PT Level I Course

8/10/2019 PT Level I Course

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Surface Methods Level I Course 2012

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Table of Contents

Chapter I General knowledge related to Non Destructive Testing ............................................................. 2

Part I LIQUID PENETRANT TESTING

Chapter 2 Basic Principles of Liquid Penetrant Testing .............................................................................. 25

Chapter 3 Equipment and Materials ............................................................................................................... 31

Chapter 4 Techniques ......................................................................................................................................

41

Chapter 5 Interpretation of Test Results ....................................................................................................... 55

Chapter 6 Codes, Standards, Procedures and Safety .................................................................................. 63


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CHAPTER 1: GENERAL KNOWLEDGE RELATING TO NON DESTRUCTIVE TESTING

1.0 Introduction To Non Destructive Testing

Non-destructive testing is a fundamental and essential tool for control of quality of engineering

materials, manufacturing processes, reliability of products in services, and maintenance of systemswhose premature failure could be costly or disastrous. Non destructive testing is normally

interpreted to mean the use of physical methods for testing materials and products without harm to

those materials and products. It is frequently important to know a property or characteristic of a

material or product which, if tested direc tly, would be destructive. Therefore it becomes necessary

to perform a non-destructive test on some property or characteristic which can be related to that

about which knowledge is desired. The test may be very simple in some cases, but in others may be

complex and difficu lt

1.1 Purposes of Non-destructive Testing

Since the 1920s, the art of testing without destroying the test object has developed from a

laboratory curiosity to an indispensable tool of production. No longer is visual examination of

materials, parts and complete products the principal tests in great variety are in worldwide use to

detect variations in structure, minute changes in surface finish, the presence of cracks or other

physical discontinuities, to measure the thickness of materials and coatings and to determine other

characteristics of industrial products. Scientists and engineers of many countries have contributed

greatly to non-destructive test development and applications.

The various non-destructive testing methods are covered in detail in the literature but it is always

wise to consider objectives before plunging into the details of a method. What is the use of

non-destructive testing? Why do thousands of industrial concerns buy the testing equipment, pay

the subsequent operating costs of the testing and even reshape manufacturing processes to fit the

needs and findings of non-destructive testing?

Modern non-destructive tests are used by manufacturers

1.

To ensure product integrity, and in turn, reliability2. To avoid failures, prevent accidents and save human

3. To ensure customer satisfaction and maintain the manufacturer's reputation

4. To aid in better product design

5. To control means of determining adequate quality manufacturing processes

6. To lower manufacturing costs;


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1.2 Applications of NDT

NDT is most commonly used where component failure may have a catastrophic consequences

such as in air planes, electric power plants, petrochemical plants, as well as gas transmission

lines, offshore drilling platforms, and ground transportation systems and structures. Primary usesof NDT are

Raw Material Inspection

Pre Service Inspection i.e. testing of newly manufactured items to make sure the parts

comply with design specifications

In Service Inspection i.e. the periodic inspection of items that are in some type of on-going

service to determine if the part is suitable for continued service

The prediction of remaining life in operating systems is highly dependent on the operating

conditions and a detailed knowledge of the precise condition of material required. NDT is used to

assess the current condition of the materials that have been in service by detecting presence of

cracking or progressive wall thinning due to long term corrosion.

1.3 Types of NDT Methods

NDT methods which are commonly used are: Visual or Optical Inspection, Dye-Penetrant Testing,

Magnetic Particle Testing, Eddy Current Testing, Radiographic Testing, Ultrasonic Testing and

Leak Testing. These methods are known as conventional NDT methods. Compared to these NDT

methods like neutron radiography, thermal and infrared testing and acoustic emission, etc. are

known as non-conventional NDT methods. A brief description of the conventional NDT methods

is given below:

1.3.1 Vi sual Testing (VT)

Often overlooked in any listing of NDT methods, visual inspection is one of the most common and

most powerful means of non-destructive testing. Visual testing requires adequate illumination of

the test surface and proper eye-sight of the tester. To be most effective visual inspection does,

however, requires special attention because it requires training, e.g. knowledge of product and process, anticipated service conditions, acceptance criteria and record keeping, and it has its own

range of equipment and instrumentation. Often the equipment needed is simple (Figure 1): a

portable light, a mirror on stem, a 2 X or 4 X hand lens and one illuminated magnifier with

magnification 5X or 10X.. For internal inspection, light lens systems such as borescopes allow

remote surfaces to be examined. More sophisticated devices of this nature using fibre optics permit


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the introduction of the device into very small access holes and channels. Most of these systems

provide for the attachment of a camera to permit permanent recording.

Figure 1 Various Optical Aids used in Visual Inspection

A. Mirror on stem: may be flat for normal view or concave for limited magnification.

B. Hand magnifying glass (magnification usually 2-3X).

C. Illuminated magnifier, field of view more restricted than D (magnification 5-10X).

D. Inspection glass, usually fitted with a scale for measurement, the front surface is placed in

contact with the work (magnification 5-10X).

E. Borescope or intrascope with built-in illumination (magnification 2-3X).

The applications of visual testing include:

1) Checking of the surface condition of the test specimen.

2) Checking of alignment of matting surfaces.

3) Checking of shape of the component.

4) Checking for evidence of leaking.

5) Checking for inner surface defects.

1.3.2 L iqu id Penetrant Testin g (PT)

This is a method which can be employed for the detection of open-to-surface discontinuities in any

industrial product which is made of a non-porous material. This method is widely used for testing

of non-magnetic materials. In this method a liquid penetrant is applied to the surface of the product

for a certain predetermined time after which the excess penetrant is removed from the surface. The

surface is then dried and a developer is applied to it. The penetrant which remains in the


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discontinuity is absorbed by the developer to indicate the presence, as well as the location, size and

nature of the discontinuity. Penetrant Testing is discussed in detailed in later chapters.

Penetrants used as liquid penetrant are either visible dye penetrant or fluorescent dye penetrant.

The inspection of indications by visible dye penetrant is made under white light while inspectionof indications by fluorescent dye penetrant is made under ultraviolet (or black) light under

darkened conditions. The liquid penetrant processes are further sub-divided according to the

method of washing of the specimen. The penetrants can be: (i) water-washable, (ii)

post-emulsifiable, i.e. an emulsifier is added to the excess penetrant on surface of the specimen to

make it water-washable, and (iii) solvent removable, i.e. the excess penetrant is needed to be

dissolved in a solvent to remove it from the test specimen surface. In order of decreasing

sensitivity and decreasing cost, the liquid penetrant processes can be listed as:

1) Post emulsifiable fluorescent dye penetrant.

2) Solvent removable fluorescent dye penetrant.

3) Water washable fluorescent dye penetrant.

4) Post emulsifiable visible dye penetrant.

5) Solvent removable visible dye penetrant.

6) Water washable visible dye penetrant.

1.3.3 M agnetic Parti cle Testin g (M T)

Magnetic particle testing is used for the testing of materials which can be easily magnetized. This

method is capable of detecting open-to-surface and just below-the-surface flaws. In this method

the test specimen is first magnetized either by using a permanent or an electromagnet or by passing

electric current through or around the specimen. The magnetic field thus introduced into the

specimen is composed of magnetic lines of force. Wherever there is a flaw which interrupts the

flow of magnetic lines of force, some of these lines must exit and re-enter the specimen. These

points of exit and re-entry form opposite magnetic poles. When minute magnetic particles aresprinkled onto the surface of such a specimen, these particles are attracted by these magnetic poles

to create a visual indication approximating the size and shape of the flaw. Figure 2 illustrates the

basic principle of this method.

Depending on the application, there are different magnetization techniques used in magnetic

particle testing.


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D

e

p

en

These techniques can be grouped into the following two categories:

a) Direct Current Techniques: These are the techniques in which the current flows through the

test specimen and the magnetic field produced by this flow of current is used for the

detection of defects. These techniques are shown in Figure 3

b) Magnetic Flux Flow Techniques: in these techniques magnetic flux is induced into the

specimen either by the use of a permanent magnet or by flowing current through a coil or a

conductor. These techniques are shown in Figure 4

Figure 2 Basic principle of magnetic particle testing

Figure 3: Circular magnetization with contact heads (left) : Prod Magnetization (right)

Figure 4 Yoke Magnetization (left) ; Longitudinal Magnetization (right)


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1.3.4 Radiographic Testing M ethod (RT)

The radiographic testing method is used for the detection of internal flaws in many different

materials and of many configurations. An appropriate radiographic film is placed behind the test

specimen (Figure 1.5) and is exposed by passing either X-rays or gamma rays through it. Theintensity of the X-rays or gamma rays while passing through the product is modified according to

the internal structure of the specimen and thus the exposed film, after processing, reveals the

shadow picture, known as a radiograph, of the product.

