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IR-Free Coupon

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Unlike other corrosion coupons, MCM’s IR-free coupon is designed to evaluate cathodic protection systems without interrupting rectifiers, foreign bonds, or sacrificial anodes.





The coupon consists of a bare, coldrolled steel cylinder head and No. 12 stranded wires, which are inserted along side a 2-inch PVC tube. The PVC tube shields the reference electrode from potential gradients, resulting in accurate, precise cathodic protection measurements. These measurements also meet anticipated federal regulations and industry standards for considering IR drop in structure-to-soil potential readings.

Coupon Specifications

  • Surface area 1.55sq. in. (10cm2)
  • Metal dimensions: 0.5 inch diameter, 0.86 inches long cylindrical shape
  • #12 AWG (4mm2) stranded wire, green-colored THHN insulation, two cables, 25 feet long
  • Silver solder
  • 3M potting compound
  • Coupons can be customized to your specifications, optional alloy and surface area designs are encouraged

Built to Last

Like all M. C. Miller products, our IR-free coupons are built to last. The wire/coupon interface is environmentally sealed to keep the steel, copper, and solder components corrosion-free, making the coupon virtually indestructible.

Easy Installation

M. C. Miller IR-free coupons can be easy installed using standard installation practices near existing test stations (see NACE Standard RP0104-2004). The M. C. Miller 2 inch diameter PVC coupon holder is a convenient way to couple a coupon with a length of 2 inch diameter PVC tubing which is typically used to shield a reference electrode positioned above the ground (inside the exposed tubing) from stray potential gradients.

Easy Polarized Potential Measurement

After an IR-free coupon has had time to polarize (after being connected to a structure under CP protection), which can take about 1 month, a reference electrode can be inserted into the top of the shielding PVC tube, contacting the compacted soil above the coupon. A high input impedance voltmeter can then be connected between the coupon (via its test station terminal) and the reference electrode. An IR-free potential reading (an accurate polarized potential) is then obtained by breaking the connection between the coupon and the structure, usually through means of a jumper, thus interrupting cathodic protection to the coupon. A coupon-to-soil potential measurement is then taken typically within two seconds of breaking the coupon-to-structure connection.


Coupon mounted in PVC holder
(Holder sold separately - see above)