A Review of Corrosion Monitoring Techniques
Authors: Fincher D.R. , Nestle A.C. 
Published: December 2007

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Abstract
Operators of metallic systems e been aware of the damage that is, be, caused by corrosion processes for many years. The search continues for new and better tools to monitor, measure, or detect changes both in the metal structure itself and in the rate of attack that the structure is experiencing. To prevent corrosion damage, it is necessary to know when, where, and why the attack is occurring. Otherwise, damage can occur before the owner has knowledge of the attack.
Corrosion can be monitored or detected using "after-the-fact" type tools for detection. Perhaps the oldest detection technique is simply a visual inspection coupled with measurement of pit depths and/or wall thickness. pit depths and/or wall thickness. Ultrasonic and X-ray equipment also can be used to determine the extent of damage. Downhole tubing and casing calipers, possibly in conjunction with wall thickness measurements, can be used periodically to assess the extent of corrosion damage.
Perhaps the most desirable monitoring Perhaps the most desirable monitoring techniques are those that are used more or less continually to determine the rate of corrosion attack. These methods also are suitable to assess the success or failure of the corrosion mitigation measures used. Such devices include coupons, linear polarization type instruments, electrical resistance type instruments, galvanic probes and hydrogen probes. Also, a new corrosion monitor-controller is described.
Each of the methods has certain advantages and disadvantages, and this paper reviews the practical application paper reviews the practical application of all of these different techniques.

Introduction
The field of corrosion detection and control monitoring can be categorized conveniently in four parts. These are:"After-the-fact" methods including Equipment Service Records, direct and indirect physical examination, inspection" of the equipment;Non-destructive testing methods usable without shut down, i.e., not necessary to open-up the equipment;"Probing" methods, using devices to probe the system, a pilot small scale probe the system, a pilot small scale system, an alternate (by-pass) system.