In the process of cracking furnace tube crack petroleum

it will occur carburizing phenomenon.When the furnace tube carburize to a certain depth

it will brittle rupture and its plastic will be decrease

Therefore

it will lead to great economic losses and induce security accidents.Giant magneto-resistance sensor is selected for magnetic detection by using the method of increasing carburizing layer thickness to increase the magnetic.In the condition of AC excitation

by using the iron plate to simulate the change of carburizing layer thickness

the characteristic of giant magneto-resistance sensor including the excitation frequency

terminal effect and lift-off effect are studied.It provides a theory basis for detecting instrument design.