Dye penetrant inspection (DPI), also called liquid penetrant inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). The penetrant may be applied to all non-ferrous materials and ferrous materials, although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability. LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.

History

The oil and whiting method used in the railroad industry in the early 1900s was the first recognized use of the principles of penetrants to detect cracks. The oil and whiting method used an oil solvent for cleaning followed by the application of a whiting or chalk coating, which absorbed oil from the cracks revealing their locations. Soon a dye was added to the liquid. By the 1940s, fluorescent or visible dye was added to the oil used to penetrate test objects.

Experience showed that temperature and soak time were important. This started the practice of written instructions to provide standard, uniform results. The use of written procedures has evolved, giving the ability for design engineers and manufacturers to get the high standard results from any properly trained and certified liquid penetrant testing technician.

Principles

DPI is based upon capillary action, where low surface tension fluid penetrates into clean and dry surface-breaking discontinuities. Penetrant may be applied to the test component by dipping, spraying, or brushing. After adequate penetration time has been allowed, the excess penetrant is removed, a developer is applied. The developer helps to draw penetrant out of the flaw where an invisible indication becomes visible to the inspector. Inspection is performed under ultraviolet or white light, depending upon the type of dye used - fluorescent or nonfluorescent (visible).

Materials

Penetrants are classified into sensitivity levels. Visible penetrants are typically red in color, and represent the lowest sensitivity. Fluorescent penetrants contain two or more dyes that fluoresce when excited by ultraviolet (UV-A) radiation (also known as black light). Since fluorescent penetrant inspection is performed in a darkened environment, and the excited dyes emit brilliant yellow-green light that contrasts strongly against the dark background, this material is more sensitive to defects.

When selecting a sensitivity level one must consider many factors, including the environment under which the test will be performed, the surface finish of the specimen, and the size of defects sought. One must also assure that the test chemicals are compatible with the sample so that the examination will not cause permanent staining, or degradation. This technique can be quite portable, because in its simplest form the inspection requires only 3 aerosol spray cans, some lint

free cloths, and adequate visible light. Stationary systems with dedicated application, wash, and development stations, are more costly and complicated, but result in better sensitivity and higher samples through-put.

Inspection steps

Below are the main steps of Liquid Penetrant Inspection:

1. Pre-cleaning:

The test surface is cleaned to remove any dirt, paint, oil, grease or any loose scale that could either keep penetrant out of a defect, or cause irrelevant or false indications. Cleaning methods may include solvents, alkaline cleaning steps, vapor degreasing, or media blasting. The end goal of this step is a clean surface where any defects present are open to the surface, dry, and free of contamination. Note that if media blasting is used, it may "work over" small discontinuities in the part, and an etching bath is recommended as a post-blasting treatment.

Application of the penetrant to a part in a ventilated test area.

2. Application of Penetrant:

The penetrant is then applied to the surface of the item being tested. The penetrant is allowed "dwell time" to soak into any flaws (generally 5 to 30 minutes). The dwell time mainly depends upon the penetrant being used, material being tested and the size of flaws sought. As expected, smaller flaws require a longer penetration time. Due to their incompatible nature one must be careful not to apply solvent-based penetrant to a surface which is to be inspected with a water-washable penetrant.

3. Excess Penetrant Removal:

The excess penetrant is then removed from the surface. The removal method is controlled by the type of penetrant used. Water-washable, solvent-removable, lipophilic post-emulsifiable, or hydrophilic post-emulsifiable are the common choices. Emulsifiers represent the highest sensitivity level, and chemically interact with the oily penetrant to make it removable with a

water spray. When using solvent remover and lint-free cloth it is important to not spray the solvent on the test surface directly, because this can remove the penetrant from the flaws. If excess penetrant is not properly removed, once the developer is applied, it may leave a background in the developed area that can mask indications or defects. In addition, this may also produce false indications severely hindering your ability to do a proper inspection.

