Non-Destructive Testing is the branch of engineering concerned with all methods of detecting and evaluating flaws in materials. Flaws can affect the serviceability of the material or structure, so NDT is important in guaranteeing safe operation as well as quality control and assessing plant life. The flaws may be cracks or inclusions in welds and castings, or variations in structural properties that can lead to loss of strength or failure in service.
The essential feature of NDT is that the test process itself produces no deleterious effects on the material or structure under test. MATRIX provide highly skilled, experienced and motivated personnel qualified and certified in accordance with international certification schemes (e.g. PCN (EN 473/ IS0 9712), ANSI CP-189 and SNT-TC 1A) in the conventional techniques that have underpinned the NDT industry from its earliest days.
List of Conventional NDT Services Providing by MATRIX
- Radiographic Testing
- Ultrasonic Testing (UT)
- Magnetic Particle Testing (MPT)
- Liquid Penetrant Testing (LPT)
- Hardness testing (HT)
- Positive Material Identification (PMI)
- Ferrite Content Measurement (FM)
Radiography Testing
Radiographic Testing (RT) is the method of inspecting materials for hid-den flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials.
It is a well-established technique to inspect internal defects in materials such as welds, casting during fabrication as well as during shutdown.
Radiographic testing provides a permanent record in the form of a radiograph and provides a highly sensitive image of the internal structure of the material.
ULTRASONIC TESTING
It is a non-destructive testing (NDT) method in which beams of high frequency sound waves that are introduced into the material being tested are used to detect surface and sub-surface flaws. The sound waves travel through the materials with some attenuation of energy and are reflected at interfaces. The reflected beam is detected and analyzed to define the presence and location of flaws.
Cracks, laminations, shrinkage, cavities, bursts, flakes, pores, bonding faults and other discontinuities that can act as metal-gas interfaces can be easily detected. Inclusions and other inhomogenities in the metal being inspected can also detected by causing partial reflection or scattering of the ultrasonic waves, or by producing some other detectable effect on the ultrasonic waves
Ultrasonic Inspection is a very useful and versatile NDT method. Some of the advantages of ultrasonic inspection that are often cited include:
- It is sensitive to both surface and subsurface discontinuities.
- The depth of penetration for flaw detection or measurement is superior to other NDT methods.
- Only single-sided access is needed when the pulse-echo technique is used.
- It is highly accurate in determining reflector position and estimating size and shape.
- Electronic equipment provides instantaneous results.
- Detailed images can be produced with automated systems.
- It has other uses, such as thickness measurement, in addition to flaw detection.
APPLICATION OF ULTRASONIC EXAMINATION
- Ultrasonic inspection is used for quality control and materials inspection in all major industries.
- Ultrasonic inspection is used for finding flaws in production of metallic and composite materials.
- It is used in fabrication of structures such as airframes, piping and pressure vessels, ships, motor vehicles, machinery, jet engines and submarines.
- In-service ultrasonic inspection for preventive maintenance is used for detecting the impending failure of rails, rolling-stock axils, mill rolls, mining equipment and nuclear systems.
- Also used for thickness measurement in refinery and chemical pressure
- Thickness gauging is an example application where instruments have been refined make data collection easier and better.
- Many ultrasonic flaw detectors have a trigonometric function that allows for fast and accurate location determination of flaws.
- Inspection of large Weldments, castings and forging, for internal soundness, before carrying out expensive machining operations.
- Inspection of moving strip or plate (for laminations) as regards its thickness.
- Routine inspection of locomotive axles and wheel pins for fatigue cracks.
- Inspection of rails for bolt-hole breaks without dismantling rail-end assemblies.
Weld Inspection
By using Angle Beam Probes we can scan weld. Angle Beam Transducers and wedges are typically used to introduce a refracted shear wave into the test material. An angled sound path allows the sound beam to come in from the side, thereby improving detectability of flaws in and around welded areas.
Angle Beam Transducers and wedges are typically used to introduce a refracted shear wave into the test material. The geometry of the sample below allows the sound beam to be reflected from the back wall to improve detectability of flaws in and around welded areas.
Lamination Checking:
Ultrasonic Testing of rolled sections of plates, pipes are carried out for primary manufacturing defects i.e. lamination check, inclusion, cracks etc.
