Ultrasonic Thickness Gaging Considerations
Ultrasonic thickness gaging techniques permit quick and reliable measurements with accuracies up to ±0.0001 inch. Besides selecting the appropriate instrument, transducer, and couplant, there are other factors as those given below which affect the accuracy of measurements.
Condition Monitoring
Employers Urged to Verify Level III Certificates
According to ASNT (American Society for Nondestructive Testing) two companies have reported cases of falsified ASNT Certificates. Both perpetrators were bound by ASNT to cease and desist in the use of falsified documents. ASNT will, without charge verify the certification of those claiming to be ASNT level III. Call ASNT at 800.222.2768 or 616.274.6003 or fax 614.274.6899. Valid certificate holders should be able to show:
Unscrupulous individuals may deceive their employers about their qualification. Such deception may invalidate contracts and threaten the quality of workmanship.
Eddy current testing (ET) is a nondestructive test technique based on inducing electrical currents in the material being inspected and observing the interaction between those currents and the material. Eddy currents are generated by electromagnetic coils in the test probe, and monitored simultaneously by measuring probe electrical impedance. Since it's an electromagnetic induction process, direct electrical contact with the sample is not required; However, the sample material has to be conductive.
Eddy current testing is a versatile technique. It's mainly used for thin materials; In thick materials, penetration constraints limit the inspected volume to thin surface layers. In addition to flaw inspection, ET can be used to indirectly measure mechanical and metallurgical characteristics which correlate with electrical and magnetic properties. Also, geometric effects such as thickness, curvature and probe-to-material spacing influence eddy current flow and can be measured.
Ultrasonic Flaw Detection
Ultasonic flaw detectors range from low-cost, hand-held instruments to complex multi-probe systems for on-line inspection, some with advanced data handling for automated recognition of significant flaws. Pulsed beams of ultrasound (typically 1-25MHz) from a transmiter probe pass though the object and are reflected by free surfaces and most types of flaw. A receiver probe detects these reflected signals which, after amplification and signal analysis, are displayed in various ways (eg as A-scans, B-scans or C-scans) to locate the defect. A single probe can act as both transmitter and receiver, and inspection is generally from one side only. Ultrasound is excellent for detecting planar defects, eg internal cracks, delaminations, dis-bonds, lack-of-fusion and lamellar inclusions, as well as voids, prosity, etc. It is suitable for most 'clean' materials, less so with large grain or multi-phase microstructures (eg astenitic steels, some castings, concrete) but results need expert interpretation. Accurate defect sizing and characterisation can be difficult unless special ultrasonic techniques are used.
Detection of Corrosion Under Paint
A new family of fluorescent dyes allows the detection of rust and surface defects that are hidden under a coat of paint. This new method eliminates the need to remove the paint prior to aircraft corrosion inspection, which can cost up to $250,000 for a large four engine aircraft.
The fluorescent dyes can be blended with existing paint formulations. The US Air Force Wright Laboratories chemist Bruce Reinhardt developed the technology in conjunction with Paras Prasad of the State University of New York at Buffalo. The development is based on earlier work at Cornell University in the area of two-photon confocal microscopy. Two photon absorption occurs when a material absorbs two low energy photons and emits a single high energy photon.
The technique has not been previously used due to the low activity of two-photon fluorescent dyes. Prasad realized that low-energy infrared radiation penetrates multiple coating layers. Most coatings are thin and translucent, and allow visible light to penetrate them to some extent. Reinhardt developed a family of low molecular weight disubstituted fluorenes that showed 100 times greater two-photon absorption than previous materials. Illuminating the new materials with an IR laser reduces problems with light-scattering due to background fluoresence. A two-photon confocal microscope is used to record data, and a computer generated 3D map is built on the metal surface. Corrosion and scratches stand out, and the process can be carried out rapidly. The Air Force will make dyes available to researchers and hopes to license the new technology.
For more information, contact:
Bruce Reinhardt
Portable Scattermeter for Contamination Measurement
A new approach for measuring contaminants on solid surfaces has been developed by NASA. A rugged, portable, Fourier Transform Infrared (FTIR) Scatterometer has been developed for use in rapidly and nondestrictively identifying and measuring quantities of greasy and oily contaminants on solid surfaces. This instrument is meant to be used in conjunction with other contamination measuring instrumentation to ensure that inspected surfaces are clean enough for subsequent coating and/or adhesive bonding.
Contaminants to be detected include fluorocarbons, silicones, hydrocarbons, and other organic compounds. Commerical laboratory FTIR spectrometers have been used to identify and measure such contaminants, but are too large and delicate to be carried into the field to inspect surfaces at all orientations in situ. Normally, it is necessary to use destructive inspection procedures to cut small coupons out of the inspected surfaces and bring them to the laboratory for analysis.
FTIR spectroscopy involves measurement of either transmittance, diffuse reflectance, or specular reflectance. The effectiveness of each measurement method depends on the particular type of sample to be inspected. The instrument presented in NASA's new approach uses diffuse reflectance, which is preferable for measurements on rough and/or cured surfaces.
The instrument is an automated, computer controlled, high-performance FTIR that includes a diffuse-reflectance optical measurement head, all in a compact, rugged, lightweight package suitable for field use. The FTIR spectometer is a commercially available unit adapted to fit into the package. The diffuse-reflectance optical measurement head is a half-scale version of a commercial unit that contains elipsoidal (barrel ellipse) and off-axis paraboidal reflectors; the barrel-ellipse design allows collection of scattered radiation and excludes specularly reflected radiation. The instrument weighs less than 13 lbs (6kg). The computer can be programmed to provide spectral matched filtering, enabling automated identification of spectral features.
For more information, refer to the April 1997 issue of NDT Update:
Taso Malapetsas, Editor
Contact:
Gauging Thickness With Microwaves
The Refractory Corrosion Monitor remotely measures the thicknesses of refractory brick linings inside operating furnaces without the need for any internal access. This is accomplished using frequency-tunable microwave radiation remotely transmitted into the furnace from outside. Developed jointly by MIT, Cambridge, and DOE's Pacific Northwest National Laboratory, Richland, Wash., the device provides operators with real time information on the condition of furnace linings.