Figure 5 Basic Principle of Radiographic Testing


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It is then interpreted to obtain data about the flaws present in the specimen. This method is used on

wide variety of products such as forgings, castings and weldment.

Radiography is an important tool in nondestructive testing. The method offers a number of

advantages over other NDT methods, but one of its disadvantages is the health risk associated withthe radiation. Health effects can occur due to either long-term low level exposure or short-term

high level exposure. X-rays and gamma rays are ionizing radiation and as such they are harmful to

human beings. If received in higher doses, these radiations can be lethal. The most dangerous thing

about X-rays and gamma rays is that their presence cannot be felt even if being received in large

doses and causing damage to the human body. For example, a lethal dose of radiation will cause

only a 0.002 C rise in temperature of human body which cannot be perceived by the human

senses. The effects of ionizing radiation on human beings can be classified as somatic and genetic.

1.3.4.1 Somatic effects

The damage caused by the ionizing radiation to the exposed individual is known as somatic effect.

These effects can be further divided into immediate and delayed somatic effects. Immediate

somatic effects are the effects which are apparent in the exposed individual within hours or a few

days. These effects include vomiting, nausea, fatigue, paleness, loss of hair, loss of appetite, etc.

The delayed somatic effects may appear in the exposed individual years after the exposure. These

effects may include:

1. Cataract of the lenses of the eyes which may cause partial or total blindness.

2. Cancer such as bone and lung cancer and leukemia.

3. A plastic anemia caused by radiation damage to bone marrow.

4. Shortening of life span and premature ageing.

1.3.4.2 Genetic effects

Genetic effects, which are caused by the damage to the genes of the exposed individual, affect the

off-spring of the exposed individual. This is the most important of long term effects of low level

radiation exposure. Genetic effects are significant only if gonads receive radiation exposure.


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1.3.5 Ultrasonic T estin g (UT)

Ultrasonic inspection is a non-destructive method in which high frequency sound waves are

introduced into the material being inspected. Most ultrasonic inspection is done at frequencies between 0.5 and 20 MHz well above the range of human hearing which is about 20 Hz to 20 kHz.

The sound waves travel through the material with some loss of energy (attenuation) due to material

characteristics. The intensity of sound waves is either measured, after reflection (pulse echo) at

interfaces (or flaw) or is measured at the opposite surface of the specimen (pulse transmission).

The reflected beam is detected and analyzed to define the presence and location of flaws. The

degree of reflection depends largely on the physical state of matter on the opposite sides of the

interface, and to a lesser extent on specific physical properties of that matter. For instance, sound

waves are almost completely reflected at metal-gas interfaces. Partial reflection occurs at

metal-liquid or metal-solid interfaces. Ultrasonic testing has a superior penetrating power than

radiography and can detect flaws deep in the test specimen (say up to about 6 to 7 metre of steel). It

is quite sensitive to small flaws and allows the precise determination of the location and size of the

flaws. The basic principle of ultrasonic testing is illustrated in Figure 1.6.

Figure 6 Basic Principle of Ultrasonic Testing (Pulse echo technique)

Ultrasonic testing method is:

1) Mostly used for detection of flaws in materials

2) Widely used for thickness measurement

3) Used for the determination of mechanical properties and grain structure of materials


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4) Used for the evaluation of processing variables on materials

1.3.6 Eddy Cur rent Testin g (ET )

This method is applicable to electrically conductive materials only. In this method eddy currentsare produced in the product by bringing it close to an alternating current carrying coil. The

alternating magnetic field of the coil is modified by the magnetic fields of the eddy currents. This

modification, which depends on the condition of the part near to the coil, is then shown as a meter

reading or cathode ray tube presentation. Figure 1.7 (a & b) gives the basic principles of eddy

current testing.

Figure 7 Generation of eddy currents in the test specimen (left) Distortion of eddy currents due to defect(right)

There are three types of probes (Figure 8) used in eddy current testing. Internal probes are usually

Figure 8 Eddy Current Probes : Surface Probes (left) ; Internal Probe (bobbin) (middle) ; Encircling Probe (right)


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used for the in-service testing of heat exchanger tubes. Encircling probes are commonly used for

the testing of rods and tubes during manufacturing. The uses of surface probes include the location

of cracks, sorting of materials, measurement of wall and coating thickness, and case depth

measurement. This method is used:1) For the detection of defects in tubings

2) For sorting of materials

3) For the measurement of thin wall thicknesses from one surface only

4) For measuring thin coatings and

5) For measuring case depths

1.3.7 L eak Testin g (L T)

Since many structures are designed to be pressurized or pressure tight, defect is often a leak. There

are several methods (Table 1.1) for locating leaks ranging from simple liquid seepage onto a dry

surface, perhaps mixed with a dye, to highly precise measurement of the escape of helium or

radioactive gas. The level of sensitivity depends upon the method used and is chosen in relation to

the severity of the application.

Table 1.1 COMPARISON OF LEAK TESTING METHODS

Method Detector Relative sensitivity

Air/soap solution

Air/water

Visual bubbles 1 x

Air Sound of escaping gas

(Ultrasonic detector)

10 x

Hydrogen/Methanol Visual bubbles 100 x

Hydrogen Pirani gauge 100 x

Halogen gas Heated anode

(Electron capture gauge)

700 x

Hydrogen or helium Mass spectrometer 800 x

Radioactive gas (Krypton-85) Counter 800 x


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However, a person having a Level-1 certificate shall not be responsible for the choice of the test

method or technique to be used not for the assessment of test result.

1.3 MATERIALS

1.3.1 Properties of Materials

1.3.1.1 Physical properti es

1.3.1.1.1 Specific gravity

Specific gravity is a unit of measurement based on the mass of a volume of material compared withthe mass of an equal volume of water.. When two molten metals are mixed together the metal withthe lower specific gravity will be forced to rise to the top

1.3.1.1.2 Density

A metal is said to be dense when it is compact and does not contain defects such as slag inclusions orgas pockets. Density is expressed as the quantity per unit volume. The density of low carbon steel,for example, is 0.238 pounds per cubic inch (7.85 gm per cm 3). The density of aluminium, a muchlighter metal, is only 0.096 pounds per cubic inch (2.7 gm per cm 3).

1.3.1.1.3 Porosity

Porosity is the opposite of density. Some materials are porous by their nature and allow liquids under pressure to leak through them

1.3.1.1.4 Melting point

The melting point is the temperature at which a substance passes from a solid to a liquid state. Forwater this is 32 F (0 C). Steel has a melting point around 2700 F (1482 C) depending upon thecarbon range. Higher the melting point, greater is the amount of heat needed to melt a given volumeof metal.

1.3.1.1.5 Volatility

Volatility is the ease with which a substance may be vaporized. A metal which has a low melting point is more volatile than a metal with a high melting point. Volatility is measured by thetemperature at which a metal boils under atmospheric pressure.

1.3.1.1.6 Weldability

Weldability is the capacity of a metal substance to form a strong bond of adherence while under pressure or during solidification from a liquid state.


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be formed, when hot or cold, into useful shapes. If the application of load is increased in the plastic

region a stage comes when the material fractures. Some of the important mechanical properties are

discussed below

1.3.1.2.1 Strength

Strength is the ability of a material to resist deformation. It is usually expressed as the ultimate

tensile

strength in pounds per square inch

1.3.1.2.2 Hardness

The ability of one material to penetrate another material without fracture of either is known ashardness. The greater the hardness, the greater is the resistance to marking or deformation. A hard

material is also a strong material, but it is not very ductile. The opposite of hardness is softness.

1.3.1.2.3 Toughness

A material may be assumed to be tough if it has high tensile strength and the ability to deform

permanently without breaking. Toughness may be thought of as the opposite of failure through

deformation whereas a brittle material breaks without any warning. Copper, nodular iron and steel

are tough materials.

