In June we had our first lunchtime meeting at Maggiano’s Post Oak! Dr. Guillermo Ramirez, with ABS Group, presented on Root Cause Analysis of a Pressure Vessel Failure.
Root cause analysis seeks to identify all relevant events and conditions that lead to a failure and link recommendations to causal factors. Dr. Ramirez demonstrated the SOURCE (Seeking Out the Underlying Root Cause of Events) process with an example failure of a pressure vessel. This vessel was designed to contain sour condensate at a pressure less than 40 psi and at a temperature less than 122˚F. The failure initiated at the head, where the section transitions away from the cylinder, i.e. at the knuckle of the head. A crack propagated from the interior of the head and progressed through to the outer surface ultimately resulting in a sudden failure of the pressure vessel.
The vessel was specified as 70 ksi steel, however through material testing they found that the knuckle of the head was closer to 100 ksi and the dish section of the head was closer to 50 ksi. ABS found that the proximate cause was sulfide stress cracking which resulted from operation in sour service with the presence of high residual stresses during the forming and fabrication process. They recommended 4 preventative steps to limit future failures: 1) that all similar vessels used in sour service and made with carbon steel be normalized, 2) that the cold-formed part of the structure be heat-treated for stress relieving, 3) that going forward they contractually require heat-treatment for vessels used in sour service and 4) that these pressure vessel designs be ASME stamped.
This was an excellent SEAoT seminar. Dr. Ramirez’s presentation sparked great conversation among repeat and new SEAoT attendees. Thanks to Emily McCarthy for providing this summary, as I was unable to attend! Be sure to come to our September meeting, which will be held on the 19th at Maggiano’s at Memorial City Mall. Note that this is not the Post Oak location that we met at during our last meeting! I will be presenting “Condition Assessment of Maritime Piers”, which will highlight a project our team recently completed in Puerto Rico.