Most common non-electrically conductive refractory materials such as alumina and alumina-chrome bricks are readily penetrated by microwaves. A small fraction of the microwave energy however is reflected by each surface between different refractory layers. Since the microwave energy is coherent, reflected microwaves from pairs of reflecting surfaces interfere coherently to produce a detected reflection signal that varies as the frequency is slowly tuned. For a given index of refraction the period of the peaks and the minima is linearly proportional to the distances between the reflecting surfaces. Using this technique, the monitor overcomes the limitations of other invasive or expensive methods. In addition, these capabilities permit the refractory corrosion monitor to nondestructively measure the thickness of ice in frozen lakes.
Temperature Limitations of Magnetic Particle (MP) Inspection
Dry powder magnetic particle inspection has typically been routinely conducted at temperatures up to approximately 200° F (93° C). This limit is dictated by the coating on the iron or iron oxide particles which is used to enhance visibility; at sufficiently high temperatures, these coatings break down, affecting the mobility of the particles. Three grades of coated dry powders (fine, intermediate and coarse) are available which are suitable for use at temperatures to 600° F (316° C). For temperatures up to 750° F (399° C) a black coated powder is available. It should be noted that since as the temperature increases, there is a corresponding decrease in magnetic permeability of the iron particles with accompanying decrease in the production of magnetic poles on opposite sides of surface flaws and corresponding reduction in visibility of these these flaws by buildup of particles.
Acoustic Emission Applied to Aging Cranes
Sudden, catastrophic fatigue failures in 40 to 50 year old Navy cranes pose a significant danger to personnel and facilities. Cranes are used to lift nuclear materials and other sensitive payloads. Nondestructive methods of fatigue crack analysis are needed before more cranes experience failures the cause uncontrolled dropping of loads.
The problem is quite large. There are over 11,000 cranes in use by the Navy (twenty different types), and 1,000 of these are 40 to 50 years old. The cranes were designed on the basis of working stress considerations alone, with high reliability in key component material properties. The diagnosis of areas that are hidden from easy access, such as rotating gears and drive shafts, is particularly important. Fatigue cracks have been found in drive shafts, gantry I-beams, and other structural members.
To solve the problem, NDE methods are required for detecting, locating, and characterizing fatigue cracks and for providing information about crack growth. The test method needs to be nondestructive, simple to carry out, and able to screen crane elements for possible failures before the crane is taken out of service. The ideal approach should avoid costly crane disassembly, long shutdown times, and should not require complex methods and equipment.
The Naval Facility Construction Command (NAVAFAC), under the technical guidance of the Naval Facilities Engineering Service Center(NFESC) at Port Hueneme, CA has established contracts with two research groups to investigate this problem using acoustic emission technology. The results from these investigations should be relevant to the in-situ diagnosis of fatigue cracks in other types of rotating machinery and booms.
NDT International, Inc. conducted acoustic emission tests during December of 1996 on the boom and main driveshaft of Navy Portal crane #PC-15, located at Long Beach National Shipyard (Contract #CNT N47408-96-C-7245). Background noise was analyzed, and mock acoustic emission signals were introduced into the crane boom and shaft using pencil lead breaks and Dunegan crackers. Acoustic emission data were collected and will soon be available in the project final report.
Texas Research Institute Austin, Inc. located in Austin, Texas, teamed with the Ferguson Structural Engineering Laboratory at the University of Texas in Austin during a recently completed Phase I SBIR effort involving the analysis of acoustic emission signals from actual crane shafts subjected to loading torques in the laboratory (Contract #N47408-96-C-7204). Evidence of crack growth and information about crack location were obtained via full waveform capture using a digital AE system; the crack location was verified using ultrasonic techniques. Phase II of his effort is currently underway (Contract #N47408-96-C-7249), and will involve the on-site AE analysis of a crane located in Pearl Harbor, Hawaii that has shown evidence of cracked shafts during ultrasonic analysis. This investigation is scheduled to take place in late February, 1997. Fatigue testing to examine crack growth in currently underway at the Ferguson Structural Engineering Laboratory.
For further information on the Navy crane problem, contact:
Dr. Ted Shugar
In-Situ NDE of Buried Piping For Water Distribution
The piping in aging water distribution systems in North America is beginning to require large scale replacement. As populations increase, this problem becomes more important. Replacement decisions for these pipes have traditionally been based upon failure data. Advances in NDE technologies and inspection techniques have resulted in more robust, lower cost inspection in determining replacement schedules. The water industry has recently evaluated the potential to develop NDE solutions that can inspect water pipes to determine their integrity before failures occur, and evaluated the potential of adapting NDE methods used in other piping industries to water pipe inspection.
Cast and ductile iron comprise appropriately 70% of the length of North American water distribution pipes. Reinforced concrete and asbestos (AC) constitute about 15-20% of piping. The remaining pipe is primarily plastic, and the plastic pipes are relatively new. Unfortunately, NDE methods for concrete and cast iron (most commonly used in water mains) have historically lagged behind the techniques used to inspect other materials.
Unlike oil and gas pipelines, water mains consist of many short sections of pipe jointed with 90 degree bends and valves that do not fully open. The pipe inspection units developed for the oil and gas industries are designed to be self contained units that traverse many miles of straight pipeline with fully opening valves. Bend radii are typically many feel in length. The short section length and many valves in water pipes pose problems because many access points are required for insertion and extraction of pipe inspection units.
NDE techniques for water pipes have advanced considerably in the past few years, with vendors providing systems and services that can detect and size the common defects such as graphitization, cracking, pitting, and strand failure. These techniques were designed to work with concrete, AC, and iron pipes; inspection techniques for polymer pipes still need considerable advancement.
Remote field eddy current (RFEC) techniques are now commercially available for inspecting steel, cast and ductile iron pipes, and "pigs" that measure wall thickness and pit depth ultrasonically are advancing rapidly. The magnetic flux leakage techniques used in oil and gas pipe inspection have proven ineffective for water pipes.