1.3.1.2.4 Shock (impact) resistance

Shock resistance may be defined as the ability of a material to withstand a maximum load applied

suddenly. The shock resistance of a material is often taken as an indication of its toughness.

1.3.1.2.5 Brittleness

Brittle materials fail without any warning through deformation, elongation, or a change of shape. It

may be said that a brittle material lacks plasticity and toughness. A piece of chalk is very brittle.

1.3.1.2.6 Ductility

Ductility is the ability of materials to be permanently deformed (stretched) by loading, and yet resist

fracture. When this happens, both elongation and reduction in area take place in the material.. Metals


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with high ductility may be stretched, formed, or drawn without tearing or cracking. Gold, silver,

copper and iron are metals with good ductility. A ductile metal is not necessarily a soft metal. A

metal may be ductile and yet possess hardness.

1.3.2 Types of Metals

Metals are divided into two general types, Ferrous and nonferrous. Ferrous metals have iron as their

major element. Iron is the basis of all steels. Non-ferrous metals contain no iron in appreciable

amount. Following are the types of ferrous metals.

1.3.2.1 I ron

Cast iron is produced by resembling pig iron and scrap iron in a furnace. Some of the impurities in

the molten metal are removed by using various chemical agents called "flux". Cast iron has somedegree of corrosion resistance and has a low tensile strength. Many pump casings and machinery

housing are made from cast iron.

Wrought iron is a highly refined iron that has very low carbon content and contains uniformly

distributed particles of "slag". Wrought iron is considerably softer that cast iron. Like cast iron,

wrought iron is fairly resistant to corrosion and fatigue. Because of these characteristics, wrought

iron is used extensively for low pressure pipe and rivets.

1.3.2.2 Steel

Steel is one of the most important materials used in manufacturing and construction. It is an unusual

material because there are so many variations. There are over 10,000 different grades of steel that

have been developed for specific properties. Steel may be hard or soft, tough or brittle; they may rust

easily or not at all.

Plain steels that have small additions of sulfur and sometimes phosphorus are called" free cutting

steels". The plain steels are classified by their percentage of carbon.

Low-carbon steel contains less than 0.25 percent carbon. Low-carbon steel is usually referred to as

"mild steel". Theses steels can be easily cut and bent and do not have great tensile strength.

Medium-carbon steels contain 0.25-0.55 percent carbon. Medium carbon steels are stronger and

harder that mild carbon steels. As a result, they are harder to form. Parts made form medium-carbon

steels include gears, axles, drive shafts, levers and other parts that must be strong and durable.


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High-carbon steels have more than 0.55 percent carbon. They have the greatest hardness and

strength, but they are the most difficult steels to cut and form. High carbon steels are used to make

cutting tools, hand tools such as files and hammer and machine parts.

1.3.2.3 Alloy steel

When other elements are added to iron during the refining process, the resulting metal is called

"alloy steel". Alloy steels are further identified as "low-alloy steel" or "high-alloy steel" depending

on the amount of alloying material present.

The low-alloy nickel steels contain less than 5 percent nickel. The nickel is used to increase strength

and toughness. Nickel steels containing more that 5 percent nickel have increase resistance to

corrosion.

A great many steels are included in the group known as stainless steels. Most of these are chromium

steels or Chromium- nickel steels. Stainless steels are in general referred to as corrosion-resistance

steels. Stainless steels retain their strength at high temperatures and are easy to form. They are used

in highly corrosive environments and are very expensive.

1.3.3 Welding processes

Welding can be defined as the metallurgical method of joining, applied to the general problem of

construction and fabrication. It consists of joining two pieces of metal by establishing a metallurgicalatom-to-atom bond, as distinguished from a joint held together by friction or mechanical

interlocking. This metallurgical atom-to-atom bond is achieved by the application of heat and

sometimes pressure or both.

Different welding processes along with their abbreviations are listed below:

Shielded metal arc welding (SMAW), flux cored arc welding (FCAW), gas metal welding

(GMAW), gas tungsten arc welding (GTAW), submerged arc welding (SAW), resistance welding(RW), stud welding (SW), electroslag welding (ESW), plasma arc welding (PAW), oxyfuel

(OFW), torch brazing (TB) and electron beam welding (EBW), etc.


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1.4 DISCONTINUITIES IN METALS AND WELDS

The term 'discontinuity' is used to describe any breakage in the normal physical structure of a

material. A discontinuity in a product may or may not be harmful to the safe operation of the

product. A discontinuity may grow into a defect due to the cyclic loading (fatigue) of the product or

due to the corrosive environment in which the product is working. A small discontinuity started by

corrosion, a slight scratch, or a defect that is inherent in the material, may develop into a crack from

the stress concentration that, under varying loads, propagates with time until there is no longer

sufficient solid material to carry the load. Sudden total failure by fracture then occurs. A

discontinuity is called a defect when it is of such size, shape and location that it creates a substantial

chance of failure of the product in service.

Defects may be classified as follows:

1.4.1 I nh erent defects

These defects are usually formed when the metal is in a molten state. These can be further classified

into categories of (a) inherent wrought defects, and (b) inherent cast defects. Inherent wrought

defects are those defects which occur during the melting and solidification of the original ingot,

while the inherent cast defects are those defects which occur during melting, casting and

solidification of a cast article. Typical defects found in an ingot (Figure 10) are non-metallic

inclusions, porosity and pipe .

Figure 10 Typical defects in an ingot


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1.4.2 Processing defects

These are defects which occur during various manufacturing processes such as welding, forging,

rolling, machining and heat treatment, etc.

1. 4.2.1 Weldin g Defects

A variety of defects occur in welds. Some of these are discussed below:

1.4.2.1.1 Gas inclusions

Gas may develop during welding due to many factors like the quality of the parent metal, the

electrodes used and poor regulation of the arc current, etc. The gas may get entrapped and take

various forms.

i) Gas pore

It is a small bubble of gas entrapped within the molten metal. It has a diameter usually less than 1.6

mm (1/16 inch). A group of gas pores is termed as porosity. The type of porosity within a weld is

usually designated by the amount and distribution of the pores. Some of the types are classified as

follows:

Uniformly scattered porosity: It is characterized by pores scattered uniformly throughout the

weld.

Cluster porosity: It is characterized by cluster of pores that are separated by porosity free areas.

Linear Porosity: It is characterized by pores that are linearly distributed and which generally

occurs in the root pass and is associated with lack of penetration.

ii) Blow hole

It is similar to a gas pore except that it is a little larger in dimension.

1.4.2.1.2 Slag inclusions

Most weld inclusions contain slag that has been trapped in the deposited metal during solidification.

The slag may come from the electrode coating or flux employed. Slag inclusions are frequently

associated with lack of penetration, poor fusion, and oversize root faces, too narrow a groove and

faulty electrode manipulation.


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1.4.2.1..3 Lack of penetration

Frequently the root of a weld will not be adequately filled with weld metal and a void is left. In joints

requiring complete penetration this type of defect is generally not acceptable and requires complete

removal of the weld bead and rewelding.1.4.2.1.4 Lack of fusion

This is due to the lack of union in a weld between the weld metal and parent metal or between parent

metal and parent metal or between weld metal and weld metal. Consequently the lack of fusion can

be of three types namely lack of side fusion, lack of root fusion and lack of inter-run fusion.

1.4.2.1.5 Tungsten inclusion

Tungsten inclusion is characteristic of the inert atmosphere welding methods. If the tungsten

electrode which supports the electric arc comes into contact with the weld metal, some tungsten particles are trapped in the deposited metal. These may be in the form of small splinters or even as

pieces of the tungsten wire.

1.4.2.1.6 Crack

A crack is a discontinuity due to the fracture of the metal during or after solidification. Depending

upon the causes, cracks have been classified as under:

i) Hot tear

This type of crack develops near solidification temperature when the metal is weak. The defect

occurs mainly at, or near, to a change of section and may not be continuous.

ii) Stress crack

A well defined and approximately straight crack, formed due to large stresses after the metal has

become completely solid.

1.4.2.1.7 Root pass oxidation

Oxidation is the result of insufficient protection of the weld and heat affected zone(HAZ) from the

atmosphere. Severe oxidation will occur on stainless steels, for example, reducing corrosion

resistance if the joint is not purged with an inert gas.

