PTLEVEL2 Course Notes

7/29/2019 PTLEVEL2 Course Notes

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Liquid Penetrant Testing Level 2


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Program Syllabus Introduction

History of dye penetrant testing

Pre-cleaning & preparation

Penetration Removal of Excess penetrant

Drying

Development

Inspection

Post Cleaning Penetrant Systems


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1. Introduction Definition : Penetrant Testing is a NDT Method to detect

discontinuities open to surface in non porous materials

Advantages:

1. All stage of materials can be checked 2. No Limitation in size

3. Any shape any Material can be Inspected

4. Part geometry is not a problem

Limitation : 1. Discontinuity should be open to surface

2. Inspection can be done on Non Porous materials only

3. Inspection fairly messy.


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2. History of Penetrant Testing

The origin of Penetrant Testing lies with the Oil and Whitening method.

Cracks in Steam railway locomotive parts were found by immersing thecomponent in oil for several hours. After removing the excess oil, with a ragmoistened in paraffin, a white coating was applied . The coating was a mixture

of methylated spirit and chalk . This dried to a fine white powder, The oilretained in surface breaking cracks would seep back out into the chalk tobecome visible as dark steaks.

The first penetrant was developed during the second world war.- Fluorescentdye

The first visible dye was developed in late 1940s.

The latest development of DPI Includes Water washable penetrants, PostEmulsifiable penetrants , and Penetrant kits with Aerosols.


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Method of Penetrant Testing


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Method of Penetrant Testing


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Penetrant testing & vision

The advantage that a liquid penetrant inspection (LPI) offers

over an unaided visual inspection is that it makes defects

easier to see by the inspector. There are basically two ways

that a penetrant inspection process makes flaws more easilyseen. First, LPI produces a flaw indication that is much larger

and easier for the eye to detect than the flaw itself. Many

flaws are so small or narrow that they are undetectable by the

unaided eye. Due to the physical features of the eye, there is athreshold below which objects cannot be resolved. This

threshold of visual acuity is around 0.003 inch for a person

with 20/20 vision.


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3. Pre-Cleaning & Preparation To ensure a proper Inspection it is very important that any

discontinuities shall be free from contaminants

Types of Contaminants

a. Machine Oils b. Scale and Slag

c.Welding flux

d. Corrosion Preventatives

e. Paint

f. Oxide films

g. Burnt Oil

h. Carbon

I. Acid/Alkali

j. Water


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Pre-Cleaning & Preparation Physical Cleaning. A. Brushing - Wire Brush - Removes dry scales

B. Blasting - Grit Blasting - Remove Debris ( Usually follow Chemical

etching to avoid peening.)

Chemical Cleaning a. Hot Solvent degreasing( The parts are boiled inside the solvent-

trichloroethane)

b. Vapor degreasing- same solvent, parts are suspended above the

tank. c. Solvent cleaning

d. Alkaline Cleaning - removes soaps and salts( Not used on aluminumalloys.

E. Acid pickling - removes rust. F. Steam cleaning. G. Paint removal.


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4. Penetration & Properties of

Penetrant Once the Pre-cleaning is completed, the next stage is applying the

penetrant, the penetrant requires a reasonable time to enter into thediscontinuities , A minimum of 5 minutes is required in accordance withBSEN standard, and the maximum time will vary based upon what kind

of discontinuities to be detected.

at ambient temperature evaporation is unlikely.

The penetrant seeps through the discontinuities by the principle ofCapillary action.

The time required by the penetrant to enter the discontinuity is called

as Dwell time or Penetration time


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Penetration & Properties of Penetrant


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Penetrant Properties Surface Tension: To be a good penetrant a liquid must have high surface tension, but a

material with high surface tension is not necessarily a good

penetrant.Water has high surface tension but it is a poor penetrant.

Wetting ability. The second property is a good penetrant must have high wetting

ability, It can be measured by the contact angle of the material, eg.

Mercury wets a small area on glass and thus has a high contact angle.A good penetrant must have small contact angle.


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Penetrant Properties


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Capillarity or capillary action: The ability of the material or penetrant to enter into a discontinuity is

call ed capillarity and the pressure shall be based on the formula

P = 2 S cos / w where, P = capillary pressure, S= surfaceTension, = Contact angle, W= width of the crack.

