10-06-2017, 06:58 AM
[attachment=3204]
Abstract
Destructive and non-destructive methods have been used for the determination of micro-traces of antimony in high-purity silicon powder. The destructive method was based on sub-stoichiometric radio-activation analysis with solvent extraction using BPHA and cupferron as organic reagents. The antimony contents in high-purity silicon can be determined by the proposed method.
A new non-destructive method was developed for the detection of refrigerant leakage at an evaporator's inflow. Nitrogen and oxygen gas were successively blown through the evaporator. A gas analyser was applied at the outflow of the evaporator and the oxygen concentration measured. It was possible to detect any leakage by investigating the oxygen concentration time history diagram.
Non-destructive method for detecting zones with non-conductive materials, such as materials that include glass fibres, in a part made of a conductive composite, such as a composite whose reinforcing fibres are carbon fibres, provided with an organic coating, that comprises the following stages: a) providing a device for applying an electric potential on the surface of said part; b) determining the dielectric breakdown potential Pr corresponding to the thickness E of the coating; c) applying said dielectric breakdown potential Pr with said device to the part for the purpose of identifying those zones that have non-conductive materials when dielectric breakdown does not occur in them
Key Words:
Leakage detection, analyzer, reagents, fibres, silicon powder, refrigeration, plate evaporator
Introduction
The advantages of using light-weight, corrosion resistant composite materials and structures for deepwater developments have become increasingly important in recent years and many composite components are being used or developed for use in the exploration and production of oil and gas. Early composite applications have been lightly-loaded, i.e., pipes and gratings which are primarily constructed of glass fiber and epoxy resin. Most qualification and in-service re-qualification to date have been based on test data and visual inspection. Advanced composite applications are now emerging for critical, primary structural components, such as drilling and production risers, drill pipe, spoolable high-pressure pipe, subsea pipelines, tendons, and synthetic fiber mooring ropes. These components are much more highly-loaded and therefore structurally demanding, and their remoteness from the surface introduces inspection and monitoring challenges. Alternative carbon, polyester, and other fibers as well as advanced resins are being proposed for applications. One of the main issues which has been identified as a technology deficiency inhibiting the deployment of composite components offshore is the effect of damage to components and the associated issue of how to find and determine the extent of damage. At issue is Are there reliable, affordable Non Destructive Evaluation (NDE) methods which could be used to ascertain the fitness for service of components following manufacture and during service? Reliable NDE methods that can economically monitor the performance and continuing integrity of composite component in critical structural applications could provide better understanding and confidence and lead to the development of rationale and realistic inspection strategies.
Composite manufacturing defects such as delamination and voids as well as damage experienced in service can lead to premature failure of the component. It is important that Non-Destructive Examination (NDE) methods be available to examine composite structure components to determine their state of fitness-for-service following manufacture as well as at scheduled and special times during the service life. Some of the NDE methods used for metals such as x-ray are also applicable to composites, but for the most part a completely different set of NDE tools must be used. There has been considerable research in recent years to develop NDE methods for the inspection of composite aerospace and automotive components. With a small amount of adaptation, some of these methods can be applied to composite structures used offshore. Methods such as ultrasonic, radiography, thermography and acoustic emission are well established, but require skilled technician interpretation. Other promising methods such as fiber optic sensors, trip metal strain sensors and embedded sensors are just emerging. In addition, considerable research results are emerging from NDE applications in other industries.
Interferometry methods such as shearography are being used to inspect large aerospace structures and may have merit for oil industry components. The lack of familiarity with the unique problems and challenges of the oil industry by NDE experts and similar unfamiliarity by the oil industry of the advancements that have been made in NDE technology currently inhibit the utilization of NDE methods.
The primary barriers to applying NDE technology in the oil industry are thus both technical and inadequate communications including: (1) lack of opportunity to develop experience-base inspection strategies based on actual in-situ performance of these new components, (2) need for advancements in applying NDE methods to the specific needs of the oil industry and (3) lack of information to assess the potential benefits, costs and limitations in applying NDE methods. The workshop on Non-Destructive Evaluation Methods for Inspecting Offshore Composite Components sponsored by the Texas A&M University Offshore Technology Research Center and the Minerals Management Service held on November 21, 2002 was designed to address these issues. The long-term benefit is expected to be to sort out what is needed, what is available, what can be developed, and to serve as a catalyst for development efforts to make available the technology to inspect composite components used in the offshore oil industry. The availability of reliable NDE inspection methods is important not only to the operators, but also for regulatory authorities to gain the both experience and confidence in the safe application of critical composite components being introduced offshore.
