Pipeline (C-34) · Lesson 5 of 6

Cathodic Protection of Underground Steel Gas Pipe: Criteria and Test Schedule

"Cathodic Protection of Underground Steel Gas Pipe: Criteria and Test Schedule" is lesson 5 of 6 in the Pipeline (C-34) Learning Hub. It opens with "What the Code Requires Underground" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. What the Code Requires Underground
  2. The Pass Criteria: Pipe-to-Soil Voltage
  3. The Test Schedule for Sacrificial Anodes
  4. Impressed Current, Failed Tests, and Records
  5. Installation Details That Protect the System

The worked example in the course applies this lesson to a realistic job in 6 steps, from "Find the criterion for the half cell you are using" through "If the test failed, set the repair deadline".

What you'll be able to do

  • Explain the main idea of "Cathodic Protection of Underground Steel Gas Pipe: Criteria and Test Schedule" in plain language you can use on the exam.
  • Apply this step with confidence: "The Test Schedule for Sacrificial Anodes".
  • Apply this step with confidence: "Impressed Current, Failed Tests, and Records".
  • Apply this step with confidence: "Installation Details That Protect the System".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Cathodic Protection Test on Underground Gas PipeCOATED STEEL GAS PIPEanodeanode-0.92 VCu/CuSO4half celltestleadSACRIFICIAL ANODE TEST SCHEDULE (1310.1.3.4)1. At installation, or within 180 days if climate prevents2. 12 to 18 months after the initial test3. Then at intervals not over 36 monthsPIPE-TO-SOIL VOLTAGECMC 2025 1310.1.3.3Cu/CuSO4: -0.85 V or more negativeCalomel: -0.78 V or more negativeAg/AgCl: -0.80 V or more negativeField readings (Cu/CuSO4):-0.92 V is more negative: PASS-0.81 V is not enough: FAILFailing system: repair within180 days, then restart tests.Impressed current: rectifiercheck every 2 months at most;pipe-to-soil test every year.A reading of -0.92 V on a Cu/CuSO4 cell meets the -0.85 V criterionKeep the two most recent test results on file (1310.1.3.7)California Mechanical Code 2025 section 1310.1.3 (underground steel fuel gas piping); not to scaleCC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: What the Code Requires Underground

Steel gas pipe buried in soil corrodes unless it is protected. California Mechanical Code (CMC) 2025 section 1310.1.3.1 says zinc coating (galvanizing) is not adequate protection for underground gas piping. Section 1310.1.3.2 requires underground piping to comply with one or more of these: corrosion-resistant material suitable for the environment; a factory-applied, electrically insulating coating (with fittings and joints coated per the coating manufacturer's instructions); or a cathodic protection system that is maintained under section 1310.1.3.3 or 1310.1.3.6. In practice a coated pipe plus anodes does both jobs.

Step 2: The Pass Criteria: Pipe-to-Soil Voltage

Section 1310.1.3.3 requires cathodic protection systems to be monitored by testing, with documented results that show one of these: a pipe-to-soil voltage of -0.85 volts or more negative measured against a saturated copper-copper sulfate half cell; -0.78 volts or more negative against a saturated KCl calomel half cell; -0.80 volts or more negative against a silver-silver chloride half cell; or compliance with a method in Appendix D of 49 CFR Part 192. The number depends on the reference electrode you use, and more negative means better protected, so -0.92 volts passes where -0.81 volts does not.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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