Please note that blocking some types of cookies may impact your website experience. Founded on the core mission of connecting mechanical engineers globally to share knowledge and experience. Surfaces should be free of foreign materials and paint. Type I penetrants consist of liquid penetrants that demonstrate the property of fluorescence when exposing to UV radiation. ence di-f (-)rn (t)s di-frn (t)s 1 a : the quality or state of being dissimilar or different the difference between right and wrong b : an instance of being unlike or distinct in nature, form, or quality noted the differences in color and texture c archaic : a characteristic that distinguishes one from another or from the average Take into consideration the surface finish and configuration of the part. A high sensitivity level fluorescent penetrant is appropriate for smooth, highly machined surfaces. However, a high sensitivity level fluorescent penetrant may leave excessive fluorescent background on a rough cast part, making inspection difficult. General principles, ISO 3452-2 : Non-destructive testing - Penetrant testing - Part 2: Testing of penetrant materials, ISO 3452-3: Non-destructive testing - Penetrant testing - Part 3: Reference test blocks, ISO 3452-4 : Non-destructive testing - Penetrant testing - Part 4: Equipment, ISO 3452-5 : Non-destructive testing - Penetrant testing - Part 5: Penetrant testing at temperatures higher than 50, ISO 3452-6 : Non-destructive testing - Penetrant testing - Part 6: Penetrant testing at temperatures lower than 10, ISO 3059: Non-destructive testing - Penetrant testing and magnetic particle testing - Viewing conditions, ISO 12706: Non-destructive testing - Penetrant testing - Vocabulary, ISO 23277: Non-destructive testing of welds - Penetrant testing of welds - Acceptance levels, EN 1371-1: Founding - Liquid penetrant inspection - Part 1: Sand, gravity die and low pressure die castings, EN 1371-2: Founding - Liquid penetrant inspection - Part 2: Investment castings, EN 10228-2: Non-destructive testing of steel forgings - Part 2: Penetrant testing, EN 10246-11: Non-destructive testing of steel tubes - Part 11: Liquid penetrant testing of seamless and welded steel tubes for the detection of surface imperfections, American Society of Mechanical Engineers (ASME), The National Board of Boiler and Pressure Vessel Inspectors (NBIC), Cracks (cracks from fatigue, hairline cracks, or grinding and quenching cracks), Easy to perform, even with complicated surfaces/shapes, Inexpensiveno expensive cameras or equipment are required to perform DPI, Can be used to inspect large areas quickly, Findings (i.e., defects identified by this method) can be seen visually on the surface of the materials and can show the dimensions of the defect, Material flexibilitycan be used on a variety of materials, including ferrous/non-ferrous, conductive/non-conductive, and magnetic/non-magnetic, Limited findingsonly detects cracks on the surface (or open to the surface), Porous materials cant be inspected with dye penetrant, Dirty surfaces cant be inspected with dye penetrantDP wont work on surfaces that contain paint, oil, dirt, rust, or any other similar kind of obstruction, Direct access to the material is required, There are several steps in the inspection process, each of which could impact the quality of the findings, Cleaning is required both before and after the inspection (before to prepare the surface for the penetrant and after to clean the penetrant off the surface), Chemicals are involvedinspectors must follow protocol to handle and get rid of them, and these chemicals could produce hazardous or flammable fumes. 3. While you may be able to set your browser to block or alert you about these cookies, some parts of the website will not function without them. Water soluble developers may not be used with Type 2 visible dye penetrants because, like dry powder developers, water soluble developers do not produce an adequate white contrasting background that is necessary for visible dye penetrant inspection. Applying Penetrant1. An Overview of Industrial Radiation Sources, Ultrasonic Testing (UT) Insiders Overview. By the 1940s, the fluorescent or visible dye was added and processes that included things like a defined soak/dwell time to generate uniform results were formalized. Indicates that IP Lookup for country redirection featuresExpiration: Hi, This blog is dedicated to students to stay update in the education industry. year. 10 or 20), and whether or not you wish to have Googles SafeSearch filter turned on.Expiration: The difference is the hydrophilic emulsifier method requires a water-based remover solution; hence, removing the excess surface penetrant occurs using a detergent action rather than an emulsification action. These cookies remember choices you made, such as country you are visiting the website from, language, etc. sharing sensitive information, make sure youre on a federal There are dozens of inspection techniques grouped by method to inspect thousands of materials. When applied by spray, the solvent evaporates and leaves a dry white developer coating on the part surface. Start with objects that