NON-DESTRUCTIVE TESTING

The field of NDT is a very broad, interdisciplinary field that plays a critical role in Emerging concepts like intelligent processing of materials, expert systems, neural networks, use of multisensors are used for exploitation of signal analysis and imaging for evaluation of engineering and integrity and life assessment of the materials or structures without impairing their properties for quality control of the products, failure analysis, defects, stresses, microstructures.

NDT tests allows Flaw detection and evaluation, leak detection, location determination, dimensional measurements, structure, microstructure characterization, estimation of mechanical and physical properties, stress (Strain) and dynamic response measurements, material sorting and chemical composition determination, material conditions and flaws that might cause planes to crash, reactors to fail, trains to derail, pipelines to burst, and variety of less visible, but equally troubling events. This method are physically derived parameters that are used for assessing defects performed on metals, plastics, ceramics, composites, cermet’s, and coatings to detect cracks, internal voids, surface cavities, delamination, incomplete defective welds and any type of flaw that could lead to premature failure.

Nondestructive testing (NDT) is the process of dimensional inspection, indentation test, chemical composition test and degradation inspection can be used to evaluate and assist in product development, screen or sort incoming materials to monitor, improve or control manufacturing processes, verify proper processing such as heat treating, verify proper assembly and inspect for in-service damage for processes of design, fabrication, construction, maintenance, demolition and storage impacts characteristics are more effective like resistance, ductility, yield and ultimate tensile strength, fracture toughness and fatigue strength inspections.

EN 1435: Non-destructive examination of welds — Radiographic examination of welded joints
ISO 17636: Non-destructive examination of welds— Radiographic testing of fusion-welded joints
EN 444: Non-destructive testing — General principles for radiographic examination of materials by X-and gamma-rays
EN 462: Non-destructive testing — Image quality of radiographs
EN 584: Non-destructive testing — Industrial radiographic film
ISO 1 1699: Non-destructive testing — Industrial radiographic film
IS05580: Non-destructive testing — Industrial
EN25580: radiographic illuminators
EN1711: Non-destructive examination of welds —Eddy Current Examination of welds by complex plane analysis.
EN 12062: Non-destructive examination of welds General rules for metallic materials
ISO 17635: Non-destructive examination of welds — General rules for fusion welds in metallic materials.
ISO 17636: Non-destructive examination of welds —Radiographic testing of fusion welded joints
EN 1289: Non-destructive examination of welds Penetrant testing of welds — Acceptance levels.
EN 1291: Non-destructive examination of welds Magnetic Particle testing — Acceptance levels.

EN 473: Qualification and certification of NDE personnel – General principles
IS05817: Arc-welded joints in steels — Guidance on quality levels for imperfections.
EN 25817: Arc-welded joints in steels – Guidance on quality levels for imperfections,
EN 26520: Classification of imperfections in metallic fusion welds with explanations.
EN 30042: Arc-welded joints in aluminum and its weldable alloys — Guidance on quality levels for imperfections.
EN 1330: Non-destructive testing — Terminology
PrEN 13860: Non-destructive testing — Eddy currents —Verification of equipment.
IAC’S: International Association of Classification Societies-Recommendation No. 47, Shipbuilding and repair Quality Standard
IACS: International Association of Classification societies — Rec. No. 68 Guidelines for non-destructive examination of hull and machinery steel forgings
IACS: International Association of Classification societies — Rec. No. 69 Guidelines for non-destructive examination of marine steel castings
EN 473: Qualification and certification of NDT personnel — General principles
ASNT: SNT-TC-IA American Society for Non-destructive testing Recommended Practice.
EN 1290: Non-destructive testing Magnetic particle testing of welds
ISO 9934-1: Non-destructive testing — Magnetic particle-testing — General Principles
EN 10160: Ultrasonic testing of steel and fiat product of thickness equal or greater than 6 mm (reflection method)
ISO 9712: Non-destructive testing — Qualification and certification of personnel
EN 1712: Non-destructive examination of welded joints — Acceptance levels
EN 1713: Non-destructive testing of welds — Ultrasonic examination — Characterization or indications in welds
EN 1714: Non-destructive examination of welds — Ultrasonic examination of welded joints
ASME V: ASME Boiler and Pressure vessel code; Non-destructive Examination
ASTM A 609: Standard Practice for Castings, Carbon, Low-Alloy, and Martensitic Stainless Steel, Ultrasonic Examination
ASTM 388: Standard Practice for Ultrasonic Examination of Heavy Steel Forgings
EN 25817: Arc-welded joints in steel — Guidance on quality levels for imperfections
EN 12668: Characterization and verification of ultrasonic of ultrasonic equipment; Part I — Instruments, Part 2 — Probes, Part 3— Combined equipment.

PrEN 1956: Non-destructive testing — Penetrate testing—Magnetic Particle testing — Viewing conditions.

