What is a corrosion coupon and how is it used in pipe integrity programs?

• A. A corrosion coupon is a small plate installed in a pipeline to act as a sacrificial anode.
• B. A corrosion coupon is a small device used to measure flow rate.
• C. A corrosion coupon is a protective coating for pipelines.
• D. A corrosion coupon is a small metal sample placed in a pipeline or vessel to measure corrosion rate by weight loss.

Answer: (D)

A corrosion coupon is a small metal sample placed in a pipeline or vessel to measure corrosion rate by weight loss. In pipe integrity programs, coupons are installed in representative locations and periodically removed to determine how much metal has been lost over a defined exposure period. By weighing the coupon before and after exposure, you can calculate the corrosion rate, typically expressed as thickness loss per year, which provides a direct, comparable metric of how the asset material is being attacked by the process environment.

This approach gives real-world data on internal corrosion, helps assess the effectiveness of inhibitors or protective measures, and supports decisions on inspection intervals, material selection, and mitigation strategies. Coupons are made from the same or a similar material as the pipeline so the results reflect actual service conditions. They are intended to monitor trends over time and in different sections of the system.

Other options describe different concepts: a sacrificial anode is used for galvanic protection, not for sampling corrosion rate; a device that measures flow rate serves a different purpose; and a protective coating is a barrier, not a sampled metal piece for directly measuring corrosion.