The penetrant materials used today are much more sophisticated than the kerosene and whiting first used by railroad inspectors near the turn of the 20th century. Today's penetrants are carefully formulated to produce the level of sensitivity desired by the inspector. To perform well, a penetrant must possess a number of important characteristics. A penetrant must:
All penetrant materials do not perform the same and are not designed to perform the same. Penetrant manufactures have developed different formulations to address a variety of inspection applications. Some applications call for the detection of the smallest defects possible and have smooth surfaces where the penetrant is easy to remove. In other applications, the rejectable defect size may be larger and a penetrant formulated to find larger flaws can be used. The penetrants that are used to detect the smallest defect will also produce the largest amount of irrelevant indications.
penetrants
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Penetrant materials are classified in the various industry and government specifications by their physical characteristics and their performance. Aerospace Material Specification (AMS) 2644, Inspection Material, Penetrant, is now the primary specification used in the USA to control penetrant materials. Historically, Military Standard 25135, Inspection Materials, Penetrants, has been the primary document for specifying penetrants but this document is slowly being phased out and replaced by AMS 2644. Other specifications such as ASTM 1417, Standard Practice for Liquid Penetrant Examinations, may also contain information on the classification of penetrant materials but they are generally referred back to MIL-I-25135 or AMS 2644.
Fluorescent penetrants contain a dye or several dyes that fluoresce when exposed to ultraviolet radiation. Visible penetrants contain a red dye that provides high contrast against the white developer background. Fluorescent penetrant systems are more sensitive than visible penetrant systems because the eye is drawn to the glow of the fluorescing indication. However, visible penetrants do not require a darkened area and an ultraviolet light in order to make an inspection. Visible penetrants are also less vulnerable to contamination from things such as cleaning fluid that can significantly reduce the strength of a fluorescent indication.
Water washable (Method A) penetrants can be removed from the part by rinsing with water alone. These penetrants contain an emulsifying agent (detergent) that makes it possible to wash the penetrant from the part surface with water alone. Water washable penetrants are sometimes referred to as self-emulsifying systems. Post-emulsifiable penetrants come in two varieties, lipophilic and hydrophilic. In post-emulsifiers, lipophilic systems (Method B), the penetrant is oil soluble and interacts with the oil-based emulsifier to make removal possible. Post-emulsifiable, hydrophilic systems (Method D), use an emulsifier that is a water soluble detergent which lifts the excess penetrant from the surface of the part with a water wash. Solvent removable penetrants require the use of a solvent to remove the penetrant from the part.
The major US government and industry specifications currently rely on the US Air Force Materials Laboratory at Wright-Patterson Air Force Base to classify penetrants into one of the five sensitivity levels. This procedure uses titanium and Inconel specimens with small surface cracks produced in low cycle fatigue bending to classify penetrant systems. The brightness of the indication produced is measured using a photometer. The sensitivity levels and the test procedure used can be found in Military Specification MIL-I-25135 and Aerospace Material Specification 2644, Penetrant Inspection Materials.
An interesting note about the sensitivity levels is that only four levels were originally planned. However, when some penetrants were judged to have sensitivities significantly less than most others in the level 1 category, the level was created. An excellent historical summary of the development of test specimens for evaluating the performance of penetrant materials can be found in the following reference.
Appreciating and compensating for the inherent variability associated with percutaneous absorption is essential in optimizing (trans)dermal therapy. In this study, the variability in human skin permeability associated with model penetrants of differing lipophilicity (caffeine (CF), methyl paraben (MP), and butyl paraben (BP)) was examined in a standardized intra-laboratory study (Franz cell experiments) using epidermal tissue from various donors. Experimentally derived permeability coefficients (K(P)) were also compared to that derived from two skin permeation models namely, Potts & Guy and Robinson (revised) models in order to further validate the Franz diffusion method employed and also elucidate the potential permeation pathway(s) employed by the model penetrants. Intra-subject variability associated with skin permeation of the model penetrants was generally found to be lower than inter-subject variability. Experimental K(P) values were found to be the same order of magnitude as predicted by the mathematical models. Calculated residual variance suggested the Potts and Guy's model to be relatively accurate in predicting skin permeability of the two parabens whilst the Robinson (revised) model was more effective for CF. The high variability in CF permeation compared to the parabens may suggest the in vitro skin permeation of solutes becomes more sensitive to intra- and/or inter-subject variation in skin lipid content, appendageal density, and imperfections (pores, cracks) as the hydrophilic nature of the solute increases. Such variability in skin permeability suggests a difference in CF permeation kinetics relative to the parabens. As such when performing in vitro drug permeation studies, it is essential that the variability in the absorption of the model permeants, according to their physicochemical properties, is considered when they are used to normalize or standardize any resulting data.
