1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-17a71 Center Point of Contact: MSFCa71 Submitted by: Wil HarkinsSubject: Penetrant Testing of Aerospace Materials Practice: Penetrant testing improves hardware reliability by detecting surface flaws and defects in solid ma
2、terials and structures. The discontinuities must be open to the material surface.Programs that Certify Usage: This practice has been used on Saturn I, IB&V, Apollo, Skylab, Space Shuttle External Tank (ET), Space Shuttle Solid Rocket Motor (SRM), Space Shuttle Main Engine (SSME), Space Shuttle Solid
3、 Rocket Booster (SRB), and other Marshall Space Flight Center programs.Center to Contact for Information: MSFCImplementation Method: This Lesson Learned is based on Reliability Practice number PT-TE-1426 from NASA Technical Memorandum 4322A, NASA Reliability Preferred Practices for Design and Test.B
4、enefit:Penetrant Testing is a cost effective, nondestructive method for determining cracks, porosity, gouges, laps, seams, and other flaws that are open to the surface of metallics and selected non-metallics.Implementation Method:Liquid penetrant testing is a nondestructive method of detecting surfa
5、ce flaws in solid material and structures. Cracks, porosity, gouges, laps, seams, and other types of flaws can be found using this technique. Penetrant testing is a process in which the liquid penetrant is drawn into small openings by capillary action when it is applied to a surface. After a specifi
6、ed time, excess penetrant is removed from the surface and developer is applied to the surface. The developer absorbs residual penetrant drawn from the flaw leaving a bright-colored penetrant bleeding through the developers white background giving a clear visual indication of cracks, porosity, and ot
7、her flaws.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-There are numerous types and sensitivities of penetrants. The penetrant systems, consisting of penetrant, developer, and cleaner, must be selected for component compatibility and be suitable f
8、or use on the test article. In addition to the specific requirements for actual penetrant test, initial surface preparation and final cleaning often requires detailed procedures. Table 1 shows five sensitivity levels for penetrants.Penetrants have been developed for specific applications for ferrous
9、 metals, nonferrous metals, glass, polymers and ceramics. The penetrant must also be compatible with the test article to avoid material degradation and possible explosion. For example, the chemical combination of incompatible penetrant materials, the container material, and liquid oxygen, combined w
10、ith impact or shock, can cause an explosion. Common properties and characteristics of suitable penetrants are listed in Table 2.refer to D descriptionD Table 1. Sensitivity Levels for Penetrants refer to D descriptionD Table 2. Properties and Characteristics of Penetrants There are six basic steps r
11、equired to perform a penetrant test. These six basic steps are shown in the flow diagram on Figure 1.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refer to D descriptionD Figure 1. Penetrant Test Flow Diagram The most common cleaning methods are ap
12、plication of solvents, vapor degreasing, detergent cleaning, steam cleaning and ultrasonic cleaning. Mechanical cleaning using wire brushes, abrasives, emery cloths, or metal scraping are not recommended. However, if mechanical cleaning must be used, light chemical etching is required to reopen any
13、closed flaws. Penetrant testing should be accomplished before any paint or metallic coating is applied since these coatings will close any flaws.The success of penetrant testing depends upon the visibility of flaw indications. To ensure visibility, the penetrant contains either a colored dye easily
14、seen in white light, or a fluorescent dye visible under black (ultraviolet) light. A list of penetrants typically used is listed in reference 4. The penetrant is applied by either dipping, spraying, brushing, or flowing. After penetrant application, a sufficient time (dwell time) is provided to perm
15、it the penetrant to permeate the flaw. The manufacturers of penetrants provide the minimum dwell times charts. A typical dwell time chart is shown in Table 3. The penetrant must not be allowed to dry during the dwell time, and must remain wet until the excess penetrant is removed. If penetrant has d
16、ried, then the process must be repeated.refer to D descriptionD Table 3. Typical Dwell Time Chart Removal of the penetrant depends upon the type used. The most common methods used are water washable, post emulsified, and solvent removed. Care must be exercised to ensure that the specimen is not over
17、 cleaned, thereby removing the penetrant from the flaw.Generally, a developer is required, although some penetrants are formulated for use without a developer. A whitish powder in the developer is very absorbent and acts as a blotter. This blotting action carries the penetrant from the flaw into the
18、 powder, forming a flaw pattern.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Inspection of the specimen consists of analysis of the patterns on the developer and determining their cause. Inspection may reveal patterns that are either true indicati
