LIQUID PENETRANTS USER'S MANUAL in
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1. 1 3 Mechanical cleaning To remove paint oxidation deposits or similar foreign matters from the surface the use of the sandblasting aluminium or stainless steel wire brush or grinding could be needed This cleaning process tends to mask discontinuities limiting the efficacy of the penetrant Sandblasting through special abrasive plastic substances Plastic Media is a process now approved in the aeronautical field as well because it does not alter the finish the surface hardness and it does not seal off possible cracks NDT Italiana provides different units permanent as well as mobile designed in view of users and abrasive Plastic Media specific needs 2 PENETRANT APPLICATION The penetrant has to be applied to the entire surface to be inspected by adopting whatever method assuring a complete coverage of the area under examination such as dipping spraying or brushing All surfaces must be completely wet with penetrant in order to have it drained back into discontinuities by capillary effect Dwell time needed to have an optimal penetration can be determined through Tab 3 or by adopting applicable specifications If penetrant is applied by dipping the piece has to be removed from the tank and left dripping during penetration time if necessary because the presence of blind holes or the geometry cause the liquid to be stagnant the piece must be dipped again in the tank Liquids and surfaces temperatures must be in a range between 12. turn the spray can up side down and continue spraying till only gas exists 5 2 Aqueous Wet Developer Two types of Aqueous Wet Developer are commonly in use in one of them the powder is suspended in water in the other one it is completely soluble in water Aqueous Wet Developer can be applied by dipping brushing or spraying Heavy quantity of developer must be avoided because it might mask indications Before use the Developer has to be shaken vigorously to restore full suspension of the particles Commonly Aqueous Wet Developer is applied to the surface when it is still wet after excess penetrant has been rinsed off When using these types of products dipping instead of spraying is recommendable in order to avoid a not uniform distribution of the Developer due to residual drops of washing water With respect to the drying of the Developer hot air is preferable or alternatively the pieces can be put into recirculation type ovens as previously indicated under point 4 Drying 5 3 Dry Developer Dry Developer differentiates from Aqueous Wet Developer because of the softness of the powder and the very low weight in spite of its great volume Dry Developer is blown over the surface after penetrant removal and drying The excess is removed by not compressed air or by shaking the piece Dried parts may be also dipped in a tank filled in with powder and the powder may be applied by a soft brush By adhering to the surface the small parti
3. by dipping the piece into an emulsifier for a determined period of time and subsequently by spray washing the area under examination or dipping it in a tank of water Emulsifiers recommendable to make penetrants water soluble are classified into two categories 1 Lipophylic or oily products 2 Hydrophylic or aqueous products Emulsifying time is critical normally it ranges from 30 sec to 3 min not only washing time but also pressure and temperature of the water affect the emulsifying process Parameters vary according to the chemical formulation of the emulsifier and in accordance with its emulsifying characteristics Before applying the hydrophylic emulsifier a pre cleaning by dipping into water or spraying is useful to remove most of the excess penetrant Final cleaning with both emulsifying products is to be performed by flushing with clean water at a pressure not higher than 280 kPa and at a temperature ranging from 10 C to 38 C 4 DRYING Surfaces have to be accurately dried before applying the developer Drying can be accomplished by natural evaporation in free air or accelerated by filtered forced air with clean and dry cloths or by warm air stream also inside recirculation type ovens if necessary In the latter case air must not exceed 71 C and the temperature of the piece has to reach no more than 38 C 5 WHITE DEVELOPER APPLICATION White developer serves the function of bringing out to surface the penetrant
4. entrapped in the cracks after washing and spreading it over the surface to enlarge also indications regarding the smallest discontinuities It evidences red indications in contrast with a white background as well as the yellow green ones under ultra violet light for fluorescent penetrant A too long developing time could broaden too much the indication provided by the penetrant resulting in a lack of definition Developing time should range from 10 to 30 min however for some specific applications developing time could vary In this case it must be defined in advance Developing time starts e After drying if a liquid developer is being used e After application if a dry developer is being used 5 1 Quick evaporating developer The white powder of the developer is suspended into a quick evaporating solvent Said solvent serves the function of bringing out the entrapped penetrant from the discontinuity and speeding up drying time so that a further drying is unnecessary The application of two thin layers of liquid is recommended allowing drying time between the two applications Spray can or gun are the most advisable methods to create this thin layers To make it work properly the spray can has to be stored at a temperature not lower than 15 C At lower temperature the result is a not uniform coating a lengthened evaporating time dripping or entrapment risks Shake properly the Developer before using and once the process has terminated
