Where the Primary Objective is Diagnosis in a New Situation

Typically the nature of the corrosion processes involved and the controlling parameters are uncertain. It may be difficult to decide on the most appropriate technique, but it is in any case often advantageous 

Linear polarization (polarization resistance) Corrosion rate is measured by the electrochemical polarization resistance method with two or three electrode probes Suitable for most engineering alloys providing the process fluid Is of suitable conductivity. Portable instruments at modest cost, to more expensive automatic units are available Frequent 

Electrical resistance Integrated metal loss is measured by the resistance change of a corroding metal element. Corrosion rates can be calculated Suitable for measurements in liquid or vapor phase on most engineering metals and alloys. Probes as well as portable and more expensive multi-channel units are available Frequent 

Potential monitoring Potential change of monitored metal or alloy (preferably plant) with respect to a reference electrode Measures directly state of corrosion of plant, e.g. active, passive, pitting, stress corrosion cracking, via use of a voltmeter and reference electrode Moderate 

Corrosion coupon testing Average corrosion rate over a known exposure period by weight loss or weight gain Most suitable when corrosion is at a steady rate. Indicates corrosion type. Moderately cheap method with corrosion coupons and spools readily made Frequent 

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