19、ons or false indications of a flaw. The true indications are those caused by penetrant bleeding from the actual flaws. Improper cleaning in the initial cleaning step and incomplete removal of the excess penetrant are common causes of false indications. False indications sometimes look like and may h
20、ide true indications. If there is doubt about the source of a pattern on the developer, the test should be repeated and the patterns carefully analyzed as they develop.The ability to identify true indications requires much practice. For example, cracks, cold shunts, seams, and forging laps all show
21、up as a continuous line. The same flaws may show up as an intermittent line indicating that the flaw may be partially closed at the surface. Small dots and round indications generally indicate porosity, small inclusions, or blow holes. If the defect is located below the surface, the sensitivity of t
22、his method diminishes rapidly with depth.Penetrant inspectors should be qualified and certified in accordance with MIL-STD-410E or SNT-TC-1A. To provide permanent records, photographs of the specimen should be taken prior to post cleaning. Post cleaning is only required of those specimens that are f
23、ound free of defects. Defects are described by engineering or as specified in MIL-STD-1907. Post inspection cleaning is necessary since the penetrant and developer residue tend to attract moisture, which can cause corrosion or can interfere with subsequent processing or usage. The cleaning methods f
24、or post inspection cleaning are generally the same as those recommended for precleaning. Advantages and disadvantages of the penetrant testing method are shown in Table 4.refer to D descriptionD Table 4. Advantages and Disadvantages of Penetrant Testing Method The hazardous properties that should al
25、ways be considered when using a dye penetrant are liquid flashpoint and toxicity. The flashpoint of penetrant processes can be as low as 40oF to as high as 200oF. The penetrants should be used per manufacturers instructions. Most penetrants are not actually toxic and do not present a particular haza
26、rd in normal use. However, there are precautions that should be followed. Practically all liquid materials used in penetrant, cleaner, and developer have good wetting and detergent properties. Therefore, they exhibit excellent solvent power for fats and oils. These materials, when allowed to contact
27、 the skin for an extended period, will dry out the natural oils from the skin, causing it to become rough, red, and if left untreated to eventually crack open, which could cause a severe secondary infection. This is preventable by wearing neoprene-type gloves and aprons, face shield, and protective
28、clothing. If exposed to this skin drying, replenishing the oils on the exposed skin should prevent any cracking.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Another hazard with penetrants is the using of dry developers which could be inhaled and b
29、ecome a health hazard. The use of any of the penetrant processes should be performed in a well-ventilated area. If working in a confined area such as a tank, the inspector should have an individual air supply with a full helmet over the head.The black light used when inspecting fluorescent penetrant
30、s can cause severe sunburn and damage to the eyes. The blacklight source should always be checked for missing, cracked, or broken filters and repaired before use. Store penetrants in an approved fire container.Technical Rationale:Marshall Space Flight Center has successfully used the penetrant testi
31、ng method for years. It is a proven method for locating flaws in surface areas of highly stressed areas of components and structures. In addition, it is an effective method for both metallic and nonmetallic materials.References:1. Bray, Don E. and Don McBride: “Nondestructive Testing Techniques,“ Jo
32、hn Wiley & Sons, Inc., New York, NY, 1992.2. Metals Handbook, Vol. 17: “Nondestructive Inspection and Quality Control,“ pp. 71-88 ASM International, Metals Park, OH 1989.3. CT-6-2: “Nondestructive Testing Liquid Penetrant,“ Fourth Edition, Class Room Training Handbook, General Dynamics, Convair Divi
33、sion, 1977.4. P1-4-2: “Nondestructive Testing, Liquid Penetrant,“ Fourth Edition, Programmed Instruction Handbook, General Dynamics, Convair Division, 1977.5. MIL-STD-410E: “Nondestructive Testing Personnel Qualification and Certification,“ Military Standard, January 1991.6. MIL-STD-6866: “Liquid Pe
34、netrant Inspection,“ Military Standard, 1989.7. MIL-I-25135: “Penetrant Inspection Materials,“ Military Specification, 1989.8. MIL-STD-1907: “Penetrant and Magnetic Particle Inspection, Soundness Requirements for Materials, Parts and Weldments,“ Military Standard, 1990.9. SNT-TC-1A, “Recommended Pra
35、ctice, Personnel Qualification and Certification in Nondestructive Testing,“ American Society for Nondestructive Testing, Columbus, OH, 1988.Impact of Non-Practice: Failure to locate surface flaws in critical stressed areas of parts and structures could result in loss of part or structure, loss of m
36、ission, and in extreme cases loss of life.Related Practices: N/AAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2000-04-17a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