NDE equipment for both passive and active acoustic monitoring of reinforced concrete pipes have been developed, and may reach widescale use in the near future. Passive monitoring systems are based upon inserting hydrophones into the water column and leaving the system in service. Breaks in reinforcing strand and cracks in the concrete can be detected, located, and characterized by evaluating specific attributes of acoustic signals received by the hydrophones. Active monitoring is performed by impact-echo (hammer) testing. An impacter of known mass imparts a known force into the body of a dewatered concrete or AC pipe, and an accelerometer or piezoelectric sensor monitors the concrete response to the impact. Pipe damage is detected by measuring factors such as signal travel time, received signal amplitude, and other waveform attributes. In general, damaged pipe will have slower wave velocities, and will propagate less energy from the impacter to the receiver.
The NDE systems described above can inspect about 90% of all water distribution piping, but thermoplastic pipe is not inspectable with any currently available techniques. NDE of thermoplastics has been commercially achieved for other applications, but will require significant adaptation to the inspection of buried water pipes.
Comments regarding buried water pipe inspection should be directed to:
Russell Austin
Making Choices in Nondestructive Evaluation
This article is intended to review considerations taken prior to the employment of nondestructive evaluations. It offers general guidelines that may be used in applying NDE.
As NDE professionals, we devote a great deal of effort towards implementation (and promoting) effective NDE applications and practices. As new materials, components, assemblies, and complete units are introduced the question of how to utilize NDE in a specific application is often asked. Furthermore the scope of NDE is expanding because it is becoming more common to consider the use of NDE technologies for characterization of advanced materials, in addition to the traditional or historic efforts directed towards detecting flaws and defects.
The first step to be considered in the proposed use of NDE in a program is: whether NDE is needed and why. There are many valid reasons to employ NDE, however, there is a danger that specifying NDE may become a routine practice instead of the result of real need. In some instances NDE is required simply for administrative reason, viz.: the contract requires it. All programs should certainly consider the use of NDE but automatic use should be avoided. It should always have an identifiable purpose that justifies the expense.
Fortunately, we most often find that NDE is specified to satisfy a legitimate requirement. Even though this is true, NDE use may still be inappropriate. Since almost all NDE techniques provide secondary or indirect evidence, they may sometimes be replaced by direct methods (granted, these are often destructive in nature.) For example, assessing the strength of adhesive bonds may be performed using NDE. Simple direct proof tests, which require limited assumptions, standards, corrections, or other inferred relationships, measure the critical properties directly.
When the reasons to use NDE have been established, it is prudent to determine if the requirements be eliminated or reduced through the use of better materials, or better process control, or a better design. Remember NDE has no intrinsic value; inspecting a part does not make it stronger or better. Although alternatives to NDE should be considered first, the requirement of NDE cannot always be removed. Once it becomes clear that NDE is appropriate or otherwise required, the designer must consider another important aspect. This is whether the design can be effectively inspected and if it can be improved to make the inspection more reliable or efficient.
It is important to decide when and where during the manufacture and life cycle of the system NDE should and will be employed. One of the most important factors perhaps of primary importance, is definition of critical flaw sizes, ships, and locations that must be detected. The first question often asked relates to critical flaw sizes. In many instances the requester can provide no answers to this question. This may be because the determination of critical flaws is not easy. Accepting this fact, this should certainly not lead to specifications such as "no proposity is allowed" or "determine the smallest crack." Although some may consider that it desirable to test to his degree, it is generally not affordable. The engineering team (designers, members from production, stress, failure analysis, and materials science) can determine the types of flaws expected and maximum allowable flaw limits to achieve or maintain design goals. An important addition to this team may be the NDE professional so that NDE might be designed into the system from the beginning instead of being added as an afterthought (the situation seen most often). This would ensure that critical flaws could be effectively and reliably detected. When this is not done at the design level, choices are eliminated, often resulting in a reduction of the original design or acceptance of less reliable end products.
Only when the critical flaw specification have been determined can NDE professionals answer other fundamental question. These include: what method (or most often multiple methods) are required, and what equipment, standards, procedures, personnel, controls, and documentation are necessary? Of course, trade-off studies relating equipment costs, reliability and maturity of the technology, inspection, speeds, etc. must also be considered.
The capabilities of NDE, used both in identifying an assessing flaws/defects and in controlling the quality of manufacture, continue to grow. Proper employment of NDE presents a real challenge, in both current and new applications. Correctly answering that challenge can result in a property designed and managed NDE program. Through effective use of the NDE program, significant savings can be realized in the areas of waste minimization, increased product through-put, and improved quality of the finished product throughout its life cycle.
Impact-Echo, Nondestructive Evaluation of Concrete and Masonry, Mary J. Sansalone and William B. Streett, Bullbrier Press For the first time, information on Impact Echo techniques has been cited and drawn together in a single book. The information has been collected from numerous technical reports and over 50 research papers in a variety of scientific and technical journals. The majority of the work stems from the pioneering work of the book's first author in creating and developing the field. This book will serve as an authoritative source for engineers, scientists, and others who wish to understand the theory and practical uses of the impact-echo method. Case studies are presented throughout the chapters; this book will also fill an important role as a text for undergraduate and graduate courses on the nondestructive testing and evaluation of structures. Impact-echo methods have achieved success in locating flaws and defects in highway pavements, bridges, building, tunnels, dams, piers, sea walls, and many other types of structures. Its use has resulted in savings of millions of dollars in repair and retrofit costs on bridges, retaining walls, and other large structures. 339 pages. List Price: $70. Available from Bullbrier Press, RR 1, Box 332, Jersey Shore, PA 17740. Tel and Fax: (717) 769-7345.
3rd Conference on the Nondestructive Evaluation of Civil Structures and Materials Working Group Reports, Atkinson-Noland & Associates, Inc The 3rd Conference on the Nondestructive Evaluation of Civil Structures and Materials was held on September 9-11, 1996 to provide a forum for the exchange of concepts, information, and experiences related to nondestructive evaluation. A major theme of the Conference was standardization of test procedures and evaluation guidelines, and was attended by professional engineers, researchers, and equipment manufactures interested in design, repair, rehabilitation and testing. This booklet, sponsored in party the National Science Foundation Grant No. CMS-9400589, describes the reports of working groups that discussed basic issues and makes recommendations for standardization of nondestructive test methods for different areas. The working groups were successful in stimulating communication among NDE researchers, user groups, and those persons acting in standardization of testing procedures. Each report was prepared independently and therefore does not reflect any bias or direction imposed by the sponsors or organizers. 23 pages. List price: $5. Conference proceedings are also available. Available from Atkinson-Nolan & Associates, Inc., 2619 Spruce Street, Boulder, Colorado 80302. Tel: (303) 444-3620.
