Non-Destructive Testing and Inspection

Non-destructive testing (NDT) is a procedure which is a combination of analysis techniques that is used to find out more about the properties of a number of materials, parts, products, welds, or systems without causing any harm to the integrity of the unit while undergoing the test.

NDT laboratories are a great help for a number of industries that includes civil, forensic, mechanical, electrical, systems, aerospace and aeronautical engineering, and even various medical applications.
The two terms namely NDI, non-destructive inspection and NDE or Non-destructive evaluation can help describe the various testing methodology of non-destructive testing.

The Different Kind of NDT Techniques or Inspection
There are various conventional methods of training techniques that have over the year have changed and developed a lot and have become well-documented with different codes, standards, and best practices.  The setup of a conventional technique is rather simple in comparison to advanced methods. Some of the testing methods are as follows,

The Conventional Techniques

• Acoustic Emission Testing or AET
• Leak testing or LT
• Infrared Testing or IR
• Electromagnetic testing or ET
• Liquid Penetrant Testing or LPT
• Magnetic Particle Testing or MPT
• Radiographic Testing or RT
• Ultrasonic Testing or UT
• Film Radiography or FR
• Vibration Analysis or VA
• Visual Inspection or VI
• Straight Beam

Advanced NDT Techniques

Advanced  methods are slightly more difficult to understand as they are emerging technologies and may have certain limitations as they lack technician qualification criteria and no industry codification.

As far as advanced techniques are concerned, only an expert technician can interpret the data, understand the setup and hence cater to such advanced NDT techniques.

Also, there are some methods, which can be further broken down into both conventional and advanced techniques. Like if you consider two forms of ultrasonic testing, for example, straight beam ultrasonic testing (UT) which is a conventional technique used in simple applications and then there is phased array ultrasonic testing (PAUT) which can be regarded as an advanced UT technique.

Advantages of Non-destructive Training over Destructive Training

There is no doubt that NDT boasts of a myriad of advantages over destructive testing. We must first focus on the testing equipment of NDT testing which is often portable and can be performed more than once on a single component.

The component can then be evaluated minutely both externally and internally for any kind of flaws which may prove to be detrimental to the component.

The only disadvantage of NDT is that the results are more qualitative and can be repeated and interpreted differently with varying results by various inspectors.

 The Various Industry Applications of NDT

NDT inspections are a part of a number of industries and that includes the oil and gas and petrochemical industries, along with other industries such as automotive, chemicals, aerospace, and defense. So, the only way to detect and reduce flaws is by including NDT tests.

Some Considerations before Undergoing an NDT Testing

When you plan an NDT inspection, there are four considerations that you must keep in mind,

• The different types of damage mechanism which has to be inspected for.
• The orientation of the defect along with the shape and size of the flaw.
• The location of the defect and whether it is external or internal.
• The various limitations of the NDT method

Having considered the above factors the operators can optimize the production of facilities and increase both personnel and environmental safety.

Applications of NDT in Aerospace Industry

Non Destructive Testing Applications in Aerospace

Non-Destructive Testing occupied very important role in recent times in industrial applications like Aerospace, aircraft overhaul, automotive, petrochemical and gas, railway, mining, agriculture, power generation, iron, shipbuilding, steel, pipe and tube manufacturing industries etc as a powerful quality tool. Mainly in Aerospace industry in view of high quality requirements safety and stringent Airworthiness requirements. All components are inspected before they are assembled into the aircraft and then they are periodically inspected throughout their useful life.

Most of the inspections done to an aircraft are visual inspections. During heavy maintenance work, much of the interior of the aircraft is stripped out so inspectors can look for damage on the inside surface of the fuselage. Aircraft suffer many types of structural deterioration including corrosion, fatigue, fabrication defects, operation and maintenance, and unforeseen loading. In aircraft maintenance, it is critical to inspect surfaces for any damage that may exist in order to determine the extent of repair work needed, whether that occurs as the result of manufacturing or while the aircraft is in service.


