What are often used to check cathodic protection on pipelines and made of the same material as the one being tested?

Coupons are an effective method for evaluating the cathodic protection system on pipelines because they closely mimic the material properties of the pipeline itself. Essentially, a coupon is a small sample, typically made from the same material as the pipeline (such as steel), which is exposed to the same conditions as the pipeline. This allows for accurate measurements of corrosion rates and the effectiveness of the cathodic protection being implemented.

By placing these coupons within the cathodically protected environment, corrosion engineers can reasonably predict how the actual pipeline will behave under similar conditions. This process helps in assessing whether the cathodic protection is functioning as intended, as the coupons will reflect any significant changes in corrosion rates or effectiveness of protection over time.

The other choices, while relevant to various aspects of monitoring and evaluating corrosion, do not serve this specific purpose of being direct indicators of pipeline material performance in the context of cathodic protection. Electrodes are typically used for measuring potentials and currents, detectors serve to identify and monitor specific signals or features, and monitors may refer to larger systems that gather data without necessarily being made of the same material used in the cathodic protection assessment.