Portable Electronically Based Method for the Nondestructive Remote Sensing of Crevice Corrosion

Corrosion in the crevices of gasketed joints in the presence of seawater have been particularly troublesome for the Navy and may cause serious damage in assembled seawater pipe joints. The disassembling of numerous pipe joints comprising gasketed flanges is tedious, slow and is a costly way for crevice corrosion inspection. Therefore, a need exists for new nondestructive techniques of crevice corrosion detection. Some of the existing nondestructive techniques, e.g., electrochemical techniques, scanning current probe, and scanning potential probe, are based on corrosion examination from the water side, i.e., sensors have to be introduced inside the pipelines. These are impractical and not necessarily relevant to localized crevice corrosion. Techniques which may be used without penetrating the pipline system include ultrasonics, radiography, eddy current measurements and neutral radiographic spectroscopy. However, most of them suffer from low signal-to-noise ratios. The innovative approach proposed here is based on the application of four probe resistivity measurements for the detection of pit formation and thickness changes of flange alloys in gasketed pipe joints caused by crevice corrosion. This approach has the dual advantages of being nondestructive and very simple. The probe is attached on the outer surface of the flange, and there is no need for disassembling a flange. If shown to be successful in the detection of thickness changes due to pits formed at the netal part of the gasket/flange crevices, this technique has the potential to be easily designed as a fast remote sensing technique for crevice corrosion detection of gasketed pipe joints. The main advantages would be that the sensing probe apparatus can be easily adapted for inspection of different sizes of flanges, quickly mounted and dismantled, easily maneuvered on the outer side of the joint, and the costs for development and application of this technique will be very low. By means of multiple and repeated resistivity measurements of the whole area of possible attack by crevice corrosion, and after graphical data processing by computer, an image may be obtained. aookucatuib