Ultrasonic testing pipelines

For pipelines in service in chemical plants, it is not usually convenient to place a radiation source inside the pipe and position it to irradiate each welded joint. The radioisotope source container maybe placed on the outer surface of the pipe. The radiation beams then pass through two pipe wall thicknesses to expose films placed diametrically opposite the radiation source, also on the outside of the pipe wall. Other methods, such as magnetic particle inspection of welds in steel pipe, or ultrasonic inspection of welds in pipes of all materials, supplement x-rays in many critical appHcations. The ultrasonic tests can often detect the thin, laminar discontinuities parallel to the pipe surface or the incomplete fusion discontinuities along the weld... 

Improved Performance of Guided Wave Ultrasonic Testing for Long Range Inspection of Pipelines using Multi-Channel Systems... 

Pipeline systems shall be tested after construction to the requirements of this Code except for pretested fabricated assemblies, pretested tie-in sections, and tie-in connections. The circumferential welds of welded tie-in connections not pressure tested after construction shall be examined by radiographic, ultrasonic, or other nondestructive methods in accordance with para. PL-3.19.2. 

A number of nondestructive test (NDT) techniques have been developed that permit detection and measiu-ement of both internal and surface flaws. Such techniques are used to examine stmctmal components that are in service for defects and flaws that could lead to premature faUme in addition, NDTs are used as a means of quahty control for manufacturing processes. As the name implies, these techniques do not destroy the material/structure being examined. Furthermore, some testing methods must be conducted in a laboratory setting others may be adapted for use in the field. Several commonly employed NDT techniques and their characteristics are listed in Table 8.2. One important example of the use of NDT is for the detection of cracks and leaks in the walls of oil pipelines in remote areas such as Alaska. Ultrasonic analysis is utilized in conjunction with a robotic analyzer that can travel relatively long distances within a pipeline. 

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