Nondestructive Testing, Louis Cartwheels This book is intended to assist in understanding and selecting the best NDE method or methods to solve a particular problem. It presents information on the basic processes to realize the advantages of each available NDE technology. In addition to practical hints and pertinent comments for resolution of day to day problems, this book will provide sufficient basic theory to comprehend the principles of each method so that the most appropriate can be used to the fullest advantage. It also includes illustrative calculations and a comprehensive bibliography. The book should be particularly useful to advance technicians involved with level III preparation, engineers concerned with quality control, general scientists and technologists dealing with material problems but who are not NDE specialists, and engineering students taking an NDE course. List price $98.00. ASM Internationl, P. O. Box 473, Novelty, OH 44072-9901. Tel: (800) 336-5152, ext. 900, Fax: (216) 338-4634.
American Society for Nondestructive Testing (ASNT)
ASNT is an organization which provides NDT education materials, personnel training programs,standards and services for the certification and qualification of NDT personnel. It promotes the discipline of NDT as a profession; and facilitates and supports NDT research and the application of NDT technology.
The Society publishes Materials Evaluation, a monthly journal; Research in Nondestructive Evaluation, a quarterly research journal; the Nondestructive Testing Handbook; and training materials. It also organizes conferences, exhibitions, educational programs on topical subjects, and distributes a selection of books relating to nondestructive testing.
ASNT headquarters is at:
1711 Arlington Lane
Send general inquiries via e-mail to geary@asnt.org
ASNT's Web site is http://www.asnt.org
American Society for Testing and Materials (ASTM)
ASTM is a nonprofit organization devoted to development of voluntary full consensus standards for materials, products, systems and services and the promotion of related knowledge.
ASTM Standardization News is the official monthly magazine of ASTM. The feature and news sections report on the research, testing and new activities of the ASTM standards-writing committees. Also included are the legal, governmental and international events impacting on the standards development process.
News from ASTM committees; discussions of new standards; and general features on the development, use and significance of standards are solicited for publication.
American Society for Testing and Materials Headquarters is at:
100 Barr Harbor Dr.
Visit ASTM's web site http://www.astm.org
To contact ASTM staff directly via e-mail:
Advances in NDE Through Thermal Insulation
Thermal insulation is often required for pipes, columns and pressure vessels used in the chemical processing, petroleum, and power generation industries. These components often operate in harsh environments and may contain potentially hazardous chemicals. Changes in regulations driven by environmental concerns have caused these industries to strive for "zero" leaks. A comprehensive Preventive Maintenance Program (PMP) is required to maintain the high reliability of this equipment.
Implementation of PMK requires regularly scheduled inspections of the piping or vessel. Unfortunately, many NDE methods require direct access to the inspection surface which can be covered with several inches of insulation and sheathed in protective jacketing. This often forces inspectors to remove and replace insulation during each inspection. The cost can be tremendous when literally miles of tubing must be inspected. Recent advances in NDE offer promising solutions to this problem.
Damage in tubing or in processing vessels can occur on both the ID and OD in the form of large area defects (corrosion or erosion) or smaller flaws (cracks, pits, etc.) Condensation and water ingress into the insulation are common causes of OD corrosion while high temperatures, high pressures, particulates, and corrosiveness of the fluid can contribute to ID corrosion, erosion, pitting and cracking.
Infrared thermography and ultrasonic thickness measurements have sometimes been used for Nondestructive Inspection Through Insulation (NITI). Thermography is rapid and noninvasive, but may not detect all of the damage. Ultrasonic equipment is available that can accurately gauge wall thickness, although mapping large areas is prohibitively expensive. This method is only used to spot check areas where damage is expected to occur. An additional problem with thickness gauging is that it may overlook pits, cracks, or other small area defects.
Pulsed and low frequency eddy current NITI techniques were developed during the 1980s. Pulsed methods are suitable for detection of large area wall thinning, and low frequency techniques can detect small area flaws. These techniques are not well suited for full body inspections. Other electromagnetic techniques involving the use of fully encircling coils have also been developed in the laboratory.
Gamma ray and X-ray radiography systems have been adapted to the detection of both small area defects and wall thinning for NITI applications. Inspection systems are currently available that quantify both ID and OD defects and measure wall thickness. These methods raise the usual radiation concerns and 100% inspection is slow. A through-transmission system also requires access to both sides of the component under inspection.
Ultrasonic guided wave methods have been developed for NITI applications. These methods require the removal of small areas of insulation for transducer access to the component surface. Once in place, the transducers generate and receive guided waves that propagate through the component wall in a "pitch-catch" manner. Ideally, guided waves allow inspectors to quickly and inexpensively access component state-of-health. In practice, difficulties can arise in the generation and reception of the waves.
Acoustic emission tests are similar to guided wave inspections in that small areas of the insulation must be removed for transducer placement. AE techniques do not use transducers to generate signal; the system is pressurized to stimulate the emission of elastic strain waves from the area of the defect. AE techniques provide good estimates of the general health of the component, but may have limitations in determining the detailed characteristics of the defect.
Recent work in the area of NITI promotes a two step program to provide a cost effective solution to the problem. A global quality estimate using methods such as acoustic emission or ultrasonics can allow rapid, inexpensive certification of large sections of systems. A follow up comprehensive NITI technique can be used to investigate regions that are deemed suspect by the global survey. Several equipment manufactures are currently using this approach in an attempt to provide a cost effective solution to an important and difficult NDE problem.
NDT and Modern Information Processing - Can We Expect a Computer to Become a Skilled Inspector?