Destructive Testing:
In destructive testing, tests are carried out to the specimen's failure, in order to understand a specimen's structural performance or material behavior under different loads. These tests are generally much easier to carry out, yield more information, and are easier to interpret than non-destructive testing.
Destructive testing is most suitable, and economic, for objects which will be mass produced, as the cost of destroying a small number of specimens is negligible. It is usually not economic to do destructive testing where only one or very few items are to be produced (for example, in the case of a building).
Some types of destructive testing:
Stress tests
Crash tests
Hardness tests
Metallographic tests
Testing of large structures
The above figure shows the shake-table video of a 6-story non-ductile concrete building
Building structures or large non-building structures (such as dams and bridges) are rarely subjected to destructive testing due to the prohibitive cost of constructing a building, or a scale model of a building, just to destroy it.
Earthquake engineering requires a good understanding of how structures will perform at earthquakes. Destructive tests are more frequently carried out for structures which are to be constructed in earthquake zones. Such tests are sometimes referred to as crash tests, and they are carried out to verify the designed seismic performance of a new building, or the actual performance of an existing building. The tests are, mostly, carried out on a platform called a shake-table which is designed to shake in the same manner as an earthquake. Results of those tests often include the corresponding shake-table videos.
As structural performance at earthquakes is better understood, testing of structures in earthquakes is increasingly done by modeling the structure using specialist finite element software.
Destructive software testing
Destructive software testing is a type of software testing which attempts to cause a piece of software to fail in an uncontrolled manner, in order to test its robustness.
Non Destructive Testing:
NDT is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage. Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation, troubleshooting, and research. Common NDT methods include ultrasonic, magnetic-particle, liquid penetrant, radiographic, and eddy-current testing. NDT is a commonly-used tool in forensic engineering, mechanical engineering, electrical engineering, civil engineering, systems engineering, medicine, and art.
Methods
NDT methods may rely upon use of electromagnetic radiation, sound, and inherent properties of materials to examine samples. This includes some kinds of microscopy to examine external surfaces in detail, although sample preparation techniques for metallography, optical microscopy and electron microscopy are generally destructive as the surfaces must be made smooth through polishing or the sample must be electron transparent in thickness. The inside of a sample can be examined with penetrating electromagnetic radiation, such as X-rays, or with sound waves in the case of ultrasonic testing. Contrast between a defect and the bulk of the sample may be enhanced for visual examination by the unaided eye by using liquids to penetrate fatigue cracks. One method (liquid penetrant testing) involves using dyes, fluorescent or non-fluorescing, in fluids for non-magnetic materials, usually metals. Another commonly used method for magnetic materials involves using a liquid suspension of fine iron particles applied to a part while it is in an externally applied magnetic field (magnetic-particle testing).
Weld verification
1. Section of material with a surface-breaking crack that is not visible to the naked eye.
2. Penetrant is applied to the surface.
3. Excess penetrant is removed.
4. Developer is applied, rendering the crack visible.
In manufacturing, welds are commonly used to join two or more metal surfaces. Because these connections may encounter loads and fatigue during product lifetime, there is a chance that they may fail if not created to proper specification. For example, the base metal must reach a certain temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold the surfaces together, or cracks may form in the weld causing it to fail. The typical welding defects, lack of fusion of the weld to the base metal, cracks or porosity inside the weld, and variations in weld density, could cause a structure to break or a pipeline to rupture.
Welds may be tested using NDT techniques such as industrial radiography using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing or via eddy current and flux leakage. In a proper weld, these tests would indicate a lack of cracks in the radiograph, show clear passage of sound through the weld and back, or indicate a clear surface without penetrant captured in cracks.
Welding techniques may also be actively monitored with acoustic emission techniques before production to design the best set of parameters to use to properly join two materials.
Structural mechanics
Structures can be complex systems that undergo different loads during their lifetime. Some complex structures, such as the turbo machinery in a liquid-fuel rocket, can also cost millions of dollars. Engineers will commonly model these structures as coupled second-order systems, approximating dynamic structure components with springs, masses, and dampers. These sets of differential equations can be used to derive a transfer function that models the behavior of the system.
