These events show the importance of preventing combustible gas mixtures from accumulating in piping. In both of the above described events, hydrogen and oxygen gases apparently accumulated to a combustible level which then catastrophically failed…

Recommendation 1 - Overhaul and replace the diaphragms on all cells showing low-purity results. Check on a routine basis the individual cell purity levels to monitor the deterioration of performance of individual cells. Certain…

• Operation and management of the hydrodesulfurization unit should be strengthened to account for abnormal phenomena such as local corrosion.
• The safety review system for remodeling existing equipment and facilities should be…

1. Carbon steel Nelson curve methodology cannot be depended on to prevent HTHA equipment failures and cannot be reliably used to predict the occurrence of HTHA equipment damage. Revisions to recommended practices should be considered…