Quality control of heat treatment of oil and gas pipes using magnetic structuroscopy

The problem of the development of in-line nondestructive testing of mechanical properties of heat-strengthened oil and gas steel pipes remains topical. In this work, the effect of heat treatment conditions represented by the quenching temperature (in the range of 765–980°C) and cooling rate from the quenching temperature (in the range of 500–720°C, after quenching in water) on the structure, hardness, and magnetic properties (coercive force, residual induction, maximum magnetic permittivity, and saturation magnetization) is studied for the widely used pipe steels of 22KhG2A, 30KhMA, and 32G2 brands. The magnetic parameters are measured both in a closed magnetic circuit and using the attached magnetic devices on model and full-scale samples. A possible application of the coercimetric method as an alternative for the durametric one is shown for continuous underheating testing for quenching and the tempering quality of the pipes made from the steels under study during fabrication.