More and more emphasis is being placed on the development of advanced information processing tools to aid the NDE professional. New procedures, especially those based on neural networks, seek to employ these "laborsaving" tools. Most of these systems' goal is the ability to make reasonable decisions in real time. Efforts to develop automated inspection systems are being driven by the desire to remove factors such as fatigue, boredom, inattention, variability, and subjectivity from inspections.
The NDE field is served by a core of dedicated and experienced technicians, engineers and scientists. The emphasis on experience is intentional; this is the foundation of successful NDE method applications and development. This knowledge base has, in most cases, been gained through many years of hands-on involvement. Aid to the practitioner, when using computer-based decisions making NDE systems, relies on the effective transfer of this experience.
Most developments in computer-based decision making NDE systems use two general approaches. Both require NDE information that must come from the real world. Neural networks using training by example in an iterative manner similar to experience gained by experienced NDE personnel. An alternative approach to training by example is the expert system. This uses a set of rules deduced from first hand experience (most often provided by the NDE expert) that can be codified by a knowledge engineer and employed in decision making using the computer. In addition to the set of rules, this system also needs a sound decision making algorithm.
At this time, most NDE computer-based decision making applications have been developed only to act as an aid to the human operator. There is no question that these successful systems can help to mitigate problems associated with fatigue, boredom, inattention, variability, and subjectivity from inspections. They can be used to "flag" problem areas, then the operator is required to make the final decision.
Future goals, however, seem directed towards replacing the operator entirely. This raises the question of how well the computer-based decision maker can be developed to provide "error free" decisions. Neural networks require a "complete" set of faults for training. When this is possible, it must be recognized the networks work well when interpolating between training points but exhibit greater difficulties when required to extrapolate outside of known sets. For expert systems, they are only as good as the rules and decision making algorithm that they contain. These rules need to be tested at the highest level to ensure that they contain all conceivable situations. Furthermore, as the software for both of these systems becomes increasingly complex, it is more and more difficult to confirm that there are no faults contained in the coding.
The development of computer-based decision aiding (as opposed to making) systems will certainly continue to assist in NDE efforts. At this time, and very likely for the foreseeable future, the NDE operator must remain in the loop so that their experience and judgment can be used to deal with unanticipated and/or borderline conditions.
Technical Reports and papers given below are available from:
The National Technical Information Service
Email addresses:
Laser-Ultrasonics: From the Laboratory to the Shop Floor
J.P. Monchalin, C. Neron, et al- National Research Council of Canada P. Bouchard, C. Padioleau, et al- UltraOptic Inc. J.A. Nilson - J.A. Nilson & Assoc.
Ultrasonics is a powerful non-contact technique for inspecting and characterizing industrial materials. It cannot only be used to detect bulk and surface flaws, but also to obtain information on material microstructure, and determining engineering properties, such as elastic moduli and ultimate strength. This technique is unlike traditional ultrasound that requires liquid or contact coupling which makes it difficult or impossible to apply in many industrial situations. This is particularly true on curved parts and on parts at elevated temperature, a situation widely found during the processing of industrial materials.
Through a continuing effort begun more than 10 years ago, the Industrial Materials Institute of the National Research Council of Canada working in collaboration with UltraOptec Inc. has developed a technique called laser-ultrasonics, that circumvents the limitations of the conventional techniques. This novel technique is based on the generation and detection of ultrasound with lasers. The technology developed has been proven applicable under many industrial environments. This system was demonstrated in a pipemill for on-line measurement of the wall thickness of tubes at 1000 degrees C moving at 4m/s. The capability of this system was also demonstrated on a CF-18 aircraft in a maintenance hangar where it was used to inspect advanced composite materials. UltraOptec is in the process of commercializing this technology for the aforementioned applications.
This article was first published in the Journal of the Canadian Society for Nondestructive Testing, Volume 19, No. 5, Sept/Oct 1997, and appears here with their kind permission.
The NDE Institute of Canada was established in December 1976, receiving a status as a charitable, educational institute under Federal Charter. The NDE Institute's objectives are:
The CSNDT Journal is published six times a year. Individual annual subscriptions are available: $80 in Canada, $110 in the USA and $135 overseas. Copies of current and (if available) past issues can be obtained at the cover price of $15 each.
Canadian Society for Nondestructive Testing Inc.
The National Board of Boiler and Pressure Vessel Inspectors
The National Board of Boiler and Pressure Vessel Inspectors was created in 1919 to promote greater safety to life and property through uniformity in the construction, installation, repair, maintenance and inspection of boilers and pressure vessels. The National Board membership represents government agencies empowered to assure adherence to code construction and repair of boilers and pressure vessels.
The National Board Inspection Code is the only standard recognized worldwide for in-service inspection repairs and alterations of boilers and pressure vessels. This American National Standard has been adopted by a number of states and jurisdictions, as well as Federal regulatory agencies, including the U.S. Department of Transportation.
The National Board helps maintain safety within the boiler and pressure-vessel industry through the commissioning and training of third-party inspectors who inspect boilers and pressure vessels during the manufacturing process. It offers an extensive training program involving continuing education in various areas of the boiler and pressure-vessel industry. In addition the National Board commissions inspectors who passed an extensive examination enabling them to inspect all boilers and pressure vessels that will be registered with the National Board. It supervises the testing of pressure relief valves. It investigates accidents and Code compliance problems involving boilers and pressure vessels. It is responsible for registering all boilers and pressure vessels. It maintains a pressure relief testing laboratory that is considered the industry standard. It maintains detailed records of all National Board-registered vessels.
Journal: National Board Bulletin; published quarterly,is available without charge from the National Board Communications Department ISSN 0894-9611.
