Question: What’s the minimum level of cathodic protection for buried steel pipe? Why doesn’t Subpart I of the regulatory pipe code include the voltage requirement?
Answer: A copper-copper sulfate reference cell and DC voltmeter are used to measure the cathodic protection potential of steel piping. An acceptable level must be at least or more negative than – 0.85 volts DC.
Part 192, Subpart I – Requirements for Corrosion Control discusses the cathodic protection required in 192.463, but it also references Appendix D. You can find Appendix D – Criteria for Cathodic Protection and Determination of Measurements near the back of the Federal Safety Standards. Its opening section contains the information you’re looking for, under Criteria for Cathodic Protection: “(1) A negative (cathode) voltage of at least 0.85 volt, with reference to a saturated copper-copper sulfate half cell.”Always refer to the company’s corrosion-related procedural requirements. With regard to the reference cell, below are a few helpful tips:
- Keep the reference cell filled with water and copper sulfate crystals.
- When the cell is not in use, always install the cap on the reference cell’s porous plug to prevent the liquid from evaporating.
- Add water to dry soil to obtain accurate readings.
- Don’t try to get an accurate pipe-to-soil reading with the reference cell on asphalt.