The Dark Side of Misreading the Relevance of Coating Testing

Abstract

Many people quote, “Hubble, bubble, toil and trouble†as the witches’ famous line in Shakespeare’s play, Macbeth (Act 4, Scene 1, vv. 10-11). So the general populace might assume the quote is correct. But it is not. The real quote is “double, double, toil and trouble.†The incorrect quote is assumed bona fide because of its repeated use. This article discusses similar assumptions made about many coating specifications and the trouble the assumptions cause. In the discussion, the toil is in the tests. Aside from the use of successful track records, it is common for coating specifications to be based on test criteria deemed important by specification authorities. But are the tests relevant to the intended service environment? Has the meaning of the test data been misinterpreted? Have the tests been ascribed a level of accuracy and dependency that the test method simply cannot deliver? These vital questions, addressed in this article, must be considered if a coating specification is to be supported in a meaningful way and to prevent all sorts of problems. The authors relate tales—from the water storage, Canadian oil patch, and bridge industries—in which specifiers assumed things were in order, where coating tests and specifications were considered to be in harmony, and where repeated use suggested all was well. But all was not well. The coating specifications were built upon inappropriate uses of certain test data, and dark consequences loomed. The authors also propose ways to conduct testing that potentially offer more meaningful correlations with real world coating performance.