Popular Detection Methods of Stainless Steel Pipe
Having identified unique aspects of detecting corrosion in stainless steel, we will briefly overview some of the more popular detection techniques.
Visually inspecting for corrosion with your own eyes is the simplest method of all. If you have only a small amount of pipes or tubes, it may be the cost-effective approach as well. However, for the large systems home to most stainless steel tubes and pipes, visual inspection becomes the least cost-effective approach due to the enormous amount of labor required. In addition, you can’t visually inspect what your eyes can’t see, so if there is insulation, you can’t inspect anything that you do not cut off, making it extremely difficult to detect non-uniform corrosion such as cracking. Furthermore, the human eye has proved notoriously inept at detecting stress corrosion cracks, which can start out incredibly small. Relying solely on visual inspection is almost always not recommended.
X ray (radiography) can be used for corrosion detection without requiring insulation removal. One disadvantage is that X-rays produce radiation, and the precautions that need to be put in place when conducting X-ray testing may be impractical in many environments. Another disadvantage is that X-ray does not detect cracking and pitting; however it can be very useful for detecting other kinds of defects.
Eddy Current Technique
The Eddy Current Technique (ECT) has likely become the most frequently recommended corrosion detection method for stainless steel. This technique uses electromagnetic induction to apply alternating “Eddy” currents to the pipe or tube. As the electromagnetic field interacts with the material, the impedance of the coil in the testing probe changes; the impedance paints the picture of the defect in the tube.