Abstract
Corrosion monitoring is an important activity in any situation where valuable assets handle corrosive or potentially corrosive substances. This is especially true in cases where failure of these assets has severe economic, environmental or dangerous consequences. Typically, on-line corrosion monitoring has been accomplished with coupons, electric resistance probes and other intrusive devices. These techniques provide information helpful in establishing corrosive trends, yet the results can not generally be used directly to determine the amount of damage suffered by the corroded equipment. Often, various non-destructive testing techniques such as radiography and ultrasonics are used to ascertain the extent and severity of corrosion in the system.
Advances in microcomputers in the last decade have resulted in the advent of computer-controlled field ultrasonic systems adapted to many requirements in modern industry. Integrated, automated scanner and ultrasonic systems are now available that gather wall thickness readings frequently enough to generate an accurate definition of the remaining thicknesses of corroded components. Of course, ultrasonic examination of components necessitates access to one surface of the items to be inspected. In some situations this requirement would have an unacceptable economic impact on the desire to examine large areas of a potentially corroded system. Radiography can be used to examine components for evidence of corrosion without requiring direct access to one surface. For example, the desire to inspect large amounts of insulated piping for possible corrosion can be satisfied by employing Real-time Radioscopy.
Examples of these technologies used in field conditions to ascertain the extent of corrosion in oil field piping and vessels are presented. An extensive, five year program of inspecting insulated, cross-country pipelines with real-time radioscopy is discussed, followed by an example of automated ultrasonic testing to inspect piping and vessels in oil separation facilities. In addition, a case history of corrosion monitoring using an automated ultrasonic system is also addressed. Not only do these inspection techniques provide a method of on-line corrosion monitoring, but they also allow the analyst to determine the mechanical integrity of the corroded part.
