Magnetic Particle Testing
Magnetic Particle Testing is the method used to detect surface and slightly subsurface discontinuities in ferromagnetic materials such as iron, nickel, cobalt, and some of their alloys. The principle of the method is that
the specimen is magnetised to produce magnetic lines of force, or flux, in the material.
If these lines of force meet a discontinuity, such as a crack, secondary magnetic poles are created at the faces of the crack. Where these secondary magnetic fields appear at the surface of the metal, they can be revealed by applying magnetic particles, as a powder, or in a liquid suspension, to the surface. The particles are attracted to the flux leakage and clump round the flaw, making it visible.
The particles may be black, or coated with a fluorescent dye to increase their visibility. The magnetic flux lines should be at right angles to a flaw to give the best indication, as this creates maximum flux leakage.
This governs the choice of a suitable magnetising technique.
Often, more than one technique must be used to give a 100% coverage A flaw attracts more particles if it cuts more magnetic lines of force, so the ability to show a flaw depends on the depth of the flaw, the angle of the flaw to the lines of force, and the magnetic field strength induced during magnetisation. The method is limited to ferromagnetic materials - iron, cobalt and nickel - as other paramagnetic and diamagnetic materials cannot hold a flux which is strong enough to attract magnetic particles.
Liquid Penetrant Testing technique is a method that supplements visual inspection, revealing defects such as fine cracks or micro-porosity that would be invisible or difficult to detect by the naked eye in all non-porous materials (metals, plastics, or ceramics) Liquid Penetrant Testing is a simple, cheap and easily portable inspection method that requires no equipment apart from spray cans. It can detect surface breaking imperfections only and relies on a coloured or fluorescent dye, sprayed on the surface and penetrating the imperfection.
About 20 minutes is generally specified to enable the dye to penetrate very fine imperfections (penetrant dwell time).
After the dwell time, the excess dye is cleaned off and the dye in the discontinuities is drawn to the surface by spraying on a developer in the case of the colour contrast dye or exposing the surface to ultra-violet light
in the case of a fluorescent dye.
The imperfections are then revealed by the dye staining the developer or fluorescing The fluorescent dye gives greater sensitivity than the colour contrast dye and does not require the use of a developer.
It does however require the use of an ultra-violet light source and preferably a darkened room which makes it a less portable inspection method than the contrast dye technique. The dye used as a penetrant must be able to
penetrate tight cracks but must not be capable of being removed from more open imperfections during the cleaning operation carried out prior to applying the developer.
Although a simple inspection process to use, interpretation can be a problem if the surface is naturally rough – coarsely ground or rough machined for example - or contains acceptable geometric features that trap the dye. Training of personnel to recognise genuine and spurious indications is therefore essential.
Eddy Current Testing (ET)
Method of using electromagnetic induction to detect flaws in electrically conductive materials .Continuous wave eddy current testing is one of several non-destructive testing methods that use the electromagnetism principle.
Conventional eddy current testing utilizes electromagnetic induction to detect discontinuities in conductive materials.
A specially designed coil energised with alternating current is placed in proximity to the test surface generating changing magnetic-field which interacts with the testpiece producing eddy current in the vicinity.
Variations in the changing phases and magnitude of these eddy currents is then monitored through the use of receiver-coil(s), or by measuring changes to the alternate current flowing in the primary excitation-coil.
The electrical conductivity variations or magnetic permeability of the testpiece, or the presence of any discontinuities, will cause a change in eddy current and a corresponding change in phases and amplitude of the measured current. The changes are shown on a screen for easy interpretation.
* Detection of very small cracks in or near the surface of the test part
* Physically complex geometries can be investigated
* Electrical conductivity measurement
* Coating thickness measurement
* Provides immediate feedback
* No couplant is required
* Checking for surface breaking cracks on metal
* Metal tube inspection for discontinuities
* Heat treat verification of metals
* Checking conductivity of metals, thickness of coatings and of thin metals
* Inspection of friction stir welds
* Testing gas turbine blades
* Inspection of a cast iron bridge
* Inspection of Hurricane propeller hubs
* Testing nozzle welds in nuclear reactore
Ultrasonic testing is one of the more common non-destructive testing methods performed on materials using very short ultrasonic pulse-waves to detect internal flaws or to characterize materials and also measure material thickness. This testing utilises high frequency mechanical energy, i.e. sound waves, to conduct examinations and measurements on a test area.