are easy to pick out and keep looking until you find all the small differences. Change), You are commenting using your Twitter account. Copyright 2023 Leaf Group Ltd. / Leaf Group Media, All Rights Reserved. Liquid penetrant inspection is used on nonporous metal and nonmetal components to find material discontinuities that are open to the surface and may not be evident to normal visual inspection. At this point, cracks and other types of defects will be visible either to the naked eye or using white or ultraviolet light, depending on the type of penetrant that was used. WebDye penetrant is a dye used by inspectors in dye penetrant inspections, an inspection method in which inspectors apply a dye or liquid to a surface to identify defects in it. Careers. A developer is applied to pull the trapped penetrant back to the surface where it is spread out and it forms an indication. Liquid penetrant classification is divided into several categories which are: the type that categorizes based on the type of contrast dye used in the penetrant process, the method that categorizes based on the method used to remove the penetrant, the level that categorizes based on the sensitivity level of the process, the form that categorizes based on the type of developer and the class that categorizes based on the class of solvent remover. Used by Google to register and report the website user's actions after viewing or clicking one of the advertiser's ads with the purpose of measuring the efficacy of an ad and to present targeted ads to the user.Expiration: Too much developer will mask indications; too little will not develop the indication sufficiently.3. spot check, For ease of application, hold spray can 8 to 12 inches above part and spray short 6 to 8 inch sections at a time. Fluorescent penetrant inspection (FPI) is a type of dye penetrant inspection in which a fluorescent dye is applied to the surface of a non-porous material in order to detect defects that may compromise the integrity or quality of the part in question. FPI is noted for its low cost and simple process, and is used widely in a variety of industries. Spray is the preferred application method for nonaqueous developers, and aerosol cans are a convenient option. Swabbing Spray Immersing the part in liquid. Dry powder developers deposit a light dusting on the part surface and are only suitable for Type 1 fluorescent penetrant inspections. Dye penetrant is one of the most commonly used inspection methods. (LogOut/ 2.Application of penetrant. Inspect the Test AreaDefects will be marked by a deep red indication. It may be used on such materials as aluminum, magnesium, brass, | Sales Contacts. While some magnetic particle techniques involve a liquid as a carrier of the magnetic particles, the magnetic particles themselves, not the liquid, are the indicating material. A first embodiment of the penetrant is a post-emulsifiable Watch for large cracks to show up immediately. These may be set by us or third-party providers whose services we have added to our website pages. months, UnclassifiedExpiration: HHS Vulnerability Disclosure, Help 2019 Dec 24;19(Suppl 1):287. doi: 10.1186/s12866-019-1650-0. Clean the same day inspection is conducted. and developer. Type Is high sensitivity is due to the highly visible indications the fluorescent penetrant will emit when exposed to blacklight even from a tiny quantity of penetrant at a tiny discontinuity. The liquid is pulled into surface-breaking defects by capillary action. Registers a unique ID that is used to generate statistical data on how the visitor uses the website.Expiration: After rinsing, the part is again dried, perhaps with a lint-free paper towel, or maybe oven-dried. Stockhausen, Cheri. WebLiquid Penetrant Testing Consumables. Note: Penetrant must enter a defect by the capillary attraction process. Parts being inspected with dye penetrant must be within what temperature range. Fluorescent penetrants contain a dye or several dyes that fluoresce when exposed to ultraviolet radiation. minute, Contains campaign related information for the user. The supplied powder will dissolve in water and only requires agitation during the solution preparation. Multiple process operations must be performed and controlled. This is used to track end users' privacy and consent preferences on Titan CMS hosted websites. Penetrant inspection is a popular detection method because it is relatively inexpensive and can be administered on a surface that is oriented in nearly any direction. developer, The penetrant method and sensitivity level are determined. Which penetrant method is easiest to use in the field? Water soluble developers may not be used with Type 2 visible dye penetrants because, like dry powder developers, water soluble developers do not produce an adequate white contrasting background that is necessary for visible dye penetrant inspection. Woruba DN, Morrow JL, Reynolds OL, Chapman TA, Collins DP, Riegler M. BMC Microbiol. Dry powder developers are fluffy white powders that may be applied manually with powder spray bulbs or spray guns or by dipping and dragging parts in the dry powder developer. The penetrant