While penetrant inspection attracts little research and investigation it remains one of the most widely used methods of non-destructive testing in many industries including aerospace and power generation where many critical components are inspected in this way. One of the basic requirements for the successful application of penetrant testing is that the surfaces to be tested must be clean and dry before the penetrant is applied. The reason which is generally given for this need is that any residual material which remains entrapped in discontinuities will be an effective barrier to the penetrant which simply will not get into defects and therefore no indications will be formed. Unfortunately little has been published in support of this proposal but extensive anecdotal evidence exists for the idea to be accepted. There is, however, a further problem in that many components are treated with a variety of chemicals and mixtures immediately before penetrant testing. Many of these chemicals are very aggressive to fluorescent penetrant and may compromise them in one or both of two ways. The pre-treatment chemicals may attack the fluorescent dyes in the penetrant directly so that at very low levels of contamination the penetrant loses all capability to fluoresce, alternatively they may be strongly coloured and compete with the penetrant residue for light or absorb the incident UV, also masking any indications: some pretreatment chemical mixtures have both effects so posing a triple threat to the success of the inspection. This paper reports specifically on the effect of acid Iron III chloride etching on subsequent penetrant testing, a number of cast components were tested first with a penetrant process approved to Type I, method D, level 2 according to Mil-I-25135E directly after straightforward cleaning and the defect indications.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 2, pages 1231 - 1234 Publisher:Ashgate Publishing Company
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