General Information: Richard McGuire
The National Board of Boiler and Pressure Vessel Inspectors
Ultrasonics
Cheng. A.; Achenbach, J.D.; Rogers, R.; Peterson M.-Proceeding of the 22nd Ultrasonic imaging of anomalies in truck tires-Proceedings of the 22nd Symposium on Quantitative Nondestructive Evaluation, Seattle, Washington (United States), 30 Jul.-4 Aug. 1995. Vol. 15A. Edited by D.O. Thompson and D.E. Chimenti. pp. 869-874. Plenum Press (1996) ISBN 030645310X
Hunt, H.-Vibrating pig for measuring free spans, depth of cover-Pipeline and Gas Journal, Vol. 223, No. 8, pp. 70-71 (Aug. 1996)
Leschenko, A.S.-Couplant materials in high-temperature inspection of components and methods of reducing signal aborption in the acoustic circuit when using these materials-Technial Diagnostics and Nondestructive Testing. Vol. 8, No. 1, pp. 24-29 (1966)
Jeong, H.-Effects of voids on the mechanical strength and ultrasonic attentuation of laminated composites-Journal of Composite Materials, Vol. 31, No. 3, pp. 276-292 (1977)
Sattar, T.P.; Chen, S.; Khalid, A.; Bridge, B.-Development of pneumatic and magnetic climbing robots for deployment of dry-contact ultrasonic transducers in hazardous environments-International Conference on Remote Techniques for Hazardous Environments, Leicestershire (United Kingdom), 29-30 Apr. 1996, pp. 119-126, Thomas Telford Publishing (1996) ISBN 0727725378.
Ketellar, K.C.J.; Krutzen, G.C.R.; Broere, C.-Inservice surveillance and diagnostic ultrasonic system of steam generator tubing International Conference on Remote Techniques for Hazardous Environments, Leicestershire (United Kingdom), 29-30 Apr. 1996, pp. 315-322, Thomas Telford Publishing (1996) ISNB 0727725378.
Radiography
Pugliesi, R.; Andrad, M.L.G.-Study of cracking in concrete by neturon radiography-Applied Radiation and Isotopes, Vol. 48, No. 3, pp. 339-344 (1997)
Szabo, J. L.; Boutine, J. L.-Some examples of industrial uses of neutron sources-Radiation Protection Dosimetry, Vol. 70, Nos. 1-4, pp. 193-196 (1997)
Magnetic
Scriverner, R. W.-Magnetic flux leakage inspection of gas pipelines: experience with a collapsible tool. Final Report, July 1996.
Tandon, K.K.- MFL tool hardware for pipeline inspection-Materials Performance, Vol. 36, No. 2, pp. 75-79 (Feb. 1997)
Bruno, A. Ç.; Barbosa, C.H.; Zimmerman, J.E.; Ribeiro, P.C.; Lima, E.A.; Scavarda, L.F.; Kelber, C.; Szcsupak, J.; Camerini, C.S.-Imaging flaws under insulation using a squid magnetometer-Proceedings of the 22nd Symposium on Quantitative Nondestructive Evaluation, Seattle, Washington (United States), 30 Jul.4-Aug. 1995. Vol. 15A. Edited by D.O. Thompson and D.E. Çhimenti, pp. 911-916. Plenum Press (1996) ISBN 030645310X.
Çochran, A.; Donaldson, G.V.; Carr, C.; McKirdy, D.McA.; Walker, M.E.; Klein, U.; Kuznik, J.; McNab, A.-Advances in the theory and practice of squid NDE-Proceedings of the 22nd Symposium on Quantitative Nondestructive Evaluation, Seattle, Washington (United States), 30 Jul.4-Aug. 1995. Vol. 15A. Edited by D.O. Thompson and D.E. Çhimenti, pp. 1151-1158. Plenum Press (1996) ISBN 030645310X.
Thermal
Del Grande, N.K.; Durbin, P.F.-Prcise termnal NDE for quantifying structural damage- Proceedings of the 22nd Symposium on Quantitative Nondestructive Evaluation, Seattle, Washington (United States), 30 Jul.4-Aug. 1995. Vol. 15A. Edited by D.O. Thompson and D.E. Çhimenti, pp.525-532. Plenum Press (1996) ISBN 030645310X.
Saintey, M.B.; Almond, D.P.-Mathematical modelling of transient thermography and defect sizing -Proceedings of the 22nd Symposium on Quantitative Nondestructive Evaluation, Seattle, Washington (United States), 30 Jul.4-Aug. 1995. Vol. 15A. Edited by D.O. Thompson and D.E. Çhimenti, pp. 503-510. Plenum Press (1996) ISBN 030645310X.
Wu, D.; Rantala, J.; Karpen, W.; Zenzinger, G.; Schonbach, B.; Rippel, W.; Steegmuller, R.; Diener, L.; Busse, G.-Applications of lockin-thermography methods-Proceedings of the 22nd Symposium on Quantitative Nondestructive Evaluation, Seattle, Washington (United States), 30 Jul.4-Aug. 1995. Vol. 15A. Edited by D.O. Thompson and D.E. Çhimenti, pp. 511-518. Plenum Press (1996) ISBN 030645310X.
Visual
Habiv, K.; Al-Sabti, F.- Optics and lasers in the corrosion laboratory-Corrosion Prevention and Control, Vol. 43, No. 6, pp. 158-170 (Dec. 1996).
Lewis, K.D.; Bowring, N.A.-Visual inspection of Sizewell B steam generators-Nuclear Energy-Journal of the British Nuclear Energy Society, Vol. 36, No. 1, pp. 55-58 (1997).
Acoustic Emission
Lemaster, R.L.; Beal, F.C.; Lewis, V.R.-Detection of termites with acoustic emission-Forest Products Journal, Vol. 47, No. 2, pp. 75-79 (1997).
Connolly, M.P.; Dinh, H.-Fleet inspection of compressed national gas cylinders for natural gas vehicles using source location acoustic monitoring-Society of Automotive Engineer Paper No. 961174 (SP-1181).
Newsgroups - A Useful Net Resource
The term UseNet refers to a mechanism that supports discussion groups--called newsgroups in the UseNet vocabulary--that allow users from anywhere on the Internet to participate. Originally conceived for the exchange of technical information, the UseNet soon became much more. Newsgroups were developed for nontechnical subjects, such as hobbies, news items, and social subjects.
A newsgroup is a series of messages covering the topic of that particular group. You can just read the messages, you can reply to any of them, or you can ask a question. Your reply or question will be seen and may be commented upon by all the readers of that particular group. Newsgroups are extremely valuable sources of information, and can also be effective as a means of communication. There are about thirteen thousand public newsgroups, called Usenet. Some individual groups have more than a hundred thousand regular subscribers.