In NDT testing, the structure undergoes a dynamic input, such as the tap of a hammer or a controlled impulse. Key properties, such as displacement or acceleration at different points of the structure, are measured as the corresponding output. This output is recorded and compared to the corresponding output given by the transfer function and the known input. Differences may indicate an inappropriate model (which may alert engineers to unpredicted instabilities or performance outside of tolerances), failed components, or an inadequate control system.
Radiography in medicine
Chest radiography indicating a 'Peripheres Bronchialcarcinom'.
As a system, the human body is difficult to model as a complete transfer function. Elements of the body, however, such as bones or molecules, have a known response to certain radiographic inputs, such as x-rays or magnetic resonance. Coupled with the controlled introduction of a known element, such as digested barium, radiography can be used to image parts or functions of the body by measuring and interpreting the response to the radiographic input. In this manner, many bone fractures and diseases may be detected and localized in preparation for treatment. X-rays may also be used to examine the interior of mechanical systems in manufacturing using NDT techniques, as well.
Notable events in early industrial NDT
1854 Hartford, Connecticut: a boiler at the Fales and Gray Car works explodes, killing 21 people and seriously injuring 50. Within a decade, the State of Connecticut passes a law requiring annual inspection (in this case visual) of boilers.
1895 Wilhelm Conrad R ntgen discovers what are now known as X-rays. In his first paper he discusses the possibility of flaw detection.
1880 - 1920 The "Oil and Whiting" method of crack detection is used in the railroad industry to find cracks in heavy steel parts. (A part is soaked in thinned oil, then painted with a white coating that dries to a powder. Oil seeping out from cracks turns the white powder brown, allowing the cracks to be detected.) This was the precursor to modern liquid penetrant tests.
1920 Dr. H. H. Lester begins development of industrial radiography for metals. 1924 Lester uses radiography to examine castings to be installed in a Boston Edison Company steam pressure power plant [1].
1926 The first electromagnetic eddy current instrument is available to measure material thicknesses.
1927 - 1928 Magnetic induction system to detect flaws in railroad track developed by Dr. Elmer Sperry and H.C. Drake.
1929 Magnetic particle methods and equipment pioneered (A.V. DeForest and F.B. Doane.)
1930s Robert F. Mehl demonstrates radiographic imaging using gamma radiation from Radium, which can examine thicker components than the low-energy X-ray machines available at the time.
1935 - 1940 Liquid penetrant tests developed (Betz, Doane, and DeForest)
1935 - 1940s Eddy current instruments developed (H.C. Knerr, C. Farrow, Theo Zuschlag, and Fr. F. Foerster).
1940 - 1944 Ultrasonic test method developed in USA by Dr. Floyd Firestone.
1950 The Schmidt Hammer (also known as "Swiss Hammer") is invented. The instrument uses the world s first patented non-destructive testing method for concrete.
1950 J. Kaiser introduces acoustic emission as an NDT method.
(Source: Hellier, 2001) Note the number of advancements made during the WWII era, a time when industrial quality control was growing in importance.
Applications
NDT is used in a variety of settings that covers a wide range of industrial activity.
Automotive
Engine parts
Frame
Aviation / Aerospace
Airframes
Space frames
Power plants
Propellers
Reciprocating Engines
Gas turbine engines
Rocketry
Construction
Structures
Bridges
Maintenance, repair and operations
Bridges
Manufacturing
Machine parts
Castings and Forgings
Industrial plants such as Nuclear, Petrochemical, Power, Refineries, Pulp and Paper, Fabrication shops, Mine processing and their Risk Based Inspection programmes.
Pressure vessels
Storage tanks
Welds
Boilers
Heat exchangers
Turbine bores
In-plant Piping
Miscellaneous
Pipelines
In-line Inspection using "pigs"
Pipeline integrity management
Leak Detection
Railways
Rail Inspection
Wheel Inspection
Tubular NDT, for Tubing material
Corrosion Under Insulation (CUI)
Amusement park rides
Submarines and other Naval warships
Medical imaging applications (see also Medical physics)
Methods and techniques
NDT is divided into various methods of nondestructive testing, each based on a particular scientific principle. These methods may be further subdivided into various techniques.
The various methods and techniques, due to their particular natures, may lend themselves especially well to certain applications and be of little or no value at all in other applications. Therefore choosing the right method and technique is an important part of the performance of NDT.
An example of Ultrasonic Testing (UT) on blade roots of a V2500 IAE aircraft engine.
