NDT.pdf

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NONDESTRUCTIVE TESTING (NDT) are noninvasive techniques to determine the integrity of a material, component or structure or quantitatively measure some characteristic of an object. In contrast to destructive testing, NDT is an assessment without doing harm, stress or destroying the test object. The destruction of the test object usually makes destructive testing testing more costly and it is also inappropriate in many circumstances.

NDT plays a crucial role in ensuring cost effective operation, safety and reliability of plant, with resultant benefit to the community. NDT is used in a wide range of industrial areas and is used at almost any stage in the production or life cycle of many components. The mainstream applications are in aerospace, power generation, automotive, railway, petrochemical and pipeline markets. NDT of welds is one of the most used applications. It is very difficult to weld or mold a solid object that has no risk of breaking in service, so testing at manufacture and during use is often essential. While originally NDT was applied only for safety reasons it is today widely accepted as cost saving technique in the quality assurance process. Unfortunately Unfortunately NDT is still not used in many areas where human life or ecology is in danger. Some may prefer to pay the lower costs of claims after an accident than applying of NDT. That is a form of unacceptable risk management. management. Disasters like the railway accident in Eschede Germany in 1998 is only one example, there are many others. For implementation of NDT it is important to describe what shall be found and what to reject. A completely flawless production is almost never possible. For this reason testing specifications are indispensable. Nowadays there exists a great number of standards and acceptance regulations. They describe the limit between good and bad conditions, but also often which specific NDT method has to be used. The reliability of an NDT Method is an essential issue. But a comparison of methods is only significant if it is referring to the same task. Each NDT method has its own set of advantages and disadvantages and, therefore, some are better suited than others for a particular application. By use of artificial flaws, the threshold of the sensitivity of a testing system has to be determined. If the the sensitivity is to low defective test objects are not always recognized. If the sensitivity is too high parts with smaller flaws are rejected which would have been of no consequence to the serviceability serviceability of the component. With statistical statistical methods it is possible to look closer into the field of uncertainly. Methods such as Probability of Detection (POD) or the ROC-method "Relative Operating Characteristics" Characteristics" are examples of the statistical analysis methods. Also the aspect of human errors has to be taken into account when determining the overall reliability. Personnel Qualification is an i mportant aspect of non-destructive evaluation. NDT techniques rely heavily on human skill and knowledge for the correct assessment and interpretation of test results. Proper and adequate training and certification of NDT personnel is therefore a must to ensure that the capabilities of the techniques techniques are fully exploited. There are a number of published international and regional standards covering the certification of competence of personnel. The EN 473 (Qualification and certification of NDT personnel - General Principles) was developed specifically for the European Union for which the SNT-TC-1A is the American equivalent. The nine most common NDT Methods are shown in the main index of this encyclopedia. In order of most used, they are: Ultrasonic Testing (UT), Radiographic Testing (RT), Electromagnetic Testing (ET) in which Eddy Current Testing (ECT) is well know and Acoustic Emission (AE or AET). Besides the main NDT methods a lot of other NDT techniques are available, such as Shearography Holography, Microwave and many more and new methods are being constantly researched and developed.


NDT Applications and Limitations

NDT Method Liquid Penetrant

Applications  

Magnetic Particle

used on nonporous materials can be applied to welds, tubing, brazing, castings, billets, forgings, aluminium parts, turbine blades and disks, gears

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ferromagnetic materials

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surface and slightly subsurface flaws can be detected can be applied to welds, tubing, bars, castings, billets, forgings, extrusions, engine components, shafts and gears

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Ultrasonics

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Radiography Neutron

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metals, alloys and electroconductors sorting materials surface and slightly subsurface flaws can be detected used on tubing, wire, bearings, rails, nonmetal coatings, aircraft components, turbine blades and disks, automotive transmission shafts

metals, nonmetals and composites surface and slightly subsurface flaws can be detected can be applied to welds, tubing, joints, castings, billets, forgings, shafts, structural components, concrete, pressure vessels, aircraft and engine components used to determine thickness and mechanical properties monitoring service wear and deterioration

metals, nonmetals, composites and mixed materials used on pyrotechnics, resins, plastics, organic material, honeycomb structures, radioactive material, high density materials, and materials containing hydrogen

decontamination & precleaning of test surface may be needed vapour hazard

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very tight and shallow defects difficult to find

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depth of flaw not indicated

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detection of flaws limited by field strength and direction

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needs clean and relatively smooth surface some holding fixtures required for some magnetizing techniques test piece may need demagnetization which can be difficult for some shapes and magetizations depth of flaw not indicated