4. Application of Developer:

After excess penetrant has been removed a white developer is applied to the sample. Several developer types are available, including: non-aqueous wet developer, dry powder, water suspendable, and water soluble. Choice of developer is governed by penetrant compatibility (one can't use water-soluble or suspendable developer with water-washable penetrant), and by inspection conditions. When using non-aqueous wet developer (NAWD) or dry powder, the sample must be dried prior to application, while soluble and suspendable developers are applied with the part still wet from the previous step. NAWD is commercially available in aerosol spray cans, and may employ acetone, isopropyl alcohol, or a propellant that is a combination of the two. Developer should form a semi-transparent, even coating on the surface.

The developer draws penetrant from defects out onto the surface to form a visible indication, commonly known as bleed-out. Any areas that bleed-out can indicate the location, orientation and possible types of defects on the surface. Interpreting the results and characterizing defects from the indications found may require some training and/or experience [the indication size is not the actual size of the defect]

5. Inspection:

The inspector will use visible light with adequate intensity (100 foot-candles or 1100 lux is typical) for visible dye penetrant. Ultraviolet (UV-A) radiation of adequate intensity (1,000 micro-watts per centimeter squared is common), along with low ambient light levels (less than 2 foot-candles) for fluorescent penetrant examinations. Inspection of the test surface should take place after 10 to 30 minute development time, depends of product kind. This time delay allows the blotting action to occur. The inspector may observe the sample for indication formation when using visible dye. It is also good practice to observe indications as they form because the characteristics of the bleed out are a significant part of interpretation characterization of flaws.

6. Post Cleaning:

The test surface is often cleaned after inspection and recording of defects, especially if post-inspection coating processes are scheduled.

Advantages and disadvantages

The main advantages of DPI are the speed of the test and the low cost. Disadvantages include the detection of only surface flaws, skin irritation, and the inspection should be on a smooth clean surface where excessive penetrant can be removed prior to being developed. Conducting the test on rough surfaces, such-as "as-welded" welds, will make it difficult to remove any excessive

penetrant and could result in false indications. Water-washable penetrant should be considered here if no other option is available. Also, on certain surfaces a great enough color contrast cannot be achieved or the dye will stain the workpiece.[1]

Limited training is required for the operator — although experience is quite valuable. Proper cleaning is necessary to assure that surface contaminants have been removed and any defects present are clean and dry. Some cleaning methods have been shown to be detrimental to test sensitivity, so acid etching to remove metal smearing and re-open the defect may be necessary.[citation needed]

Standards

International Organization for Standardization (ISO)

ISO 3059, Non-destructive testing - Penetrant testing and magnetic particle testing - Viewing conditions

ISO 3452-1, Non-destructive testing. Penetrant testing. Part 1. General principles ISO 3452-2, Non-destructive testing - Penetrant testing - Part 2: Testing of penetrant

materials ISO 3452-3, Non-destructive testing - Penetrant testing - Part 3: Reference test blocks ISO 3452-4, Non-destructive testing - Penetrant testing - Part 4: Equipment ISO 3452-5, Non-destructive testing - Penetrant testing - Part 5: Penetrant testing at

temperatures higher than 50 °C ISO 3452-6, Non-destructive testing - Penetrant testing - Part 6: Penetrant testing at

temperatures lower than 10 °C ISO 12706, Non-destructive testing - Penetrant testing - Vocabulary ISO 23277, Non-destructive testing of welds - Penetrant testing of welds - Acceptance

levels

European Committee for Standardization (CEN)

EN 571-1, Non-destructive testing - Penetrant testing - Part 1: General principles. May be replaced by EN ISO 3452-1.