1.4.2.1.8 Undercut

During welding of the final or cover pass, the exposed upper edges of the bevelled weld preparation

tend to melt and run down into the deposited metal in the weld groove. Undercutting occurs when


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insufficient filler metal is deposited to fill the resultant grooves at the edge of the weld bead. The

result is a groove that may be intermittent or continuous and parallel to the weld bead. Undercutting

may be caused by excessive welding current, incorrect arc length, high speed or incorrect electrode

manipulation, etc.

1.4.2.1.9 Excessive penetration

In welds, sometimes, molten metal runs through the root of the weld groove producing an excessive

reinforcement at the back side of the weld. In general this is not continuous but has an irregular shape

with characteristic hanging drops of the excess metal.

1.4.2.1.10 Electrode spatter

If improper electrodes or long arcs are used, droplets of molten metal are spattered about the weld

region. These drops stick to the metal surface near the weld seam.

1.4.2.1.11 Grinding marks

When weld reinforcements are not ground out smoothly, the resultant thickness varies above and

below that of the base metal.

1.4.3 Service defects

These are defects which occur due to various service conditions such as corrosion, stress, fatigue,

etc.


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PART-I LIQUID PENETRANT TESTING


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CHAPTER 2: BASIC PRINCIPLES OF LIQUID PENETRANT TESTING

1.0 GENERAL

Liquid penetrant testing, a nondestructive means of locating and determining the severity ofsurface discontinuities in materials, is based upon capillarity. Capillarity, or capillary attraction, is

the action by which the surface of a liquid, where it is in contact with a solid, is elevated or

depressed. The materials, processes, and procedures used in liquid penetrant testing are designed

to facilitate capillarity and to make the results of such action visible and capable of interpretation.

2.0 PHYSICS

2.1 General

The phenomenon of capillary action is one of the most important forces in nature. The rate and

extent of the action associated with capillarity depends upon such factors

as forces of cohesion and adhesion, surface tension, and viscosity.

Capillarity can be observed when a plastic straw is inserted into a glass of

water. When the straw is inserted, the water molecules enter the straw and

begin to attract other nearby molecules, pulling them up the straw by

cohesion. This process continues as the water rises higher and higher. The

water continues to rise until the pull of surface tension is equalized.

Cohesive forces prevent the water from falling back down the straw.

Capillary action as applied in nondestructive testing is somewhat more complex, since various

surface conditions hindering or assisting the action are encountered. Liquid penetrants in

nondestructive testing have low tension and high capillarity. Capillary

action is illustrated in Figure 11.

2.2 Application of Penetrant

In liquid penetrant testing, the liquid penetrant is applied to the surface

of the specimen, and sufficient time is allowed for penetration into

surface discontinuities. (See Figure 12.) If the discontinuity is small or

narrow, as in a crack or pinhole, capillarity assists the penetration. When

the opening is gross in nature, such as a tear, the liquid may be trapped

when poured over the specimen.

Figure 11 Capillary Action

Figure 12 Penetration of SurfaceDiscontinuity


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2.3 Discontinuity Indications

After sufficient time has passed for the penetrant to enter the surface discontinuities, the excess

surface penetrant is removed. The removal .process clears the surface of the specimen but permits

the penetrant in the discontinuities to remain. Capillary action is again employed in the process. Adeveloper -which acts as a blotter is applied to the test surface. (See Figure 13). The blotting action

of the developer draws the penetrant from the discontinuity and the penetrant appears on the

surface of the specimen as an indication. The size of the indication, because of the diffusion of the

penetrant in the developer, is usually larger than the discontinuity. There are also penetrants that

provide sufficient dis continuity indication without the use of a developer; the developer is not

required.

3.0 VISIBILITY OF INDICATIONS

The ultimate success of liquid penetrant testing depends upon the visibility of indications. To

ensure utmost visibility, the liquid penetrant contains either a colored dye easily seen in white

light, or a fluorescent dye visible under black (ultraviolet) light. The dyes are obtainable in a

variety of colors.

4.0 TEST PROCEDURE

The sequence of the test procedure, basically the same for all penetrant tests, can be broken into sixmain steps. These steps are illustrated in Figure 14, where it is shown that:

1. The surface of the specimen is first cleaned and allowed to dry

2. Penetrant is applied to the test surface and allowed sufficient time to seep into openings

3. The penetrant remaining on the surface is removed without removing the penetrant from

openings

Figure 13 Reversed Capillary Action


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5.2 Processes

Processes employing penetrants that are self-emulsifying or removable with plain water are further

classified as water-washable processes. Processes where a separate emulsifier is used to make the

penetrant water washable are referred to as post-emulsified processes. And those processes inwhich the penetrant is removed by a solvent are identified as solvent- removed processes. Figure

15 illustrates the processing sequence used with visible dye and fluorescent penetrants.

Figure 15 Visible Dye and Fluorescent Penetrant Processes

6.0 PROCESS SELECTION

Selection of the suitable penetrant type and process for a particular liquid penetrant test depends

upon

1.The sensitivity required


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Large areas and large volumes of parts/materials can be inspected rapidly and at low cost.

Parts with complex geometric shapes are routinely inspected.

Indications are produced directly on the surface of the part and constitute a visual representationof the flaw.

Aerosol spray cans make penetrant materials very portable.

Penetrant materials and associated equipment are relatively inexpensive.

Primary Disadvantages

Only surface breaking defects can be detected.

Only materials with a relatively nonporous surface can be inspected.

Precleaning is critical since contaminants can mask defects.

Metal smearing from machining, grinding, and grit or vapor blasting must be removed prior to

PT.

The inspector must have direct access to the surface being inspected.

Surface finish and roughness can affect inspection sensitivity.

Multiple process operations must be performed and controlled.

Post cleaning of acceptable parts or materials is required.

Chemical handling and proper disposal is required


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CHAPTER 3: EQUIPMENT AND MATERIALS

3.0 GENERAL

The specific equipment and materials used in any liquid penetrant test are determined by the

inherent requirements of the test procedure; the composition of the article under test; the size of the

article; the frequency of like tests; and the size and type of suspected discontinuities. This chapter

discusses the equipment and materials required to perform the various penetrant tests and the

required pre-cleaning and post-cleaning.

3.1 PRECLEANING AND POSTCLEANING EQUIPMENT

3.1.1. General

Proper cleaning is essential to liquid penetrant testing for two reasons:

1) If the test article is not clean and dry, penetrant testing is ineffective; and

2) If all traces of penetrant test materials are not removed after test, they may have a harmful

effect when the article is placed in service.

All coatings, such as paints, varnishes, plating, and heavy oxides must be removed to ensure that

defects are open to the surface of the part. If the parts have been machined, sanded, or blasted prior

to the penetrant inspection, it is possible that a thin layer of metal may have smeared across the

surface and closed off defects. It is even possible for metal smearing to occur as a result of cleaning

operations such as grit or vapor blasting. This layer of metal smearing must be removed beforeinspection. Common coatings and contaminates that must be removed include: paint, dirt, flux,

scale, varnish, oil, etchant, smut, plating, grease, oxide, wax, decals, machining fluid, rust, and

residue from previous penetrant inspections. Some of these contaminants would obviously prevent

penetrant from entering defects, so it is clear they must be removed. A good cleaning procedure

will remove all contamination from the part and not leave any residue that may interfere with the

inspection process.

The cleaning processes commonly used with penetrant testing are discussed in the following

paragraphs. The equipment and material routinely used with these processes are all that are

necessary for the cleaning required by penetrant testing.

3.1.2. Detergent Cleani ng

Immersion tanks and detergent solutions are a common means of accomplishing the cleaning

required by liquid penetrant tests. The detergents wet, penetrate, emulsify and saponify (change to


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soap) various soils. The only special equipment requirement imposed by penetrant test cleaning is

the need for suitable rinsing and drying facilities. When thoroughly rinsed and dried, detergent

cleaning leaves a test surface that is both physically and chemically clean.

3.1.3 Vapor DegreasingCleaning by vapor degreasing is particularly effective in the removal of oil, grease, and similar

organic contamination. However, there are restrictions as to its use before and after liquid

penetrant testing. Nickel alloys, certain stainless steels, and titanium have an affinity for specific

elements (e.g., sulfur or chlorine) and if exposed to them will become structurally damaged.

Degreasing must be limited to those materials that have been approved for this method of cleaning.