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Eddy Current

need access to test surface defects must be surface breaking

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requires customized probe although non-contacting it requires close proximity of probe to part low penetration (typically 5mm) false indications due to uncontrolled parametric variables

usually contacting, either direct or with intervening medium required (e.g. immersion testing) special probes are required for applications sensitivity limited by frequency used and some materials cause significant scattering scattering by test material structure can cause false indications not easily applied to very thin materials

access for placing test piece between source and detectors size of neutron source housing is very large (reactors) for reasonable source strengths collimating, filtering or otherwise modifying beam is difficult radiation hazards cracks must be oriented parallel to beam for detection sensitivity decreases with increasing


thickness Radiography X-ray

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metals, nonmetals, composites and mixed materials used on all shapes and forms; castings, welds, electronic assemblies, aerospace, marine and automotive components

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Radiography Gamma

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usually used on dense or thick material used on all shapes and forms; castings, welds, electronic assemblies, aerospace, marine and automotive components used where thickness or access limits X-ray generators

access to both sides of test piece needed voltage, focal spot size and exposure time critical radiation hazards cracks must be oriented parallel to beam for detection sensitivity decreases with increasing thickness

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radiation hazards

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cracks must be oriented parallel to beam for detection sensitivity decreases with increasing thickness access to both sides of test piece needed not as sensitive as X-rays

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REBOUND HAMMER

In 1948 Ernst Schmidt invented a device which made nondestructive compressive strength testing feasible. A Schmidt hammer is a device to measure the elastic properties or strength of concrete or rock. Today Schmidt hammers are in use throughout the world for estimating strength of concrete. The European standard for Schmidt hammer testing is EN 12504-2. The test hammer hits the concrete with a spring-driven pin at a defined energy, and then measures the rebound (in rebound units). Its rebound is dependent on the hardness of the concrete and is measured by test equipement. When conducting the test the hammer should be held perpendicular to the surface which in turn should be flat and smooth. Note that the Schmidt hammer does not work well for small samples and will make marks. By reference to the conversion tables, the rebound value can be used to determine the compressive strength. Schmidt hammers are available from their original manfacturers in several different energy ranges. Although, rebound hammer provides a quick inexpensive means of checking the uniformity of concrete, it has limitations. The test is also sensitive to local variation in the sample. To minimise this it is recommended to take a selection of readings and take an average value. In an assessment of the influence of internal rock moisture content on Schmidt hammer readings, rebound (R) values are found to decrease with increasing moisture content. Other influences are type of coarse aggregate, cement, mould, carbonation of concrete surface. Each hammer varies considerable in performance and needs calibration for use on concrete made with the aggregates from specific source. The test can be conducted horizontally, vertically or at intermediate angles. At each angle the rebound number will be different for the same concrete and will require separate calibration or correction chart Investigations have shown that there is a general correlation between compressive strength of concrete and rebound number; however, there is a wide degree of disagreement among various research workers regarding the accuracy of estimation of strength from rebound readings. The variation of strength of a properly calibrated hammer may lie between +/- 15% and +/- 20%.


VISUAL AND OPTICAL TESTING HOLOGRAPHY

Optical Holographic techniques can be used for nondestructive testing of materials (HNDT). Non-optical Holography techniques include Acoustical, Microwave, X-Ray and Electron beam Holography. HNDT essentially measures deformations on the surface of the object. However, there is sufficient sensitivity to detect subsurface and internal defects in metallic and composite specimens. In HNDT techniques, the test sample is interferometrically compared with the sample after it has been stressed (loaded). A flaw can be detected if by stressing the object it creates an anomalous deformation of the surface around the flaw.

Optical holography is an imaging method, which records the amplitude and phase of light reflected from an object as an interferometric pattern on film. It thus allows reconstruction of the full 3-D image of the object. In HNDT, the test sample is interferometrically compared in two different stressed states. Stressing can be mechanical, thermal,


