Induced AC (Alternating Current) on pipelines is a potential shock hazard to personnel as well as a source of corrosion damage. Current technology to detect and monitor induced AC current include the use of portable or permanent reference electrodes to measure voltage, and/or buried “current density coupons” to measure levels of AC current density.
Monitoring the current density, rather than just AC voltages, is a key factor in assessing the AC current related corrosion risk. A simple and effective method of determining current densities is to install a steel coupon, of a known surface area, in the soil adjacent to the structure. By connecting the coupon to the pipeline through a current measurement shunt or meter, the induced AC current density can be easily calculated.
Until now, only permanently installed AC current density coupons have been available. Unfortunately, the cost to install these permanent coupons can be thousands of dollars per site when considering the materials, planning, permitting, mobilization, equipment and labor.
The Farwest model AC-10 portable steel coupon/probe is the answer to this issue. Used much like a portable reference electrode and similar to a soil pin, the coupon is driven into the soil and functions like a permanent AC current density coupon. Since it’s portable, the AC-10 coupon/probe allows the CP technician a method of measuring AC current density on demand or during a normal pipeline corrosion survey.
- Durable steel construction.
- Multiple cable connection options.
- Replaceable 10 cm2 conical tip for soil contact.
- Simple to use. AC current density readings are achieved within seconds.
The conical tip of the AC-10 coupon/probe must be in good contact with the soil to obtain an accurate measurement. Once this is done, the current density measurement is taken via a digital multimeter (DMM) and wire connections to the coupon/probe and the pipeline. As the coupon/probe is 10 cm2 in size, the conversion from milliamps (mA) to Amperes/Meter2 is a direct numeric conversion.
Example: 25.0 mA (measured) = 25 A/m2 AC current density.