So by the above formula you can say the width of the discontinuity alsoplays a important role . The narrower the opening the higher the

capillary pressure.


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Penetrant PropertiesViscosity: Viscosity does not affect significantly the ability of a liquid to enter a

discontinuity, Well high viscosity will take longer time to fill in. when

dipping or spraying process is adopted then it takes more time todrain.

Flash Point : The flash point is the temperature of a material at which vapor is given

off to form a combustible mixture. The flash point is not mentioned in BS standard, even though some US

specification says that the Minimum flash point value shall be 200degree f.


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Penetrant PropertiesVolatility: Many penetrant materials are unfortunately volatile.

Chemical Inertness : Chemicals must be non corrosiveand toxic.

Solubility : Solubility is required which aids in the cleaning process.

Tolerance to contaminants , Healthhazards, availability and cost.


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Penetrant Types of penetrant a. Color contrast b. Fluorescent c. Combined color &

fluorescent.

Pentrant : Hydrocarbon Mixtures include red or fluorescent dye , this ispost Emulsifiable the same used for solvent removable.

Or Hydrocarbon Mixtures include red or fluorescent dye in asolution plus an emulsifier - these are water washable penetrants.

Color contrast penetrant usually dyed red and they are inspected in day

light or artificial light. Fluorescent penetrant are most sensitive than visible dye penetrant.

They are viewed under dark conditions using a UV lamp, which has anwavelength of 365nm.


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Penetrant Method of Application: The most common method of applying color contrast penetrant is by

aeroso.

For overhead position alternative methods ( thixotropic or gelpenetrant)

When using fluorescent penetrants for production work is normally by

Dip and Drain

Spray and Drain

Electro static spray.

Aerosol spray


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Penetrant Application


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Dwell Time


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5. Removal of Excess Penetrant

After the penetration time, the excess penetrant haveto be removed without affect the penetrant inside thediscontinuity. This is a vital stage for the surface

must not be cleaned excessively or defects will beleached out.

I f proper removal of excess penetrant is not done,then it will reflect in a high background whichreduces the contrast and affect the test results.

The common methods of removal of excesspenetrant are a. Solvent b. Water C.Hydrophilic d. Lipophilic.


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5. Removal of Excess Penetrant


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Removal of Excess Penetrant

Solvent Removal : A lint free paper towel or rag is wiped the excess penetrant.

The paper is moistened with solvents and wiped over the test area.

Then use a lint free cloth to wipe again

Care should be taken to avoid over cleaning.

Water Washable : A water or air /water spray is used to remove water removable

penetrants .Fluorescent penetrant shall be washed under UV light.

The water pressure shall be fairly coarse, high volume, droplet spray atmaximum pressure 2 bar. Temperature shall be between 15- 30degrees.


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Removal of Excess Penetrant

Post Emulsifier: Lipophilic process : The Lipophilic material is an

emulsifier which mixes with oil and makes the wholemiscible with water. The normal method is immersionfollowed by draining. This method is suitable toidentify wide shallow discontinuities.


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Lipophilic process


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Hydrophilic Emulsifier

A Hydrophilic Emulsifier is a detergent which when mixed in atank with water has the ability to break down the surfacetension of penetrant, in contact with a test surface, and lift or

scrub the penetrant from the surface.

Usually applied by Immersion

Remover time is usually 3 minutes

It finds difficult to remove the penetrant from crevices andthreads or roots


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Hydrophilic Emulsifier


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6. Drying Drying the Test specimen or test surface is an

important stage after penetrant removal. If

the solvent removable method is used, thepart being inspected will dry quickly as thesolvent remover evaporates.

Other Methods are

Hot air re-circulating oven

Forced warm air

Dry clean compressed air


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7. Development In Development all the Images which

are invisible are revealed.

The main functions are

# Providing Contrast back ground

# Bleed out action (Reverse Capillaryaction).


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Development

Developer Properties: Absorptive ( To perform blotting action)

Easily and evenly applicable

It must form a light and even coat

No fluorescent when fluorescent penetrant is used

Readily removable

Non Toxic and Non irritant

It should provide high contrasting color with the penetrant

It must be easily wetted by the penetrant bleeding from adiscontinuity


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Mechanism of Developer action

A) Capillarity

B) Light scattering

C) Solvent action

Let us see what Capillarity means:

Capillarity usually comes with the color contrast penetrant

The Capillarity action of the developer particles overcomes theopposing attraction of the discontinuity and therefore increasesthe surface area of the indication.


