State-of-the-art in-line pipe inspection

More than three million kilometers of high pressure liquid and gas pipelines are installed around the world. Generally steel pipelines provide the most safe means to transport large quantities of oil, oil related products and natural gas. However, just like any other technical component they can deteriorate. As a result flaws can appear and grow until the pipeline fails. Besides metal loss caused by corrosion, the appearance of stress corrosion cracking is of increasing concern. Such flaws must be identified, befor they endanger the integrity of the line and the environment. The paper will introduce the most common non-destructive techniques (NDT) applied to in-line inspection by using intelligent pigs as inspection tools. In gas lines such tools basing on the magnetic flux leakage of the flaws and in liquid lines ultrasonic inspection tools. All of them are pumped through the section of the pipe to be inspected together with the medium being transported therein in order to detect, size and locate flaw in the body and welds of transmission pipelines. They enable an inspection of the entire circumference and the length of the pipe of up to several hundred kilometers in a single run. The special emphasis of the contribution is on the characterisation and discussion of crack-inspection tools, the non-destructive testing principles applied and defect specifications