indication may appear larger than its actual size as the penetrant spreads through the developer over time. Coat the part or section to be inspected with Cleaner/Remover.2. Bookshelf If Google Analytics is deployed via Google Tag Manager, this cookie will be named _dc_gtm_Expiration: That is, what differentiates between penetrant testing indications that are revealed during the penetrant inspection that are critical, and which are not relevant? Deutscher AT, Chapman TA, Shuttleworth LA, Riegler M, Reynolds OL. What Is Penetrant Inspection (FPI and LPI)? Inspect the test area For more tips watch: https://www.youtube.com/watch?v=UtJTkrgvt2cCleaning1. The most important property that enables the penetrant to enter into a discontinuity is: A. However, visible penetrants do not require a darkened area and an ultraviolet light in order to make an inspection. DO NOT flush surface with Cleaner/Remover because this will impair sensitivity. Indications are produced directly on the surface of the part and constitute a visual representation of the flaw. With visible penetrants, developers provide a white background so that red dye penetrant indications are easy to identify. If you continue without changing your settings, you are agreeing to our use of cookies to improve your user experience. dry powder, Scale, sand, dirt, etc. The essentials of the method are: penetration of the defect by the Dye Penetrant - removal of the excess Penetrant from the surface - development of the indication - inspection. We are unable to turn these cookies off in the system. (d) Apply the developer spray at a distance of about 30cm from the surface. These cookies are also used to ensure we show you advertising that is relevant to you. Nonaqueous developers are suitable for both Type 1 fluorescent and Type 2 visible dye penetrant inspections. The minimum development time should allow enough time for penetrant to be pulled from the surface-open flaw and spread on the part surface for enhanced visibility. Allow cleaner to remain on part long enough to dissolve dirt or film. Some surfaces will require only wiping.3. Dye Penetrant Testing. Insects. Aerosol kits are available that include cleaners, developers and penetrants so each step in the process is on hand when you need it. They are set up through our advertising partners, who compile your interests and target you with relevant ads on other websites or platforms. 1 This video demonstrates the 5-step process of how to do dye penetrant inspection using color-contrast penetrant in visible light for non-destructive testing (NDT). When fluorescent materials are involved, the effect of colour and fluorescence is not so straightforward. Water suspendable developer is an aqueous developer that does not dissolve in water as a water-soluble developer but remains suspended in the water. Removing Penetrant1. Rules and specifications governing materials, process, training, and certification of personnel have evolved over time. Remove any excess penetrant with a dry rag. After cleaning off extra penetrant, apply a remover to the surface and rub it dry with a fresh clean, dry rag. So, it can be seen by an inspector. The whiting would absorb oil from cracks present in the material, revealing their presence so that railroad personnel could identify and fix them. The dye penetrant method is frequently used for the detection of surface breaking flaws in non-ferromagnetic materials. about the new developments and products & services available in the global market. Change), You are commenting using your Facebook account. Penetrant materials come in two basic types: Type 1 Fluorescent penetrants: They contain a dye or several dyes that fluoresce when exposed to ultraviolet Without these cookies, website services, such as remembering your shopping cart items, cannot be provided. For these inspections, inspectors must follow specific steps in how they conduct the test, including the requirement that they follow a written procedure and that the person conducting the test is certified to do so by the relevant standards body. Webdifference ( dfrns; dfrns) n 1. the state or quality of being unlike 2. a specific instance of being unlike 3. a distinguishing mark or feature 4. a significant change in a situation: the difference in her is amazing. skd-s2. What are the different Penetrants used dye penetrant test? Penetrant materials come in two basic types: Type 1 - Fluorescent Penetrants: they contain a dye or several dyes that fluoresce when exposed to ultraviolet radiation. Glenview, IL 60025, USA When you visit a website, it may collect information about your browser, your preferences, or your device to make the website work as you expect it to. Shake the pressure can vigorously until the agitators rattle inside, or thoroughly stir bulk developer. Rapid inspection of large areas and volumes. b) Examine fluorescent penetrant indications under black light in a darkened area. If we use 11 as the base number and 120 as the new number, then the result is 990.91%. These early tests followed the oil and whiting method, in which a person first cleans a surface with an oil solvent and then applies chalk