Ultrasonic Inspection Technique for Inside Pressurized Pipe Elbows

Elbows in pressure pipes are important parts in the pipe inspection, which may become serious corrosion locations. Ultrasonic detection is a main technique for pipe inner inspection, and the use of traditional ultrasound and phased array technique for in-line inspection are advanced, long-term interesting and known by researchers. Several devices were invented for inside pipeline inspection and is suitable to some extent such as detecting long-distance pipelines. However, elbows especially tight elbows are still difficult to implement inner detection or travelling. To obtain a good effect in detecting elbows with ultrasound, the inner inspection technique was investigated. Spherical and flat cylindrical probe holder structures were proposed to ensure the ability to pass through elbows, while the spherical holder has a large number of conventional probes in its shell with a uniform arrangement and was designed to give a full view for ultrasonic detecting. As regards the flat cylindrical probe structures, it is more suitable for phased array ultrasonic technique to form a convex array. Both methods were proposed for better echo directions and amplitudes, and aimed to obtain the information of elbow characteristics. CIVA simulation was conducted based on the above design, and the focal effects were analyzed. Comparing with detecting precision and manufacture process, the phased array technique with flat cylindrical probe holder was chosen, and its device manufacturing and elbow inspection experiments were carried out. CIVA simulation was also used to analyze the influence of array and element parameters on the echo detection, and the design parameters were determined about the convex phased array. The experimental elbow was designed and manufactured with specific artificial defects. The ultrasonic system was taken by a robot to travel through the elbow, and the experimental data were used to verify the applicability of the ultrasonic inspection technique.