What does penetrant testing mean?

Penetrate Testing (PT) is a non-destructive testing method that makes use of the phenomenon of penetration. Its main application is precisely penetrate testing. The principle behind penetrate testing involves applying a penetrant with strong penetrating capabilities – one with low surface tension or a small contact angle with solids – to the surface of a thoroughly cleaned test piece, either by spraying, brushing, or dipping. This penetrant can be a colored penetrant that appears bright red under white light, or a fluorescent penetrant that emits yellow-green fluorescence when exposed to ultraviolet light. After allowing sufficient time for the penetrant to penetrate any open defects on the surface of the test piece due to capillary action, any excess penetrant is removed from the surface through wiping or rinsing. Next, a developer, in either dry powder or liquid form, is applied to the surface; this developer attracts and guides the penetrant that has penetrated the defects to the surface. The developer itself provides a background with a color that contrasts sharply with that of the penetrant, so that the penetrant that has seeped back out forms visible traces at the locations of the defects on the surface, thereby revealing information about the defects’ shape, orientation, and size in two dimensions. Depending on the type of penetrant used, such traces can be observed under white light with colored penetrants due to the color contrast (this is known as colored penetrant inspection), or they can be observed under ultraviolet light because of the fluorescent properties of fluorescent penetrants (this is known as fluorescent penetrant inspection). Depending on the type of penetrant used and the method of display, penetrant testing is mainly divided into colored penetrant testing and fluorescent penetrant testing. The basic testing procedures for these methods are as follows: 1. Basic testing procedure for colored penetrant testing: (1) Pre-cleaning of the test piece surface: The surface of the test piece can be cleaned using methods such as acid washing, alkali washing, or solvent cleaning, in order to remove surface contaminants that could conceal defects or create an uneven background that makes it difficult to identify them. It is also necessary to remove any fillers from surface openings as much as possible. After cleaning, the surface must be dried to ensure proper penetration of the penetrant. During the pre-cleaning process, it is particularly important to ensure that the cleaning medium used does not affect the performance of the penetrant being applied (that is, it should not react with the penetrant in such a way as to render it ineffective or reduce its performance). (2) Penetration: The coloring penetrant used in coloring penetration testing is generally an organic solvent to which a red dye has been added, along with surfactants that enhance penetration ability and other additives designed to ensure the performance of the penetrant. There is also a type of coloring penetrant that is reactive; it is colorless and transparent on its own, but it undergoes a chemical reaction when it comes into contact with a developer, resulting in a red color under white light. The application of the penetrant can usually be done by spraying it using a spray can with special packaging, or by brushing it on; this method is suitable for on-site inspections or for partial inspections of large structures and components. For use on production lines or with small batches of parts, immersion is employed, allowing the penetrant to be evenly applied to the parts under inspection and to remain in that wet state for a certain period of time (referred to as the penetration time in processing terms) to ensure thorough penetration. (3) Cleaning: Cleaning after penetration, also known as intermediate cleaning, involves different methods depending on the type of penetrant used. For solvent-based penetrants, a specialized solvent-based cleaning solution should be used, while for water-based penetrants, plain water can be used directly. The purpose of the cleaning step is to remove any excess penetrant from the surface of the test piece by wiping or rinsing. It is important to avoid excessive cleaning time or too high water pressure, as this can lead to over-cleaning (i.e., the penetrant that has penetrated into defects is also removed, thereby compromising the reliability of the inspection). On the other hand, insufficient cleaning can result in residual penetrant on the test piece’s surface, which creates a chaotic background that hinders the identification of detection traces when a developer is applied. (4) Drying: The cleaned specimens also need to undergo a certain period of natural drying (in the case of solvent-based cleaning agents) or artificial drying (such as washing with plain water, drying using cold or hot air, or using sawdust for drying). (5) Development: The developer used in colored penetrant inspection is generally a white powder (such as zinc oxide, magnesium oxide, etc., which is used to increase the background contrast on the test piece), added to an organic solvent along with a certain amount of gum material (which helps to fix and contain the traces, preventing them from spreading and becoming difficult to identify), thereby forming a homogeneous suspension. The method of applying the developer can also include spraying with a spray can, brushing, or rapid immersion followed by immediate removal and hanging to allow dripping and drying; the key is to quickly apply a thin, even layer of developer over the surface of the test piece that is to be inspected. After applying the developer, depending on the requirements of the specific developer product, there is a required development time during which the penetrant in the defects can flow back out to form traces; this time is generally very short (usually just a few seconds, with some allowing visualization immediately after spraying). (6) Visual inspection and evaluation: The surface of the specimen under inspection is observed with the naked eye under sufficiently bright white light or natural light, and the visible marks are judged and evaluated. Since color contrast is determined by the human eye, in addition to certain requirements regarding the light intensity used for observation, there are also certain requirements for the vision and color discrimination ability of the inspector (for example, they cannot be color-blind). (7) Post-cleaning: The test pieces that have undergone coloring penetration testing must be cleaned promptly to prevent the testing agents (penetrant, developer) from causing corrosion to the test pieces. 