When I first started working in cathodic protection, I giggled all the time at the word rectifier. To an outsider (a mid-20s sometimes questionably mature outsider), rectifier sounds more like anatomy than an essential tool to protecting long-distance pipelines. So, what is a rectifier?
For impressed current systems, we don't rely on the natural chemistry between an anode and the steel structure. It's simply not cost-effective. For impressed current, there is generally a hole dug 300-500 feet deep with cast iron or graphite anodes lowered in specific increments with the super thick HMW-PE wire to ensure the cables are protected and will last the typical 20 years expected.
Through those anodes, electricity is applied to make them activate to get that magical -0.850mv reading. The application of electricity is accomplished through a rectifier. The rectifier will take alternating current (AC), which occasionally reverses direction, and convert it into direct current (DC), which only flows one direction. This "rectifies" the current, so it is always pushing through the anodes to the soil.
Rectifiers come with a variety of capabilities. Some of them are air-cooled, some are submersed in oil, others still are qualified as explosion proof. The volt-amp rating can vary from 20-10 to 100-80. Some units feature a convenience plug. All rectifiers need to have a log book to monitor for optimal operation. The rectifier will need a copper buss bar to distribute the electricity through shunts to the impressed current anodes, too.
The smaller units can run about $600, and Farwest Corrosion usually has some in stock. Larger units can have a 7-9 week lead time, and the cost can get pretty high. The highest I've seen is $5,500.
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