Step 1: The UT probe is placed on the root of the blades to be inspected with the help of a special bore-scope tool (video probe).
Step 2: Instrument settings are input.
Step 3: The probe is scanned over the blade root. In this case, an indication (peak in the data) through the red line (or gate) indicates a good blade; an indication to the left of that range indicates a crack.
An example of a 3D replicating technique.
The flexible high-resolution replicas allow surfaces to be examined and measured under laboratory conditions. A replica can be taken from all solid materials.
Acoustic emission testing (AE or AT)
Dye penetrant inspection Liquid penetrant testing (PT or LPI)
Electromagnetic testing (ET)
Alternating current field measurement (ACFM)
Alternating current potential drop measurement (ACPD)
Barkhausen testing
Direct current potential drop measurement (DCPD)
Eddy-current testing (ECT)
Magnetic flux leakage testing (MFL) for pipelines, tank floors, and wire rope
Magnetic-particle inspection (MT or MPI)
Remote field testing (RFT)
Ellipsometry
Hardness testing (Brinell) (HT)
Impulse excitation technique (IET)
Infrared and thermal testing (IR)
Thermographic inspection
Laser testing
Electronic speckle pattern interferometry
Holographic interferometry
Profilometry
Shearography
Leak testing (LT) or Leak detection
Absolute pressure leak testing (pressure change)
Bubble testing
Halogen diode leak testing
Hydrogen leak testing
Mass spectrometer leak testing
Tracer-gas leak testing method Helium, Hydrogen and refrigerant gases
Magnetic resonance imaging (MRI) and NMR spectroscopy
Optical microscopy
Positive Material Identification (PMI)
Radiographic testing (RT) (see also Industrial radiography and Radiography)
Computed radiography
Digital radiography (real-time)
Neutron radiographic testing (NR)
SCAR (Small Controlled Area Radiography)
X-ray computed tomography (CT)
Scanning electron microscopy
Ultrasonic testing (UT)
Electro Magnetic Acoustic Transducer (EMAT) (non-contact)
Laser ultrasonics (LUT)
Internal rotary inspection system (IRIS) ultrasonics for tubes
Phased array ultrasonics
Time of flight diffraction ultrasonics (TOFD)
Time of Flight Ultrasonic Determination of 3D Elastic Constants (TOF)
Visual inspection (VT)
Pipeline video inspection
TERMINOLOGY
Indication
The response or evidence from an examination, such as a blip on the screen of an instrument.
Interpretation
Determining if an indication is of a type to be investigated. For example, in electromagnetic testing, indications from metal loss are considered flaws because they should usually be investigated, but indications due to variations in the material properties may be harmless and non-relevant.
Flaw
A type of discontinuity that must be investigated to see if it is rejectable. For example, porosity in a weld or metal loss.
Evaluation
Determining if a flaw is rejectable. For example, is porosity in a weld larger than acceptable by code?
Defect
A flaw that is rejectable - i.e. does not meet acceptance criteria. Defects are generally removed or repaired.
(Source: ASTM E1316 in 'Vol. 03.03 NDT)
Penetrant testing
Non-destructive test typically comprising a penetrant, a method of excess removal and a developer to produce a visible indication of surface-breaking discontinuities.
(Source: ISO 12706:2000, Note: To be replaced by ISO/DIS 12706 (2008-03).)
Reliability and statistics
Defect detection tests are among the more commonly employed of non-destructive tests. The evaluation of NDT reliability commonly contains two statistical errors. First, most tests fail to define the objects that are called "sampling units" in statistics; it follows that the reliability of the tests cannot be established. Second, the literature usually misuses statistical terms in such a way as to make it sound as though sampling units are defined. These two errors may lead to incorrect estimates of probability of detection. [2] [3].
References
Cartz, Louis (1995). Nondestructive Testing. A S M Internationl.
Blitz, Jack; G. Simpson (1991). Ultrasonic Methods of Non-Destructive Testing. Springer-Verlag New York, LLC.
Bibliography
ASTM International, ASTM Volume 03.03 Nondestructive Testing
ASNT, Nondestructive Testing Handbook
Bray, D.E. and R.K. Stanley, 1997, Nondestructive Evaluation: A Tool for Design, Manufacturing and Service; CRC Press, 1996.
Hellier, C., Handbook of Nondestructive Evaluation, McGraw-Hill Professional; 2001
Shull, P.J., Nondestructive Evaluation: Theory, Techniques, and Applications, Marcel Dekker Inc., 2002.