Non-destructive testing (NDT) is one of the quick and most economical ways to perform inspections in Scheduled maintenance and the only way to discover defects that are not visible to the naked eye.

NDT Methods Used in the Aerospace Industry
Several types of non destructive testing methods like liquid penetrant testing, ultrasonic testing, magnetic particle testing and eddy current testing are used to test airplanes.

Liquid Penetrant Testing (LPT)
To reveal the cracks on the surface of airplane, Liquid penetrant testing is one of the most commonly used method in NDT in aerospace industry.

“The fundamental purpose of penetrant testing is to increase the visible contrast between a discontinuity and its background,” said a report on NDT techniques used in the aerospace industry.
Structural damages or surface defects of aircraft materials were observed with LPT. Fluorescent penetrants are used in critical areas for more sensitive evaluation.
Ultrasonic Testing (UT)
The most common sub-surface inspection technique, ultrasonic NDT uses high-frequency sound waves to locate defects under the surface.UT has many uses in the aerospace industry including detection of:

Surface and subsurface defects in welds;
Main structural fittings of landing gear legs and engine attachments;
Aircraft structure joints and pylons;
Bolts located in critical areas;
Adhesive bond quality of lap joints and composite structure;
Thickness measurement after damage or corrosion removal.


Magnetic Particle Testing (MPT)
In magnetic particle testing, fine particles are applied to the surface to monitor magnetic flux. If damage exists, flux “leaks” from the item’s surface, attracting particles to the area.
In the aircraft, MPT is conducted on engines, pumps, landing gear, gearboxes, shafts, and shock struts. It is also widely used for bolt inspection.
Obviously, this task requires trained professionals who are capable of performing a variety of different NDT techniques to get a complete and accurate status of the airplane.
Eddy current Testing (ECT)
In any aerospace maintenance and repair organization Eddy current testing plays an important role.

Eddy current testing is used in Surface Crack Detection on Aluminum alloys
Intersect the inner surface of holes in the component to be inspected.
Automated Inspection of Aircraft Wheels / Wheel Hub / Rotor Disc
Subsurface Corrosion Detection
There is no question that the success of the airplane industry is dependent on NDT. Without NDT, the cost of maintaining and flying in airplanes would increase dramatically, while the safety of flying would decrease. When people step into an airplane they trust that it will get them to their destination with as little turbulence as possible. NDT plays a vital role in keeping air travel one of the safest modes of transportation.

Subjective and Objective Visual Acuity Testing Techniques

The Future NDT institute in Hyderabad is a reputed institute, which caters to millions of NDT jobs in Hyderabad and all over the world. Here students are trained with various engineering skills such as welding, piping, quality audit and NDT. Besides the expert faculty also teaches other practical skill sets such as visual inspection, radiography testing, ultra sound testing, magnetic particles testing and so on. One can also get NDT training in Chennai, from Future NDT institute in Chennai.

Visual testing (VT)

Visual testing is one of the significant courses taught as a part of NDT training in Chennai. It is a high-end non-destructive training method used to detect flaws, cracks, holes and fusion in welded machinery, beads and gas holes. Often overlooked in listings of NDT methods, visual inspection is one of the most common and powerful means of non-destructive testing. It is a process of enhancement of mechanical systems by human sensory systems like touching, twisting, shaking and smelling alike. Visual inspection uses some of the proper testing tools like microscope, dental picks, magnifying lens and stethoscope, for minute screening of the flaws. Visual testing requires adequate illumination of the test surface and proper eye-sight of the tester. To be most effective, visual testing requires training (knowledge of product and process, anticipated service conditions, acceptance criteria, record keeping, for example).

