The Anatomy of a Coating Failure

Rarely does acoatingfail because of only one contributing factor. Rather, it is usually two or more factors working in conjunction that cause a coating to fail on a particular site, when that same coating has performed as expected on other sites.

The following is a graphic example of this premise; it was an actualfailure. The names have been redacted to avoid embarrassment to any of the parties involved.

Scope of the Job

Remove oldcoal tar epoxycoating system on sheet piling in a harbor, and replace it withhigh solids,high-build,immersion-gradeepoxy. (Related reading:Review of Solvent-Free Epoxy Protection for Secondary Containment Concrete.)

The Specification

A reputable engineering firm, with many years of experience in construction and maintenance of municipal and marine facilities, prepared a detailedcoating specificationthat required experienced contractors with a marine background. (For more about the difficulties of a marine environment, seeMarine Structures Create Unique Challenges for Third-Party Inspectors.) The specification required the old coal tar epoxy coating to be removed byabrasive blastingto meet the requirements ofNACE2/SSPC-SP10 Near White Blast with an angular profile of 2 to 4 mils (50 to 100µm). The specification listed three approved coating systems, all of which had extensive, successful case histories.

第一个因素Coating Failure

The job was awarded to a contractor with extensive marine experience with harbor facilities, but mainly with physical construction activities, including piling placement andweldingof harbor structures.

The contractor had worked for this Port Authority before, had performed acceptably, and had good relationships with the Port Authority staff. Unfortunately, his expertise insurface preparationand application ofprotective coatingswas minimal.

Second Contributing Factor to the Coating Failure

The successful contractor sublet the coatings part of the job to a local company with a reasonable background in protective coatings work, but with very little experience in dealing with tidal variances in a harbor. Almost immediately, they ran into problems with the heat of the dry abrasive blasting process softening the old coal tar epoxy, making it a very slow process to get the level of surface cleanliness required by the specification. (Be sure to readSubstrate Surface Preparation for Corrosion Preventionto learn how to do it correctly.)

Third Contributing Factor to the Coating Failure

Predictably, the job began to fall behind schedule and the subcontractor looked at options to regain time lost. He attempted to usewet abrasive blastingand power tool cleaning—without success. He looked for acceptable coating systems that could be applied over marginally prepared surfaces, and found one that had a solid track record on industrial projects.

Unfortunately, while the selected coating system had good low-temperaturecuringcapabilities, it had never been applied on pilings subject to immersion by tidal surges in cool to cold weather.

Fourth Contributing Factor to the Coating Failure

The summer weather soon turned into winter weather because the work had slipped behind schedule.Recoat windowswere severely affected. Prior to being coated, immersion of surfaces occurred due to tidal changes with the seasons. As a result,delaminatingof the newly applied epoxy coating system occurred both between coats and from the bare metal.

Conclusion

This case is a good example of good intentions that met the requirements of the job, but slowly became inconsistent with the requirements of the job by third-party decisions that were based more on relationships than on qualifications.