Laminations in rolled plate or strip are formed when blowholes or internal fissures are not welded tight during rolling, but are enlarged and flattened into sometimes quite large areas of horizontal discontinuities. Laminations may be detected by magnetic particle testing on the cut edges of plate, but do not give indications on plate or strip surfaces, since these discontinuities are internal and lie in a plane parallel to the surface. Ultrasonic mapping techniques are used to define them. When inspecting parts fabricated from sheet or plate, laminations can be detected by noting a reduction in the distance between back reflection multiples.
Ultrasonic Testing of rolled sections of plates, pipes are carried out for primary manufacturing defects i.e. lamination check, inclusion, cracks etc.
Ultrasonic thickness measurement (UTM):
Confirmation of component thickness can assist in the determination of life expectancy of any part. Ultrasonic Thickness Gages accurately measure wall thickness and corrosion of all metals, including steel and aluminum, plastic, ceramics and others.
Thickness gauging is a method of performing non-destructive measurement (gauging) of the local thickness of a solid element (typically made of metal, if using ultrasound testing for industrial purposes) basing on the time taken by the ultrasound wave to return to the surface. This type of measurement is typically performed with an ultrasonic thickness gauge.
Multi-Mode thickness gauge Machines that has the ability to measure through painted or coated surfaces and eliminate the thickness of the paint using a dual element style transducer in echo-echo mode.
Advantages
- Does not require access to both sides of the sample
- Can be engineered to cope with coatings, linings, etc
- Good accuracy (0.1 mm and less) can be achieved using standard timing techniques
- Can be easily deployed, does not require laboratory conditions
- Digital UTM gives directly Thickness on display.
MAGNETIC PARTICLE TESTING
Magnetic particle inspection (MPI) is a non-destructive testing (NDT) process for detecting surface and subsurface discontinuities in ferroelectric materials such as iron, nickel, cobalt, and some of their alloys. The process puts a magnetic field into the part.
Florescent method Dry Particle Method
Applications
The method is used to inspect a variety of product forms including castings, forgings, and weldments. Many different industries use magnetic particle inspection such as structural steel, automotive, petrochemical, power generation, and aerospace industries. Underwater inspection is another area where magnetic particle inspection may be used to test items such as offshore structures and underwater pipelines
Advantages of the Magnetic Particle method of Non-Destructive Examination are:
- It is quick and relatively uncomplicated
- It gives immediate indications of defects
- It shows surface and near surface defects, and these are the most serious ones as they concentrate stresses
- The method can be adapted for site or workshop use
- It is inexpensive compared to radiography
- Large or small objects can be examined
- Elaborate pre-cleaning is not necessary
Disadvantages of the Magnetic Particle method of Non-Destructive Examination are:
- It is restricted to ferromagnetic materials – usually iron and steel, and cannot be used on austenitic stainless steel
- It is messy
- Most methods need a supply of electricity
- It is sometimes unclear whether the magnetic field is sufficiently strong to give good indications
- The method cannot be used if a thick paint coating is present
- Spurious, or non-relevant indications, are probable, and thus interpretation is a skilled task
- Some of the paints and particle suspension fluids can give a fume or fire problem, particularly in a confined space
LIQUID PENETRANT TESTING
Liquid Penetrant Testing (LPT) is one of the most widely used nondestructive evaluation (NDE) methods. Its popularity can be attributed to two main factors: its relative ease of use and its flexibility. LPT can be used to inspect almost any material provided that its surface is not extremely rough or porous.
Materials that are commonly inspected using LPT include the following:
- Metals (aluminum, copper, steel, titanium, etc.)