Fortunately, there exists a nondestructive testing newsgroup, identified as:
sci.techniques.testing.nondestructive
In addition, the following newsgroups frequently have subscribers who have an interest in nondestructive testing:
sci.techniques.testing.misc, sci.engr.joining.welding, sci.engr.manufacturing, sci.engr.metallurgy, and sci.materials
1999 Calandar of Coming Events
March 8-12 - ASNT Spring Conference and 8th Annual Research Symposium, Orlando, FL. Contact: ASNT.
June - International Chemical and Petroleum Industry Inspection Technology (ICPIIT) VI Topical, Houston, TX. Contact: ASNT.
Oct 11-15 - ASNT Fall Conference and Quality Testing Show, Phoenix, AZ. Contact: ASNT.
Impact-Echo: NDT for Concrete and Masonry
Impact-echo is an acoustic method for nondestructive testing of concrete and masonry structures, based on the use of impact-generated stress (sound) waves that propagate through concrete and masonry and are reflected by internal flaws and external surfaces. Impact-echo can be used to make accurate, nondestructive measurements of thickness, and to determine the location and extent of flaws such as cracks, delaminations, voids, honeycombing, and debonding in plain, reinforced and post-tensioned concrete structures, including plates (slabs, walls, pavements, decks), layered plates (including concrete with asphalt overlays), columns and beams (round, rectangular and many I and T cross sections), and hollow cylinders (pipes, tunnels, mine shaft liners, tanks). It can be used to locate voids in the grouted tendon ducts of many types of post-tensioned structures, and to locate voids in the subgrade beneath slabs and pavements and behind the walls of tunnel and mine shaft liners. It can be used to determine the thickness and to locate cracks, voids and other defects in masonry structures where the brick or block units are bonded together with mortar.
In the impact-echo method, stress waves are generated by the impacts of small steel spheres (ball bearings) with diameters between about 3mm and 19mm (1/8-inch to ”-inch). These spheres, which are attached to short lengths of spring wire, are tapped lightly against a concrete surface, generating stress waves of relatively low frequency, typically from less than 1 kHz to a maximum of about 70 kHz. (The range of useful frequencies determined mainly by the diameter of the impacting sphere.) At these frequencies stress waves travel through concrete as though it were a homogeneous elastic medium. They are reflected by cracks, voids, internal interfaces, and external surfaces. The arrival of reflected stress waves at the surface produces small displacements that are detected by a piezoelectric transducer, producing and analog voltage-time signal that is digitized and fed to a portable computer for analysis.
Multiple reflections of stress waves within a structure produce transient resonances, resulting in periodic voltage-time signals that are dominated by the resonant frequencies. By mathematically transforming these signals into the frequency domain (using the Fast Fourier Transform method) the resonant frequencies can be identified. The depth, d, from which reflections occur is found from the simple equation, d = Cp/(2f) where Cp is the wave speed and f is the frequency.
The impact-echo method was invented at the U.S. National Bureau of Standards (now the U.S. National Institute of Standards and Technology) in the mid-1980‚s and developed at Cornell University from 1987 to the present time. Portable impact-echo systems for on-site testing typically weigh less than 30 pounds (14 kg), and are powered by 110/220 volts or by a 12-volt car or truck battery.
For more information about the method, a book on impact-echo, high-profile case studies, and commercial equipment for impact-echo testing, see the web site of Impact-Echo Instruments, LLC, at
Have you Visited the ASNTnet Bulletin Board at NDT Link?
To get to ASNTnet, go to the ASNT web site at www.asnt.org and choose ASNTnet from the buttons on the home page. Use your member number as both the ID and the password to log in. You may then change your password anytime you like. ASNTnet is a members-only internet service.
ASNTnet includes a live chat function for real time discussions with other members who are logged in at the same time. A schedule of planned discussions is in the works, too, and information about the schedule is posted on the ASNTnet login page.
Technical reports and papers given below are available from the National Technical Information Service, U.S. Department of Commerce, Springfield, Virginia 22151, U.S.A. Phone 703.487.4600; Fax 703.321.8547
Email addresses: For information -
info@ntis.fedworld.org
To order - orders@ntis.fedworld.org
•••General NDT Topics
1) Qualification of large diameter
duplex stainless steel girth welds intended for low temperature
service - Prosser, K.; Robinson, A.G.; Rogers, P.F.
Proceedings of the 28th Offshore Technology Conference, Houston, TX
(United States), 6-9 May 1996, pp. 237-245 (1996)
2) Nondestructive Testing of
adhesively-bonded joints - Adams, R.D.; Drinkwater, B.W.
NDT and E International, Vol. 30, No. 2, pp. 93-98 (Apr.
1997)
3) Pipeline failure investigations:
analytical techniques and case studies - Wilson, B.R.
Proceedings of the International Conference: Pipelining in a Changing
Competitive Environment, Calgary (Canada), 9-14 Jun. 1996. Vol. 2,
pp. 409-416. Edited by M. Yoon, M. Mensik, and M. Mohitpour. American
Society of Mechanical Engineers (1996) ISBN 0791817679
4) Nuclear power plant pressure
vessels. Inservice inspections - Finnish Centre for Radiation and
Nuclear Safety
STUK/YVL-GUIDE-3.8, 13 pp. (1995) ISBN 9517120907,
DE97615990
5) Risk-formed inservice inspection
evaluation procedure - Electric Power Research Institute
Electric Power Research Institute, Palo Alto, California (United
States), TR-106706, 98 pp. (Jun. 1996)
6) Nondestructive tests for
structural adhesives - Vincent, C.T.
Stanford Research Institute, Menlo Park, California (United States),
AD-A307-565/2GAR, 27 pp. (Aug. 1957)
•••Miscellaneous Techniques
7) Colonian's experience with finding
longitudinal defects with internal inspection devices - Johnson,
D.C.; Thomas, S.S.
Proceedings of the International Conference: Pipelining in a Changing
Competitive Environment, Calgary (Canada), 9-14 Jun. 1996. Vol. 2,
pp. 369-376. Edited by M. Yoon, M. Mensik, and M. Mohitpour. American
Society of Mechanical Engineers (1996) ISBN 0791817679
8) Ultra-wideband radar detects
buried mines - Nordwall, B.D.
