Evaluation of Stresses Generated by Welding in API 5L X65 Steel Using Acoustoelasticity

API 5L X65 steels are used to manufacture pipe for gas and oil pipelines. Several countries use a manual welding process that utilizes coated electrodes. During the process of welding by deposition, residual stresses appear in the welding region. It is crucial that these stresses be known in order to accurately assess the service life of the junction, since these stresses may combine with applied stresses and result in failures. This paper describes the use of acoustoelasticity to evaluate the stress profile in welded joints. The technique is based on the measurement of speed variation of ultrasonic longitudinal critically refracted waves and the relationship between this speed variation and the change in stress patterns. The variation of speed is also directly related to the properties and the manufacturing characteristics of the material analyzed. Stresses were measured in the longitudinal direction of the welding cord. The original plates were stress relieved. The ultrasound results show good agreement with the expected stress profile, although additional studies are needed to assess the magnitude of stresses in the thermally affected areas resulting from structural changes and the addition of welding material.