Dye penetrant = inspection

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1. Section of material with a = surface-breaking=20 crack that is not visible to the naked eye.
2. Penetrant is applied = to the=20 surface.
3. Excess penetrant is removed.
4. Developer is applied,=20 rendering the crack visible.

This article needs additional citations=20 for verificatio= n.=20 Please help improve=20 this article by adding citations to reliable=20 sources. Unsourced material may be challenged= =20 and removed.=20 (November 2009)

Dye penetrant inspection (DPI), also called liquid = penetrant=20 inspection (LPI) or penetrant testing (PT), is = a widely=20 applied and low-cost inspection method used to locate surface-breaking = defects=20 in all non-porous materials = (metals,=20 plastics, or ceramics). The penetrant may be applied to all non-ferrous=20 materials and ferrous materials, although for ferrous components magnet= ic-particle=20 inspection is often used instead for its subsurface detection = capability.=20 LPI is used to detect casting, forging and welding surface defects such = as=20 hairline cracks, surface porosity,=20 leaks in new products, and fatigue=20 cracks on in-service components.

[edit]=20 History

The oil and whiting method used in the railroad industry in the early = 1900's=20 was the first recognized use of the principles of penetrants to detect = cracks.=20 The oil and whiting method used an oil solvent for cleaning followed by = the=20 application of a whiting or chalk coating, which absorbed oil from the = cracks=20 revealing their locations. Soon a dye was added to the liquid. By the = 1940's,=20 fluorescent or visible dye was added to the oil used to penetrate test=20 objects.

Experience showed that temperature and soak time were important. This = started=20 the practice of written instructions to provide standard, uniform = results. The=20 use of written procedures has evolved, giving the ability for design = engineers=20 and manufacturers to get the high standard results from any properly = trained and=20 certified liquid penetrant testing technician.

[edit]=20 Principles

DPI is based upon capillary=20 action, where low surface tension fluid penetrates into clean and = dry=20 surface-breaking discontinuities. Penetrant may be applied to the test = component=20 by dipping, spraying, or brushing. After adequate penetration time has = been=20 allowed, the excess penetrant is removed, a developer is applied. The = developer=20 helps to draw penetrant out of the flaw where a invisible indication = becomes=20 visible to the inspector. Inspection is performed under ultraviolet or = white=20 light, depending upon the type of dye used - fluorescent or=20 nonfluorescent (visible).

[edit]=20 Materials

Penetrants are classified into sensitivity levels. Visible penetrants = are=20 typically red in color, and represent the lowest sensitivity. = Fluorescent=20 penetrants contain two or more dyes that fluoresce when excited by ultraviolet (UV-A) = radiation=20 (also known as black light). Since Fl= uorescent=20 penetrant inspection is performed in a darkened environment, and the = excited=20 dyes emit brilliant yellow-green light that contrasts strongly against = the dark=20 background, this material is more sensitive to small defects.

When selecting a sensitivity level one must consider many factors, = including=20 the environment under which the test will be performed, the surface = finish of=20 the specimen, and the size of defects sought. One must also assure that = the test=20 chemicals are compatible with the sample so that the examination will = not cause=20 permanent staining, or degradation. This technique can be quite = portable,=20 because in its simplest form the inspection requires only 3 aerosol = spray cans,=20 some lint free clothes, and adequate visible light. Stationary systems = with=20 dedicated application, wash, and development stations, are more costly = and=20 complicated, but result in better sensitivity and higher samples=20 through-put.

[edit]=20 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=20 loose scale that could either keep penetrant out of a defect, or cause=20 irrelevant or false indications. Cleaning methods may include solvents, alkaline = cleaning=20 steps, vapor=20 degreasing, or media blasting. The end goal of this step is a clean = surface=20 where any defects present are open to the surface, dry, and free of=20 contamination. Note that if media blasting is used, it may "work over" = small=20 discontinuities in the part, and an etching bath is recommended as a = post-bath=20 treatment.

2. Application of Penetrant:

The penetrant is then applied to the surface of the item being = tested. The=20 penetrant is allowed "dwell time" to soak into any flaws (generally 5 to = 30=20 minutes). The dwell time mainly depends upon the penetrant being used, = material=20 being testing and the size of flaws sought. As expected, smaller flaws = require a=20 longer penetration time. Due to their incompatible nature one must be = careful=20 not to apply solvent-based penetrant to a surface which is to be = inspected with=20 a water-washable penetrant.

3. Excess Penetrant Removal:

The excess penetrant is then removed from the surface. The removal = method is=20 controlled by the type of penetrant used. Water-washable, = solvent-removable, lipophilic=20 post-emulsifiable, or hydrophilic=20 post-emulsifiable are the common choices. Emulsifiers = represent the=20 highest sensitivity level, and chemically interact with the oily = penetrant to=20 make it removable with a water spray. When using solvent remover and = lint-free=20 cloth it is important to not spray the solvent on the test surface = directly,=20 because this can remove the penetrant from the flaws. If excess = penetrant is not=20 properly removed, once the developer is applied, it may leave a = background in=20 the developed area that can mask indications or defects. In addition, = this may=20 also produce false indications severely hindering your ability to do a = proper=20 inspection.

4. Application of Developer:

After excess penetrant has been removed a white developer is applied = to the=20 sample. Several developer types are available, including: non-aqueous=20 wet developer, dry powder, water suspendable, and water soluble. = Choice of=20 developer is governed by penetrant compatibility (one can't use = water-soluble or=20 suspendable developer with water-washable penetrant), and by inspection=20 conditions. When using non-aqueous wet developer (NAWD) or dry powder, = the=20 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=20 commercially available in aerosol spray cans, and may employ acetone, isopropyl = alcohol, or=20 a propellant that is a combination of the two. Developer should form a=20 semi-transparent, even coating on the surface.

