Cathodic Protection Guide: Where to Start

Cathodic protection (CP) keeps buried and submerged metal from corroding by making it the cathode of an electrochemical cell, either with galvanic anodes or with a rectifier and impressed current anodes. This cathodic protection guide is for pipeline and tank operators, water and gas utility staff, facility owners, and engineers who are new to corrosion work or have just been handed a CP survey report.

The articles below are the ones we would give a new colleague, in the order we would give them. Each section also links the calculator or interactive explainer that fits, and the service page for that part of the work if you would rather talk to an engineer.

1. Start with the basics

• What cathodic protection is and how it works: Start here. It explains why buried and submerged metal corrodes, how cathodic protection stops it, where it is used and how you can tell that a system is working.
• The two types of cathodic protection systems: Compares galvanic (sacrificial anode) and impressed current systems and how to choose between them.
• The role of anodes: Covers the anode types used in both kinds of system and the maintenance and monitoring that keep them working.
• Factors affecting cathodic protection: Soil conductivity, coatings, the metal of the structure and other metal nearby all change how well a structure is protected.
• Soil resistivity and corrosion: What soil resistivity is and why lower resistivity usually means a more corrosive soil.

For an overview of the whole service, from design to annual testing, see our cathodic protection services.

2. How cathodic protection is tested

• How to interpret CP survey data: Explains on, instant-off and depolarized potentials and what the readings mean for your structure. Read it before your first survey report arrives.
• Four CP testing methods: A short overview of rectifier output checks, close interval potential surveys, galvanic anode readings and AC interference surveys.
• How a close interval survey works: The three survey types, what the readings show and what they miss, and what the federal rules require.
• ACVG vs. DCVG surveys: Both surveys find coating defects on buried pipe. This explains the difference and which one fits your line.
• How a DCVG survey works: A closer look at how a direct current voltage gradient survey pinpoints coating defects and when to schedule one.
• CP testing equipment: The reference electrode, voltmeters, multimeters and soil resistivity meter a survey crew carries, and what each one measures.
• Read a CP test station (interactive): Take on, instant-off and IR drop readings at a test station with an interrupter you can adjust.

To choose a survey, see our cathodic protection potential surveys page, which describes each survey we run and the question it answers.

3. Standards and rules

• The annual CP survey under 49 CFR 192.465: What the federal pipeline rules require of the annual survey, rectifier and bond inspections, remedial action and records, and what to have ready.
• CP compliance by type of line: Written for Colorado, it shows how the rules differ for gas pipelines, hazardous liquid pipelines and flowlines.
• CP specialist vs. licensed engineer: The legal difference between an AMPP CP4 certification and a PE license, and why it matters for who signs a design.
• What NACE (now AMPP) certification means: The cathodic protection certification levels and how to verify that someone holds one.
• Preparing for a CP inspection: Practical steps before an inspection: notify nearby structure owners, use certified people and arrange site access.

4. Design and commissioning

• Common challenges in CP design: Interference, uneven current distribution and high soil resistivity: the problems a design has to solve.
• Deep groundbed systems: When and why anodes go deep, and how a deep anode groundbed is designed and installed.
• Pipeline electrical isolation: How isolation keeps protective current on the structure it is meant to protect.
• CP commissioning on a construction site: What commissioning covers on a new build and what the commissioning report records.
• Turn up the rectifier (interactive): Adjust a rectifier and watch the pipe-to-soil potential change along a coated pipeline.
• Plot Wenner soil resistivity readings (interactive): Enter four-pin readings from two traverses and see a two-layer screening fit.

The matching services are cathodic protection design, soil corrosivity analysis and start-up and commissioning.

5. Common problems

• Why CP systems stop working: The common causes, from rectifier faults and depleted anodes to coating damage and interference, and the readings that flag each one.
• What causes CP interference: How nearby CP systems, stray current and power lines interfere with a structure, and how interference is tested and mitigated.
• Stray current corrosion: Where stray current comes from and how it is found and prevented.

When readings point to interference, our interference testing service finds the source and designs the mitigation.

6. Calculators and tools

• Cathodic protection calculator: Estimates the current requirement from bare area and current density, and the life of magnesium, zinc or aluminum galvanic anodes. Use it for screening; a design needs measured data.
• Galvanic corrosion chart: Shows which of two metals in contact will corrode and how serious the pairing is.
• All engineering calculators: Our free calculators and interactive explainers in one place.

How Dreiym Engineering Can Help

We design, install, test and commission cathodic protection systems, run potential surveys and interference testing, and measure soil corrosivity, so one firm can take a structure from the first soil test to its annual survey. Our corrosion team includes Stepan V. Eero, M.S., P.E., NACE CP Specialist (CP4), and Brian J. Brackensick, M.S., P.E., NACE CP Technologist, and designs are PE-stamped where required. Contact us or call (866) 621-6920 for a free quote. We typically respond within one business day.