IR-Free Coupons can be used to determine the true polarized potential of a buried metallic structure without having to interrupt all sources of current flowing in the soil that have an influence on the structure to soil potential. As indicated in the 2004 NACE Standard (Recommended Practice) on "The Use of Coupons for Cathodic Protection Monitoring Applications" (RP-0104-2004), the size of a CP coupon should simulate the largest anticipated coating holiday size on the buried structure occurring in the area of the coupon (the area under investigation). Also, the NACE Standard indicates that the coupon material should be similar to the material of the structure under investigation. Finally, the Standard indicates that coupons can be in ring, cylindrical, circular-plate, and rectangular-plate shapes. MC Miller manufactures a variety of "standard" coupon designs for the cathodic protection industry and we also encourage custom orders.
Regarding custom coupons, the following parameters should be specified to MC Miller:
· Material requirement (to match the structure): Carbon steel (with desired AISI number), ductile iron etc. Area of exposed metal requirement (surface area of coupon metal that will be in contact with the soil) Coupon shape requirement: Cylindrical, circular plate, etc.
· Cable requirement: AWG # of standard wire (or mm²), type of insulation (THHN, HMWPE, XLPE/PVC etc.) and color of the insulation, number of cables (one or two) and length of cables.
MC Miller manufactures a variety of coupon designs as "standard" and the specifications. MC Miller also manufactures a 2 inch diameter PVC coupon holder that can be used to secure the coupon. The holder with coupon attached can be conveniently cemented to a customer's 2 inch diameter PVC tube.