- Glass
- Many ceramic materials
- Rubber
- Plastics
Liquid penetrant inspection can only be used to inspect for flaws that break the surface of the sample. Some of these flaws are listed below:
- 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
Advantages of the penetrant method of Non-Destructive Examination are:
- It is a very sensitive method, capable of finding extremely fine flaws
- It can be used on magnetic and non-magnetic metals, some plastics and glass
- Small objects, with awkward shapes, can be inspected
- A power supply is not needed for some methods of penetrant testing
- The method requires no great skill and is easy to understand
- Lots of small articles, in batches, can be examined using automated systems
Disadvantages of the penetrant method of Non-Destructive Examination are:
- Can only detect defects open to the surface
- Preparation, before testing, can be time consuming and costly
- The method takes time and can rarely be completed in less than 30 minutes
- The method cannot normally be applied to painted objects
- It is messy
- Interpretation of results is sometimes difficult
- There may be a problem disposing of contaminated cleaning and penetrant fluids
- Dry, clean, conditions are essential, as is careful cleaning of the surfaces to be examined
- The method is often abused and skimped, or not fully understood
- There can be a fume exposure problem, particularly in confined spaces
Discontinuity Images
EDDY CURRENT TESTING (HARDNES SORTER)
The high velocity of sweep in all test criteria like material-mix-up or different hardness-depth is ideal for the sorting of screws, balls, needles, camshafts etc. Approved from the industry under the most different working conditions, 100% or alternatively manual testing is possible. Different probes and spools can be connected to allow high flexibility as well as reasonable prices.
Because of its high repeat-accuracy and the comfortable handling it is worldwide approved from the automobile industry and its suppliers. Eddy-current testing is one of many electromagnetic testing methods used in NDT making use of electromagnetic induction to detect and characterize surface and sub-surface flaws in conductive materials
Applications:
Typical applications are mixtures, heat-treatment, surface-hardness, and hardness-depth or material mix-up. Either probes or spools are used, depending on the application. The limits for good/reject-parts are compared with the masterpieces and adjusted through a potentiometer
HARDNESS TESTING
Hardness is the measure of how resistant solid matter is to various kinds of permanent shape change when a force is applied. Macroscopic hardness is generally characterized by strong intermolecular bonds, but the behavior of solid materials under force is complex; therefore there are different measurements of hardness: scratch hardness, indentation hardness, and rebound hardness.Hardness is dependent on ductility, elasticity, plasticity, strain, strength, toughness, viscoelasticity, and viscosity
Monitoring the Hardness of Metals
Metals undergo different processes before being converted into a final product. Each process can have an effect on the mechanical and chemical attributes of metal. For example, the strength of steel is determined by its chemical composition and micro structural transformations. Macroscopic variables are used to control the final product quality. Hardness is one characteristic of metal that can be easily monitored.
Application
- In stores for Material identification
- Measurement of Hardness in confined spaces.
- Variation in hardness over large work piece.
- Large & heavy components.
- Permanently installed parts.
- Surface hardened component or hardness on coatings
For Brinell hardness method
Advantages:
- Takes heavy loads for testing
- Easy to operate the testing equipment
- Indentation made during the test can be observed under microscope or eyepiece
- Not sensitive to deflection and so easy to test
- Easy to calculate tensile strength also from hardness value by multiplying with constant values based on the material on which testing is done
Limitations:
- Developing of residual stress because of indentation
- Parallel ax error during operation
- Accurate surfaces required for testing
- Only flat surfaces can be tested
Vickers hardness tester
Advantages:
- Huge range of materials can be tested
- Structural characteristics can also be seen
- Not sensitive as brinell test
Limitations
- Takes time for the experiments
- Can only be observed by optical microscopy
- Required surface preparation for testing
POSITIVE MATERIAL IDENTIFICATION
Positive metal identification is rapidly emerging as an integral part of process safety management and quality control in many industries such as electric power generation, construction, manufacturing, chemical processing, oil refineries and petrochemical plants. Using modern, hand-held, portable X-Ray Fluorescence analyzers, we provide material identification and quantitative elemental determination for a wide range of items, even in arduous conditions, including:
- Pipes
- Tubes
- Forged bars
- Valves
- Weld seams
- Tanks
- Vessels
- Structural supports
This means that positive material identification (PMI) in alloys used throughout the physical plant is no longer a choice, but a necessity. Simply relying on spot testing of parts and subassemblies is too risky and totally unacceptable. Today’s best practices include 100% positive material testing of all critical materials
ADVANTAGES
- Rapid and accurate analysis
- Highly portable digital technology, can be used on site
- Certifies components requiring NACE MR0175/ISO 15156
- Leaves no trace of testing on test sample
- Care must be taken to ensure that the surface of the test specimen is representative of the material as a whole
- The instrument must be able to maintain surface contact with the material
LIMITATIONS
- The depth of penetration of the x-ray for most elements is less than one thousandth of an inch in steel. Care must be taken to ensure that the surface of the material being analyzed is chemically representative of the whole
- Surface of the item must be accessible and subject to satisfactory cleaning and visual inspection
- Analyzers are limited to identifying only those alloys that are listed in the manufacturer’s library for the analyzer
- Material verification cannot be performed where the material temperature is in excess of approximately 200 °F, unless specialized equipment and techniques are used
- Identification of small amounts of a specific element in an item can be difficult
- Carbon, sulfur and phosphorous cannot be identified with x-ray fluorescence
FERRITE CONTENT MEASUREMENT
Ferrite testing is a technique used to measure the delta ferrite content in austenitic stainless steel and duplex stainless steel. The delta ferrite content is measured to better understand an austenitic or duplex stainless steel’s susceptibility to corrosion, susceptibility to solidification cracking and other types of material failure. Ferrite testing commonly employs magnetic induction as a means to measure the ferrite content of a material, although there are other methods that are used.