5. 0 C and 38 C The method with penetrants can be adopted even at a temperature out of this range if specific procedures and or products are used see our relevant cards 3 EXCESS PENETRANT REMOVAL During checking process a too intense washing of pieces removes the penetrant from the discontinuities conversely a scarcely accurate washing or a penetrant scarcely washable leaves an excessive residue which could mask indications Commonly the suitability of washing is determined by visual inspection during the operation When using red penetrant the removal of the visible colorant indicates the completion of the washing phase When using fluorescent penetrant the rinse has to be performed under ultra violet light stopping the washing phase as soon as the basic fluorescence has been removed Washing waters have to be properly conditioned before being discharged see relevant cards 3 1 Water Washable Penetrants Generally excess penetrant is removed by flushing with low pressure water no more than 280 kPa at a temperature ranging from 10 C to 38 C 3 2 Solvent Removable Penetrants Excess solvent removable penetrants shall be removed by wiping the surface under examination with a dry cloth or absorbent paper Remaining traces shall be removed with another cloth slightly moistened with a quick evaporating solvent remover ELITE BC1 3 3 Emulsifiers Removable Penetrants Commonly excess post emulsifying penetrant is removed
6. LIQUID PENETRANTS USER S MANUAL in accordance to specifications EN 571 ASTME 1417 AMS 2644 MIL ASME DIN UNI BS AFNOR etc The liquid penetrant examination method is an effective means for detecting and locating quickly economically and accurately surface flaws such as cracks porosities and laps The dyes in penetrants are either red visible under white light or fluorescent visible under ultra violet light In order to understand the method correctly three terms which are fundamental have to be defined 1 Signal it evidences discontinuities in the materials Some signals could be irrelevant or false 2 Flaw a break in the normal physical structure or configuration of a part like for instance a crack a forging lap a drawing groove an inclusion or a porosity The existence of a discontinuity does not necessarily prevent the use of the part 3 Defect it is a flaw which is deemed unacceptable according to the specifications followed because it interferes with the use of the piece PROCEDURE In order to make the inspection reliable and of high quality ensuring homogenous and reproducible results a personalised procedure has to be drawn up To this purpose please make use of the information hereinafter provided and take into consideration Tab 1 Products Classification Tab 2 Procedures and Tab 3 Minimum Dwell Time For each group of products Technical Cards available upon request showing the char
7. acteristics of each product as well a Sample of the Examination Certificate have been prepared 1 SURFACE PRE CLEANING AND PREPARATION A proper cleaning is essential to obtain reliable indications To detect defects the penetrant has to leach even in a microscopic crack It s clear that imbedded foreign materials such as oil dirt water paint oxide and residual matters can seal off voids from the penetrant The cleaning technique to be used depends on the type of the residue 1 1 Cold cleaning with fast evaporating solvents ELITE BC1 Products are flammable so proper fire precautions have to be observed when operating next to flames or other sources of ignition The solvent has to be sprayed over the dirty surface to such an extent that the area to be examined is covered completely 10 30 seconds must elapse before cleaning the area with a cloth prior to complete evaporation of the solvent 1 2 Hot cleaning with aqueous detergents ELITE 20 Protective Detergent This products works on the basis of electronic affinity so it can remove oily residues not only from the surface but also from the inside of the cracks It is a neutral product suitable for every type of metals to be used at a temperature of 50 60 C Rinsing with cold water allowing the self drying of parts can be avoided because eventual residues of products are compatible with penetrant liquids because it allows the penetration and does not cause false indications
8. cles of the Developer tend to absorb the penetrant bringing it out from the discontinuity Following the application indications appear within few minutes while penetrant is absorbed by the Developer INSPECTION When scheduled developing time has terminated the surface is ready to be inspected and evaluated The type of light used depends on the type of penetrant used e White light minimum 1000 lux intensity if a method with red penetrants is adopted e Ultraviolet light with fluorescent penetrants minimum light intensity 1000 microWatt em on the surface of the part being examined with white ambient light not exceeding 20 lux Should a new inspection of pieces already treated with penetrant liquids be required the Developer has to be removed first and oil must be wiped off from the piece The process shouldn t be repeated more than two times Applying fluorescent penetrant over pieces already treated with the red ones is prohibited TABLE 1 PRODUCT CLASSIFICATION Penetrant Liquid Penetrant Removal Developer Type Description Method Description Form Description 1 1 Fluorescent A Water a Dry type Penetrant Liquid B Lipophylic b Water Soluble Emulsifier 2 11 Red Penetrant C Solvent c Water Liquid Suspension D Hydrophylic d e Quickly Emulsifier evaporating solvent base TABLE 2 Preliminary cleaning and drying METHOD A METHOD B D METHOD C Apply water washable Apply post
9. emulsifying Apply solvent penetrant liquid and allow penetrant liquid and allow removable penetrant penetration time penetration time liquid and allow penetration time Wash with water Wipe with cloth and solvent Pre washing with water Apply hydrophylic emulsifier Apply lipophylic emulsifier Excess Penetrant Removal Check Apply water based Apply quickly developer aes evaporating ae ry type developer eveloper Developing Time Final Inspection TABLE 3 Recommended Penetration Times Material Form Penetration Time Aluminium and Magnesium Casting From 5 up to 15 min Others From 5 up to 15 min Carbon Steel Casting From 5 up to 15 min Others From 10 up to 20 min Brass and bronze All From 5 up to 15 min Titanium Stainless Steel All From 10 up to 30 min Austenitic alloys Low alloy Steel DEVELOPER PENETRANT THROUGH CRACK LEAK gt To find through crack only apply the penetrant on one surface and the developer on the opposite
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