It is also a fact that all defects found by other NDT methods ultimately must be substantiated by visual testing. Visual testing can be classified into direct visual testing, remote visual testing and translucent visual testing. The equipment needed for visual testing is simple-

A portable light, a mirror on stem, a 2X or 4X hand lens, one illuminated magnifier with magnification 5X or 10X. For internal inspection, light lens systems such as bore scopes, enable examination of remote surfaces.

More sophisticated devices of this nature use fiber optics, to enable the introduction of the device into very small access holes and channels. Most of these systems are equipped with a camera, to permit permanent recording of the visual testing process.

TYPES OF OPTICAL USED IN VISUAL INSPECTION  

(A) Mirror

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

(C) Illuminated magnifier; field of view more restricted than D (magnification 5–10X)

(D) Inspection glass (magnification 5–10X

(E) Bore scope or intrascope with built-in illumination (magnification 2–3X).

APPLICATION FOR VISUAL TESTING

(a) Checking of the surface condition of the component.

(b) Checking of alignment of mating surfaces.

(c) Checking of shape of the component.

(d) Checking for evidence of leaking.

(e) Checking for internal side defects.

ADVANTAGE OF VISUAL TESTING

(a) Testing is simple

(b) Testing speed is high

(c) Cost is low

(d) Less training

(e) On-line testing possibility

(f) Permanent record available

LIMITATION FOR VISUAL TESTING

(a) Can detect only surface defects

(b) Difficulty in sizing depth of defects

PHYSICAL REQUIREMENTS

 

Engineering personnel have to go through an annual vision test, to assure natural or corrected near distance acuity, such that they are capable of reading standard J-1 letters, on standard Jaeger test type charts for near vision. Candidates who have equivalent or near vision tests, are acceptable for visual testing process.

DIRECT VISUAL EXAMINATION

Direct visual examination may usually be made when the eye has sufficient access of within 24 in. (600 mm) of the surface to be examined and is at an angle not less than 30 degrees to the surface to be examined.

INSPECTION DOCUMENTATION-

At the end of the visual inspection the following things need to be recorded-

(a) The date of the examination

(b) Procedure identification and revision used

(c) Technique used.

(d) Results of the examination

(e) Examination personnel identity, and, when required by the referencing Code Section, qualification level.

(f) Identification of the part or component examined.

Visual testing is an essential NDT training requirement, quite helpful in increasing the scope for NDT jobs in Hyderabad and all over the world. It is applicable in different industries and manufacturing sectors such as Iron and steel, pharmaceuticals, aviation, automobiles, fabrication and petroleum.

What Are The Advantages of Magnetic Particle Inspection?

NDT training institute in Hyderabad, is a reputed institute which prepares students for different kinds of training related to engineering services. Here the students pursue courses in different backgrounds like ultrasonic testing, radiography testing and magnetic particle testing. They prepare students to get on the job oriented training programs in industries such as, fabrication, manufacturing, fabrication,  automobile, aerospace, power plants, oil and gas sector and inspection companies. They also offer courses in organizational behavior and communication skills. Both NDT institutes in Hyderabad and NDT institute in Vishakhapatnam provide students a sound knowledge of core engineering sector.

BASIC PRINCIPLE OF MAGNETIC PARTICLE INSPECTION –

NDT training in Hyderabad opens up an enormous scope for students to get NDT jobs in Hyderabad. Out of all the premier courses offered at NDT training institute in Hyderabad, is the magnetic particle inspection. It is a practical training course that could be pursued by engineering students as well as working candidates. Magnetic particle testing is used mostly in inspection of mechanically welded heavy metals which is used in various sectors like automobiles, aviation, maintenance, power plants and hydroelectricity. It is used to detect discontinuities and leakage in ferromagnetic substances of the heavy metals manufacturing sector. .

 It has a wide scope of knowledge and usage as of today. Let’s learn in details about this valuable course and its functionality.

The magnetic particle inspection (MPI) is a relatively simple concept. The main principle behind this magnetic particle inspection is magnetic flux leakage.

