Liquid penetrant testing developer consists of 5 different types as following:
This type of liquid penetrant testing developerr is only can be used with fluorescent technique and appropriate for rough surfaces. This might not be enough sensitive for smooth surfaces. Besides, should not be used with visible technique and if used it would have very low sensitivity. The overall sensitivity is lower than water soluble. The powder is fine and fluffy. The dry powder can be applied by electrostatic sprayer or immersing the test object on the dry powder container or with air blast in the specific chamber.
It is the powder crystal and should be mixed and dissolved in the water based on manufacturer instruction. This kind of developer can be applied by spraying or immersing in the tank. The gravity of the developer liquid should be measured frequently with a hydrometer since it loses concentration by evaporation. This type of developer is appropriate for the liquid penetrant test lab.
The powder is mixed with water and forms a white suspension liquid and need to be agitated frequently. The amount of powder and water should be based on powder manufacture instruction. The specific gravity should be measured frequently by hydrometer since the water is lost by evaporation and this changes the suspension concentration. The suspension developer can be sprayed or immersed in the developer tank. This type of developer is appropriate for the liquid penetrant test lab.
This type is provided in the spray can (aerosol). It is wet powder suspension in the can that mixed with the volatile solvent. As you spray on the test object, a thin layer covers the test object and solvent evaporates instantly and a thin white film will be visible. These are most sensitive developer type. The aerosol should be agitated before application and if there is large surface, should be agitated frequently.
There two products available one for visible technique and the other one for fluorescent technique.
The developing time depends on approved test procedure, and after elapsing developer dwell time, then the evaluation/ interpretation is performed by a qualified ASNT Level II or Level II liquid penetrant specialists. The evaluation is performed based on the acceptance criteria indicated on the procedure or referenced code or standard.
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