Corrosion coupons are generally used in weight loss tests. Properly selected, such coupons will provide quantitative estimates of corrosion rates as well as physical evidence of the type of corrosion occurring in the process environment. In order to provide reproducible data, selected coupons must have a uniform shape, size, surface area, and surface finish. Coupons should be fabricated of an alloy that is similar in composition to the process equipment of interest.
NACE has published a Recommended Practice RP-0775 entitled Preparation and Installation of Corrosion Coupons and Interpretation of Test Data in Oil Production Practice.
Strip coupons are available in two standard sizes: 2-7/8″ x 7/8″ x 1/8″ (73 mm x 22 mm x 3 mm) and 6″ x 7/8″ x 1/8″ (152 mm x 22 mm x 3 mm). Both sizes have two mounting holes for attachment to the Strip Coupon Holder. Strip coupons are supplied complete with nylon insulation for mounting purposes. Strip coupons are typically mounted in pairs and need to be oriented such that they are parallel to the direction of flow.
Flush Disc Coupons
These circular coupons are most commonly used with holders that mount the coupon flush with the interior of the pipe or vessel. They have a chamfered hole which permits recessed mounting with a stainless steel flathead screw. Flush disc coupons are most frequently used where pigging would otherwise require the removal of intrusive-type coupon assemblies prior to the pigging operation; or alternatively where water-drop out in the bottom of horizontal pipe runs gives rise to corrosion problems. The disc coupon diameter is 1¼” (32 mm) with a thickness of 1/8″ (3 mm). The insulation and mounting screw is provided with the coupon holder.
Ladder Strip Coupons
These coupons are rectangular with the following dimensions: 2″ x 7/8″ x 1/8″ (51 mm x 22 mm x 3 mm). They are designed to be mounted in pairs with three pairs of ladder strip coupons attached to a single ladder coupon holder. Ladder strip coupons are supplied with nylon insulation for mounting.
Scale coupons are rectangular with a series of holes of varying sizes, and are used to determine scaling tendency. The strength of this tendency can be determined by the largest size hole that has accumulated scale. Scale coupons are typically used with strip coupon holders.
Coupons are supplied ready for use.
C1018 coupons are stamped with a sequence number. All alloy coupons are stamped with the alloy and the sequence number.
Coupons are pre-weighed and individually packaged in a vapor corrosion inhibitor (VCI) bag.
Coupons are supplied with a mill test report and a weight log chart.
Coupons are cleaned of all contaminants and have a 120 grit-blasted finish.