- To detect and evaluate the discontinuities open to the surface for wrought, forged materials and weldments of various size and shapes as required by construction drawing, by penetrant technique using be Solvent Removable Visible Color Contrast penetrant and non aqueous developer.
- This work instruction is applicable when the material and penetrant is within the temperature range of 50F (10C) to 125F (52C).
ASME 2010 SECTION V. ARTICLE 1 AND 6
- ASNT – SNT- TC IA , 2001 Edition. ( For Reference / Personnel Qualification ).
Personnel performing examination to this work instruction shall be qualified and certified according to our written practice, based on ASNT document SNT-TC-1A 2001 Edition.
Personnel performing Liquid Penetrant Examination
Certified P.T. Examiner or PT Level I / II And Personnel evaluating Liquid Penetrate Examination – PT Level II
EQUIPMENT AND SUPPLIES
- Temple stick / Surface thermometer to check the examination surface temperature.
- Penetrant cleaner and developer used for PT examination shall be solvent removable visible color contrast type which are procured from the approved suppliers backed by manufacturers est certificate
- Intermixing of chemicals of different manufacturers is not permitted.
- The total chlorine (in the form of ionic chloride) contents of the penetrant materials shall not exceed 1% (25 ppm) of the residue by weight as certified by manufacturer.
- The sulfur (in the form of ionic sulfate) contents of the penetrate materials shall not exceed 1% (25 ppm) of the residue by weight as certified by the manufacturer.
- Batch Test Certificates containing manufacturers’ batch numbers and the test result as per Applicable Codes & Standards.
- Surface Preparation
Surfaces to be examined may be in the as welded, as rolled, as cast or as forged condition. Grinding may be necessary in certain cases where surface irregularities could mask unacceptable discontinuities.
- Pre-Examination Cleaning
- Prior to penetrant application, the surface to be examined and all the adjacent areas within at least 1 in. (25 mm) shall be cleaned by mechanical means followed by lint free cloth sock with solvent to remove any dirt, grease, lint, scale, welding flux or spatter, oil or other matter which could interfere with the examination.
- Operations that may peen / close the discontinuity openings and compromise the integrity of the examination such as shot, sand, grit blasting are not recommended. When these operations are performed, precautions such as alkaline or acid etching shall be performed to ensure reopening of those discontinuities.
- A minimum of 3 minutes shall be allowed for drying the surface to be examined accomplished by normal evaporation or with forced hot or cold air before applying penetrate.
Application of Penetrate
The temperature of the penetrate and the surface of the part to be examined shall not be below 500 F (100 C) nor above 1250 F (520 C). Local heating or cooling is permitted, provided the part temperature remains in the temperature range as specified.
The penetrate shall be applied by swabbing ,spraying or brushing, so that all surface under examination shall be thoroughly and uniformly covered by penetrate.
Penetrate dwell time
After application, excess penetrate is drained out from the part allowing suitable dwell time of minimum 10 minutes. The area to be examined shall remain covered by the penetrate throughout the entire dwell time.
After the minimum penetrate dwell time the excess penetrate on the surface shall be removed as far as possible by using clean lint free cloths & jute. This operation shall be repeated until most traces of penetrate on the surface have been removed.
- The remaining traces of penetrant shall then be removed by lightly wiping the surface with a clean cloth moistened with solvent cleaner. To minimize removal of penetrant from discontinuities care shall be taken to avoid the use of excess solvent cleaner. If wiping is not effective the part shall be dried in ambient temperature.
- Flushing the surface with solvent cleaner following application of the penetrant and prior to developing is strictly prohibited.
Drying after Excess Penetrate Removal
For this solvent removable technique, drying shall be accomplished by exposure to ambient temperature. Local heating / cooling is permitted but with proper care to the component provided the temperature of the part remains within the temperature range of 500 F (100 C ) to 1250 F ( 520 C). Minimum time of drying should be 3 minute before application of developer.
Application of Developer
The developer is of solvent suspended non-aqueous wet type and shall be applied as soon as possible after the excess penetrant (shall not exceed 15 min.) has been removed and the part has been dried. Developer shall be applied by spraying from spray cans after good agitation in such a manner to assure complete part coverage with a thin uniform film. The spray nozzle tip of the spray can should be held about 12 in. from the examination surface approximately perpendicular. The second coat may be applied across the direction of first coat. Dipping, Flooding is prohibited.
- Where safety or restricted access makes it impractical to apply developer by spraying; developer shall be applied by brushing. Drying shall be by normal evaporations.
Developing time start immediately as soon as the wet developer coating is dry. The length of time the developer is to remain on part being examined, prior to final interpretation shall be minimum 10 minutes.
Light meter shall be calibrated at least once in a year or whenever the meter has been repaired.
INTERPRETATION OF INDICATIONS
- All examination shall be performed in ordinary white light. The white light intensity at the inspection surface shall be minimum of 100 foot-candles (1000 Lux).
- Observation of the formation of indications shall be performed during the application of developer. If defects are present, they will show up as red indications on white developer coating. Some may appear immediately while some may take a little longer to develop.
- Final interpretation of indications shall be made within 10 – 60 minutes after the wet developer coating is dry. If the surface to be examined is so large that a complete examination cannot be completed within the prescribed time, then only portions shall be examined at time.
- The rate of bleeding is an indication of the width & depth of defect while the extent and spread of bleeding is an indication of the volume of flaw. Relevant indications are those caused by discontinuities that are open to the examination surface.
- Non-relevant indications are those caused by the conditions other than discontinuities such as surface irregularities due to machining, grinding, faying surfaces, press-fits, poorly removed paint etc. These indications, which may mask discontinuities, shall be removed, cleaned and re-examined.
- Linear indications are those having a length greater than 3 times the width.
- Rounded indications are those of circular or elliptical shape with a length equal to or less than 3 times the width
EVALUATIONN OF INDICATIONS
- Indications whose major dimensions are greater than 1/16 in. (1.5mm) shall be considered relevant. All indications shall be evaluated in terms of acceptance standards as specified in this procedure.
- Discontinuities at the surface will be indicated by bleed back feature of the penetrant. Any indication, which is believed to be non-relevant, shall first be regarded as a defect and shall be re-examined to verify whether or not actual defects are present. Surface conditioning may precede the re-examination. No relevant indications and broad areas of pigmentation, which would mask indications of defects, are unacceptable and shall be eliminated from the surface and re-examined.
- Indication of a discontinuity may be larger than the actual discontinuity that causes it; however, the size of the final indication and not the size of the discontinuity is the basis of acceptance or rejection it.
ACCEPTANCE STANDARD ( As per ASME VIII Div 1 ).
The surface under examination shall be free of following relevant indications.
- Any cracks lack of fusion and Lack of Penetration.
- Relevant linear indications greater than 1.5 mm.
- Relevant rounded indications with dimension greater than 5.0 mm.
- Four or more relevant rounded indications in a line separated by 1⁄16 in. (1.5 mm) or less (edge to edge).
DEFECT REMOVAL ( Repairning ).
Any unacceptable indications shall be repaired and re examined to assure the complete removal.
Wherever the defect is removed the excavated area shall be blended in to the surrounding surface so as to avoid sharp notches, crevices or corners , if required excavated area may be welded by using qualified welders.
Completedrepairs shall be re-examined by the same method as described above.
POST EXAMINATION CLEANING
Post examination cleaning is necessary only in those cases where specified by customer. If post cleaning is deemed necessary it shall be done promptly after evaluation by coarse water rinsing or water spray or solvent wiping, which does not adversely affect the part.