Abstract
Destructive and non-destructive methods have been used for the determination of micro-traces of antimony in high-purity silicon powder. The destructive method was based on sub-stoichiometric radio-activation analysis with solvent extraction using BPHA and cupferron as organic reagents. The antimony contents in high-purity silicon can be determined by the proposed method.
A new non-destructive method was developed for the detection of refrigerant leakage at an evaporator's inflow. Nitrogen and oxygen gas were successively blown through the evaporator. A gas analyser was applied at the outflow of the evaporator and the oxygen concentration measured. It was possible to detect any leakage by investigating the oxygen concentration time history diagram.
Non-destructive method for detecting zones with non-conductive materials, such as materials that include glass fibres, in a part made of a conductive composite, such as a composite whose reinforcing fibres are carbon fibres, provided with an organic coating, that comprises the following stages: a) providing a device for applying an electric potential on the surface of said part; b) determining the dielectric breakdown potential Pr corresponding to the thickness E of the coating; c) applying said dielectric breakdown potential Pr with said device to the part for the purpose of identifying those zones that have non-conductive materials when dielectric breakdown does not occur in them
Key Words:
Leakage detection, analyzer, reagents, fibres, silicon powder, refrigeration, plate evaporator
Introduction
The advantages of using light-weight, corrosion resistant composite materials and structures for deepwater developments have become increasingly important in recent years and many composite components are being used or developed for use in the exploration and production of oil and gas. Early composite applications have been lightly-loaded, i.e., pipes and gratings which are primarily constructed of glass fiber and epoxy resin. Most qualification and in-service re-qualification to date have been based on test data and visual inspection. Advanced composite applications are now emerging for critical, primary structural components, such as drilling and production risers, drill pipe, spoolable high-pressure pipe, subsea pipelines, tendons, and synthetic fiber mooring ropes. These components are much more highly-loaded and therefore structurally demanding, and their remoteness from the surface introduces inspection and monitoring challenges. Alternative carbon, polyester, and other fibers as well as advanced resins are being proposed for applications. One of the main issues which has been identified as a technology deficiency inhibiting the deployment of composite components offshore is the effect of damage to components and the associated issue of how to find and determine the extent of damage. At issue is Are there reliable, affordable Non Destructive Evaluation (NDE) methods which could be used to ascertain the fitness for service of components following manufacture and during service? Reliable NDE methods that can economically monitor the performance and continuing integrity of composite component in critical structural applications could provide better understanding and confidence and lead to the development of rationale and realistic inspection strategies.
Composite manufacturing defects such as delamination and voids as well as damage experienced in service can lead to premature failure of the component. It is important that Non-Destructive Examination (NDE) methods be available to examine composite structure components to determine their state of fitness-for-service following manufacture as well as at scheduled and special times during the service life. Some of the NDE methods used for metals such as x-ray are also applicable to composites, but for the most part a completely different set of NDE tools must be used. There has been considerable research in recent years to develop NDE methods for the inspection of composite aerospace and automotive components. With a small amount of adaptation, some of these methods can be applied to composite structures used offshore. Methods such as ultrasonic, radiography, thermography and acoustic emission are well established, but require skilled technician interpretation. Other promising methods such as fiber optic sensors, trip metal strain sensors and embedded sensors are just emerging. In addition, considerable research results are emerging from NDE applications in other industries.
Interferometry methods such as shearography are being used to inspect large aerospace structures and may have merit for oil industry components. The lack of familiarity with the unique problems and challenges of the oil industry by NDE experts and similar unfamiliarity by the oil industry of the advancements that have been made in NDE technology currently inhibit the utilization of NDE methods.
The primary barriers to applying NDE technology in the oil industry are thus both technical and inadequate communications including: (1) lack of opportunity to develop experience-base inspection strategies based on actual in-situ performance of these new components, (2) need for advancements in applying NDE methods to the specific needs of the oil industry and (3) lack of information to assess the potential benefits, costs and limitations in applying NDE methods. The workshop on Non-Destructive Evaluation Methods for Inspecting Offshore Composite Components sponsored by the Texas A&M University Offshore Technology Research Center and the Minerals Management Service held on November 21, 2002 was designed to address these issues. The long-term benefit is expected to be to sort out what is needed, what is available, what can be developed, and to serve as a catalyst for development efforts to make available the technology to inspect composite components used in the offshore oil industry. The availability of reliable NDE inspection methods is important not only to the operators, but also for regulatory authorities to gain the both experience and confidence in the safe application of critical composite components being introduced offshore.