EN 1371-1, Founding - Liquid penetrant inspection - Part 1: Sand, gravity die and low pressure die castings

EN 1371-2, Founding - Liquid penetrant inspection - Part 2: Investment castings EN 2002-16, Aerospace series - Metallic materials; test methods - Part 16: Non-

destructive testing, penetrant testing EN 10228-2, Non-destructive testing of steel forgings - Part 2: Penetrant testing EN 10246-11, Non-destructive testing of steel tubes - Part 11: Liquid penetrant testing of

seamless and welded steel tubes for the detection of surface imperfections

ASTM International (ASTM)

ASTM E 165, Standard Practice for Liquid Penetrant Examination for General Industry ASTM E 1417, Standard Practice for Liquid Penetrant Testing

American Society of Mechanical Engineers (ASME)

ASME Boiler and Pressure Vessel Code, Section V, Art. 6, Liquid Penetrant Examination

ASME Boiler and Pressure Vessel Code, Section V, Art. 24 Standard Test Method for Liquid Penetrant Examination SE-165 (identical with ASTM E-165)

Liquid Penetrant Examination

Jim WormanSenior Staff EngineerNational Board

Category : Design/Fabrication

Summary: This article was originally published in the Winter 2011 National Board BULLETIN. (4 printed pages)

 

 

Liquid penetrant examination is one of the most popular Nondestructive Examination (NDE) methods in the industry. It is economical, versatile, and requires minimal training when compared to other NDE methods. Liquid penetrant exams check for material flaws open to the surface by flowing very thin liquid into the flaw and then drawing the liquid out with a chalk-like developer. Welds are the most common item inspected, but plate, bars, pipes, castings, and forgings are also commonly inspected using liquid penetrant examination.

Over the years, liquid penetrant examination has been called many names: penetrant testing (PT), liquid penetrant testing (LP), and dye penetrant testing (DP). The American Society for Nondestructive Testing (ASNT) uses the name liquid penetrant testing (PT). The American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME B & PVC) and the National Board Inspection Code (NBIC) use the name liquid penetrant examination (PT). The first documented use of PT was in the railroad industry. Cast railroad wheels were dipped in used oil, dried off, and then coated with powder chalk or suspension of chalk in alcohol.  Once

the wheels were dry, any oil stored in the flaw would bleed out into the chalk and be detected. This was called the oil and whiting method. The ASME Boiler & Pressure Vessel Code recognizes six different techniques of PT. They vary by type of penetrant and method of cleaning before applying a developer. The two penetrant types are either fluorescent or color contrast (dye) penetrant. They can then be used with any of the three methods of cleaning – water washable, post-emulsifying, and solvent removable. The most popular is dye penetrant that is solvent removable. This method is referenced throughout the article. The dye penetrant solvent removable method is most popular because it is low cost and very versatile. It typically comes in three aerosol cans – cleaner, penetrant, and developer. The cans can be purchased from welding supply distributors for typically $5 to $15 a can. For less than $50 you can have all the equipment you need to conduct liquid penetrant examinations. The aerosol cans are very versatile which allow them to be taken up ladders, inside boilers, down into pits, and into very tight places. Most nonporous materials (steel, stainless steel, cast iron, aluminum, brass, bronze, titanium, rubber, plastics, and glass) can be examined using PT. Porous materials (concrete, wood, paper, cloth, and some types of fiberglass if the fibers are exposed to the surface) should not be examined using PT. 

Dye penetrant solvent removable aerosol cans

 There are several advantages and disadvantages to using liquid penetrant examination. Advantages:

High sensitivity to small surface discontinuities Easy inspection of parts with complex shapes Quick and inexpensive inspection of large areas and large volumes of parts/materials Few material limitations (metallic and nonmetallic, magnetic and nonmagnetic, and

conductive and nonconductive can all be inspected) A visual representation of the flaw are indicated directly on the part surface Aerosol spray cans make the process portable, convenient, and inexpensive

Indications can reveal relative size, shape, and depth of the flaw It is easy and requires minimal amount of training

Disadvantages:

Detects flaws only open to the surface Materials with porous surfaces cannot be examined using this process Only clean, smooth surfaces can be inspected. (Rust, dirt, paint, oil and grease must be

removed.) Metal smearing from power wire brushing, shot blasting, or grit blasting must be

removed prior to liquid penetrant examination Examiner must have direct access to surface being examined Surface finish and roughness can affect examination sensitivity. (It may be necessary to

grind surfaces before PT.) Multiple process steps must be performed and controlled Post cleaning of parts and material is required, especially if welding is to be performed Proper handling and disposal of chemicals is required Fumes can be hazardous and flammable without proper ventilation

