هادی ابراهیم فتح آبادی

Various destructive and nondestructive methods are used for in line inspection of pipelines. A pipe may fail because of different causes such as corrosion, pitting, stress corrosion cracking (SCC), weld cracks and mechanical impacts and damages. Corrosion failures in a pipe can take place in different ways, some of them are easy to detect and others require special facilities and methods. The best selection of the inspection tools depends on the type of application, mechanism of corrosion, chemical environment and the material. This paper investigates and compares different types of in-line inspection tools for pipelines and compare their advantages and disadvantages. Today, the most common method for In Line Inspection of pipelines is Magnetic Flux Leakage (MFL), which is used for detection of wall thickness reduction of pipelines, various cracks, corrosion and pitting in pipes. Therefore, it can’t be applied for nonmagnetic materials. The Eddy Current (EC) test is a non-contact test with relatively low velocity which is sensitive to the stand off from the material surface during the test and it is used only for conductive materials. Ultrasonic testing is a common method with high accuracy. It is widely used for detection of different defects and is based on sending short wavelength high frequency ultrasonic waves into the material and receiving their reflections. By interpreting the results, various defects and reduction in the wall thickness of the pipes can be detected. Acoustic Emission (AE) testing, which is based on interpretation of elastic deformations, elastic strain energy changes and stress distribution, is not considered as a common test for inspection of pipelines, yet. Electromagnetic Acoustic Transducers (EMAT) are a new type of ultrasonic testing method which do not require liquid coupling but should be used at a definite distance from the pipe wall during the test. It is concluded that the fastest and most reliable method for In-Line Inspection (ILI) of pipelines is currently the Magnetic Flux Leakage (MFL) method.