Destructive Testing:
In destructive testing, tests are carried out to the specimen's failure, in order to understand a specimen's structural performance or material behavior under different loads. These tests are generally much easier to carry out, yield more information, and are easier to interpret than non-destructive testing.
Destructive testing is most suitable, and economic, for objects which will be mass produced, as the cost of destroying a small number of specimens is negligible. It is usually not economic to do destructive testing where only one or very few items are to be produced (for example, in the case of a building).
Some types of destructive testing:
Stress tests
Crash tests
Hardness tests
Metallographic tests
Testing of large structures
The above figure shows the shake-table video of a 6-story non-ductile concrete building
Building structures or large non-building structures (such as dams and bridges) are rarely subjected to destructive testing due to the prohibitive cost of constructing a building, or a scale model of a building, just to destroy it.
Earthquake engineering requires a good understanding of how structures will perform at earthquakes. Destructive tests are more frequently carried out for structures which are to be constructed in earthquake zones. Such tests are sometimes referred to as crash tests, and they are carried out to verify the designed seismic performance of a new building, or the actual performance of an existing building. The tests are, mostly, carried out on a platform called a shake-table which is designed to shake in the same manner as an earthquake. Results of those tests often include the corresponding shake-table videos.
As structural performance at earthquakes is better understood, testing of structures in earthquakes is increasingly done by modeling the structure using specialist finite element software.
Destructive software testing
Destructive software testing is a type of software testing which attempts to cause a piece of software to fail in an uncontrolled manner, in order to test its robustness.
Non Destructive Testing:
NDT is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage. Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation, troubleshooting, and research. Common NDT methods include ultrasonic, magnetic-particle, liquid penetrant, radiographic, and eddy-current testing. NDT is a commonly-used tool in forensic engineering, mechanical engineering, electrical engineering, civil engineering, systems engineering, medicine, and art.
Methods
NDT methods may rely upon use of electromagnetic radiation, sound, and inherent properties of materials to examine samples. This includes some kinds of microscopy to examine external surfaces in detail, although sample preparation techniques for metallography, optical microscopy and electron microscopy are generally destructive as the surfaces must be made smooth through polishing or the sample must be electron transparent in thickness. The inside of a sample can be examined with penetrating electromagnetic radiation, such as X-rays, or with sound waves in the case of ultrasonic testing. Contrast between a defect and the bulk of the sample may be enhanced for visual examination by the unaided eye by using liquids to penetrate fatigue cracks. One method (liquid penetrant testing) involves using dyes, fluorescent or non-fluorescing, in fluids for non-magnetic materials, usually metals. Another commonly used method for magnetic materials involves using a liquid suspension of fine iron particles applied to a part while it is in an externally applied magnetic field (magnetic-particle testing).
Weld verification
1. Section of material with a surface-breaking crack that is not visible to the naked eye.
2. Penetrant is applied to the surface.
3. Excess penetrant is removed.
4. Developer is applied, rendering the crack visible.
In manufacturing, welds are commonly used to join two or more metal surfaces. Because these connections may encounter loads and fatigue during product lifetime, there is a chance that they may fail if not created to proper specification. For example, the base metal must reach a certain temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold the surfaces together, or cracks may form in the weld causing it to fail. The typical welding defects, lack of fusion of the weld to the base metal, cracks or porosity inside the weld, and variations in weld density, could cause a structure to break or a pipeline to rupture.
Welds may be tested using NDT techniques such as industrial radiography using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing or via eddy current and flux leakage. In a proper weld, these tests would indicate a lack of cracks in the radiograph, show clear passage of sound through the weld and back, or indicate a clear surface without penetrant captured in cracks.
Welding techniques may also be actively monitored with acoustic emission techniques before production to design the best set of parameters to use to properly join two materials.
Structural mechanics
Structures can be complex systems that undergo different loads during their lifetime. Some complex structures, such as the turbo machinery in a liquid-fuel rocket, can also cost millions of dollars. Engineers will commonly model these structures as coupled second-order systems, approximating dynamic structure components with springs, masses, and dampers. These sets of differential equations can be used to derive a transfer function that models the behavior of the system.
