Non-existent or poor preventive maintenance programs has been a recurring root cause in CSB investigations. The CSB has identified in many of its investigations instances wherein a robust preventive maintenance program would have identified compromised equipment which led to the incident. Given the number of incidents that the CSB has investigated resulting from delayed maintenance or no maintenance, the CSB identified “Preventive Maintenance” as a Driver of Critical Chemical Safety Change.
More specifically, the CSB has found the following primary root causes in several of its previous investigations:
CSB Safety Alert: Preventing High Temperature Hydrogen Attack (HTHA)
As a result of the Tesoro Anacortes investigation, the CSB found:
- The heat exchanger that failed was nearly forty years old.
- The immediate cause was long-term, undetected High Temperature Hydrogen Attack (HTHA) in which localized microscopic cracks form which are difficult to identify.
- An unreliable inspection strategy was used based upon design operating conditions rather than actual operating parameters.
- Carbon steel in processes that operate above 400 degrees Fahrenheit and greater than 50 psia hydrogen partial pressure are susceptible to HTHA.
- Unlike carbon steel, high-chromium steels are highly resistant to HTHA.
- The Nelson Curves in the previous version of API RP 941 were missing several data points where failure occurred below the curve.
- The current version of API RP 941 did not incorporate all the data from the Tesoro incident.
In the absence of industry guidance that incorporates findings from the Tesoro Anacortes failure, the CSB issued a safety alert to provide the following additional direction for industry.
1. Identify all carbon steel equipment in hydrogen service that has the potential to harm workers or communities due to catastrophic failure;
2. Verify actual operating conditions (hydrogen partial pressure and temperature) for the identified carbon steel equipment;
3. Replace carbon steel process equipment that operates above 400 °F and greater than 50 psia hydrogen partial pressure; and
4. Use inherently safer materials, such as steels with higher chromium and molybdenum content.
Last Updated February 6, 2017