2 Basic inspection procedures for fluorescent penetrant testing (1) Inspection procedure for self-emulsifying fluorescent penetrants: a. Pre-cleaning and drying of the test piece surface: Same as §2.5.1(1). b. Penetration: The method of applying the penetration fluid is the same as that in §2.5.1(2). In addition to fluorescent substances, organic solvents, surfactants, and appropriate additives, self-emulsifying fluorescent penetrants also contain emulsifiers; as a result, they can be cleaned with plain water right after penetration. They exhibit high fluorescence intensity and are relatively inexpensive, but their detection sensitivity is lower than that of post-emulsifying fluorescent penetrants, and the frequency of repeated detection of defects (repeatability) is also lower. c. Cleaning: Cleaning after penetration, also known as intermediate cleaning, can be done by rinsing with plain water at a controlled water pressure and temperature. d. Drying: The same as §2.5.1(4). e. Imaging: The most common method for fluorescent penetrant inspection is dry imaging (wet imaging, which uses an imaging solution, is also used but less frequently). Dry, fluffy, and fine magnesium oxide powder (white) is used as a developer; it does not emit fluorescence under ultraviolet irradiation. When evenly spread over the surface of the test piece, it attracts the penetrant that has penetrated into defects. The penetrant then emits fluorescence under ultraviolet light, thereby revealing the traces of defects. However, after repeated use, the magnesium oxide powder becomes contaminated with the fluorescent substances from the penetrant, resulting in chaotic fluorescence under ultraviolet light that interferes with the background and hinders the observation and evaluation of defect traces; in such cases, it is necessary to replace the magnesium oxide powder. f. Observation and evaluation: The test specimen is irradiated with sufficiently strong ultraviolet light (generated by an ultraviolet lamp) in a dark room, and the resulting defect traces are examined and evaluated. Ultraviolet light is harmful to human skin, especially the eyes, so protection is necessary. g. Post-cleaning: Parts that have undergone fluorescent penetrant inspection also must be cleaned promptly to prevent the inspection media (penetrant, developer) from causing corrosion to the parts. (2) Inspection procedure for post-emulsified fluorescent penetrants: a. Pre-cleaning and drying of the test piece surface: as in §2.5.1(1). b. Penetration: The method of applying the penetration fluid is the same as that in §2.5.1(2). Post-emulsified fluorescent penetrants do not contain emulsifiers; they require a separate emulsification step after penetration in order to improve washability, before they can be cleaned with plain water. c. Emulsification: The emulsifier is applied evenly and in a thin layer onto the surface of the permeated specimen by spraying or rapid immersion. Fluorescent penetrant inspection using post-emulsified fluorescent penetrants offers high sensitivity, a short penetration time, and good reproducibility of defects; however, it is not suitable for inspecting specimens with rough surfaces. d. Cleaning: It can be rinsed directly with clean water at a limited water pressure and temperature. e. Drying: Same as §2.5.1(4). f. Imaging: The same as the self-emulsifying fluorescent penetrant test. g. Observation and evaluation: The same as the self-emulsifying fluorescent penetrant test. h. Post-cleaning: The same as for the self-emulsifying fluorescent penetrant inspection. Factors that affect the quality of penetrant testing include: ① Surface finish of the test piece: When the surface of the test piece is rough, excess penetrant cannot be easily removed, which can lead to an unclear background during imaging. This may result in false indications or distortions, as well as hinder the identification and assessment of defect traces. ②Pre-cleaning and post-permeation cleaning of test pieces: If the pre-cleaning of the test pieces is inadequate, surface contamination will hinder the progress of permeation. In particular, when there is too much filler within surface defects, these defects become blocked, preventing the penetration fluid from reaching them, which may result in the defects not being detected. During cleaning after penetration or emulsification, excessive cleaning (such as too long a cleaning time, high water pressure or temperature used for cleaning) can wash away some of the penetrant that has penetrated into the defects, thereby preventing the detection of those defects. On the other hand, insufficient cleaning results in an excess of penetrant remaining on the surface of the test piece, which creates a chaotic background when a developer is applied, interfering with the identification of detection traces and even leading to false indications. ③Properties of the penetrant: including its penetration ability, the color of the colored penetrant and its contrast with the developer, as well as the fluorescence intensity of fluorescent penetrants, etc. ④Contrast agent performance: includes the ability to absorb the penetrant, contrast with the penetrant (background contrast), and degree of contamination (especially fluorescent contamination from magnesium oxide powder used in the dry powder method for fluorescent penetrant inspection), among