When you bury a steel pipe underground and leave it there for years, there’s a risk of corrosion. That’s something pipeline operators work really hard to prevent – as we’ve shared in previous blog posts about cathodic protection and sophisticated coatings that help protect pipelines from corrosion.
Coating applied to a pipeline weld. Photo courtesy of Specialty Polymer Coatings.
Bob Humble of Proco Inspection Services Ltd. is a certified coating inspector through the National Association of Corrosion Engineers (NACE), and an independent contractor. We asked him to explain how pipeline coatings are inspected before a pipeline goes in the ground, and the role the inspector plays in ensuring pipeline integrity:
“The coating inspector’s function is quality assurance,” said Bob. “They inspect and test the pipeline coatings for compliance to the specifications and to ensure that they meet industry standards.”
Essentially, the inspector is checking to ensure that there is nowhere for oxygen to get to the pipeline. “The short answer is: no oxygen, no corrosion,” he stated.
Bob explained that these inspections are the only way to ensure the integrity of the coating. “It’s very important for the inspector to check the work as it’s being done. Sometimes a company might wait until the coating has been applied and cured, but if any kind of flaw is discovered at that late stage, the affected area, or even the entire coating, has to be removed and reapplied.”
The four key areas a pipeline inspector checks
- After the surface of the pipe is grit blasted to prepare it for the coating application, the inspector uses a micrometer to test the surface profile for the right texture, or roughness.
- The environmental conditions are monitored – factors such as the temperature of the steel, dew point and relative humidity all play a role in the longevity of the coating.
- After application, the thickness of the coating is tested magnetically using a DFT gauge.
- Finally, after being cured, the coating is tested for any voids or pinholes.
Jeeping for holidays
That may sound like an off-roading vacation, but in fact it’s just a strange phrase used by pipeline coating inspectors. Voids or pinholes in the coating are called holidays, and jeeping is the process of using a high voltage ‘holiday detector’ which can find even the tiniest flaws using an electrical current.
We’d love to tell you where this phrase originated, but so far we’ve come up blank. Do you know? If so, please add a comment to this post and let us know.
If you’d like to know more about corrosion, and how pipeline companies protect against it, check out our corrosion factsheet.
The Canadian Energy Pipeline Association represents Canada’s transmission pipeline companies who operate approximately 117,000 kilometres of pipelines in Canada. In 2014, these energy highways moved approximately 1.2 billion barrels of liquid petroleum products and 5.4 trillion cubic feet of natural gas. Our members transport 97 per cent of Canada’s daily natural gas and onshore crude oil from producing regions to markets throughout North America.