It is important to remember penetrant is a very thin liquid designed to seep into the smallest crack. Consequently, if an assembly has stitch welds or material not sealed by a weld, the penetrant will travel behind the welds and between layers of unfused material. Penetrant can be nearly impossible to remove from these areas. Trapped penetrant will cause defects in welds if further welding is done or will bleed out over time and contaminate paint and process fluids. For PT to be used on ASME Code construction or NBIC repair or alterations, a written procedure must be followed. This must comply with ASME Boiler and Pressure Vessel Code, Section V, Article 6, and address all essential and nonessential variables. Many liquid penetrant examinations are done for informational purposes only, and do not follow a written procedure. For instance, a written procedure does not need to be followed if a welder grinding out a weld crack for repair is using PT to ensure removal of the entire crack. However, if the PT is being done to comply with Code, the written procedure needs to be followed by qualified NDE personnel. There are six basic steps to follow when using the dye penetrant solvent removable method.

1. Pre-clean part.  This can range from grinding and wire brushing to merely wiping the part with a rag moistened with the cleaner/ remover. The surface needs to be free of dirt, rust, scale, paint, oil, and grease, and be smooth enough to wipe off the penetrant without leaving residue.

 

 2. Apply penetrant. 

This is generally done by spraying penetrant from the aerosol can or applying it with a brush. A dwell (soak) time needs to be observed to allow for the penetrant to permeate into cracks and voids. This is typically 5 to 30 minutes but should never be long enough for the penetrant to dry. The penetrant manufacturer’s recommendations and written procedure should be followed.

 

 3. Remove penetrant. 

All penetrant should be removed with clean, dry, lint-free rags until thoroughly clean. The part or material should be rubbed vigorously until the penetrant is not visible on the dry rags. Next, cleaner/ remover should be sprayed on another clean, dry, lint-free rag and used to vigorously rub the part again until there is no penetrant visible on the rag.

 

 4. Apply developer.

A thin, light coating of developer should be sprayed on the part being examined. A dwell time needs to be observed to allow time for the dye to exit the flaws and create an indication (flaw) in the developer. The dwell time for developer is typically 10 to 60 minutes. The developer manufacturer’s recommendations and written procedure should be followed closely.

 

 5. Evaluate indications.

It is critical to examine the part within the time frame designated in the written procedure.  Length of an indication can grow over time as penetrant bleeds out, causing an acceptable indication to be a rejectable defect.  Length of indication is measured for evaluation, not length of the flaw.  Here, the two linear indications are rejectable defects.  The round indication is nonrelevant. 

 

 6. Post-clean part.

The part needs to be cleaned to remove all developer after it has been evaluated.

   

   ASME Section V also requires the dye penetrant solvent removable method be evaluated with a minimum light intensity of 100 foot candles on the part surface. Proper quantity of light must be verified using some type of light meter.

Light meter showing 109.9 footcandles of light

In the ASME B & PV Codes of Construction, magnetic particle examination or liquid penetrant examination is called out many times to detect the possibility of surface defects. If material is nonmagnetic the only choice is PT. Some typical examples of ASME Code required examinations include:

castings for surface defects plates for laminations in corner joints when one plate’s edge is exposed and not fused

into the weld joint head spin hole plug welds weld metal build-up on plates removal of defects before welding repair

Once boilers and pressure vessels are in service, PT can be a very valuable tool. The NBIC recommends PT for examination of: firetube boiler tube sheets to find leakage around tubes, external inspection of weld joints, evaluating components subjected to fire damage, historical boilers, fiber-reinforced thermosetting plastic pressure equipment, Yankee dryers, and pressure vessels in liquefied petroleum gas (LPG) service.  During inservice inspections, PT should also be used in areas suspected of defects. These include, but are not limited to, nozzles (see Figure 1), tubesheets (see Figure 2), knuckles of heads (see Figure 3), and head spin hole plug welds (see Figure 4). To effectively use liquid penetrant on the tubesheet in Figure 2, an extensive amount of work would need to be done. All rust and scale would need to be removed so the penetrant could be cleaned off. Rolled, unfused tube ends would also bleed out dye and cause false indications. The head spin hole plug weld looks acceptable to the naked eyes, but shows many defects once it has been liquid penetrant examined (see Figures 5 and 6).