others. ⑤Environmental conditions for visual inspection: include the intensity of white light during colored penetrant inspection, the intensity of ultraviolet radiation during fluorescent penetrant inspection, and the darkness level of the environment. ⑥The operator’s experience and skill level, as well as physical condition. In penetrant testing, to ensure the quality of the inspection, relevant auxiliary equipment includes penetrant sensitivity test blocks, penetrant performance verification test blocks, fluorescence intensity meters, white light illuminometers, ultraviolet intensity meters, and so on. Penetrant testing is suitable for metals and non-metals with non-absorbing, smooth surfaces, especially materials that cannot be inspected using magnetic testing methods, such as aluminum alloys, magnesium alloys, titanium alloys, copper alloys, austenitic steels, etc. It can detect surface open defects in forgings, castings, welds, ceramics, glass, plastics, and mechanical parts. The advantages of penetrant testing include high sensitivity (it is capable of detecting cracks with an opening width of up to 0.5 μm), low testing costs, simple equipment and materials required, easy and straightforward operation, intuitive result presentation that allows for further visual verification (such as by using a magnifier or microscope), as well as results that are easy to assess and interpret, resulting in high testing efficiency. The disadvantage is that it is highly affected by the surface condition of the test specimen and can only be used to detect surface-opening defects; if the defects contain a large amount of impurities, it will affect the sensitivity of detection. This post was last edited by brucehan on 2009-3-11 11:17]

Common inspection methods include: X-ray inspection, ultrasonic inspection, magnetic particle inspection, penetrant inspection (color inspection), eddy current inspection, gamma ray inspection, and fluorescence inspection. Based on the dye components contained in the permeate, they can be divided into two main categories: the fluorescence method and the coloring method. The penetrating solvent contains a fluorescent substance; the fluorescence method is one in which defect images can emit fluorescence under ultraviolet light. The permeant contains a colored dye, and the defect image becomes visible under white light or daylight; this is known as the coloring method. Generally, the coloring method is used, as it is inexpensive and easy to apply. However, for containers in critical areas or those with high-risk components, X-ray inspection or other radiation-based inspection methods should be used, as such inspections yield more accurate results.

Thank you. Now I understand a bit better. Thanks; I thought that penetrant testing was just a test for airtightness

The application of titanium materials is mainly related to the corrosion and wear of the medium as well as the operating temperature

The source of this content is the Internet. Penetrant testing can detect surface defects in non-magnetic materials, thus providing a complementary method to magnetic particle testing, which is unable to detect non-magnetic materials. The penetrant testing method works as follows: first, the surface of the workpiece is cleaned thoroughly. After drying, apply the penetrant to the surface by brushing or spraying, so that the dye can penetrate into the defects. After about 5 minutes, wash away the excess dye with water or a solvent. Then spray a layer of white talc color-developing agent on its surface. As soon as the color-developing agent comes into contact with it, it dries out and turns white, and defects such as cracks become visible very quickly. A dry color-developing agent can also be used; thanks to its adsorption properties and capillary action, it draws out the dye that has penetrated into the defects, thereby revealing the extent and size of those surface defects. If there are no defects, nothing will happen; finally, the colorant on the component is washed off to prepare it for use. The closer the surface temperature of the workpiece is to 38°C, the faster the color-developing agent works. However, if the surface temperature exceeds 120°C, the color-developing agent may evaporate, resulting in unsatisfactory results. However, new types of penetrant materials are now available that can be successfully used at 288°C. I. Classification of penetrant testing 1. Classification based on the dye components in the penetrant: Based on the dye components present in the penetrant, it can be divided into two main categories: the fluorescent method and the colored method. The permeant contains a fluorescent substance; the fluorescence method is used when the defect image can emit fluorescence under ultraviolet light. The permeant contains a colored dye, and the defect image becomes visible under white light or daylight; this is known as the coloring method. In addition, there is another type of penetrant that contains both fluorescent and colored dyes; the defect images become visible under white light or visible light, while fluorescence is emitted under ultraviolet light. 2. Classification by osmotic fluid removal method: Based on the method of removing osmotic fluid, it can be divided into the water-washing type. There are two main categories: post-emulsification type and solvent removal type. The water-wash type penetration method involves the use of a penetrant that contains a certain amount of emulsifier; the excess penetrant on the surface of the parts can be removed directly with water. There are also penetrants that do not contain emulsifiers, but whose solvent is water – namely water-based penetrants – and the excess penetrant on the part surfaces can likewise be removed with water. This method also falls under the category of water-wash penetration methods. The penetrant in the post-emulsification penetration method cannot be washed off the surface of the parts with water directly. An emulsification step must be added; that is, the excess penetrating liquid on the surface of the parts must be \"emulsified\" using an emulsifier before it can be washed away with water. The solvent removal penetration method uses organic solvents to remove excess penetrant from the surface of the parts. 