Damage assessment of process heater tube by magnetic technique : a case study

Ferromagnetic properties of steel change with the microstructure, composition and the stress state of the materials. Such variations are also taking place when the steel components are in service. Hence magnetic techniques may be used as a potential tool for integrity assessment of engineering components. The present work deals with the magnetic characterisation of process heater tube made of austenitic steel HP-40 grade employed in naphtha cracking unit of a petrochemical industry. The tube was non-magnetic in the virgin state and became magnetic during service exposure. The origin of magnetism in service exposed tube will be discussed here. Feasibility of using magnetic non¬destructive evaluation technique for damage assessment of the studied process heater tube will also be explored in the present investigation