Pipelines have become one of the most efficient means of transporting liquids and gas safely from point of origin to point of use. According to the Bureau of Transportation Statistics, the United States has over 218,387 miles of oil pipelines and over 1,626,959 miles of gas pipelines. The American Society of Civil Engineers (ASCE) indicates there are over a million miles of water pipe providing drinking water across our country. We have become reliant on pipelines for our way of life.
Unfortunately, pipelines are not without their challenges. Each year thousands of water main breaks occur and prolific gas pipeline failures such as the explosion in Stanford, KY (one killed, 5 injured) and another in Audrain County, Missouri (stress corrosion cracking) make the front-page news. The need for adequate corrosion protection of pipelines has never been greater. According to the US Department of Transportation, Pipeline & Hazardous Materials Safety Administration, “Corrosion is the root cause of approximately 18% of all pipeline incidents.” The average annual corrosion-related cost is estimated at $7 Billion just to monitor, replace and maintain these assets[1].
Industry organizations such as SSPC: The Society for Protective Coatings (SSPC), NACE International, American Water Works Association, ASCE, American Petroleum Institute and many others are working to mitigate the threat of corrosion to our nation’s infrastructure. Comprehensive corrosion engineering is the overarching approach to corrosion prevention and the use of protective coatings is one of the most significant pillars of protection.
SSPC revised their Painting Application Standard No. 2 in November 2018. The primary focus was on establishing a uniform approach on how to measure coating thickness on industrial structures and included Appendix 7 – Method of Measuring Dry Film Thickness on Coated Steel Pipe Exteriors. Although the appendices are a mandatory part of the standard, this appendix is applicable for determining the thickness of the applied coating to determine whether the material is in conformance with the specification. This appendix can be used at the pipeline fabricator’s facility or in the field and may be invoked by the contract documents.
SSPC-PA 2 references ASTM D7091[2], which describes the proper use of Type 1 and Type 2 gages and provides the methods for verifying the accuracy and adjusting dry film thickness gages. SSPC-PA 2 provides direction on the number of spot and area measurements required based on the total square footage of the pipe. Each spot measurement consists of a minimum of three individual gage readings. This can be done on an individual stick of pipe or for the total amount of pipe on a cart or rack. The total sq. ft. is calculated by multiplying the length of pipe (feet or meters) x the outside diameter (feet or meters) x pi (π). The recommended location and number of readings taken for each section of pipe are listed below:
Appendix 7 also enables the specifier to employ a “DFT Frequency Factor” that is typically applied for multiple sections of small diameter pipe located on a cart or rack. The core standard requires five spot measurements per 100 square foot area. The specifier can increase the number of readings taken on that cart or rack of pipe sections by using a frequency factor.
A frequency factor of 2, 3, 4, 5 or 6 increases the number of spot measurements required per cart or rack. For example, SSPC-PA 2 requires 5 spot measurements for the first 100 square feet of pipe. If a frequency factor of 2 is specified, the number of spot measurements would be 10 (5 spots {for the first 100 square feet} x 2 Frequency Factor).
Pipe spools are typically measured individually if they are not on a rack or cart per the table illustrated earlier in this article. Alternatively, the specifier may require a representative sample of the pipe spools be measured in accordance with SSPC-PA 2; for example, inspect one pipe out of every 10, especially if they were coated using automated equipment. Note that pipe spools coated in the field are a challenge for the painter and attention to the valves, flanges, elbows and varying pipe diameters is required.
Pipelines remain one of the safest modes of transporting liquids and gases across North America. The design life expectancy of our pipelines can be fully realized when coatings are properly applied and in accordance with a comprehensive corrosion engineering program that includes cathodic protection. Appendix 7 of the SSPC-PA 2 coating thickness standard is one of many key components to ensuring we protect our nation’s infrastructure.
Resources:
- US DOT Pipeline and Hazardous Materials Safety Administration Office of Pipeline Safety, Pipeline Corrosion Final Report, 2008
- Bureau of Transportation Statistics; US Oil and Gas Pipeline Mileage
- SSPC-PA 2, 2018, Procedure for Determining Conformance to Dry Coating Thickness Requirements
- American Water Works Association, Buried No Longer: Confronting Americas Water Infrastructure Challenge, February 2012
- American Society of Civil Engineers, 2017 Infrastructure Report Card, 2017
[1] Corrosion Costs and Preventative Strategies in the United States, 2002, NACE International
[2] Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic, Nonconductive Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings applied to Non-Ferrous Metals
