Pipelines are typically constructed by joining sections of pipes together using either manual or automatic welding. Such pipelines are used to transport water, oil, gas or chemicals for onshore or offshore applications. Pipelines for petroleum industries that is the objective of this paper are used mainly to operate at high percentage of yield strength and carrying dangerous and high flammable liquid or gas. Therefore, such pipelines specially the girth welds that are welded at site must be constructed and inspected to high standard. For many years traditionally Radiography (RT) has been used as Non-Destructive Testing (NDT) method for inspection of these welds. Radiography provides a real sectional or panoramic picture of the weld and a complete single girth weld can be tested by a single radiation shot. But RT has some major disadvantages like: Safety hazard of radiation, disability to detect planar defects, need for consumables (film, chemicals) and Lab for film processing and finally due to the delay to get the test results RT cannot be used as welding process control. Because of all these disadvantages of RT, specially after developing Automatic GMAW welding systems for pipeline welding and achieving smooth and uniform weld geometry, there was always a trend to replace it by Ultrasonic Testing (UT). The only possibility was to use manual UT but traditional manual ultrasonic testing has also other disadvantages like: real picture cannot be obtained, test results are hardly operator related and testing process is much more time consuming than radiography. Because of all these shortcomings, despite of accepting by most of related codes and standards, manual UT has never been used as a routine method for testing girth welds and its application was restricted for testing only repair welds or tie-in welds. But by invention of AUT and further developments like introducing Phased Array technique, New focusing probes, Time of Flight Diffraction method and using modern computer technology, AUT has been used extensively within the recent years and it has been recognized as the main NDT method and the reliable safe replacement inspection method instead of RT in pipeline construction. By this method not only the system locates the defective areas along the weld length, but by means of discrete zone discrimination it can also establish the vertical position and vertical extent of the defect. This precision defect location and assessment of vertical extent is the principle of ECA (Engineering Critical Assessment). Since some years ago International pipeline standards like API 1104, CSA Z662, DNV OS F101, and ISO 13847 have included AUT as an acceptable NDT method for pipeline girth weld inspection. The procedure for this test has been outlined in detail in ASTM E-1961 since 1988. Also in IIW (International Institute of Welding) in the framework of Quality Assurance of Welds, the Sub-commission VC who is dedicated to Ultrasonic weld testing, is currently working on a comprehensive handbook that is mainly focused on New UT methods particularly Phased array and TOFD techniques and their specific applications for pipeline girth weld inspection. Recently, trials to use Automatic welding systems as well as AUT in Iranian pipeline projects have been started and some offshore pipeline girth welds have been inspected by AUT by European contractors. In parallel National Iranian Gas Co. (NIGC) has imported 2 Automatic welding systems with 2 modern Phased Array+TOFD AUT systems for first trials. In this paper AUT for testing pipeline girth welds as well as the advanced techniques are described and the latest codes and standards are evaluated. The most common standard for this applications ASTM E-1061 is studied in details.
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