A close interval survey (CIS) – also called a close interval potential survey (CIPS) – is a systematic field inspection used to evaluate the effectiveness of cathodic protection along a buried pipeline. It is federally required for pipelines in the United States under regulations administered by the Pipeline and Hazardous Materials Safety Administration (PHMSA).
Why Are Close Interval Surveys Required?
Buried steel pipelines are constantly exposed to electrochemical corrosion from surrounding soil and moisture. Left unchecked, corrosion can thin pipe walls, cause leaks, and lead to catastrophic failures, explosions, and environmental damage. Cathodic protection systems combat this by applying a protective electrical current to the pipe – but CP systems only work if they are functioning correctly along the entire pipeline. A CIS verifies that protection criteria are being met continuously from one end of the line to the other.
Under 49 CFR regulations, close interval surveys are required for:
- Natural gas transmission lines in High Consequence Areas – at least every 7 years (49 CFR 192)
- Hazardous liquid pipelines in HCAs – at least every 5 years (49 CFR 195)
- Corrosion control monitoring on onshore non-service lines – at least every 3 calendar years
- Cathodic protection testing – at least once per calendar year, not exceeding 15 months
How Does a Close Interval Survey Work?
A CIS crew walks the pipeline route with a copper/copper sulfate reference electrode and survey trailing wire connected to a data logger. Pipe-to-soil potential readings are taken every few feet, building a complete profile of CP system performance. The survey involves three main tasks:
- Locating and marking the pipeline at regular intervals using stakes or flags
- Data collection: measuring P/S potentials and recording GPS coordinates at each measurement point
- Clearing the right-of-way of survey wire and materials after the survey is complete
Key Terms to Know
- CIPS (Close Interval Potential Survey): Often used interchangeably with CIS
- ECDA (External Corrosion Direct Assessment): A broader integrity program where CIS is a key tool
- CP (Cathodic Protection): The electrochemical method used to prevent pipeline corrosion
- P/S Potential: Pipe-to-soil voltage reading – the primary measurement taken during a CIS
What Equipment Is Used?
A typical CIS crew carries copper/copper sulfate reference electrodes, a data logger with GPS capability, interrupt switches, and survey trailing wire dispensed from hip pack or backpack spools. The survey wire is one of the most critical components – a break or failed pigtail connection can interrupt data collection and require the crew to stop and re-spool.
How Advance Electrical Supports CIS Survey Crews
Advance Electrical has supplied copper survey trailing wire to pipeline operators, contractors, and corrosion engineers for over 40 years. We spool wire in-house to your exact specifications – any gauge, any mileage – with field-proven connection options built for real survey conditions. Call (936) 588-4419 to discuss your next project.