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Light Scattering: When using the fluorescent penetrants the light scattering effect is

important.

Through this mechanism the brightness of an indication is significantlyamplified per unit area. The next figure illustrates this in simple form.

The developer particles reflect both the exciting UV-A and Fluorescentradiation.

All the actions are carried out in darkened conditions which givesimproved sensitivity than color contrast penetrant.


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M h i f D l ti


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Solvent action: This applies only to non-aqueous developers(Solvent

suspended).

The developer particles shall be sprayed from a distance suchthat the developer particles are just damp when they strike thetest surface.

The remaining solvent on the particles will bridge the gapbetween the developer particles and the penetrant in thediscontinuity.

The solvent shall not dilute the penetrant nor reduce thebrightness of a fluorescent penetrant.


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Types of DeveloperA) Dry Developer

B) Non-Aqueous Developer

C) Aqueous Developer


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8.0 Inspection Parts should be inspected initially as soon as the

developer is applied. Development time shall varybetween 5- 30 Minutes.

The Viewing condition for the color contrastpenetrant is day light and minimum illuminant on thesurface shall be 500 lux. Whereas the fluorescentpenetrant shall be viewed under UV- light having

wavelength of 365nm and minimum intensity of500uw/cm2.


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Inspection


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Common flaws identified by

PT* Fatigue cracks

Quench cracks

Grinding cracks Overload and impact fractures

Porosity , Laps, Seams ,Pin holes in

welds Lack of fusion or braising along the

edge of the bond line
http://www.cnde.iastate.edu/ncce/PT_CC/Sec.3.1/Sec.3.1.htmlhttp://knowing%20your%20eyes.ppt/http://knowing%20your%20eyes.ppt/http://knowing%20your%20eyes.ppt/http://knowing%20your%20eyes.ppt/http://www.cnde.iastate.edu/ncce/PT_CC/Sec.3.1/Sec.3.1.html


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9.0 Post Cleaning It is often necessary to clean residues from test material.

However, in some cases, such as when a high quality paintsurface is to be applied, it is vital to remove penetrant anddeveloper residues.

If dealing with intricate parts, it is often necessary to scrubthem in a warm water detergent mixture, to remove developerresidues.

Specimens tested by fluorescent method using dry powder

developer are often just subjected to a dry air blast. This maybe followed by cleaning with cold solvent or in a hotliquid/vapor degreaser.


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10. Penetrant Systems


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Step by Step Procedure for Color contrast

Penetrant with Non-aqueous Liquid Developer

1. Pre-cleaning of Surface:

* Normal site pre-cleaning is by cold solvent spray and wipe.

2.Application of penetrant:

* By Spraying (aerosol), dip and drain, swabbing or brushing . * Minimum dwell time is 10 minutes and maximum 30 minutes.

3. Removal of excess penetrant :

This is a three stage process .First clean with a lint free cloth,Then use a solvent dampened cloth, then use a fresh cloth towipe, never spraydirectly


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Penetrant with Non-aqueous Liquid Developer Application of Developer:

Agitate developer thoroughly, Make a test spray on redundantsurface, Spray from a distance exceeding 300mm leaving a thin

even coat of developer on test surface. The developer coatshould be light and even.

Inspection:

Inspection starts when the developer is applied, It isrecommended to have a development time of 30 minutes, view

under good bright white light conditions and vary the angle ofthe test surface, eyes and light for optimum inspection.


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Penetrant with Non-aqueous Liquid Developer Evaluation of Welds:

The following are the discontinuities shall be identified usingDPI.

Keep in mind discontinuity shall be open to surface Cracks, Surface porosity's, Undercut.

Basically Indications shall be classified into

False indications

Relevant Indications

Non-Relevant Indication


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Penetrant with Non-aqueous Liquid Developer

Post Cleaning and protection: If necessary apply excess coat of developer to absorb

penetrant.

Brush of developer with bristle brush

Persistent coatings of developer should be removed withdetergent and water, then dried with a lint free rag. Protectwith appropriate material.


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Penetrant Testing-Level II

THE END

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PTLEVEL2 Course Notes

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