In NDT testing, the structure undergoes a dynamic input, such as the tap of a hammer or a controlled impulse. Key properties, such as displacement or acceleration at different points of the structure, are measured as the corresponding output. This output is recorded and compared to the corresponding output given by the transfer function and the known input. Differences may indicate an inappropriate model (which may alert engineers to unpredicted instabilities or performance outside of tolerances), failed components, or an inadequate control system.
Radiography in medicine
Chest radiography indicating a 'Peripheres Bronchialcarcinom'.
As a system, the human body is difficult to model as a complete transfer function. Elements of the body, however, such as bones or molecules, have a known response to certain radiographic inputs, such as x-rays or magnetic resonance. Coupled with the controlled introduction of a known element, such as digested barium, radiography can be used to image parts or functions of the body by measuring and interpreting the response to the radiographic input. In this manner, many bone fractures and diseases may be detected and localized in preparation for treatment. X-rays may also be used to examine the interior of mechanical systems in manufacturing using NDT techniques, as well.
Notable events in early industrial NDT
1854 Hartford, Connecticut: a boiler at the Fales and Gray Car works explodes, killing 21 people and seriously injuring 50. Within a decade, the State of Connecticut passes a law requiring annual inspection (in this case visual) of boilers.
1895 Wilhelm Conrad R ntgen discovers what are now known as X-rays. In his first paper he discusses the possibility of flaw detection.
1880 - 1920 The "Oil and Whiting" method of crack detection is used in the railroad industry to find cracks in heavy steel parts. (A part is soaked in thinned oil, then painted with a white coating that dries to a powder. Oil seeping out from cracks turns the white powder brown, allowing the cracks to be detected.) This was the precursor to modern liquid penetrant tests.
1920 Dr. H. H. Lester begins development of industrial radiography for metals. 1924 Lester uses radiography to examine castings to be installed in a Boston Edison Company steam pressure power plant [1].
1926 The first electromagnetic eddy current instrument is available to measure material thicknesses.
1927 - 1928 Magnetic induction system to detect flaws in railroad track developed by Dr. Elmer Sperry and H.C. Drake.
1929 Magnetic particle methods and equipment pioneered (A.V. DeForest and F.B. Doane.)
1930s Robert F. Mehl demonstrates radiographic imaging using gamma radiation from Radium, which can examine thicker components than the low-energy X-ray machines available at the time.
1935 - 1940 Liquid penetrant tests developed (Betz, Doane, and DeForest)
1935 - 1940s Eddy current instruments developed (H.C. Knerr, C. Farrow, Theo Zuschlag, and Fr. F. Foerster).
1940 - 1944 Ultrasonic test method developed in USA by Dr. Floyd Firestone.
1950 The Schmidt Hammer (also known as "Swiss Hammer") is invented. The instrument uses the world s first patented non-destructive testing method for concrete.
1950 J. Kaiser introduces acoustic emission as an NDT method.
(Source: Hellier, 2001) Note the number of advancements made during the WWII era, a time when industrial quality control was growing in importance.
Applications
NDT is used in a variety of settings that covers a wide range of industrial activity.
Automotive
Engine parts
Frame
Aviation / Aerospace
Airframes
Space frames
Power plants
Propellers
Reciprocating Engines
Gas turbine engines
Rocketry
Construction
Structures
Bridges
Maintenance, repair and operations
Bridges
Manufacturing
Machine parts
Castings and Forgings
Industrial plants such as Nuclear, Petrochemical, Power, Refineries, Pulp and Paper, Fabrication shops, Mine processing and their Risk Based Inspection programmes.
Pressure vessels
Storage tanks
Welds
Boilers
Heat exchangers
Turbine bores
In-plant Piping
Miscellaneous
Pipelines
In-line Inspection using "pigs"
Pipeline integrity management
Leak Detection
Railways
Rail Inspection
Wheel Inspection
Tubular NDT, for Tubing material
Corrosion Under Insulation (CUI)
Amusement park rides
Submarines and other Naval warships
Medical imaging applications (see also Medical physics)
Methods and techniques
NDT is divided into various methods of nondestructive testing, each based on a particular scientific principle. These methods may be further subdivided into various techniques.
The various methods and techniques, due to their particular natures, may lend themselves especially well to certain applications and be of little or no value at all in other applications. Therefore choosing the right method and technique is an important part of the performance of NDT.
An example of Ultrasonic Testing (UT) on blade roots of a V2500 IAE aircraft engine.
Step 1: The UT probe is placed on the root of the blades to be inspected with the help of a special bore-scope tool (video probe).