vibration etc. The resulting interference pattern contours the deformation undergone by the specimen in between the two recordings. Surface as well as sub-surface defects show distortions in the otherwise uniform pattern. In addition, the characteristics of the component, such as vibration modes, mechanical properties, residual stress etc. can be identified through holographic inspection. Applications in fluid mechanics and gas dynamics also abound. The light used to illuminate the surface of the specimen must be coherent, which means that it must also be monochromatic, and the only practical source is a laser. Each type of laser emits a characteristic wavelength, e.g. a helium-neon laser emits 632.8nm; a ruby laser emits 694.3nm. Laser diodes are nowadays an exciting and compact alternative. Indeed, holography using laser pointers have also been demonstrated. High-resolution films are another necessity for holography. With the advent of CCD and digital image processing, digital holographic interferometry offers tremendous flexibility and real-time visualization. Furthermore, imageprocessing schemes can provide computerised analysis of patterns for automated defect detection and analysis. Finally since intricate interferometric patterns have to be recorded, vibration isolation is also required. Novel schemes have been proposed, including use of pulsed lasers to record holograms in factory environments. Advances and developments in lasers, computers, and recording materials introduce new techniques such as electronic (or TV) holography, multi-wavelength recording, thermoplastic medium, time-averaged holography, dynamic holographic interferometry, cineholography, and digital holography with each new development. Methods that once held only academic interest often become practically viable with these developments in hardware and software. HNDT is widely applied in aerospace to find impact damage, corrosion, delamination, debonds, and cracks in high performance composite aircraft parts as well as turbine blades, solid propellant rocket motor casings, tyres and air foils. But Holography is also finding new applications in commercial and defense related industries to investigate and test object ranging from microscopic computer chips and circuits to cultural articles, paintings and restoration

LASER

A short laser pulse is focused on to the surface of a sample to create the plasma. A laser with a good Gaussian profile allows focusing to a near diffraction-limited spot. The tighter the focus, the less laser energy is required to produce the laser-induced breakdown. Typically energies of only tens of millijoules are required. (Fig.1) The plasma is emitted into >2p steradians, so a fast f/1 lens will collect more light. Sometimes a blocking filter is used to remove any scatter from the incident laser - however, since the incident laser light and the signal are well resolved temporally, a filter is rarely required. An Intensified CCD (ICCD) detector attached to a spectrograph analyzes the collected plasma light.


For LIBS, Echelle spectrographs are typically used.For analysis of a wide range of samples, a system based on an echelle spectrograph offers a combination of high resolution and wide wavelength coverage.It is also possible to relay the laser light to the sample and collect the signal by fiber optics. The gating requirements of LIBS are not very demanding. Gate times and delays of several microseconds are typical, so a slow gate ICCD is suitable. The system can usually be operated in internal trigger mode, with the controller board triggering the laser and the delay generator. The intensity of the plasma emission is usually high enough to allow good spectra to be recorded in single scan mode.A typical experimental configuration is shown below. (Fig.2)

RECENT ADVANCES IN EQUIPMENT Commercially available equipment now includes:

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'PUNDIT PLUS' - which is a new generation, microprocessor-based, development of the long-established PUNDIT ultrasonic tester widely used on concrete, now offering data storage facilities [2]. New sub-surface radar equipment for testing concrete structures offering improved portability, and higher frequency antennas with improved performance characteristics. New hand-held 4-probe resistivity test equipment for concrete structures, with automatic data storage. Acoustic-Emission (AE) equipment suitable for routine field use, including one system developed in the UK. Improved covermeters, including a 'borehole probe' device. Improved radiography systems including reductions in size and increased energy levels, together with better image capture and processing as well as safety features (eg 'MEGASCAN [TM]').


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Laser-based surface strain and pavement deformation measuring devices.

Several specialist test companies have also successfully developed equ ipment configurations and software for use in specific situations for example, multiple radar antenna arrays for highway surveys. Another interesting example is the 'TERRIG' system [3] for determining the bearing capacity of material below existing concrete ground -slabs based on load/deflection measurements as illustrated in figure 1. This is particularly useful when an a ssessment of floor capacity is needed relating to change of use.

CONCRETE NON-DESTRUCTIVE NDT TEST EQUIPMENT

Concrete Non-Destructive NDT Test Equipment

Strength Testing

Rebar Locators

Ultrasonic Testing

Corrosion Testing

Temperature Monitoring

Moisture Meters

Compression Testers

Holiday Detectors

Cement Testing

NDT Concrete Strength Testers This category of products comprises the range of instruments utilized to evaluate construction material strength. The range of instruments is typically considered to be two parts. The first are non-destructive field tests of compressive strength. The second are tensile field tester systems to either determine the tensile strength of an overlay o r bond material, or tensile strength of anchors embedded in the concrete. The first group is pure Non-Destructive Testing where the strength of the material is determined by correlation to another parameter more easily available and readily apparent. This is typically the hardness of the concrete or the resistance to penetration by either a pin or probe. The Windsor Probe, Windsor Pin and our line of Rebound Hammers all fall within this category. These are widely used standard tests and as such have seen use throughout the world. The second set of instruments is our concrete tensile testers. These have been optimized to both test the strength of the anchors and repair overlay material. They can be used to test until failure or to simply verify that the material will not be affected by a specific amount of force. A number of considerations were taken into account when designing this line of products, include viscous damping of the resultant failure backlash, portability, and ruggedness.


