Avoiding Voids with a Holiday How-To
Unmasking the tiny defects that can jeopardize long-term coating performance is the focus of the latest installment in the PaintSquare Video Learning Center series.
Pinholes and holidays can pose big problems for a coating system if not detected and remedied before the system is put into service.
The how-tos of "Holiday Detection," narrated by an expert, can help users ward off such problems.
Created by KTA-Tator Inc., the Video Learning series covers a wide range of topics in protective coatings work, from quality-control and health and safety, to basics on the proper use of coatings instruments.
From Lead Detection to Ventilation
Previous titles in the video series include:
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The series of short video tutorials includes "Corrosion Assessment." |
Future topics in the series include steel surfaces and moisture testing.
Each installment is available free in the PaintSquare Video Learning Center.
Avoiding the Void
In "Holiday Detection" (4:21), KTA's William Corbett discusses how to test for holidays and pinholes in a coating system.
Testing is particularly crucial for systems applied to the interior of storage tanks, vessels, railcars, and liquid and gas pipelines.
These structures require holiday- and pinhole-free coating or lining systems, and the testing process uses detectors instead of visual inspection, Corbett explains.
"If holiday, pinhole or jeep testing is not performed and there are undetected voids in the coating or lining system, then the contents of the tank, vessel, railcar or pipeline may attack the exposed substrate and cause pitting corrosion, loss of section, and eventual perforation of the susbtrate," Corbett says.
He discusses factors that can cause pinholes and where on the substrate they are commonly found.
Testing for Holidays
Testing for pinholes and holidays is usually performed after the final coat is applied but before it is fully cured, in case the coating needs to be repaired, Corbett points out.
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"If holiday, pinhole or jeep testing is not performed and there are undetected voids in the coating or lining system, then the contents of the tank, vessel, railcar or pipeline may attack the exposed substrate and cause pitting corrosion, loss of section and eventual perforation of the susbtrate," Corbett says. |
The detectors work by applying a current to the surface of a non-conductive coating and grounding to the substrate. The current passes through the pinholes, completing an electrical circuit.
"Since the detectors will only work on non-conductive coatings applied to conductive substrates, epoxy coatings applied to steel can be tested for holidays, whereas a zinc-rich coating applied to the same steel could not," Corbett explains.
The Standards
Three standards govern holiday testing:
Additionally, a fourth standard was specifically prepared for pipeline coatings: ASTM G62, "Standard Test Methods for Holiday Detection in Pipeline Coatings."
