Jerry Wilks - Lemont Refinery
Chromium-molybdenum alloys have lower creep properties at welds, and this has led to creep cracking in high temperature vessels and piping at many refineries.
Lemont Refinery has a fluidized bed catalytic cracking (FCC) reactor made of UNS K12062 steel that operated for 38 years in the 510 535°C temperature range when the first creep crack occurred in this vessel in 2006. Follow-up inspections of the reactor conducted in 2008 revealed small cracks developing in several of the other vessel welds.
To arrest further creep cracking a new weld repair technique was tested: external reinforcement of the weld with UNS N06625 weld overlay. When the unit came down for a scheduled shut-down in 2010, those repairs were cut out and tested, and it was discovered that the weld overlay had stopped creep crack propagation. In order to extend the life of the vessel until it could be replaced, all the vertical seams in the vessel were weld overlaid with N06625.