The application of the acoustoelasticity method for the determination of stresses in anisotropic pipe steels

Abstract

Elastoacoustic coupling coefficients (EACCs) are links between acoustic parameters and mechanical stresses during their determination by the acoustoelasticity method. The magnitudes of the EACCs of a structural material can be calculated if its elasticity constants of the second and third orders are known or determined experimentally for a known stress state of a material. Unfortunately, the calculation variant is little used practically because not all moduli of nonlinear elasticity of even basic structural materials are known with sufficient accuracy. Here, the results are given of the experimental determination of the magnitudes of EACCs for three grades of low-alloy structural steels with different magnitudes of proper acoustic anisotropy, which is determined by the anisotropy of the elastic properties of a material. During the mechanical tests, samples were subjected to uniaxial tension at stepped load magnitudes. They were cut from longitudinal welded tubes of the K60 strength class, which are applied in the mounting of a linear section of gas-main pipelines. Experiments were carried out using an acoustic bench (based on an I2-26 off-the-shelf device) and an IN-5101A automated device that was developed by the ENCOTES Engineering firm, which use the ultrasonic echo method for nondestructive testing. The results of the acoustomechanical tests showed that during the calculation of biaxial stresses according to the data of precise ultrasonic measurements in pipe steels with a magnitude of greater than 3% for the proper acoustic anisotropy, computational algorithms that take the differences of the magnitudes of EACCs into account for stresses that work along and across the direction of the rolling of pipe steel should be used, i.e., along and across the longitudinal axis of the pipe.