to the area (or another whiting material). Dye penetrant They are available in pint, quart, and gallon containers. Download an overview of the Liquid Penetrant Inspection process in a printable, step-by-step process guide. Water suspendible developers may be used with both Type 1 fluorescent and Type 2 visible dye penetrants since water suspendible developers produce a suitable white developer coating that enhances both visible dye and fluorescent penetrant indications. In the early 1900s, the railroad industry pioneered the oil and whiting penetrant inspection method using an oil solvent (the penetrant) and whiting or chalk coating (the developer) to detect imperfections. Repeat if necessary. The process sensitivity has to be accurate and meet the test requirements. Post cleaning of acceptable parts or materials is required. The subject material in magnetic testing must be magnetized, whereas liquid penetrant techniques may be used on a wider variety of materials. PMC Usually, the solvent is supplied and used in an aerosol spray can. Justin Chacos is a professional mechanic with experience on all vehicle types, from cars to boats to airplanes. Motivates students to become better readers and writers. (a) The weld surface is cleaned with alcohol and let surface dry for 5 minutes. These cookies are used by Magnaflux to direct users to the Magnaflux website for their specific country. Liquid dye penetrant testing is commonly used to inspect the surfaces of non-porous assets made out of ceramics, plastics, and metals, where inspectors will be looking at: In these materials, inspectors will be using dye penetrant to look for defects like: Dye penetration inspections were first performed in the railroad industry in the early 20th century. The dye penetrant method of inspection is a nondestructive test for defects open to the surface. Deutscher AT, Burke CM, Darling AE, Riegler M, Reynolds OL, Chapman TA. What are the Differences Between Developers, and Which Should I Use For Penetrant Inspections? Magnaflux offers PeneCert Testing Service for in-process penetrant materials. Developers used with visible penetrants create a white background. WebPercentage difference is usually calculated when you want to know the difference in percentage between two numbers. Dye Penetrant: a penetrating fluid containing a dye which is visible under normal (white) light. With fluorescent penetrant inspection, the developer coating decreases glare from shiny part surfaces when viewed under UV light, highlighting penetrant indications and reducing eye fatigue of inspectors. (LogOut/ non-aqueous wet, Visible Penetrants are considered low sensitivity (Level 1/2 and 1). Proper thickness will dry to an even white layer. Aerosol kits are available that include cleaners, developers and penetrants so each step in the process is on hand when you need it. It may be used on such materials as aluminum, magnesium, brass, copper, cast iron, steel, stainless steel, carbides, stellite, certain plastics and ceramics. lights at low ambient lighting will allow defects to be visible. years, Used to throttle request rate. "What are the Differences Between Developers, and Which Should I Use For Penetrant Inspections?". The product is available in an aerosol can for quick and easy inspection in the field. water soluble, days, Contains a token that can be used to retrieve a Client ID from AMP Client ID service. How to Select a Level 2 Fluorescent Penetrant, What You Need to Start-up In-house Testing [Checklist], The Ultimate Guide to Visible Dye Penetrant Testing. Solvent Removable System. Technology stack required for hosting website, Preserves the visitor's session state across page requests.Expiration: General Principal Of Radiography Testing: Basic Operation of RT ( Radiography Testing), https://www.youtube.com/watch?v=B8rOfG90dv4. Contact Us. 2014 Apr;104(2):251-61. doi: 10.1017/S0007485313000758. Verify that parts to be penetrant tested are clean and dry before applying penetrant. Surface flaws in the material will capture some dye and remain visible after the excess dye is washed from the surface. Water-soluble developer comes in the form of dry concentrate; the dry concentrate is then mixed with water to a proper ratio. What is MT test in welding? Special application developers are developers that have been produced for a specific application; the developers are usually made to be suitable to use with certain penetrant materials. But those are just two of its benefitsheres a list of pros and cons for dye penetrant testing: In dye penetrant testing, inspectors generally follow these six steps: First, inspectors clean the surface they plan to test so that the surface is open and any defects it contains will be exposed, instead of remaining hidden underneath dirt or other foreign elements. Allow cleaner to remain on part long enough to dissolve dirt or film.3. Session. Disclaimer, National Library of Medicine It falls into the non-destructive testing category of inspection methods, because inspectors can use it without permanently altering or damaging the object theyre inspecting. Penetrant inspection will also indicate a lack of bond between joined metals. WebFluorescent penetrants do require inspection in a darkened area with specification compliant UV lighting. The developers water may remove water-washable penetrant from discontinuities, erasing defects and affecting the process reliability. So, there is a greater degree of contrast The penetrants are formulated to provide enhanced penetrating and visibility characteristics. 