DCS) worked properly to automatically shut down the process, thereby limiting the amount of process gas that 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. There were no injuries and no releases of any acutely hazardous materials covered by the Risk Management Prevention Plan (RMPP), EPA CERCLA, and SARA Title III regulations.
Metallurgical examination of the failed pipe segment revealed cracking on the pipe interior. The cracks were the result of stress corrosion cracking (SCC) of SS, caused by the presence of caustic (potassium hydroxide). The most likely source of the caustic was small amounts of potassium promoter normally present in the SMR catalyst. The section of the HTS bypass piping where the rupture occurred was normally cool and non-flowing. The piping layout allowed water and potassium hydroxide condensed from the process gas stream to collect in a low point. The SS material of construction of the bypass piping was susceptible to SCC from the concentrated caustic solution collecting in the bypass piping.
The SS 24-inch pipe that failed was replaced with 1-1/4 Cr 1/2 Mo alloy pipe that is corrosion-resistant to SCC. A revised HTS bypass piping layout was installed to prevent the hazardous conditions that lead to the failure. A detailed hazard review and evaluation of all of the materials of construction in the hydrogen plant process gas system led to preventively changing several other pieces of piping and equipment items in the SMR process to 1-1/4 Cr 1/2 Mo.