Advantages
- The test requires only a light contact which leaves no mark.
- Ferrite values are determined directly and quickly.
Limitations
- Some welds, depending on their heat treatment, may not respond to the Ferrite probe. In this case, Ferrite value must be calculated from OES, or Spark test results
It is an advanced method of ultrasonic testing and can be used for a multitude of different inspection tasks.This method is an advanced NDT method that is used to detect discontinuities i.e. cracks or flaws and thereby determines component quality. Due to the possibility to control parameters such as beam angle and focal distance, this method is very efficient regarding the defect detection and speed of testing. Apart from detecting flaws in components, phased array can also be used for wall thickness measurements in conjunction with corrosion testing.
TOFD inspection employs two longitudinal wave (L-wave) angle beam transducers arranged symmetrically opposite facing each other, straddling the weld or base material under test. One probe acts like a transmitter of ultrasonic energy while the other probe receives the ultrasound energy. The transducer, pulser, and amplifier characteristics are selected to generate as broad distribution of energy as possible over the material under test providing full weld coverage. A single-axis scan (that is, along the weld), with a position encoder records the position of the weld and enables the display of digital images in real time.
Capabilities
NDT is a basic need for Industries like Power Plants & Refineries to ensure safety and reliability. Components like Heat Exchangers & Condensers need to be checked periodically from inside in these plants since leak of any kind can lead to productivity loss and more importantly serious environment hazards.Heat Exchanger & Steam Generators tubes in power plants, especially Nuclear power plants, needs to be inspected for leaks periodically to prevent hazards. Hence, identifying and replacing damaged and weak parts is very important task and ensures safe process and reliability.
Eddy Current Tube inspection is the High Speed & Fastest way to check for damages like ID Wall loss, OD wall loss, ID & OD Pitting, ID & OD Corrosion due to stress cracking etc., in metals.
The Objective
When a magnet is in close proximity to a steel plate magnetic lines of force (flux) are created within the plate. These lines of flux prefer to travel within the plate than the air. If the magnet is of suitable power it can create a near saturated flux in the plate.
Remote field testing (RFT) is an electromagnetic method of non-destructive testing whose main application is finding defects in steel pipes and tubes. RFT may also be referred to as RFEC (remote field eddy current) or RFET (remote field eddy current technique). An RFET probe is moved through the pipeline and able to detect inside and outside defects with approximately equal sensitivity. The RFET technique works with conductive materials such as copper, brass, stainless steel, etc.
RFT is primarily used to inspect ferromagnetic tubing since conventional eddy current techniques have difficulty inspecting the full thickness of the tube wall due to the strong skin effect in ferromagnetic materials.
The ultrasonic method for measuring scale thickness is based on transmitting a wave through the tube thickness. The thickness is calculated by measuring the time difference between the signals reflected from the steel/scale interface and the tube ID surface. With advanced signal interpretation techniques, we can achieve Oxide scale Thickness measurements up to the resolution of 0.15 Microns.
Vacuum Box testing is used to check for any leaks or fault in the welding of bottom & annular plates of the storage tank.