Aviation Week and Space Technology. Vol. 146, No. 13, pp. 63-64 (31
Mar. 1997)
•••Ultrasonics
9) Long range propagation of lamb
waves in chemical plant pipework - Alleyne, D.N.; Cawley, P.
Materials Evaluation, Vol. 55, No. 4, pp. 504-508 (Apr.
1997)
10) Internal inspection device for
detection of longitudinal cracks in oil and gas pipelines - results
from an operational experience - Willems, H.H.; Barbian, O.A.;
Uzelac, N.I.
Proceedings of the International Conference: Pipelining in a Changing
Competitive Environment, Calgary (Canada), 9-14 Jun. 1996. Vol. 2,
pp. 345-352. Edited by M. Yoon, M. Mensik, and M. Mohitpour. American
Society of Mechanical Engineers (1996) ISBN 0791817679
11) Mechanized UT now can replace RT
on girth welds during pipeline construction - Raad, J.A. de;
Dijkstra, F.H.
Proceedings of the 2nd International Pipeline Technology Conference,
Ostend (Belgium), 11-14 Sep. 1995, 9 pp. (1995)
12) Surface imaging gets cracking -
Adams, T.
Materials World, Vol. 5, No. 4, pp. 199-200 (Apr. 1997)
13) NDT ultrasound detection of flaws
in insulation
ERA-TR(T)159, 14 pp. (Nov. 1994)
•••Radiography
14) Internet sites on radiography,
from planning a career to corrosion detection - Gros, X.E.
Insight, Vol. 39, No. 4, pp. 276-277 (Apr. 1997)
•••Magnetic
15) Technical advances simplify your
remote magnetic particle inspections - Chedister, W.C.
Materials Evaluation, Vol. 55, No. 4, pp. 455-459 (Apr.
1997)
16) R and D advances in corrosion and
crack monitoring for oil and gas lines - Atherton, D.L.; Czura, W.;
Krause, T.W.; Laursen, P.; Mergelas, B.; Hauge, C.
Proceedings of the International Conference: Pipelining in a Changing
Competitive Environment, Calgary (Canada), 9-14 Jun. 1996. Vol. 2,
pp. 329-336. Edited by M. Yoon, M. Mensik, and M. Mohitpour. American
Society of Mechanical Engineers (1996) ISBN 0791817679
•••Optical
17) Automatic surface inspection of
metal tubes by artificial vision - Truchetet, F.; Jender, H.; Gorria,
P.; Paindavoine, M.; Ngo, P.A.
Materials Evaluation, Vol. 55, No. 4, pp. 497-503 (Apr.
1997)
18) Taking the mystery out of machine
vision - Grosklaus, R.
Sensors, Vol. 14, No. 4, pp. 22-27 (Apr. 1997)
•••Acoustic Emission
19) Listening to the sound of
materials; acoustic emission for the analysis of material behaviour -
Wevers, M.
NDT and E International, Vol. 30, No. 2, pp. 99-106 (Apr.
1997)
20) Acoustic emission on-line
monitoring of the ammonia plant NII Secondary reformer exit (gas
channel) - Tonheim, J.; Tveit, R.
Process Safety Progress, Vol. 16, No. 2, pp. 101-104 (Summer
1997)
21) A practical monitoring strategy
for machining process control - Leem, C.S.
International Journal of Production Research, Vol. 35, No. 4, pp.
1051-1066 (1997)
22) Acoustic emission testing of
bolted connections under tensile stress - Hanel, V.; Thelen, W.
Journal of Acoustic Emission, Vol. 14, No. 2, pp. 115-118 (Apr.
1997)
Professional Societies and Associations
American Association for Laboratory Accreditation (A2LA), Gaithersburg, MD, 301-670-1377; Fax: 301-869-1495; Web: www.a2la.org. The A2LA is a nonprofit, scientific, membership organization dedicated to the formal recognition of testing and calibration organizations that have achieved a demonstrated level of competence.
American National Standards Institute (ANSI), New York, NY, 212-642-4900; Fax: 212-398-0023; Web: www.ansi.org. ANSI is a private, nonprofit administrator and coordinator of the US voluntary standardization system. ANSI does not develop standards; rather, it facilitates development by establishing consensus among qualified groups.
American Society for Quality (ASQ), Milwaukee, WI, 414-272-8575; Web: www.asqc.org. The ASQ facilitates continuous improvement and increased customer satisfaction by promoting the use of quality principles, concepts, and technologies.
American Society of Test Engineers (ASTE), Charlton City, MA; Email: mkeller@s1.drc.com; Web: www.astetest.org. The ASTE is dedicated to promoting test engineering as a profession.
Institute of Electrical and Electonics Engineers (IEEE), Piscataway, NJ, 908-981-0060; Web: www.ieee.org. The IEEE is a technical professional society that advances the theory and practice of electrical, electronics, and computer engineering as well as computer science.
Institution of Electrical Engineers (IEE), Stevenage, Herts, UK, +44-1438-313-311; Fax: +44-1438-742-840; Email: postmaster@iee.org.uk; Web: www.iee.org.uk. The IEE promotes the advancement of electrical, manufacturing, and information engineering and facilitates the exchange of knowledge and ideas.
International Society for Optical Engineering (SPIE), Bellingham, WA, 360-676-3290; Fax: 360-647-1445: Web: www.spie.org. The SPIE is an international technical society dedicated to advancing engineering, scientific, and commercial applications of optical, photonic, imaging, electronic, and optoelectronic technologies.
ISO 9000/QS-9000 Support Group, Caledonia, MI, 616-891-9114; Fax: 616-891-9462; Email: isogroup@iserv.net; Web: www.isogroup.iserv.net. The ISO 9000/QS-9000 Support Group is a network of companies that serves as a clearinghouse of ISO 9000/QS-9000 information and certified assessors.
National Institute of Standards and Technology (NIST), Gaithersburg, MD, 301-975-3058; Fax: 301-926-1630; Email: inquiries@nist.gov; Web: www.nist.gov. As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and applu technology, measurements, and standards.