3.1.4. Steam Cleanin g

Steam cleaning equipment is particularly adaptable to the cleaning of large unwieldy articles not

easily cleanable by immersion. No special equipment is required for steam cleaning of articles

destined for liquid penetrant testing.

3.1.5. Solvent Cl eani ng

Solvent cleaning may use tanks for immersion, or the solvent material may be used in a wipe-on

and wipe-off technique. Usually this cleaning process is used only when vapor degreasing,

detergent cleaning, and steam cleaning equipment are not available.

3.1.6. Ultr asonic Cleaning

Ultrasonic agitation is often combined with solvent or detergent cleaning to improve cleaning

efficiency and reduce cleaning time. The equipment is particularly useful in the cleaning of small

articles.

3.1.7. Rust and Sur face Scale Removal

Any good commercially available acid or alkaline rust remover may be used for precleaning.

Required equipment and procedures are as specified in the manufacturer's directions.

3.1.8. Paint Removal

Dissolving type "hot tank" paint strippers and bond release or solvent paint strippers may be usedto remove paint in precleaning. Required equipment and procedures are as specified in the

manufacturer's directions.

3.1.9. Etching

Articles that have been ground or machined often require etching to prepare them for liquid

penetrant testing. This process uses an acid or an alkaline solution to open up grinding burrs and


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remove metal from surface discontinuities. If an acid is used for etching, an alkaline solution is

used as a neutralizing agent; if an alkali is used for etching, an acid is used as a neutralizing agent.

The etching and neutralizing processes use either tanks and immersion or wipe-on and wipe-off

equipment and materials.10. Precleaning Processes To Be Avoided

Blast (shot, sand, grit, or pressure), liquid honing, emery cloth, wire brushes and metal scrapers

should not be employed with liquid penetrant testing. These processes tend to close discontinuities

by peening or cold working the surface. On occasion a wire brush may be helpful in removing rust,

surface scale, or paint but it is used only when no other means of removal will suffice.

3.2 STATIONARY PENETRANT TEST EQUIPMENT

3.2. 1. General

The stationary equipment used in liquid penetrant testing ranges from the simple to fully automatic

systems and varies in size, layout, and arrangement depending on the requirements of specific

tests. The size of the equipment used is largely dependent upon the size and types of articles to be

tested. The layout of the equipment, i.e., whether a "U," "L," or straight line, is determined by

the facilities available, the production rate, and the required ease of handling. The number of

stations is dependent on the process used.

3.2.2. Stati ons

Depending on the type penetrant and processing employed (see Figures 16) the liquid penetrant

test facility requires certain stations. The required equipment components (stations) are combined

to suit the particular test process. In a typical testing facility for a post-emulsification process, the

following stations are required:

1. Pre cleaning Station (usually remote from penetrant test station).

2. Penetrant Station (tank).

3. Drain Station (used with penetrant tank)

4. Emulsifier Station (tank).

5. Rinse Station (tank).

6. Developer Station (tank).

7. Dryer Station (usually an oven type).


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8. Inspection Station(enclosed booth or table with proper lighting

9. Post cleaning station (usually in remote area)

Figure 16 Typical Small - Sized Test Equipment Employing Fluorescent Post - Emuslsified

Penetrant and Dry Developer

3.2.3 Auxi li ary EquipmentFor the purpose of this handbook, auxiliary equipment is defined as the equipment located at

penetrant test stations (other than cleaning stations) required to perform penetrant testing. The

auxiliary equipment discussed may in some instances be "built-in" at one or more of the test

stations.

a. Pumps. Various pumps installed at the penetrant, emulsifier, rinse, and developer stations are

used to agitate the solutions, to pump drain-off material into the proper tank for reuse, and to

power hand-held sprayers and applicators.

b. Sprayers and Applicators Sprayers and applicators are frequently employed at the penetrant,

emulsifier, rinse, and developer stations. They decrease test time by permitting rapid and even

application of penetrant materials and water rinse. Both conventional and electrostatic sprayers are

used.


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c. Lights. White lights as well as black lights are installed as required to ensure adequate and

correct lighting at all stations. When fluorescent materials are used, black light is installed at both

the rinse and inspection stations.

d. Timers. One or more 60-minute timers with alarm are used to control penetrant, emulsifier,developing, and drying cycles.

e. Thermostats and Thermometers. These items are required and u sed to control the temperature of

the drying oven and penetrant materials.

f.Exhaust Fans. Exhaust fans are used when testing is performed in closed areas. The fans facilitate

removal of fumes and dust.

g.Hydrometers. The hydrometers used in liquid penetrant testing are floating type instruments.

(See Figure 17.) They are used to measure the specific gravity of water-based wet developers.

Figure 17 Typical Hydrometer

3.3 Portable Penetrant Test Equipment

3.3.1. General

It is possible to perform penetrant tests on a limited basis without stationary equipment. When

testing is required at a location remote from stationary equipment, or when only a small portion of

a large specimen requires test, portable liquid penetrant kits are used. Both fluorescent and

visible dye penetrants are available in kits. The penetrant materials are usually dispensed from

pressurized spray cans or applied by brush.3.3.2. Visibl e Dye Penetrant Ki t

The visible dye penetrant test kit is light in weight and contains all the materials necessary for test.

(See Figure 18.) It consists of a metal box with at least the following

1. Solvent cleaner or penetrant remover.

2. Visible dye penetrant


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3. Non-aqueous wet developer

4. Wiping cloths and brushes

3.3.3. F lu orescent Penetrant Ki t

The fluorescent penetrant kit combines portability with the high "seeability" associated with

fluorescent materials. The kit holds all the essential materials required for test, including a black

light. (See Figure 19.) The fluorescent kit consists of a metal box with at least the following:

1. Portable black light and transformer

2. Solvent cleaner or penetrant remover3. Fluorescent penetrant

4. Nonaqueous wet developer

5. Dry powder developer

6. Wiping cloths and brushes

7. Hood to provide darkened area for

viewing indications.

3.4 BLACK LIGHT

Black light equipment is required in fluorescent penetrant testing, since it supplies light of the

correct wavelengths to cause fluorescent materials to fluoresce. The equipment usually consists of

a current regulating transformer, a mercury arc bulb, and a filter (see Figure 20). The transformer is

housed separately and the bulb and filter are contained in a reflector lamp unit. For correct test

Figure 18 Typical Visible Dye Portable Kit

Figure 19 Typical Fluorescent Portable Kit


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results the lamp should produce an intensity of

at least 800 microwatts per square centimeter

at the test surface. The deep red-purple filter is

designed to pass only those wavelengths oflight that will activate the fluorescent material.

It also filters out harmful ultraviolet radiation.

Since dust, dirt, and oil greatly reduce the

intensity of the emitted light, the filter should

be frequently cleaned. In use, the full intensity

of the lamp is not attained until the mercury arc is sufficiently heated. At least 5 minutes warm up

is required to reach the required arc temperature. Since switching the lamp on and off shortens bulb

life, once turned on the lamp is usually left on during the entire test or work period. If the black

light is switched off, it may take up to 10 minutes for the bulb to cool sufficiently to reestablish an

arc.

3.5 MATERIALS

3.5.1 General

The materials used in liquid penetrant testing include penetrants, emulsifiers, removers or

cleaners, and developers. They are furnished in either liquid or powder form. The powders except

those used in the dry state are mixed with a suitable liquid (usually water) prior to use. Most of the

materials are available in pressurized spray cans as well as in bulk quantities. Concentrations,

usage, and maintenance are in accordance with the manufacturer's directions. Figure 21 illustrates

the different material combinations and usages.

3.5.2 Precleaning and Postcleanin g M ater ial s

Except for LOX compatibility, and the chlorine-free requirement in the precleaning and

postcleaning of nickel alloys, certain stainless steels, and titanium, no special cleaning materials

are required with liquid penetrant testing.3.5.3. Water -Washable Penetrants

Water-washable penetrants are highly penetrating oily liquids containing an emulsifying agent that

renders the oily vehicle emulsifiable in water. The simplest to use but least sensitive of these

penetrants are the visible dye or color contrast penetrants. They contain a dye, usually a bright red

but sometimes a special color such as blue, that can be seen under ordinary white (visible) light.

