The placement of corrosion test rings in the drill string is one of the more common techniques used to evaluate the corrosiveness of drilling-fluid environments on the drill string and other steel equipment. Removal and examination of these rings after a period of exposure down-hole can be highly informative as to the corrosiveness of the drilling fluid, as well as to the type of corrosion encountered. An examination of scales and pits on the exposed rings gives clues as to the cause of the corrosion, thus aiding in choosing proper remedial action.
The ring technique is specifically designed for detection of the type of corrosion characterized by metal loss whether it is localized pitting or generalized attack. The test ring is not designed to give information relating to hydrogen embrittlement, stress corrosion cracking, or other forms of fracture formation, except in the manner in which pitting may relate to these failures.