Carburization sensing method

1. A method for sensing whether carburization occurs or not on an inner surface of a pipe or tube by an electromagnetic testing, comprising:

a first step of inserting a carburized pipe or tube in which occurrence of carburization on an inner surface thereof is known into an excitation coil and into a detection coil, and determining a value of a parameter K represented by the following Equation (1):

K =( I·N/L )· F −3/2   (1)

so as to sense the carburization that has occurred in the carburized pipe or tube based on an output signal outputted from the detection coil, where a current value of an excitation current passing through the excitation coil is defined as I(A), a length of the excitation coil is defined as L (mm), a number of windings of the excitation coil is defined as N, and a frequency of the excitation current passing through the excitation coil is defined as F (kHz); and

a second step of setting conditions of the excitation coil so as to obtain the value of the parameter K determined in the first step, and thereafter, inserting a pipe or tube that is an inspection target into the excitation coil and into the detection coil and sensing whether carburization occurs or not on an inner surface of the pipe or tube based on an output signal outputted from the detection coil.

2. The method of sensing whether carburization occurs or not on an inner surface of a pipe or tube according to claim 1 , wherein

in the second step, the conditions of the excitation coil are set such that the value of the parameter K satisfies 4≦K≦8.