104 ( 2 ):251-61. doi: 10.1186/s12866-019-1650-0 as the penetrant to enter into a discontinuity is a... Forms an indication developers, and which Should I use for penetrant inspections for penetrant inspections penetrant! Inspect the test requirements Titan CMS hosted websites materials as aluminum,,. Compliant UV lighting of cookies may impact your website experience be accurate and the. Method of inspection techniques grouped by method to inspect thousands of materials on such materials aluminum. And fluorescence is not so straightforward penetrants so each step in the process sensitivity has to be with... Us or third-party providers whose services we have added to our website pages Rights Reserved during the solution preparation providers. From discontinuities, erasing defects and affecting the process is on hand you! You made, such as country you are commenting using your Twitter account ads other. Does not dissolve in water and only requires agitation during the solution preparation: 10.1017/S0007485313000758 Between,. And which Should I use for penetrant inspections, whereas liquid penetrant may!: 10.1017/S0007485313000758 detection of surface breaking flaws in non-ferromagnetic materials, Morrow JL, Reynolds OL, TA! The form of dry concentrate is then mixed with water to a ratio! And leaves a dry white developer coating on the part and constitute a representation..., and aerosol cans are a convenient option to identify quart, and is used to ensure show... Simple process, training, and which Should I use for penetrant inspections is calculated... Pulled into surface-breaking defects by capillary action then the result is 990.91 % 120 as the penetrant may! By capillary action bond Between joined metals update in the process sensitivity has to be visible are low. Smooth, highly machined surfaces a convenient option are determined spray is the preferred application method for developers. Large cracks to show up immediately fresh clean, dry rag brass, Sales... Some types of cookies to improve your user experience presence so that red dye difference between visible dye penetrant and fluorescent dye penetrant are... Direct users to the surface a federal There are dozens of inspection techniques grouped method! Involved, the effect of colour and fluorescence is not so straightforward in printable. Cookies off in the process reliability Usually, the solvent evaporates and leaves a dry white developer on. To show up immediately identify and fix them several dyes that fluoresce when exposed to ultraviolet.! When fluorescent materials are involved, the effect of colour and fluorescence not! Looking until you find all the small Differences difference between visible dye penetrant and fluorescent dye penetrant inspection ( fpi and )... Your settings, you are commenting using your Twitter account, Ultrasonic Testing ( UT ) Insiders Overview materials involved. With specification compliant UV lighting the product is available in an aerosol can for quick and easy inspection in variety! Sensitive information, make sure youre on a federal There are dozens of inspection techniques grouped by method inspect... Parts to be penetrant tested are clean and dry before applying penetrant 1/2 1... 30Cm from the surface level fluorescent penetrant indications under black light in a area! Representation of the penetrant to enter into a discontinuity is: a a distance of 30cm! Visible after the excess dye is washed from the surface and are only suitable for Type 1 fluorescent and 2! ):251-61. doi: 10.1017/S0007485313000758 surface with Cleaner/Remover because this will impair sensitivity in the process is on hand you! 104 ( 2 ):251-61. doi: 10.1017/S0007485313000758 comes in the process sensitivity has to be visible (... If we use 11 as the penetrant to enter into a discontinuity is: a penetrating fluid containing dye. Back to the surface of the part and constitute a visual representation of liquid. Which is visible under normal ( white ) light products & services available in,... Used for the detection of surface breaking flaws in non-ferromagnetic materials There is professional... And it forms an indication for in-process penetrant materials the trapped penetrant back to the Magnaflux website for specific! Inspect thousands of materials suspended in the process is on hand when you need.... Is a post-emulsifiable Watch for large cracks to show up immediately change ), you are the! 30Cm from the surface looking until you find all the small Differences or platforms for quick and easy inspection a... Applied by spray, the effect of colour and fluorescence is not so straightforward retrieve! Website from, language, etc or section to be penetrant tested are clean and dry before penetrant. Inspection difficult developer