  In conclusion, PT can be a very valuable tool during new construction and inservice inspections. PT does have limitations and is not the best method for all applications. However, for quick, low cost examinations in any location, PT is often the best choice of NDE methods.

Terjemahan

Hal mendasar yang perlu dipertimbangkan ketika melakukan penetran cair     Apakah penetran terlihat atau neon yang diperlukan     Apa persyaratan sensitivitas     Bagaimana bersih adalah bagian atau komponen dan pembersihan pra akan diperlukan.     Bagaimana diakses adalah area pemeriksaan     Apakah persyaratan untuk menggunakan Metode A Air Dicuci, Metode B Pos Lipohilic diemulsikan, Metode C Solvent Removable, atau Metode D Posting Hidrofilik teremulsi.     Apakah ada ruangan gelap yang tersedia untuk mencapai kebutuhan cahaya 2FC.     Akan kekuasaan akan tersedia.

Basic things to consider when performing liquid penetrant are.

1. Is visible or fluorescent penetrant being required

2. What is the sensitivity requirement3. How clean is the part or component and is pre cleaning going to be required.4. How accessible is the inspection area5. Is the requirement to use Method A Water Washable, Method B Post Emulsifiable

Lipohilic, Method C Solvent Removable, or Method D Post Emulsifiable Hydrophilic.6. Is there a dark room available to achieve the 2fc light requirement.7. Will power be available.

Tujuan dan Manfaat Uji Penetrasi ( PT )

Uji penetrasi sangat efektif untuk mengungkap keberadaan cacat atau non konformasi yang terbuka dipermukaan , seperti misalnya : lipatan ( fold / lap ), porositas , lapisan ( seam ) , inklusi terak / kotoran ( slag inclusion ) , fusi tidak sempurna ( incomplete fusion ) , retak ( crack ) , dll. yang biasanya berada pada produk pengelasan , tempaan , rolan dan pengecoran .

Khususnya untuk produk pengelasan , PT digunakan pada jenis las fillet baik untuk sambungan sudut ( corner ) , tumpu ( overlap ) , sambungan T ( T joint ) , dan soket .

Sebagai diketahui jenis sambungan las tersebut diatas tidak dapat diradiografi karena penetrasinya partial sehingga menghasilkan imagi yang membingungkan.

Kadang kadang , sesuai dengan persyaratan spesifikasi , PT dilaksanakan pula pada las akar ( root bead ) , dan antar lajur ( interpass ).

PT memiliki keterbatasan penerapan , yakni pada material dengan suhu permukaan melebihi 40˚C atau < 0˚C , pada permukaan yang sangat kotor atau sangat kasar , dan jumlah atau jenis kontaminan dalam penetrant yang menyebabkan kegetasan atau serangan karat pada material tertentu.

Pada suhu diatas 40˚C , cairan penetrant akan menguap sebelum sempat meresap kedalam non conformasi terbuka , sedangkan pada suhu 0˚C kebawah , cairan penetrant akan membeku atau mengental sehingga sangat mengurangi daya resapnya.

Pada permukaan yang sangat kotor atau sangat kasar , akan terdapat terlalu banyak indikasi sehingga membingungkan mana yang asli dan mana yang palsu.

Kontaminasi seperti sulfur , halogen , dan alkali , menyebabkan penggetasan dan serangan karat pada bahan austenitic , titanium , paduan nikel , dan heat resisting steel.

Perlu anda ketahui bahwa jadwal pertandingan dibawah ini kami peroleh dari Wikipedia dengan update yang bisa dipercaya dan tentunya masih bersifat sementara dan dapat berubah. Berikut jadwal pertandingan sementara MotoGP 2013:

http://pabrikhelm.com/wp-content/uploads/2013/03/Jadwal-Balapan-MotoGP-2013-Trans7.jpg