For example take a bar magnet. It has a magnetic field in and around the bar magnet. Any place that a magnetic line of force exits or enters the magnet is called a pole. A pole where a magnetic line of force exits the magnet is called a north pole and a pole where a line of force enters the magnet is called a south pole. If we break the bar magnet at the centre, it will result in two bar magnets, with north and south poles on each end of the magnets. There is no isolated pole in the magnets.

If the magnet is just cracked but not broken completely in two, a north and south pole will form at each edge of the crack. The magnetic field exits the North Pole and reenters into the South Pole. The magnetic field spreads out when it encounters the small air gap created by the crack, because the air cannot support as much magnetic field per unit volume as the magnet can. When the field spreads out, it appears to leak out of the material and, thus, it is called a flux leakage field.

If iron particles are sprinkled on a cracked magnet, the particles will be attracted to and cluster not only at the poles but also at the edges of the crack. This cluster of particles is much easier to see than the actual crack and this is the basis for magnetic particle inspection.

The first step in a magnetic particle inspection is to magnetize the component that is to be inspected. If any defects on or near the surface are present, the defects will create a leakage magnetic field. After the component has been magnetized, iron particles are applied to the surface of the magnetized part. The particles will be attracted and cluster at the flux leakage fields, thus forming a visible indication that the inspector can detect.

Advantages and Disadvantages

The primary advantages and disadvantages when compared to other NDT methods are:

Advantages-

·         High sensitivity (small discontinuities can be detected).

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

·         Minimal surface preparation (no need for paint removal)

·         Portable (materials are available in aerosol spray cans)

·         Low cost (materials and associated equipment are relatively inexpensive)

Disadvantages-

·         Only surface and near surface defects can be detected.

·         Only applicable to ferromagnetic materials.

·         Relatively small area can be inspected at a time.

·         Only materials with a relatively nonporous surface can be inspected.

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

Magnetic particle inspection is a process used in almost all heavy manufacturing industries like, graphite, iron and steel, automobiles, energy, defense and transportation. It is an important non-destructive testing method used in the manufacturing sector of heavy industries, during final inspection, process inspection, quality control, receiving inspection, maintenance and overhaul. The NDT training institute in Hyderabad and NDT institutes in Vishakhapatnam offer this valuable course for endless job opportunities in the engineering sector all over the world.

Basic Principles of Liquid Penetrant Inspection

Welcome to NDT institute Vijayawada, a premium institute which offers courses in various engineering platforms like welding, piping, quality audit, liquid penetrant testing and international inspection techniques and certification. NDT institute in Vijayawada gives an in-depth training to students from various backgrounds like refineries, petrochemical industries, power plants and fabrication industries. It also gives on the job training o methods like, radioactive testing, ultrasonic testing and liquid penetrant testing. One of these techniques taught here is the Liquid Penetrant Testing which has a great deal of scope for students to find NDT jobs in India and NDT jobs abroad.

 Liquid Penetrant Testing

Principle of LPT:

The basic principle of liquid penetrating testing is capillary action.

Capillary Action: The rise or fall of liquid in a narrow opening is called capillary action. Capillary action is action by which surface of liquid, where it is in contact with solid is elevated or depressed.

The technique is based on the ability of a liquid to be drawn into a "clean" surface breaking flaw by capillary action. After a period of time called the "dwell," excess surface penetrant is removed and a developer applied. This acts as a blotter. It draws the penetrant from the flaw to reveal its presence. Colored (contrast) penetrant require good white light while fluorescent penetrants need to be used in darkened conditions with an ultraviolet "black light".

Steps of Liquid Penetrant Testing

The exact procedure for liquid penetrant testing can vary from case to case, depending on several factors such as the penetrant system being used, the size and material of the component being inspected, the type of discontinuities being expected in the component and the condition and environment under which the inspection is performed. However, the general steps can be summarized as follows:

1. Surface Preparation: One of the most critical steps of a liquid penetrant testing is the surface preparation. The surface must be free of oil, grease, water, or other contaminants that may prevent penetrant from entering flaws. The sample may also require etching if mechanical operations such as machining, sanding, or grit blasting have been performed. These and other mechanical operations can smear metal over the flaw opening and prevent the penetrant from entering.