Figure 20 Typical Portable Black Light


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Greatest "seeability" is obtained with fluorescent penetrants that are viewed under black light. The

color of fluorescence is usually a brilliant yellowish green. For special applications, there are

fluorescent penetrants that glow red or blue. The dual sensitivity penetrants contain a combination

of visible and fluorescent dyes. The visible color is usually a bright red and the fluorescent color ayellow to orange-red. They permit gross discontinuities to be detected under visible light and

questionable indications to be resolved under black light.

3.5.4. Post-Emulsif ication (Solvent Removable) Penetrants

Post-emulsification penetrants have similar formulations to those of water- washable penetrants

except they do not contain the emulsifying agent and consequently are not soluble in water. These

penetrants must be treated with a separate emulsifier before they can be removed by a water rinse

or wash. Or they can be removed using an approved solvent remover or cleaner.

Post-emulsification penetrants are available as either visible dye or fluorescent penetrants.

3.5.5. Emul sif iers

Emulsifiers when applied to a post-emulsification penetrant combine with the penetrant so as to

make the resultant mixture water washable. The emulsifier, usually dyed orange to contrast with

the penetrant, may be either lipophilic -an oil base, or hydrophilic -a detergent water base. The

oil-based emulsifiers are usually employed as "contact" emulsifiers, i.e., they begin emulsifying on

contact with the penetrant. Emulsification stops when water is applied. The hydrophilic or

water-based emulsifiers also can be used as contact emulsifiers; but more often, the emulsifier is

diluted with water and sprayed under pressure.

3.5.6. Solvent Removers (Cl eaners)

Solvent removers or cleaners are used in conjunction with post- emulsification penetrants to

remove excess penetrant from test article surfaces. Example solvent removers include methylene

chloride, isopropyl alcohol, naphtha, mineral spirits (paint thinner) in addition to special- formula,

proprietary removers. In selecting a solvent remover, only those materials approved by the

penetrant manufacturer can be used.3.5.7. Dry Developer

Dry developer is a fluffy chalk-like powder that is applied to dry test surfaces (after the removal of

excess penetrant) for the purpose of absorbing penetrant from discontinuities and enhancing the

resultant penetrant indications. Of the different developers available, dry developer is the most

adaptable to rough surfaces and automatic processing. It's also the easiest to remove. Sensitivity is


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Figure 21 Penetrant Material Combination and Usages

about the same as that of the water soluble developer described in the following paragraph.

3.5.8 Water -Based Wet Developers

Water-based wet developers function similarly to dry developer except they are applied prior to

drying the test specimen. Two types of developer are available. In one, the developer particles are

held in suspension in water and require continuous agitation to keep the particles in suspension. In

the other, the developer powder is dissolved in water, forming a solution; once mixed they remain

mixed. Of the two water-based wet developers, the water-soluble developer is the more sensitive.


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3.5.9. Non aqueous Wet Developer

Non aqueous wet developer is a suspension of developer particles in a rapid- drying solvent. It is

most often employed with solvent-removableprocessing, and like dry developer, is applied only to

dry surfaces. Of all the developers, the non aqueous wet developer is the most sensitive indetecting fine discontinuities. The evaporation of the solvent carrier helps to draw- the penetrant

from discontinuities.

3.5.10. Special -Purpose Penetrant M aterials

In addition to the conventional penetrants, emulsifiers, removers, and developers employed in

liquid penetrant testing there are low sulfur and chlorine materials for testing nickel alloys, certain

stainless steels, and titanium. Special-purpose inert materials are available for testing articles that

come in contact with liquid oxygen, rubber, or plastic. Food compatible materials are also

available. There are high temperature penetrants for testing hot welds, etc., and special penetrants

for testing at low temperatures. There are supersensitive penetrants for detecting extremely fine

discontinuities, and penetrants that provide sufficient contrast and sensitivity without a developer.

There are low-energy emulsifiers and inhibited-solvent removers to slow down emulsification and

the removal of excess penetrant. There are also wax and plastic film developers that absorb and fix

penetrant indications to provide permanent records. The selection and usage of these materials is

largely dependent on the particular process used and the controlling specifications or standards.


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CHAPTER 4: TECHNIQUES

4.0 GENERAL

The techniques discussed in this chapter are based on typical liquid penetrant testing procedures

used throughout industry. Included are techniques involving the use of visible dye, fluorescent,and dual sensitivity penetrants; and water-washable, post-emulsified, and

solvent-removableprocessing. Also included are discussions on the fixing and recording of

indications.

4.1 SURFACE PREPARATION

4.1.1. General

The effectiveness of liquid penetrant testing is based upon the ability of the penetrant to entersurface discontinuities. The article to be tested must be clean and free from foreign matter. All

paint, carbon, oil, varnish, oxide, plating, water, dirt, and similar coatings must be removed prior to

the application of penetrant. The cleaning technique used is, in each case, determined by the

composition of the article under test and the type of soil to be removed. Any cleaning process that

leaves the surface of the article clean and dry, that does not harm the article, and that does not use

materials that are incompatible with the penetrant materials, is acceptable. Following the test,

postcleaning is employed to remove the residue of penetrant materials. Postcleaning is particularly

important when test articles are destined for use in an oxygen environment. Though many

specimens will receive further processing, such as etching or special cleaning prior to use, the

cleanliness of any specimen after completion of a penetrant test is the responsibility of test

personnel.

4.1.2. Detergent Cleani ng

Detergent cleaning may be used to clean almost any specimen. Since the cleaners may be either

acid or alkaline in nature, however, precautions must be taken to ensure that the selected detergent

is noncorrosive to the specimen being cleaned. Detergent cleaning is most effective when it is a hot

process accomplished in a washing machine, though it may also be used with scrub, rinse, and

wipe techniques. After detergent cleaning, the specimen is carefully rinsed and dried. The drying

process should be of sufficient time duration that all moisture is driven from the discontinuities.


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4.1.3 Vapor Degreasing

Vapor degreasing is also an effective means of precleaning. The process not only thoroughly

cleans; it heats the article so that after cleaning no moisture remains in discontinuities. Vapor

degreasing is the preferred method for removing organic soils such as oil and grease and should beused whenever practicable. The only precaution required in the use of the process is that caused by

the need of using only those degreasing materials that are not harmful to the specimen being cleaned.

4.1.4. Steam Cleanin g

Steam cleaning is an excellent method of cleaning usually employed to clean large articles, or

portions of large articles, that cannot conveniently be vapor degreased or washed with detergents.

Routine steam cleaning procedures usually suffice for penetrant precleaning. As with any cleaning

process involving water, the specimen must be thoroughly dried after the cleaning process is

completed.

4.1.5. Ultr asonic Cleaning

Ultrasonic cleaning is often combined with a solvent or detergent bath to improve cleaning

efficiency and reduce cleaning time. The method works best with water and detergent cleaning

when contaminants to be removed are inorganic, and with solvents when contaminants are

organic. Following cleaning, it is recommended that test articles be heated to aid the evaporation of

cleaning fluids.

4.1.6. Rust and Sur face Scale Removal

Rust removers (descaling solutions, either alkaline or acid), pickling solutions (acid), and

sometimes wire brushing are used to remove rust and surface scale. Wire brushing is accomplished

with a minimum of pressure to avoid closing surface discontinuities or filling them with smeared

metal. Descaling solutions are chosen so that they are noncorrosive to the article being cleaned.

Regardless of the method selected for rust and scale removal, after the process is completed the

specimen must be clean, dry, and so treated that surface discontinuities are not clogged, filled, or

contaminated.

4.1.7. Pain t Removal

Any method of paint removal that does not harm the test article is satisfactory. Chemical means

such as solvent stripping and dissolving type hot- tank stripping are preferred since any


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mechanical removal process may adversely affect the surface of the specimen.

Any method of paint removal that does not harm the test article is satisfactory. Chemical means

such as solvent stripping and dissolving type hot- tank stripping are preferred since any

mechanical removal process may adversely affect the surface of the specimen.

4.1.8. Etching

Etching is normally required on soft metallic materials (such as aluminum and magnesium) and

materials that tend to smear (such as titanium), and which have been mechanically processed by

machining, grinding, or similar procedure. The etching is accomplished with either an acid or an

alkaline solution, which is then neutralized. After neutralization, the article must be water washed

and dried, or otherwise cleaned, to remove all traces of the etching and neutralizing agents.