ASNT E1316: Standard Terminology for Nondestructive Examinations.
EN 571: Nondestructive testing — penetrate testing
EN 956: Nondestructive testing — penetrate testing — Equipment
EN ISO 12076: Nondestructive testing — Terminology — Terms used in penetrate testing.

Visual Inspection (VT)

Visual inspection is one of the most common reliable non-destructive testing in engineering structures and products process, anticipated service conditions, acceptance criteria for various applications find out defects with the help of Visual inspection tools include fiberscopes, borescopes, magnifying glasses and mirrors, portable video inspection with Zooming functions, robotic crawlers are used. A team of experienced Inspectors, Metallurgist, Engineers, certified Inspectors Visual testing requires adequate illumination of the test surface and proper eye-sight of the tester.

Visual Inspection can be classified as direct visual testing, remote visual testing and translucent visual testing for better understanding real time photographs in condition monitoring of welded joints or fabricated components, castings, forgings, rolled products, metallurgy and several other products in accordance with AS 1554 series, AS 4037, AS 4041, AS 3978, ASME V Article 9, ASME IX QW 194, EN 970, ISO 10042, ASTM standards to meet their regulations and international standards in non-destructive testing.

LIQUID PENETRATING TESTING (LT)

Liquid Penetrant Testing (LPT) is one of the most widely used non-destructive testing methods for finding defects and discontinuities opened on the surface especially in all non-porous materials. Liquid penetrant testing is largely used on nonmagnetic materials for which magnetic particle inspection is not possible.

Materials that are commonly inspected using metals are aluminium, copper, steel, titanium, glass, many ceramic materials, rubber, plastics. Use of LPT for porous materials is ruled out since the absorption into the pores would mask the presence of defects.

A clean surface is a per-requisite as penetrant cannot enter in to the cracks that is filled with dirt, oil, or other forms of contaminant. Size, shape, weight and number of workpieces to be inspected often influence the selection of a penetrant system. In the experiment, only cleaner-remover will be sufficient. Subsequent to surface cleaning, the surface is let to dry for 2 minutes.

LPT can also be used for leak testing and cracks orientation, fatigue cracks, quench cracks grinding cracks, overload and impact fractures, porosity, laps seams, pin holes in welds, lack of fusion or braising along the edge of the bond line with high sensitivity to small surface discontinuities.

EDDY CURRENT TESTING (ET)

Electromagnetic Testing (ET), especially eddy current testing, is commonly used to inspect objects throughout their life cycle. Eddy current techniques employ alternating currents applied to a conducting coil held close to the test object. In response, the test object generates eddy currents to oppose the alternating current in the coil. The eddy currents are then sensed by the same coil, separate coils, or magnetic field sensors. Changes in the induced eddy currents may be caused by changes to a material’s electromagnetic properties and/or changes in geometry, including the abrupt changes in current flow caused by cracks. Thus, ET methods are highly effective for the detection of cracks present on or below the surface of metallic objects.

ET equipment has become extremely portable and is relatively inexpensive. It is the second most common method specified for NDT of aircraft. Recent advances in eddy current technology include multichannel portable instruments, allowing faster inspections of large areas, and new magnetic sensors, such as the Giant Magneto resistive (GMR) sensors developed for computer hard drives, instead of coils.

This part defines Eddy Current testing techniques for detection of surface breaking and near surface planar defects welds – heat affected zone – parent material.ET can be applied on coated and uncoated objects. the testing can be carried out on all accessible surfaces on welds of almost any configuration. Usually, it can be applied in the as-welded condition. However, a very rough surface may prevent an efficient testing.

The Eddy Current testing method includes also Alternating Current Field Measurement (ACFM). if this method is applied; written procedures shall be established according to recognised standards and are subjected for approval by the Society before the testing starts.

Eddy current testing is particularly well suited for detecting surface cracks but can also be used to make electrical conductivity and coating thickness measurements. Here a small surface probe is scanned over the part surface in an attempt to detect a crack.

MAGNETIC PARTICLE TESTING (MT)

Magnetic particle inspection is one of the simple, fast and traditional nondestructive testing methods widely used because of its convenience and low cost. This method uses magnetic fields and small magnetic particles, such as iron filings to detect flaws in components.

The only requirement from an inspect ability standpoint is that the component being inspected must be made of a ferromagnetic material such iron, nickel, cobalt, or some of their alloys, since these materials are materials that can be magnetized to a level that will allow the inspection to be effective.


On the other hand, an enormous volume of structural steels used in engineering is magnetic. In its simplest application, an electromagnet yoke is placed on the surface of the part to be examined, a kerosene-iron filling suspension is poured on the surface and the electromagnet is energized.

If there is a discontinuity such as a crack or a flaw on the surface of the part, magnetic flux will be broken, and a new south and north pole will form at each edge of the discontinuity. Then just like if iron particles are scattered on a cracked magnet, the particles will be attracted to and cluster at the pole ends of the magnet, the iron particles will also be attracted at the edges of the crack behaving poles of the magnet.