2. Penetrant Application: Once the surface has been thoroughly cleaned and dried, the penetrant material is applied by spraying, brushing, or immersing the part in a penetrant bath.

3. Penetrant Dwell: The penetrant is left on the surface for a sufficient time to allow as much penetrant as possible, to be drawn from or to seep into a defect. Penetrant dwell time is the total time that the penetrant is in contact with the part surface. Dwell times are usually recommended by the penetrant producers

or required by the specification being followed. The times vary depending on the application, penetrant materials used, the material, the form of the material being inspected, and the type of discontinuity being inspected for.

Minimum dwell times typically range from five to 60 minutes. Generally, there is no harm in using a longer penetrant dwell time as long as the penetrant is not allowed to dry. The ideal dwell time is often determined by experimentation and may be very specific to a particular application.

4. Excess Penetrant Removal: This is the most delicate part of the inspection procedure, because the excess penetrant must be removed from the surface of the sample while removing as little penetrant as possible from defects. Depending on the penetrant system used, this step may involve cleaning with a solvent, direct rinsing with water, or first treating the part with an emulsifier and then rinsing with water.

5. Developer Application: A thin layer of developer is then applied to the sample to draw penetrant trapped in flaws back to the surface where it will be visible. Developers come in a variety of forms that may be applied by dusting (dry powders), dipping, or spraying (wet developers).

6. Indication Development: The developer is allowed to stand on the part surface for a period of time sufficient to permit the extraction of the trapped penetrant out of any surface flaws. This development time is usually a minimum of 10 minutes. Significantly longer times may be necessary for tight cracks.

7. Inspection: Inspection is then performed under appropriate lighting to detect indications from any flaws which may be present.

8. Clean Surface: The final step in the process is to thoroughly clean the part surface to remove the developer from the parts that were found to be acceptable.

Advantages &Capabilities:

·         Penetrant testing inspection is capable of examine the entire exterior surface in one operation even though object may have complex shape.

·         Penetrant inspection can detect very small discontinuities and penetrant bleed out magnifies apparent size of discontinuity making them easier to see.

·         Penetrant testing indications formed provide information on location, orientation and approximate length of discontinuity.

·         The process is relatively simple and rapid and can easily be automated where large volume of parts is to be inspected.

·         Penetrant testing inspection can be used on wide variety of materials including, ferrous and non- ferrous metals, ceramics, cements, glass and many types of plastics.

·         The process sensitivity can be varied by selection of materials and processing procedures. Aerosol spray cans make penetrant materials very portable. Penetrant materials and associated equipment are relatively inexpensive.

Disadvantages & Limitations:

·         Penetrant testing inspection will not reveal discontinuities that are not open to the surface. Subsurface discontinuities cannot be detected by penetrant inspection.

·         The part surface and interior of any discontinuities must be clean and free of contaminants, soils and moisture. If it is present organic or inorganic materials of the surface of the part or inside the discontinuities can interfere with penetrant entering and filling the discontinuity void.

·         Porous material or material with seeped-in penetrant that is not removed during post cleaning operations is difficult to inspect.

·         Penetrants usually contain petroleum based liquids that can soften, destruct or attack some non-metallic materials such as certain plastics and rubber.

·         Penetrants, emulsifier and developers contain chemicals that have wetting and detergent properties however they can dissolve and remove natural oil from human tissues if they come in contact with and remain on skin surfaces for a length of time. This causes drying and cracking which is a source for secondary infection.

Liquid penetrant testing taught in NDT institute Vijayawada is a very useful training, which helps lots of candidates to acquire NDT jobs in India  and  abroad.