Pipe dent evaluation by acoustic emission during hydraulic pressure tests

Abstract

Buried pipelines transporting gas and oil are influenced by surrounding soil during long time service. In many cases they are locally deformed by soil movement, especially by hard stones. External local pressure makes limited deformation of original shape of pipe diameter in time. Those types of local deformations are known as a dents. At those areas, the insulation layer is usually damaged and small defects (like cracks) are created in dents. Colonies of small stress corrosion cracks are observed. In this contribution, the evaluation of typical dents is investigated by hydraulic pressure tests, including the fatigue tests. Acoustic emission was used to detect the behaviour of dent in pipe section until the limit state. AE monitoring during pressure tests gave very clear answer of defect activity vs. loading pressure. Parallel to this monitoring, another NDT method, MMM was used with promising results.