4.2 APPLICATION OF PENETRANTS

4.2.1. General

Penetrants are applied by spraying, swabbing, brushing, or dipping (immersion). The area under

test is covered with penetrant and the penetrant is allowed to remain for a predetermined amount of

time called "dwell time." The means of application and the length of dwell are determined by the

test article, the type discontinuities to be detected, the penetrant used, and temperature. The

terminology used in penetrant application is listed in Table-1.Table 1 Liquid Penetrant Application Technology

4.2.2. Spraying

Spraying of penetrant when accomplished at the penetrant tank of stationary equipment refers to

the use of a hose and nozzle through which penetrant is circulated by a low pressure pump -usually


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the same pump that agitates the penetrant solution in the tank. The penetrant is flowed on the

specimen so that all of the test area is covered. No particular precautions except those of

cleanliness and neatness need be observed in this flow-on process. Spraying also is used to define

the application of penetrant from pressurized spray cans. Again the penetrant is applied so that allof the test area is covered, but personnel must make allowances for the pressure remaining in the

can and the distance the can is held from the specimen. Usually, pressurized spray cans are used in

areas where fans or blowers remove fumes, or in open areas where spot testing (testing a small area

of a large specimen) is taking place.

4.2.3. Swabbin g or Bru shi ng

Penetrants may be applied by swabbing with rags or cotton waste, or by brushing. Either method is

acceptable when spray or dip equipment is not available. Usually, swabbing or brushing is used

when testing a small, specific area of the specimen.

4.2.4. I mmersion

The best procedure for applying penetrant is to immerse the test article or specimen into a tank of

penetrant. Small specimens are placed in an open wire basket for dipping; large specimens are

handled by hand or, if required, by cranes and suitable clamping devices. This method is

impractical when dealing with large articles or assemblies, and is wasteful when only small areas

of a large specimen are to be tested. It is, however, the most thorough, and certain, means ofapplying penetrant and is used whenever possible.

4.2.5. Penetration (Dwell ) Ti me

The period of time during which the penetrant is permitted to remain on the specimen is a vital part

of the test. This time, known as dwell time, is directly related to the size and shape of the

discontinuities anticipated, since the dimensions of the discontinuities determine the rapidity with

which penetration occurs. Tight crack like discontinuities may require in excess of 30 minutes for

penetration to an extent that an adequate indication can be expected. Gross discontinuities may be

suitably penetrated in 3 to 5 minutes. Dwell time in each instance is determined by the anticipated

discontinuities and the penetrant manufacturer's recommendations. Typical minimum penetration

times are shown in Table 1A.

a) Heating the test specimen accelerates penetration and shortens dwell time. The practice,

however, is generally not recommended since heating may cause evaporation of penetrant


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and thereby reduce sensitivity.

b) Ambient temperature and humidity also affect penetration time. Generally, the higher the

ambient temperature, the shorter the dwell time required. Too high a temperature or too

Iowa humidity, however, causes the penetrant to dry too rapidly and testing becomesdifficult if not impossible. For liquid penetrant testing to be reliable, the penetrant must

remain wet. This sometimes requires the rewetting of test surfaces. If the penetrant has

been allowed to dry, the test must be started over beginning with surface preparation.

4.4 REMOV AL OF PENETRANTS

4.4.1. General

Following application of the penetrant and elapse of sufficient time for penetration, the penetrant is

removed from the surface of the specimen. This operation is meant to remove the penetrant from

the surface without disturbing any penetrant that has entered a discontinuity. Complete removal of

the surface penetrant is effected to ensure against formation of non relevant indications.

4.4.2. Water-Washable Process

The penetrants employed in the water-washable process have their own built-in emulsifier. The

penetrant is soluble in water and removal is usually accomplished by a water rinse. Care is taken in

applying the rinse to ensure that the spray volume and force does not wash the penetrant from

discontinuities. Thirty to fifty pounds per square inch maximum pressure (205 to 345 kPa) is

considered a safe pressure for the water rinse. The rinse is applied through the use of an adjustable

spray nozzle held so that the spray reaches the surface plane of the specimen at an angle of 45

degrees.

4.4.3. Post-Emulsif ied Process

The penetrants employed in the post-emulsified process do not contain an emulsifying agent. The

penetrant is not soluble in water. Removal is in most instances a two-step process. The emulsifier,

usually lipophilic (an oil base), is applied as described in paragraph 4.3 and, after suitable dwelltime, the resultant penetrant-emulsifier mixture is removed by water rinse as described in

paragraph 4.4.2. Sometimes a hydrophilic (water base) emulsifier is diluted to the point that simple

contact with penetrant does not make the penetrant water washable. Application must be

accompanied by some form of mechanical agitation or scrubbing. Usually, the emulsifier is added

to the water rinse and sprayed under pressure. By controlling solution strength and the duration of


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Table 1A: TYPICAL MINIMUM PENETRATION TIMES


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spray, the amount of penetrant removed is controlled.

4.4.4. Solvent-Removable Process

Post-emulsification type penetrants are also employed in the solvent- removable process. The

penetrant remover is a solvent designated by the penetrant manufacturer. Prior to the use of thesolvent, excess penetrant is wiped off; the specimen is then cleaned with clean, lint-free towels

dampened with solvent. The solvent is never applied directly to the specimen since it might wash

out or dilute the penetrant in a discontinuity.

4.4.5. Visual I nspection

Excess surface penetrant can result in the formation of nonrelevant indications that could obscure

or hide true discontinuity indications. When fluorescent penetrants are used, it is necessary to

observe the specimen under black light during the penetrant removal operation to ensure complete

removal of excess penetrant. For visible dye penetrants, the absence of penetrant (red) traces on the

wiping materials ensures complete penetrant removal.

4.5 APPLICATION OF DEVELOPER

4.5. 1. General

As mentioned in previous chapters, some penetrants provide sufficient discontinuity indications

without a developer. They are self-developing. But generally, when maximum sensitivity is

desired, a developer is required. The developer assists in the detection of penetrant retained in

discontinuities by aiding in the capillary bleed-out process (the developer acts as a blotting agent),

and by accentuating the presence of penetrant in a discontinuity. Developer accentuates the

presence of a discontinuity because it causes the penetrant from the discontinuity to spread out

over a greater area. It also serves as a color contrast background for the visible dye used in the

visible dye processes and for the fluorescent material used in the fluorescent processes. Developer

is available in both dry and liquid forms and the selection of developer is in accordance with the

manufacturer's recommendation for the type penetrant used. When a dry or non- aqueous wetdeveloper is used, the specimen must be completely dry before the developer is applied. When a

water-based wet developer is used, it is applied immediately after penetrant removal is

accomplished and prior to the drying operation.

4.5.2. Dry Developer

Dry developer, being a loose, fluffy talcose powder with high absorbent properties, is applied to a


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specimen by dusting, blowing, or dipping the specimen. The application is usually accomplished

in a booth with a blower or fan arrangement that removes loose powder from the atmosphere. No

preparation of the powder is necessary and the only requirement is that it be evenly distributed

over the test surface, which must be completely dry.4.5.3. Non-aqueous Wet Developer

Non-aqueous wet developer is a suspension of absorptive white powder in a solvent vehicle. It is

usually applied by spraying from a pressurized spray can or other spraying device such as a paint

spray gun. When used in bulk form, care must be exercised to keep the powder thoroughly mixed

in the solvent. The developer is applied so as to form a thin white coating on the specimen without

soaking the test surface. When properly mixed and applied, non-aqueous wet developer is the most

sensitive of all the developers in detecting fine discontinuities.

4.5.4. Water-Based Wet Developer

Water-based wet developer may be either a suspension of absorptive white powder in water, or a

water-soluble absorptive white powder mixed with water. The suspension type requires mild

agitation prior to and during use to keep the powder particles in suspension; the water-soluble

developer does not. The water-soluble powder, once mixed with the water, remains in solution.

After excess penetrant is removed from the specimen, and while it is still wet, wet developer is

applied by either dip (immersion), flow-on, or spray techniques. These fast and effective methods

of application, combined with the time saved by applying developer to the wet specimen, make

water-based wet developer well suited for use in rapid, production"' line testing. Wet developer is

applied so as to form a smooth, even coating, and particular care is taken to avoid concentrations of

developer in dished or hollowed areas of the specimen. Such concentrations of developer mask

penetrant indications and are to be avoided.