Step 2: Instrument settings are input.
Step 3: The probe is scanned over the blade root. In this case, an indication (peak in the data) through the red line (or gate) indicates a good blade; an indication to the left of that range indicates a crack.
An example of a 3D replicating technique.
The flexible high-resolution replicas allow surfaces to be examined and measured under laboratory conditions. A replica can be taken from all solid materials.
Acoustic emission testing (AE or AT)
Dye penetrant inspection Liquid penetrant testing (PT or LPI)
Electromagnetic testing (ET)
Alternating current field measurement (ACFM)
Alternating current potential drop measurement (ACPD)
Barkhausen testing
Direct current potential drop measurement (DCPD)
Eddy-current testing (ECT)
Magnetic flux leakage testing (MFL) for pipelines, tank floors, and wire rope
Magnetic-particle inspection (MT or MPI)
Remote field testing (RFT)
Ellipsometry
Hardness testing (Brinell) (HT)
Impulse excitation technique (IET)
Infrared and thermal testing (IR)
Thermographic inspection
Laser testing
Electronic speckle pattern interferometry
Holographic interferometry
Profilometry
Shearography
Leak testing (LT) or Leak detection
Absolute pressure leak testing (pressure change)
Bubble testing
Halogen diode leak testing
Hydrogen leak testing
Mass spectrometer leak testing
Tracer-gas leak testing method Helium, Hydrogen and refrigerant gases
Magnetic resonance imaging (MRI) and NMR spectroscopy
Optical microscopy
Positive Material Identification (PMI)
Radiographic testing (RT) (see also Industrial radiography and Radiography)
Computed radiography
Digital radiography (real-time)
Neutron radiographic testing (NR)
SCAR (Small Controlled Area Radiography)
X-ray computed tomography (CT)
Scanning electron microscopy
Ultrasonic testing (UT)
Electro Magnetic Acoustic Transducer (EMAT) (non-contact)
Laser ultrasonics (LUT)
Internal rotary inspection system (IRIS) ultrasonics for tubes
Phased array ultrasonics
Time of flight diffraction ultrasonics (TOFD)
Time of Flight Ultrasonic Determination of 3D Elastic Constants (TOF)
Visual inspection (VT)
Pipeline video inspection
TERMINOLOGY
Indication
The response or evidence from an examination, such as a blip on the screen of an instrument.
Interpretation
Determining if an indication is of a type to be investigated. For example, in electromagnetic testing, indications from metal loss are considered flaws because they should usually be investigated, but indications due to variations in the material properties may be harmless and non-relevant.
Flaw
A type of discontinuity that must be investigated to see if it is rejectable. For example, porosity in a weld or metal loss.
Evaluation
Determining if a flaw is rejectable. For example, is porosity in a weld larger than acceptable by code?
Defect
A flaw that is rejectable - i.e. does not meet acceptance criteria. Defects are generally removed or repaired.
(Source: ASTM E1316 in 'Vol. 03.03 NDT)
Penetrant testing
Non-destructive test typically comprising a penetrant, a method of excess removal and a developer to produce a visible indication of surface-breaking discontinuities.
(Source: ISO 12706:2000, Note: To be replaced by ISO/DIS 12706 (2008-03).)
Reliability and statistics
Defect detection tests are among the more commonly employed of non-destructive tests. The evaluation of NDT reliability commonly contains two statistical errors. First, most tests fail to define the objects that are called "sampling units" in statistics; it follows that the reliability of the tests cannot be established. Second, the literature usually misuses statistical terms in such a way as to make it sound as though sampling units are defined. These two errors may lead to incorrect estimates of probability of detection. [2] [3].
References
Cartz, Louis (1995). Nondestructive Testing. A S M Internationl.
Blitz, Jack; G. Simpson (1991). Ultrasonic Methods of Non-Destructive Testing. Springer-Verlag New York, LLC.
Bibliography
ASTM International, ASTM Volume 03.03 Nondestructive Testing
ASNT, Nondestructive Testing Handbook
Bray, D.E. and R.K. Stanley, 1997, Nondestructive Evaluation: A Tool for Design, Manufacturing and Service; CRC Press, 1996.
Hellier, C., Handbook of Nondestructive Evaluation, McGraw-Hill Professional; 2001
Shull, P.J., Nondestructive Evaluation: Theory, Techniques, and Applications, Marcel Dekker Inc., 2002.