Corrosion coupons, also known as weight loss coupons, are metal strips exposed to a specific environment to determine the metal's reaction to corrosive elements. They are crucial in corrosion management programs, particularly in industries like oil and gas. Analysis can include various measurements. Weight loss is the central measurement and the two methods of cleaning ensures very little metal loss occurs during that process. An average weight loss during cleaning is factored in to the final weights to improve accuracy of the data.
Handling: Always use gloves when handling coupons to prevent contamination and inaccurate results.
Orientation: To ensure accurate results, it's recommended to orient the coupon vertically to prevent debris accumulation and allow water to flow from the back of the coupon.
Flow Rate: Maintain a consistent flow rate (3-5 feet per second) to avoid erosion or under-deposit corrosion.
Material: The coupon material should match the material of the equipment being monitored to accurately assess corrosion rates.
Insulation: The coupon should be electrically insulated from the system to prevent galvanic corrosion.
Standard exposure periods typically range from 90 days, but can be adjusted based on the specific conditions and corrosion severity of the system.
Ensure coupons remain fully exposed to the fluid throughout the test period.
Removal: After the exposure period, the coupons are carefully removed, avoiding damage or contamination.
Cleaning: Coupons are then cleaned to remove any deposits or corrosion products. Improper cleaning can lead to inaccurate weight loss results.
Re-weighing: After cleaning and drying, the coupons are re-weighed to determine the weight loss.
The weight loss is used to calculate the corrosion rate, often expressed in mils per year (mpy).
Formula: Corrosion Rate (mpy) = (Weight Loss (g) * 22300) / (Area (in²) * Density (g/cm³) * Time (days)).
Units: The formula can be adjusted to calculate corrosion rate in different units like millimeters per year (mm/y) or micrometers per year (µm/y).
