Stress measurement in pipelines using electromagnetic acoustic transducers

Stress concentration is one of the main causes of failures in aircraft actuators and metal piping systems in ships. Traditional strain gauges can only measure stress at the bonding points, while X-ray equipment, being radiative and bulky, is unsuitable for on-site measurements. To develop a new method suitable for on-site stress measurement in pipelines, the nonlinear effects of metal pipes on guided wave velocity were investigated, and an attempt was made to establish a correlation between wave velocity and stress, enabling the back-calculation of the stress state in the pipeline through wave velocity measurements. The theoretical analysis assessed the sensitivity of specific guided wave modes to stress, and a novel electromagnetic acoustic transducer (EMAT) was designed. Its structure was optimized using the adaptive trust region Bayesian optimization (ATRBO) algorithm to selectively excite specific modes. Experiments demonstrated that this method achieves a maximum measurement error of 8.8 MPa and can complete pipeline stress scanning tasks with a spatial resolution of 100 mm. This represents a new method for stress scanning that does not require coupling, making it particularly suitable for non-contact on-site measurements in dense operational pipelines.