This cluster of particles is much easier to see than the actual crack and this is the basis for magnetic particle inspection. For the best sensitivity, the lines of magnetic force should be perpendicular to the defect.

ULTRASONIC TESTING (MT)

Ultrasonic Testing (UT) uses a high frequency sound energy to conduct examinations and make measurements. Ultrasonic inspection can be used for flaw detection evaluation, dimensional measurements, material characterization, and more.

A typical UT inspection system consists of several functional units, such as the pulser/receiver, transducer, and display devices. A pulser/receiver is an electronic device that can produce high voltage electrical pulse. Driven by the pulser, the transducer of various types and shapes generates high frequency ultrasonic energy operating based on the piezoelectricity technology with using quartz, lithium sulfate, or various ceramics.



Most inspections are carried out used frequency range of 1 to 25MHz. Couplants are used to transmit the ultrasonic waves from the transducer to the test piece; typical couplants are water, oil, glycerin and grease. The sound energy is introduced and propagates through the materials in the form of waves and reflected from the opposing surface. An internal defect such as crack or void interrupts the waves’ propagation and reflects a portion of the ultrasonic wave high frequency sound waves. The amplitude of the energy and the time required for return indicate the presence and location of any flaws in the work-piece.

As a very useful and versatile NDT method, ultrasonic inspection method has the following advantages; sensitivity to both surface and subsurface discontinuities, superior depth of penetration for flaw detection or measurement, ability to single-sided access for pulse-echo technique, high accuracy in determining reflector position and estimating size and shape, minimal part preparation, instantaneous results with electronic equipment, detailed imaging with automated systems, possibility for other uses such as thickness measurements and to inspect flaws in large parts, such as rail road wheels pressure vessels and die blocks for surfaces or flaws, cross-section, roughness, shape irregularity, smallness, thickness or not homogeneity, tears, delamination, cavities, corrosion mapping, weld inspection etc. using Phased array and time of flight diffraction(TOFD) techniques in various applications in  industries including aerospace, power generation, petrochemical, metal billet and tubular goods suppliers, pipeline construction and maintenance, structural metals, and general manufacturing for Forgings, weldments, castings, Bars and Shapes, Thickness gauging, Velocity, plate inspection, pipes and tubes etc.

Phased-array probes are composed of several piezoelectric crystals that can transmit/receive independently at different times. To focus the ultrasonic beam, time delays are applied to the elements to create constructive interference of the wavefronts, allowing the energy to be focused at any depth in the test specimen undergoing inspection.

Time of Flight Diffraction(TOFD) technique involves two separate probes of opposite axis, one acting as a transmitter and one acting as a receiver. The inspection principle of such technique modeling requires to properly calculate the diffraction echoes at the top edge and the bottom edge of the considered defects. The diffraction coefficients calculation is based on GTD approach (Geometrical Theory of Diffraction). This allows to precisely account the effects due to the misorientation of flaws or probes and the complex geometries time technique one transducer radiates ultrasonic rays, and the other receives elastic waves resulting from reflection and diffraction of those rays at the defect’s ends; the transducers are placed on opposite sides of the crack. In practice, longitudinal waves are mainly used because they have the highest velocity in the medium under study for reach the receiver first and are easily distinguished from other types of waves generated as a result of diffraction on a defect. 

RADIOGRAPHY TESTING(RT)

Radiography testing is one the of the Non-Destructive Testing methods to find out thickness difference, density, corrosion under insulation(CUI) and presence of defects in Castings & Forgings, Boiler internal & external inspections, Pistons, gears, bolts, Machined parts, Plastic and glass, Weld seams, Precision machined parts using industrial radiography and computed radiography testing in various applications are electric power generation, construction, manufacturing, chemical processing, oil refineries and petrochemical plants etc.

Radiographic inspection with the help of x-rays, gamma ray’s films for detection of the material by penetrating radioactive source emitted electromagnetic spectrum shorter wavelength for testing of material using the of principle of differential absorption.

POSITIVE MATERIAL IDENTIFICATION(PMI)

Positive material identification(PMI) is one of the more specialised non-destructive testing methods. Using a tool on spot testing as a modern hand-held Niton x-ray fluorescence(XRF) and optical emission spectrometry (OES) analyzer for critical materials accurate and fast test of ferrous and non-ferrous metallic alloys compositions material identification and percentage quantities of elemental chemical grade verification and analysis as per ASTME 1476 standards of Fe (iron), Cr (chromium), Ni (nickel), Mo (molybdenum), and Cu (copper), Ti(Titanium), Mn(Manganese),Zn(Zinc). Vanadium(V), Cobalt(Co), Selenium(Se), Niobium(Nb) etc in various applications like Pipes, Tubes, Forged bars, Valves, Weld seams, Tanks, Vessels, Structural supports etc.