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Liquid penetrant test method for large ring forgings

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Liquid penetrant test method for large ring forgings

Release date:2019-02-16 Author: Click:

Liquid penetrant test method for large ring forgings

Liquid permeation test is a method to detect the open defects on the surface of large forgings. Process of this method in a nutshell is called a penetrant materials evenly coated in the tested surface and make it into internal defects, after keep proper time to remove excess penetrant, and make the workpiece is dry, then applying imaging agent in order to suck out into internal defect penetrant, then use the appropriate way to determine the workpiece surface had tested mark.

Process parameters (e.g., pre-cleaning, penetration time, etc.) are determined by the specific material used, workpiece characteristics under test (e.g., size, shape, surface condition, alloy material), expected defect type, etc. Liquid osmosis test can indicate the existence and location of defects, and to some extent, its nature and size.

The types of liquid penetration tests are shown in table 1. Method A is called fluorescence osmosis, which can be divided into a-1, a-2 and a-3 methods according to the characteristics of the penetrant. Method B is called dye osmosis, which can be divided into B-1, B-2 and B-3 according to the properties of osmotic agents.


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Materials used for liquid penetrant testing, including fluorescence and colouring penetrants, emulsifiers (oil-based plus water-based, fast and slow reaction), detergents and imaging agents. A suitable set of liquid penetrant inspection materials consists of the manufacturer's recommended penetrant, emulsifier, detergent and developer. It is recommended not to mix penetration test materials produced by several manufacturers, and note that the materials shall not have harmful effects on large forgings under inspection. The properties of the material are identified by means of a reference block before use.

Fluorescence permeation test is a method to observe the defect trace by stimulated fluorescence under the action of ultraviolet radiation. The sensitivity of the fluorescent penetrant depends on the ability of the penetrant to remain in defects of various sizes during inspection and the luminosity of the penetrant to seep into the developer coating and produce a fluorescence display.

Washable penetrant means that the surface of the workpiece under test can be directly washed with water after the appropriate infiltration time. Since this kind of penetrant is to "mix" the emulsifier into the washable penetrant, it is necessary to train qualified operators to remove the excess penetrant from the workpiece surface and not to overwash.

Post-emulsifying penetrant is insoluble in water and cannot be washed away with water, but a special emulsifier is needed. After appropriate emulsifying time, it can react with the excess penetrant to form a mixture that can be washed away with water. Appropriate emulsification time should be determined by test.

Solvent removal type penetrant refers to the excess penetrant can be used to clean non-fluff material for wiping, so that the majority of the excess penetrant removal, its residual penetrant with non-fluff material dipped in a little detergent wipe can remove all the excess penetrant. This penetrant is used for portable and local inspection. To prevent excessive cleaning, excessive use of solvents should be avoided and direct cleaning of the workpiece surface with solvents is prohibited.

Dye penetrant test is a method of testing penetrant by visual observation under visible light. The osmotic agent used is mostly red, which shows obvious traces compared with the developer of white background. This method does not require black light but must be observed in sufficient white light.

Emulsifier is a liquid used to emulsify excess oil penetrant on the workpiece surface and can be washed off after emulsification. There are two types of emulsifiers: oil-based and water-based (containing detergents). According to the workpiece surface condition, viscosity, concentration and chemical composition, both can emulsify in a few seconds to a few minutes.

Oil-based emulsifiers are usually available on purchase. Emulsifying reaction depends on the speed of its own viscosity and chemical composition, high viscosity is generally slower than the role of low viscosity. Its function is to diffuse (dissolve) into the excess penetrant on the surface of large forgings and emulsify them. The speed of diffusion determines the time of emulsification.

Water-based emulsifiers (including detergent) are usually supplied diluted with water and used in the form of immersion or leaching. Its function is to remove excess permeable film on the workpiece surface by washing. When the permeant film is removed with detergent, the force of the water jet or the air stirring in the open immersion tank plays a scrubbing role, and the emulsification time should be determined according to the concentration of detergent in the water.

The function of the cleaning agent is to make the surface can be wiped clean by the solution of the permeant without leaving any excess permeant.

The function of the developer is through the coating of the developer adsorption so that infiltration into the defect of the agent is sucked out, and show on the surface of the workpiece, so as to show the signs of the agent, but also enhance the clarity of the signs.

Wet water suspension developer, according to its type is usually in the form of dry powder suspended in water or dissolved in water supply.

Water suspension developer is the developer particles suspended in water suspension. Its concentration, usage and storage should be in accordance with the manufacturer's instructions.

Water-soluble developing agent is made up of water-soluble powder and used according to the concentration recommended by the manufacturer.

Non-aqueous suspension developing agent is developed by suspending the developing agent particles in the carrier of non-aqueous solvent. It is very convenient to use, that is, after removing the excess penetrant on the workpiece and drying the workpiece, the developing agent is sprayed on the workpiece with ordinary or electrostatic spray gun, or by air pressure tank. After drying, a white coating is formed on the surface of the workpiece to serve as a foil to the penetrant.

Film developer, the developer is a solution or resin and polymer gel floating. Such developer will form a transparent or translucent coating layer on the surface of the workpiece, some types of coating layer can also be removed from the workpiece as a data preservation.



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