3. Types of development methods In penetrant testing, there are four methods of development: wet development, quick-dry development, dry development, and developer-free development. 1) Wet development method: The wet development method is a technique in which a white, fine powdery developing material is mixed in water to serve as a developer. Immerse the test piece in the developer, or spray the developer onto it using a sprayer. When the developer dries, a white imaging film is formed on the test piece; this white film absorbs the penetrant from the defects, thereby creating visible traces. This method is suitable for the inspection of large numbers of workpieces, among which the water-wash fluorescent penetrant inspection method is the most commonly used. However, it must be noted that the traces of defects tend to spread, so over time their size and shape will change. 2) Quick-dry development method: The quick-dry development method is a technique in which a white, fine powdery developing material is mixed in a highly volatile organic solvent to be used as a developer. The developer is sprayed onto the test piece, rapidly forming a white developing film on its surface; this white film absorbs the penetrant from within the defects, thereby creating visible traces. Due to its simplicity of operation, this imaging method is most commonly used in solvent-based fluorescent penetrant testing and colored penetrant testing. Like the wet development method, as time passes, the traces of defects displayed will spread, so it is necessary to pay attention to changes in the size and shape of these traces. 3) Dry imaging method: The dry imaging method is a type of technique that uses dry white imaging powder as the developer directly. During imaging, white imaging powder is directly sprayed onto the surface of the test piece; the developer adheres to the surface and draws out the penetrant from the defects, thereby forming visible traces. Using this method, all the developer particles attached to the defective area stick to the penetrant, while no developer adheres to the areas without penetrant. Therefore, the imaging traces do not spread over time, allowing for a clear image to be displayed. This imaging method is widely used in post-emulsified fluorescent penetrant testing and water-washable fluorescent penetrant testing. The colored penetrant testing method is not suitable for dry imaging methods due to its poor ability to identify trace marks. 4) Agent-free imaging method: The agent-free imaging method is a technique that, after cleaning, does not use any imaging agent to create traces indicating defects. It is used in the high-brightness fluorescent penetrant water-wash type fluorescent penetrant testing method, or in a method that uses penetrant testing to reveal traces while applying alternating components to the test piece. Like the dry imaging method, its drawback is that the defect traces do not spread. II. Safety management of penetrant testing: The penetrants used in penetrant testing are almost all flammable oily substances. Spray can-type flaw detectors are sometimes filled with highly flammable propane gas. When using such detectors, special attention must be paid to fire prevention, as they are considered hazardous materials under fire safety regulations; therefore, it is necessary to comply with the storage and usage requirements specified by relevant laws and regulations. The penetrants used in penetrant testing are generally non-toxic or low-toxic, but direct contact with and absorption of these penetrants, cleaning agents, etc. by the human body can sometimes cause discomfort, leading to headaches and nausea. Especially when conducting flaw detection in sealed containers or indoors, volatile and toxic gases tend to accumulate, so adequate ventilation is necessary. Regarding the use of organic solvents, the concentration of these solvents in the working environment should be limited in accordance with the rules for preventing poisoning from organic solvents. Ultraviolet light within the specified wavelength range is harmless to the eyes and skin, but it should be noted that prolonged direct exposure to the eyes and skin can sometimes cause eye fatigue and redness of the skin. Therefore, when performing flaw detection, it is necessary to pay attention to protecting the eyes and skin. III. Characteristics of penetrant testing Penetrant testing has the following characteristics: 1. Surface open defects in any type of material, except for loose and porous materials, such as steel, non-ferrous metals, ceramic materials, and plastics, can be detected using penetrant testing. 2. Components with complex shapes can also be inspected using penetrant testing, allowing for nearly comprehensive inspection in a single operation. 3. When defects exist in multiple directions at the same time, detection can be completed with a single inspection procedure; even for defects with complex shapes, it is easy to observe traces of them. 4. No large equipment is required; the portable spray can for color penetrant testing doesn’t need water or electricity, making it very convenient for use on-site. 5. The surface finish of the test specimen has a significant impact, and the inspection results are often affected by the skill level of the operator. 6. It can detect surface-opening defects, but it is unable to detect buried defects or closed surface defects. 7. There are many testing procedures, resulting in slow speed. 8. The detection sensitivity is lower than that of magnetic particle testing. 9. The materials are expensive, resulting in high costs. 10. Some materials are flammable and toxic. Titanium has strong corrosion resistance, which is better than that of metals. So it can be used to store acidic and alkaline substances.