Life management of refinery furnace tubing

Abstract The 2PTR and 3PTR furnaces at the MOBIL (Altona) Refinery have tubing that have been in operation for over 20 years. API RP 530 creep rupture life calculations showed that the tubes have limited remaining life. Therefore accelerated creep rupture testing was undertaken of a material from the likely worst case tube sample. However, going from creep rupture test results to assess the remaining life of furnace tubing is complicated by the fact that• the tested tubes may not have been exposed to the maximum temperature for the life of the furnace;• the test stress is different from the service stress because various pressure and wall thickness combinations exist. To overcome such issues detailed heat transfer calculations were carried out to understand tube temperatures based on thermography data and assessment of consumed life fraction was undertaken. Deterministic modelling of total life based on wall thickness data and operating pressure was carried out using most appropriate creep rupture database. It was found that there was sufficient remaining life for tubes in 2PTR furnace such that replacements were not required prior to the next normal outage. However, it is found that if high temperatures are experienced in 3PTR furnace a failure could occur in the near future. The information from the life assessment study was integrated into a risk based inspection program and set temperature limits to allow planned replacement of the tubing.