4.6 DRYING

When dry or non-aqueous wet developer is used, the specimen is dried after removal of excess penetrant and prior to application of the developer. When water-based wet developer is used, the

specimen is dried after the developer has been applied. Any means of drying that does not interfere

with the test process by overheating, or by contamination of materials, is acceptable, but controlled

drying at even regulated temperatures is preferred. A thermostat controlled dryer with a

temperature range up to 225 0F (107 0C) is usually employed in stationary test installations.


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Required drying time is determined by the size and shape of the specimen, and by the nature of its

suspected discontinuities. It should be of sufficient duration to dry the surface of the specimen

without affecting the penetrant in the discontinuities.

4.7 PENETRANT TESTING PROCESSES

4.7.1. General

The different processes employed in liquid penetrant testing are identified by the method of

penetrant removal used (water-washable, post-emulsified, or solvent-removed) and the type of dye

(visible dye (color contrast), fluorescent, or dual sensitivity). The basic steps involved are

illustrated in Figure 22 while step-by-step procedures are contained in the following paragraph.

Table 2 lists the preferred processes for various penetrant test problems.

Figure 22 Water Washable and Solvent RemovableProcesses

4.7.2. Water-Washabl e F luor escent Penetran t Test

The characteristic advantages and disadvantages of water-washable fluorescent penetrant tests are

listed in Table 3.

a. Penetrant Application. Either immersion, flow-on, spray, or brushing technique is used to

apply the penetrant to the precleaned, dry specimen. The penetrant is applied evenly over the entire

test area.


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b. Dwell Time. The penetrant is left on the specimen for the required length of dwell time. A

broad guide to correct dwell time is contained in Table 4-2 but the specimen size, composition, and

discontinuities, and the temperature of the specimen and the test area all affect required dwell time.

Table 2 Process Selection Guide


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Table 3 Characteristics of Water-Washable Fluorescent Penetrant Tests

c. Penetrant Removal. Excess penetrant (all penetrant except that in discontinuities) is washed

from the specimen after dwell time has elapsed. Water at 60 to 110 0F (16 to 43 0C) and a pressure

not exceeding 50 psi (345 kPa) is applied from a spray nozzle. The nozzle is held so that the water

strikes the surface of the specimen at an angle of approximately 45 degrees. Care is taken to avoid

over-washing, which causes washout of penetrant from discontinuities. The wash process is

accomplished under black light so that the operator can observe when the excess penetrant is

completely removed.

d. Drying. Upon completion of the wash process the specimen is dried prior to the application of

either dry or non-aqueous wet developer. If water-based wet developer is used, it is applied to the

still damp specimen immediately after the penetrant removal wash. Drying is best accomplished in

a thermostat- controlled oven at a temperature between 15 0 and 225 0F (66 to 107 0C). Drying time

is determined by the size and composition of the specimen, and visual observation usually fixes the

length of the drying cycle. Excessive heat or too long a drying time tends to bake the penetrant out

of discontinuities.e. Developer Application. When the drying process is complete the specimen is ready for the

application of either dry or non- aqueous wet developer. When water-based wet developer is used,

it is applied to the wet specimen immediately after excess penetrant is removed.

(i) Dry developer is applied to the specimen by brushing with a soft brush, by use of a powder gun,

or by dipping the specimen in a tank of the developer, and removing excess powder with a low


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pressure air flow.

(ii) Non aqueous wet developer is applied by spraying. It is applied sparingly so that a thin coating

covers all of the specimen test area. When using non aqueous wet developer the specimen is to be

cool enough to prevent too rapid evaporation of the developer vehicle.(iii) Water-based wet developer is applied to the specimen as it comes from the wash cycle, either

by immersion or flow-on. The developer is applied so as to form a smooth even coating over the

entire test area. After the developer is applied, the specimen is dried as described in paragraph

4.7.2.d.

f. Inspection. After sufficient time has passed for developer action to bring the penetrant from

discontinuities as indications, the specimen is ready for inspection under black light. The

interpretation of various indications discovered during inspection is discussed in Chapter 5. The

efficiency of the inspection operation is controlled by the variables of the human eye. These

variables are further complicated by the average person's lack of understanding of eye fatigue and

of the time required for the iris of the eye to dilate to a point of maximum vision in the darkness of

the black light inspection booth. For maximum visual efficiency the operator must:

(i) Let eyes become accustomed to the darkness by entering the darkened area (booth) at least 5

minutes prior to examining the specimen under the black light.

(ii) Avoid looking directly into the black light source since the eyeball contains a fluid that

fluoresces if black light shines directly into the eye.

4.3. Post-Emulsified Fluorescent Penetrant Test

The characteristic advantages and disadvantages of post-emulsified fluorescent penetrant tests are

listed in Table 4-5. This process is identical with that of the water-washable fluorescent penetrant

test except for the inclusion of an emulsification step after the completion of penetrant dwell time

and before penetrant removal.Table 4 Characteristics of Post-Emulsified Fluorescent Penetrant Tests


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a. Penetrant Application. See paragraph 4.7.2.a.

b. Dwell Time. See paragraph 4.7.2.b.

c. Emulsifier Application. After the elapse of sufficient dwell time, emulsifier is applied to the

penetrant coated specimen. Immersion, flow-on, or spray technique is used to apply the emulsifierin an even coating. The particular technique employed is determined by the number and size of the

specimens under test.

d. Emulsifier Dwell Time. The length of time the emulsifier is left to dwell before commencing the

penetrant removal cycle is determined by the emulsifier used and the type discontinuities

suspected. Detection of shallow, wide dents, machine marks, and nicks requires a minimum

emulsification time. Detection of fine, light cracks requires emulsification time of sufficient

duration that superficial discontinuities are washed clean during the penetrant removal, but the

time is not to be so long that the penetrant in the cracks is affected. One to 3 minutes emulsification

dwell time is usually required, though rough surfaced articles may require 5 minutes or more.

Actual time must be determined by experiment

e. Penetrant Removal. See paragraph 4.7.2.c.

f. Drying. See paragraph 4.7.2.d.

g. Developer Application. See paragraph 4.7.2.e.

h. Inspection. See paragraph 4.7.2.f.

4.4. Solvent-RemovableFluorescent Penetrant Test

The characteristic advantages and disadvantages of solvent-removablefluorescent penetrant tests

are listed in Table 5.Table 5 Characteristics of Solvent -RemovableFluorescent Penetrant Tests


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a. Penetrant Application. Solvent-removablepenetrant may be applied by brush-on technique but

is more often applied by use of a spray gun or pressurized spray can. With any application process,

correct application covers the test surface with an even coat of penetrant. When a spray gun or

pressurized can is used, the gun or can is held approximately 12 inches (30 cm) from the specimenand moved slowly from side to side until the specimen is evenly coated.

b. Dwell Time. See paragraph 4.7.2.b.

c. Penetrant Removal. Excess penetrant is removed from the specimen, after suitable dwell time

has elapsed, by wiping with absorbent, lint-free towels. After the bulk of the excess penetrant is

wiped off, clean, lint-free towels are moistened with the companion solvent of the penetrant

(solvent specified by the penetrant manufacturer) and the specimen is wiped clean. Solvent is

never applied directly to the specimen. The removal process is accomplished under black light so

the operator can observe that all excess penetrant is removed.

d. Developer Application Usually only dry or nonaqueous wet developer is used with solvent

removablepenetrants. A thin coating of developer is either dusted or Sprayed on the test area of the

specimen.

e. Inpection See paragraph 4.7.2.f

4.5. Visible Dye Penetrant Tests

The characteristic advantages and disadvantages of visible dye penetrants are the same as those

listed in Tables 4-4, 4-5, and 4-6 for their fluorescent counterparts, except that visible dye

penetrants are less sensitive, not as brilliantly visible, and do not require the use of black light.

a. Water Washable Visible Dye Penetrant Test Procedures for use of water-washable visible dye

penetrants are identical with those listed in paragraphs 4.7.2.a through f, except there is no

black light requirement.

b. Post Emulsified Visible Dye Penetrant Test. Procedures for use of post-emulsified visible dye

penetrants are identical with I those listed in paragraphs 4.7.3.a through h, except there is no blacklight requirement.

c. Solvent RemovableV

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