Typically, Ultrasonic inspection system consists of a transducer, pulser/receiver, and display unit.
A pulser/receiver is an electronic device that can produce high voltage electrical pulses to the transducer. When driven by the pulser, the transducer generates high frequency ultrasonic sound energy into the material in the form of sound waves. When there are discontinuities such as inclusions, porosity, cracks, etc. in the sound path, part of the mechanical energy will be reflected from the discontinuities' (reflectors') surface.
The reflected sound waves signal received by the transducer is then transformed back into an electrical signal and its intensity is shown on the display unit. The sound waves travel time can be directly related to the distance that the signal has travelled. From the signal, information about reflector location, size, orientation and other features can be determined.
* Capable of portable or highly automated operation
* Can be performed on all types of materials
* High accuracy and reproducibility in flaws detection
* Generally only one surface needs to be accessible
* Fluid level check in enclosure
* Materials characterisation
Method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials. In Radiography Testing the testpiece is placed between the radiation source and film (or detector). The material density and thickness differences of the testpiece will attenuate the penetrating radiation through interaction processes involving scattering and/or absorption.
The differences in absorption are then recorded on film(s). There are two different radioactive sources available for industrial use; X-ray and Gamma-ray. These radiation sources use higher energy level, i.e. shorter wavelength, versions of the electromagnetic waves. Because of the radioactivity involved in radiography testing, it is of paramount importance to ensure that the Local Rules is strictly adhered during operation.
* Can inspect assembled components
* Minimum surface preparation required
* Detects both surface and subsurface defects
* Provides a permanent record of the inspection
* Verify internal flaws on complex structures
* Isolate and inspect internal components
* Automatically detect and measure internal flaws
* Measure dimensions and angles within the sample without sectioning
* Sensitive to changes in thickness, corrosion, flaws and material density changes
Hardness has a variety of meanings.
* To the Metals industry, it may be thought of as resistance to permanent deformation.
* To the Metallurgist, it means resistance to penetration.
* To the Lubrication Engineer, it means resistance to wear.
* To the Design Engineer, it is a measure of flow stress.
* To the Mineralogist, it means resistance to scratching,
* To the Machinist, it means resistance to machining.
Hardness may also be referred to as mean contact pressure.
All of these characteristics are related to the plastic flow stress of materials
Hardness is a characteristic of a material, not a fundamental physical property. It is defined as a measure of the resistance to localised plastic deformation induced by either mechanical indentation or abrasion; and therefore,
it is determined by measuring the permanent depth of the indentation.
Some materials (e.g. metals) are harder than others (e.g. plastics). More simply put, an indenter is pressed into the surface of the material to be tested under a specific load for a definite time interval, and a measurement is made of the size or depth of the indentation, hence, the smaller the indentation, the harder the material.
Purpose of Hardness testing
The principal purpose of the hardness test is to determine the suitability of a material for a given application, or the particular treatment to which the material has been subjected. Determining these material properties provides valuable insight to the durability, strength, flexibility, and capabilities of a variety of component types from raw materials to prepared specimens, and finished goods.
Why is Hardness testing so Valuable?
The hardness test is, by far, the most valuable and most widely used mechanical test for evaluating the properties of metals as well as certain other materials.
The ease with which the hardness test can be made has made it the most common method of inspection for metals and alloys.
Certainly, as a material characteristic, its value and importance cannot be understated.
Principally, the importance of hardness testing has to do with the relationship between hardness and other material properties, that is, the information from a hardness test complements and is often used in conjunction with other material verification techniques such as tensile or compression to provide critical performance information.