The effect of heat on the transdermal delivery of model penetrants of differing lipophilicity through artificial membranes (non-rate limiting) and human epidermis was investigated in vitro. Saturated suspensions of the model penetrants; methyl paraben (MP), butyl paraben (BP) and caffeine (CF) in deionised water (vehicle) were used to attain maximal thermodynamic activity. Franz cell experiments were performed at temperatures ranging from 23 to 45 degrees C using the infinite dose method. Artificial membrane studies showed the penetrant diffusivity (diffusion coefficient) in the vehicle to be totally dependent on temperature and not changes in donor solubility. Epidermal flux and retention of all penetrants was found to be affected by temperature. The amount of penetrant retained in the epidermis was found to be in the order BP>CF>MP whilst the transdermal fluxes increased in the order MP>BP>CF with increasing receptor temperature. Estimated epidermal diffusivity of MP was found to be significantly affected by temperature (P
Met-L-Chek Visible penetrants are widely used in general industry for spot inspections of welds, equipment repairs, safety checks, through leak testing of heat exchangers, field tests in oil and gas equipment, and nuclear component casting inspection. The red penetrant indications are readily visible in bright white light and sunshine contrasting with the white developer.The visible penetrant test method lends itself to field applications where there are limited infrastructure resources such as electricity or water and requires limited instruction in use. All the needed materials, cleaner/removers, penetrants, and developers, come in aerosols for ease of application and storage.
To date, direct measurements of sorbed flavor molecules in the inside of films have not been established, without disruption of flavor distribution. A confocal laser scanning microscope technique (CLSM) was proposed to establish sorption visualization in films6,7. However, the CLSM technique was only applicable to fluorescence compounds. A matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS)8 method was also applied for sorption visualization, and the local distribution of penetrants in laminated films was successfully visualized. The non-destructive MALDI-IMS visualization, however, still has serious disadvantages due to limited targets with low volatility and high ionization efficiency in the mass spectrometry (MS) vacuum chamber.
In this study, the penetrating process of PG-d6 into CA film with time was clearly visualized (Fig. 6). Furthermore, distributed multiple components (l-menthol and PG-d6) in these penetration processes were simultaneously detected (Fig. 7). In previous studies26,27,28, the methods of measuring the concentration of absorbed penetrants in the bulk were the mainstream. In contrast, this would be the first-of-its-kind of in situ visualization of volatile small molecules distribution during sorption into the polymer.
Penetrant testing is a well-recognized inspection method to detect e.g. casting, forging and welding surface defects such as cracks, overlapping, folds, pinholes or other bonding failures. The so called 'penetrant system' consists of the penetrant itself, a penetrant remover and finally a developer, which helps to increase the contrast and pull out the remaining penetrant at the end of the inspection process. Whereas fluorescent penetrants are required for the part inspection under UV(A) light, color-contrast penetrants are widely used for the inspection under white light.
Benefit from a broad range of fluorescent and color-contrast penetrants as well as all relevant removers and developers. With Ardrox NDT products we are well acquainted with the high standards in the aerospace field for many years. Additionally, the high quality of the available NDT products and services has also convinced the automotive industry and its component supplier market, general industry and all areas of energy generation and transportation. The multiple approvals of our Britemor and Checkmor PT products are proof of this. 2ff7e9595c
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