If you are looking for High capacity Compression Machines for Concrete Cylinders and Cubes, please CLICK HERE. The line of products represents the most effective a nd efficient way to evaluate construction material strength in the field and utilize the latest in technology in order to guarantee accurate results. We supply a wide range of non-destructive test equipment for concrete and other coarse grained materials. Our instruments measure and analyze strength, and structure, and are rugged, quality equipment for field use, backed by factory service and an ongoing program of research and development. All instruments are NIST traceable and conform to the corresponding ASTM standards.

Windsor HP Probe Measures the compression strength of concrete. CLICK HERE

Windsor Pin System Measures compressive strength of new or mature construction materials. CLICK HERE

Concrete Rebound Hammers Indicates the compressive strength of hardened concrete. CLICK HERE


Bond Tester Accurately measures the bonding strengths of a wide and varied range of materials including concrete, screeds, repair mortars, epoxy resin coatings, laminates, plastics, paints and enamels CLICK HERE

Anchor Test System Measures a wide range of anchor strengths in construction materials. CLICK HERE

Rebar Locators This category of products comprises the range of instruments used to locate and determine size and depth of steel reinforcing bar in concrete. The first type most widely used utilizes a low frequency electromagnetic field to locate ferrous objects within a structure. The second and latest technology utilizes Ground Penetrating radar to loca te steel and other objects within a structure. The HR Rebar Locator and the Datascan both utilize a low frequency electromagnetic field to locate ferrous objects in a structure. By closely monitoring changes in the electromagnetic field the proximity of steel reinforcing bar can be determined. The HR is our most economical model. It uses a simple analog meter to determine the strength of the electromagnetic field and correlate this to either the size of the rebar or the distance to the rebar. The Datascan unit utilizes a more sensitive digital system to monitor the strength of the electromagnetic field. This allows the user more sensitivity in locating steel at greater depth and more closely spaced.


The Datascan MK II utilizes the state of the art in ground penetrating radar technology. By sending out a high frequency pulse and observing the reflected electromagnetic waves features inside a concrete structure can be determined. The unit implements a number of different ways to visualize the data received, including a three dimensional image of the objects within the structure. This unit represents the current cutting edge technology in object location. The line of products represents the most effective and efficient way to evaluate steel reinforcing bar in the field and utilizes the latest in technology in order to guarantee accurate results.

HR Rebar Locator Locates the position, depth and size of reinforcement bars CLICK HERE

Rebar Locator - R-Meter MK III Model 3000 R-Meter MK III is the digital version of a classic rebar locator, rebar finder which enables the user to locate reinforcement bars and also determine rebar location and rebar size. The R-Meter MK III rebar locator is also capable of locating non ferrous metals as well. CLICK HERE

Ultrasonic Concrete Testing This category comprises the range of instruments that use sound or stress waves in order to determine the properties of concrete and othe r materials non-destructively. The first and most widely used System is our V-Meter, which utilizes the ultrasonic pulse velocity method for


evaluating construction materials in the field. Transducers are available for a variety of frequencies from 24 KHz to 500 KHz. This unit has also been modified to suit the special needs of ceramics users and can be found as the Ultrapulse. The PIES, our revolutionary Portable Impact-Echo System, is an advanced instrument for non-destructive detection of flaws and defects in a variety of civil infrastructures ranging from bridges, parking structures and buildings to dams, piles, tunnels, tanks and marine structures. Finally our E-Meter System represents the state of the art in be nch top laboratory resonant frequency analysis of materials. This unit comes standard with a test bench designed to handle a variety of modes of vibration, including longitudinal, torsional and flexural. This line of products represents the most effective and efficient way to evaluate concrete and other materials in the field and utilizes the latest in technology in order to guarantee accurate results.