For example, both the hardness test and the tensile test measure the resistance of a metal to plastic flow, and results of these tests may closely parallel each other. In the end, the hardness test is ,therefore, preferred because it is simple, easy, and relatively non-destructive.
Holiday (Continuity) Testing
Holiday (Continuity) Testing Holiday (Continuity) Testing is a non-destructive test method applied on non-conductive protective coatings such as rubberized waterproofing to detect unacceptable discontinuities such as pinholes and voids that are not readily visible.
Discontinuities are detected by the formation of an electrical circuit (current flow to complete the electric circuit) in areas where there is an insufficient coating to resist the flow of electrical charge. If the flow of electrical charge is detected, then the test area is termed as conductive, indicating the presence of discontinuities.
The testing is usually performed on tank interiors, chemical storage vessels and buried structures because of the importance of maintaining adequate coating protection in aggressive service environments.
A holiday (continuity) test is performed with either a low-voltage or a high-voltage holiday detector, which is an electrical device used to determine the location of a gap or a void in the coating.
Low-voltage holiday testing is used when the coating system is less than 500 microns (20 mils) thick. High-voltage holiday testing is used when the coating system is thicker. High-voltage holiday testing requires special care not to damage the coating or cause injury to the operator.
Positive Material Identification
Positive Material Identification (PMI) is the analysis of metals and metallic alloys before, during and after manufacturing to establish composition by reading the quantities by percentage of its constituent elements. PMI
tools reveal the chemical composition of a metal or alloy.
This allows accurate, on-the-spot identification of the material, before expensive mistakes occur.
PMI is helpful at every link in the chain of custody. It ensures that the correct specified material reaches its intended destination and application. It's an important step in building critical process components, quality control of pipes, valves, and reaction vessels, and identifying light elements as well as trace and tramp elements.
Typical methods for PMI include:
* X-ray Fluorescence (XRF)
* Optical Emission Epectrometry (OES).
Heat Treatment is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical.
Heat Treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening,
precipitation strengthening, tempering, normalizing, stress relieving, quenching e.t.c.
It is noteworthy that while the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.
Borescope Inspection is a visual non-destructive testing technique for the detection of defects or imperfections where the area to be inspected is inaccessible by other means, or where accessibility may require destructive, time consuming and/or expensive dismounting activities.
Borescopes are used to non-destructively inspect industrial systems and equipment for condition, manufactured parts for quality.
Common inspections include internal viewing of:
* Steam turbines
* Gas turbine engines
* Internal combustion engines
* Heat Exchanger Tunes
* Gear boxes
* Foreign Object Retrieval
* Cast Parts
* Manufactured or Machined Parts
Infrared Thermography is the process of acquisition and analysis of thermal information from non-contact thermal imaging devices. The practice quantitatively measures radiative heat emissions from objects for predictive and preventative maintenance programs.
Thermographic Inspection can be used to pinpoint components that are operating at a temperature higher than other components, indicating degradation, or to locate where energy losses are occurring such as in cryogenic fluid lines or steam pipes.
Use of Thermography
Thermography is used in predictive and preventative maintenance programs to reduce equipment down time. In addition, this prolongs equipment life, prevents schedule impacts due to untimely failures, and increases
Mechanical or electrical breakdowns of components are often preceded by changes in normal operating temperature. Advance notice of developing problems results in cost savings by resolving them before catastrophic failure occurs that could also damage other associated components.
Infrared scanning is a nondestructive technique which can be performed while the equipment is operating so there is no need for machine downtime and lost production. Portable thermal imaging measurement systems
provide images that can be stored on video recorders or built-in floppy disk drives for later recall during post analysis.
Advance notice of developing problems means they can be resolved or repaired during normal machine shutdowns rather than after a catastrophic failure that would cause lost man-hours and possible damage to other components associated with the failed item.
A visual inspection or examination of objects, parts or components is the oldest and reliable non-destructive method.
Quality control of welding which by means of examination, observation, and/or measurement of welds.
Third Party Inspection
MTIS can provide highly experienced and qualified personnel to undertake third party oversight in all NDT inspection areas