The Effect of Materials and Design Geometry on Tube Plugs at High Pressure Steam Super Heater

A high-pressure (HP) steam super heater located in the primary reformer of Ammonia Plant of Saudi Arabian Fertilizer Company (SAFCO) has ruptured twice in two different tubes, in 2009 and again in 2014. On both occasions, the repair was performed by removing and plugging the failed tube. In January 2015, the new plug that was installed in 2014 failed and led to an emergency shutdown. The older plug was found to be in good condition. An investigation was initiated to determine the reason for failure of one plug within nine months of operation while another was still in good condition after 6 years of operation. The failed plug was subjected to a metallurgical failure analysis where visual and stereoscopic inspection, scanning electron microscopy, metallographic examination, and chemical analysis were performed. The two plugs had different geometric designs, and thermal and static structural finite element analyses were performed to compare the 2009 and 2014 designs. Based on the outcome of the investigation, the cause of failure and the reason for the discrepancy in lifetimes of the two plugs was determined. This paper will present the conclusions of the metallurgical failure analysis and design review which was performed, and the improved repair design that was developed as a result of the investigation.