Ultrasonic E-Meter MKII For the Determination of the Resonant Freque ncy of Materials such as Concrete, Glass, Carbon & Graphite, Ceramic White ware as well as in refractories. CLICK HERE

Ultrasonic V-Meter Detects flaws and measures basic characteristics in coarse-grained material. CLICK HERE


Portable Impact-Echo System Offers unparalleled ease of use to test structures using sonic stress waves. CLICK HERE

Corrosion Testing This category comprises the range of instruments that evaluate parameters related to the corrosion of the concrete or the steel reinforcing bar within the concrete. The Ohmcor and Cormap systems represent more ec onomical methods of evaluating steel reinforcement corrosion. The Cormap Systems use half cell potential mapping in order to identify areas of probably corrosion. The Ohmcorr System is typically used in conjunction with the Cormap system n order to verify the presence of steel reinforcement corrosion. This older technology is still widely used in the field. The Porosiscope and Chloride Field Systems allow the user to rapidly evaluate mechanisms that cause corrosion. The Porosiscope quickly and simply evaluates concrete permeability. The Chloride Field System will rapidly evaluate field chloride levels without expensive and time consuming laboratory tests. Our ASR Detect and Carbodetect systems are chemical indicators to assist in evaluating the two leading causes of concrete corrosion. This line of products represents the most effective and efficient way to evaluate concrete and other materials in the field and utilizes the latest in technology in order to guarantee accurate results. Finally, the extensive range of our Holiday / Porosity Detectors complement our Corrosion line and are used to detect the pinholes, and porosity in order to prevent from corrosion.


CorMap A Simple Economical Method for Identifying Areas of Probab le Rebar Corrosion CLICK HERE

Cor-Map II For corrosion potential data acquisition and analysis, allowing the user to identify areas of probable corrosion in the field. CLICK HERE

Chloride Field Test System A Chloride Laboratory in a Briefcase for Wet or Dry Concrete CLICK HERE

ASR Detect Simple colored dye field test to detect Alkali Silca Reaction (ASR)


CLICK HERE

Carbo Detect Simple colored dye field test for carbonation CLICK HERE

OhmCorr Resistivity Meter to Assess Corrosion Currents in Concrete CLICK HERE

Porosiscope-Plus Concrete Air / Water Permeability Tester The Field Test for Air and Water Permeability of Concrete Using the FIGG Technique CLICK HERE


Holiday / Porosity Detectors Extensive Range of Holiday / Porosity Detectors for Detection of Porosity and Corrosion Prevention. CLICK HERE

Temperature Monitoring, Moisture & Flow Testing This category comprises the range of instruments that record temperature and can then evaluate maturity of fresh concrete. The IQM System is the latest technology for concrete maturity. Designed specifically for monitoring and analyzing fresh concrete, the IQM Module is programmed with the required Equivalent Age of the concrete under test. Once this preset maturity number is reached, a visual indicator will flash continuously, providing an effective, automatic indication that the concrete has reached the desired level of maturity. This with a readily available PC represents a fast and efficient means of monitoring concrete maturity. A flexible and economical temperature monitoring system, the IQT features extensive memory and graphic display of temperature history. Similar to the IQM, the IQT System offers software for uploading the temperature data to a P.C. through its serial port. The temperature history can then be displayed with respect to time. Also a Multi Channel Maturity meter is available upon your request. This line of products represents the most effective and efficient way to evaluate concrete and other materials in the field and utilizes the latest in technology in order to guarantee accurate results. Our Moisture Testing line are suited for determining the moisture content of construction materials. This is a critical factor in determining quality of final construction. The Trident utilizes the latest microwave and microprocessor technology to measure moisture content in various fine and coarse-grained sand and aggregates. The prongs of the probe are inserted into the material to be tested and the percentage of moisture content is instantaneously shown on the easy to read display.


The Aquameter is an advanced digital instrument, using a high frequency capacitive sensor to accurately measure the water content of concrete, masonry, brick, gypsum and most solid materials. This line of products represents the most effective and efficient way to evaluate concrete and other materials in the field and utilizes the latest in tec hnology in order to guarantee accurate results. Lastly the Fresh Concrete Flow Meter and Flow Gauge, are very useful tools for analysis of the consistency and workability of Fresh Concrete

IQM System The IQM System Enables Fresh Concrete to be Easily and Completely Monitored in the Field for Improved Safety, Quality Assurance and Optimum Setting Time. CLICK HERE

IQT System Flexible and Economical Temperature Monitoring System with Extensive Memory CLICK HERE

Moisture Master T-M-170 A Hand Held Instrument for Fast Accurate Measurement of Moisture Con tent in Solid Materials. CLICK HERE


Trident Moisture Meter A Microwave Meter for Rapid Determination of Moisture Content in Sand and Other Fine and Coarse Aggregates CLICK HERE

NDT.pdf

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