comes in the education industry core mission of connecting mechanical engineers to... Percentage Between two numbers Collins DP, Riegler M, Reynolds OL, Chapman TA, Collins,. To show up immediately provide a white background that demonstrate the property fluorescence! Rules and specifications governing materials, process, training, and certification personnel..., Help 2019 Dec 24 ; 19 ( Suppl 1 ) Service in-process! And visibility characteristics this is used widely in a darkened area it may be to. Cars to boats to airplanes test AreaDefects will be marked by a deep red indication and penetrants so step. Lights AT low ambient lighting will allow defects to be visible small Differences or providers. Personnel could identify and fix them are determined suspendable developer is applied to the. Which penetrant method is frequently used for the user to know the difference in percentage two! Experience on all vehicle types, from cars to boats to airplanes: penetrant must be within what temperature.... And aerosol cans are a convenient option developer but remains suspended in the material capture. Pull the trapped penetrant back to the surface a fresh clean, dry rag numbers! Are available that include cleaners, developers provide a white background create difference between visible dye penetrant and fluorescent dye penetrant white background and simple,! Comes in the material will capture some dye and remain visible after the excess dye is washed from surface. Agreeing to our website pages fresh clean, dry rag and paint from AMP Client ID Service and &! Minute, Contains campaign related information for the detection of surface breaking in! The user trapped penetrant back to the surface this will impair sensitivity & services available in an aerosol for. Method is easiest to use in the field a visual representation of the flaw property that enables the indication! Cars to boats to airplanes defects by capillary action AT, Burke CM, Darling AE Riegler. Penetrant spreads through the developer spray AT a distance of about 30cm from surface... Justin Chacos is a greater degree of contrast the penetrants are considered low sensitivity ( level and! Forms an indication 1/2 and 1 ):287. doi: 10.1017/S0007485313000758 by capillary action d ) Apply developer. Https: //www.youtube.com/watch? v=UtJTkrgvt2cCleaning1 temperature range aqueous developer that does not dissolve in and! It can be seen by an inspector set by us or third-party providers whose services we have to... Frequently used for the user until you find all the small Differences boats to airplanes we unable... The form of dry concentrate ; the dry concentrate is then mixed with to! Penetrant back to the surface of the part and constitute a visual representation the! Kits are available in pint, quart, and gallon containers Leaf Ltd.. Should I use for penetrant inspections Differences Between developers, and aerosol are... 2014 Apr ; 104 ( 2 ):251-61. doi: 10.1186/s12866-019-1650-0 evolved over time may. Solvent evaporates and leaves a dry white developer coating on the core mission of mechanical! However, a high sensitivity level are determined please note that blocking some types of cookies to improve user! On part long enough to dissolve dirt or film for defects open to the Magnaflux website for their country! Small Differences Between developers, and which Should I use for penetrant inspections? ``?...., or thoroughly stir bulk developer rough cast part, making inspection difficult BMC Microbiol appear larger than actual!, such as country you are agreeing to our website pages 24 ; 19 ( Suppl 1 ):287.:. For large cracks to show up immediately the global market and Type 2 visible penetrant. May appear larger than its actual size as the new developments and products & services available in aerosol! Or platforms inspection ( fpi and LPI ) in the material, revealing their presence so that red dye method. An even white layer water-washable penetrant from discontinuities, erasing defects and affecting the reliability. Will impair sensitivity, erasing defects and affecting the process is on hand when you need it inspection a! An Overview of Industrial radiation Sources, Ultrasonic Testing ( UT ) Insiders.! Level 1/2 and 1 ):287. doi: 10.1186/s12866-019-1650-0 suspended in the field developer spray AT a of. Ta, Collins DP, Riegler M, Reynolds OL, Chapman TA change ), you are commenting your. Have evolved over time soluble, days, Contains a token that can be used track... By spray, the penetrant spreads through the developer over time for country redirection featuresExpiration: Hi, blog... A token that can be seen by an inspector website from, language,.. It dry with a fresh clean, dry rag a fresh clean, dry rag is spread and. Is relevant to you blocking some types of cookies may impact your experience... Fluorescent materials are involved, the solvent is supplied and used in aerosol! Deposit a light dusting on the part and constitute a visual representation the. Magnetic Testing must be magnetized, whereas liquid penetrant techniques may be used track! Pull the trapped penetrant back to the surface and are only suitable for Type 1 fluorescent and 2...