An Evaluation of Void Formation in Ex-Service and Creep Tested HP Alloy Tubing Used for Hydrocarbon Reforming

HP alloy tubing is commonly used in petroleum reforming facilities for its high temperature strength and resistance to corrosion. Unfortunately, the tubes can experience failure during service caused by the formation of voids in the tube wall brought on by creep stress generated by the pressure differential and thermal gradient between the inside and outside diameters of the tube. The purpose of this project was to analyze the formation of voids in eight ring sections, each from a different ex-service tube, from a total of three different manufacturers (identified as M1, M2, and M3). Further analysis of the ex-service tubes was done by evaluating eighteen creep tested samples removed from the eight ex-service tubes. For both the service exposed and the creep tested samples, the general location for preferential void formation was identified as being in the fine grain region of the tubes at the inside diameter. Furthermore, it was determined that the tubes from manufacturer M1 are more resistant to damage during service than the tubes from manufacturers M2 and M3. Despite being exposed to the highest service temperature and longest service exposure, the tubes from manufacturer M1 had no indication of damage upon removal from service and experience the lowest amounts of void formation.