The developer draws penetrant from defects out onto the surface to = form a=20 visible indication, commonly known as bleed-out. Any areas that = bleed-out can=20 indicate the location, orientation and possible types of defects on the = surface.=20 Interpreting the results and characterizing defects from the indications = found=20 may require some training and/or experience [the indication size is not = the=20 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=20 visible dye penetrant. Ultraviolet (UV-A) radiation of adequate = intensity (1,000=20 micro-watts per centimeter squared is common), along with low ambient = light=20 levels (less than 2 foot-candles) for fluorescent penetrant = examinations.=20 Inspection of the test surface should take place after a 10 minute = development=20 time. This time delay allows the blotting action to occur. The inspector = may=20 observe the sample for indication formation when using visible dye. It = is also=20 good practice to observe indications as they form because the = characteristics of=20 the bleed out are a significant part of interpretation characterization = of=20 flaws.

6. Post Cleaning:

The test surface is often cleaned after inspection and recording of = defects,=20 especially if post-inspection coating processes are scheduled.

[edit]=20 Advantages and=20 disadvantages

The main advantages of DPI are the speed of the test and the low = cost.=20 Disadvantages include the detection of only surface flaws, skin = irritation, and=20 the inspection should be on a smooth clean surface where excessive = penetrant can=20 be removed prior to being developed. Conducting the test on rough = surfaces,=20 such-as as-welded welds, will make it difficult to remove any excessive=20 penetrant and could result in false indications. Water-washable = penetrant should=20 be considered here if no other option is available. Also, on certain = surfaces a=20 great enough color contrast cannot be achieved or the dye will stain the = workpiece.^[1]

Limited training is required for the operator =E2=80=94 although = experience is quite=20 valuable. Proper cleaning is necessary to assure that surface = contaminants have=20 been removed and any defects present are clean and dry. Some cleaning = methods=20 have been shown to be detrimental to test sensitivity, so acid etching = to remove=20 metal smearing and re-open the defect may be necessary.^{[citation=20
needed]}

[edit]=20 Standards

International=20 Organization for Standardization (ISO)

ISO 3059, Non-destructive testing - Penetrant testing and = magnetic=20 particle testing - Viewing conditions
ISO 3452-1, Non-destructive testing. Penetrant testing. Part 1. = General=20 principles
ISO 3452-2, Non-destructive testing - Penetrant testing - Part = 2:=20 Testing of penetrant materials
ISO 3452-3, Non-destructive testing - Penetrant testing - Part = 3:=20 Reference test blocks
ISO 3452-4, Non-destructive testing - Penetrant testing - Part = 4:=20 Equipment
ISO 3452-5, Non-destructive testing - Penetrant testing - Part = 5:=20 Penetrant testing at temperatures higher than 50 =C2=B0C
ISO 3452-6, Non-destructive testing - Penetrant testing - Part = 6:=20 Penetrant testing at temperatures lower than 10 =C2=B0C
ISO 12706, Non-destructive testing - Penetrant testing -=20 Vocabulary
ISO 23277, Non-destructive testing of welds - Penetrant testing = of=20 welds - Acceptance levels

European=20 Committee for Standardization (CEN)

EN 571-1, Non-destructive testing - Penetrant testing - Part 1: = General=20 principles. May be replaced by EN ISO 3452-1.
EN 1371-1, Founding - Liquid penetrant inspection - Part 1: = Sand,=20 gravity die and low pressure die castings
EN 1371-2, Founding - Liquid penetrant inspection - Part 2: = Investment=20 castings
EN 2002-16, Aerospace series - Metallic materials; test methods = - Part=20 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=20 penetrant testing of seamless and welded steel tubes for the detection = of=20 surface imperfections

ASTM=20 International (ASTM)

ASTM E 165, Standard Practice for Liquid Penetrant Examination = for=20 General Industry
ASTM E 1417, Standard Practice for Liquid Penetrant = Testing

American=20 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=20 Method for Liquid Penetrant Examination SE-165 (identical with = ASTM=20 E-165)

[edit]=20 References

^=20 Kohan, Anthony = Lawrence (1997),=20 Boiler operator's guide (4th ed.), = McGraw-Hill=20 Professional, p. 240, = ISBN 9= 780070365742, http://books.google.com/books?id=3DtAQ-Gc2xv-UC&pg=3D= PA240.

[edit]=20 See also

Nondestructi= ve=20 testing

[edit]=20 External = links

Penetrant and Magnetic Particle Testing at Level = 2,=20 International Atomic Energy Agency, 2000 (pdf, 2.5 MB).
[1] - technical reports summarizing fluorescent = penetrant=20 inspection research efforts
[2] - an article on how to perform a sensitive = visible dye=20 penetrant examination

Retrieved from "http://en.wikipedia.org/w/index.php?title=3DDy= e_penetrant_inspection&oldid=3D468329985"

Categories: =

Non= destructive=20 testing
Ca= sting=20 (manufacturing)

Hidden = categories:=20

Dye penetrant = inspection

Contents

[edit]=20 History

[edit]=20 Principles

[edit]=20 Materials

[edit]=20 Inspection = steps

[edit]=20 Advantages and=20 disadvantages

[edit]=20 Standards

[edit]=20 References

[edit]=20 See also

[edit]=20 External = links

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