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Appendix Opportunities for Improving Reliability of Public Works Using Nondestructive Evaluation Note: This report was prepared at the request of the Committee on Infrastructure Innovation by a pane} chaired by Committee member Gordon Kino, tenth Stanley Wolf ~ the NRC task coordinator, - d including as other members: Nicholas Casino, National Bureau of Standards, Ga~thersburg, Maryland Robert Crmt, Who, Janney, Ebtner Associates, Inc. Northbrook, Illinois Kelly O'Day, Peer Systems, Inc., Philadelphia, PenneyI,rania Robert Price, Openaka Corp., Inc., Den~rille, New Jersey 61
CONTENTS I. Conclusiom =d Recommendatiom lI. Introduction III. Status of NDE ~ Selected Public Works Systems Highways Building Systems Water Piping Systems IV. Near-Term Demonstration Project Concept Project Objectives Project Approach Outline of Project Work Plan V. Research Concepts New Hardware Development of User Friendly Systerna Non<lestructive Evaluation Within a Systems Reliability Strategy VI. Institutional Needs Central and Regional Organizations Personnel Training NDE Standards VII. Glossary Table 1. Features Measured by Various NDE Methods Table 2. Representati~re Examples of U.S. Institutions Conduct- ing Research ~d Development in Nondestructive Eval- uation 63
L CONCLUSIONS ED R1:COMMENDATIONS This study outlines opportunities for greater use of nomads structive evaluation (NDE) to improve the reliability, of public works ~nfrastNcture. These infrastructure systems are complex, have long service lives (e.g., decades), and are sometimes diffi- cult to access (e.g., below grade). Their continuous operation is integral to personal and commercial activities. The operas conclusion of this study ~ that greater use of NDE, coupled with standardization and a failure analyem framework, a cost effective way to improve the reliability of public works infrastructure. By in creasing system reliability, NDE can make possible new options for design, construction, al ~ maintenance. A focused effort is needed to achieve this capability. The NDE pane} sought to delineate directions on specific Dues to show the effecti~rene" of NDE. Its conclusions and recommendations are, in order of decreasing priority: Near Term Demonstration Project NDE is at the threshold of making significantly increased contribution to the reliability of public works facilities. The ef- fectivene" of NDE can be most persuasively shown through a coordinated field demonstration of bearers techniques rather than through research add development projects. The status of NDE three public works areas ~ reviewed in Section H! of this appendix. Recommendation: A near-term demonstration project must be conducted to verify the effecti~rene" of NDE. Section IV of this appendix proposes coordinated field testing of several commer- ciaDy mailable and emerging NDE methods ~ order to evaluate their capabilities for providing reliable facility condition informs tion. One possible case study ~ the exarrunation of a set of urban streets which pa" over utility comport in different regions of the country and which are scheduled to be exca~ra~ ~ the near fu- ture. Standard methods normally used to examine the utilities and roadways should be employed to establish a baseline set of data. These should be compared with information obtained by a vaFiet~r of NDE methods. 65
~6 Institutional Focus for Reteach, Standards, and Information Public works systems can benefit firom the existing NDE can pability and the results of research on NDE. However, at present, this capability is distributed throughout several institution in in- dustry, government, and academia, none of which have a principal responsibility to public works. Recommendation: Responsibility for promoting NDE within public works must be given to a central organization In order to obtain most effective benefits from NDE. This org~ation must be capable of both fostering NDE "d amunng its relevance. As Recut in Section At, it would be-expected to (a) carry out and finance research and development, (b) provide leadership in development of standards "d user-friendly field instrumentation, and (c) disseminate information., Reliability Strategies for Public Works Reliability strategies consist of plans for continuous and cony effective provision of services or products. NDE can be most effective for public works infrastructure if integrated rhythm an overall management strategy for systems reliability (Section V). This management strategy would include an analytic framework for detection of defects, for failure analysis, ~d for accept/reject Sections. As noted in Section IT, this strategy car be the bash of predictive maintenance for public works. Such a strategy being implemented for electric power plants, where principal fail- ure modes of key components have been determined, ant NDE of these components ~ conducted both on-line and intermittently to evaluate whether repair, replacement, or continued operation warranted. Recommendation: A set of reliability strategies needs to be determined for public works systems. The range of strategies ~ broad from accepting system outages due to frequent failures (once per year) to continuous monitonug to mmimi~e the occur- rence of failures alla the ensuing outages. This effort should be hinted at identifying the distribution of reliability strategies used today, the critical components dominating system outages, and appropriate strategies for these systems depending upon factors such as the t ype of public works system and size and location.
67 Research and Development on and Standardization of Selected NDE Methods Many available NDE methods (dieted in the GIomary) appear attractive for application to public works systems, but develop ment and engineering ~ needed for these method to become com- merciaDy competitive products. In addition, standards have to be established ~ order for NDE methods to yield consistent results in the many different public works systems. Recommendation: Future research on new NDE hardware and software specifically for infrastructure systems should be con- ducted. This effort should be directed towards embedded sensors like fiber optic sensors In new structures, ultrasonic pulse echo (or impact echo) especially applied to concrete, and thermography and ground penetrating radar for undergroundstructures and pow sibly buildings. Along with this capability, user-friendly systems operating in real tune or near time should be developed for use the field. These tasks are described In Section V. Recommendation: Considerable attention must be given to NDE standardization. Section V! notes that standards should be established in the areas of methodologies, data analysis, and paw fail rules or criteria. Methodology includes both the equipment and its employment; analysis extends Tom simple to complex signal processing; pas~fail criteria refer to data interpretation in the context of accep~reject Sections for continued operation. II. INT1LODUCTION Facilities deteriorate over time, and the cumulative eEects of corrosion, wear and tear, fatigue, freeze-thaw cycles, etc., can e~ren- tuaDy undermine the structural integrity or functional capability of facilities comprising our nation's infrastructure. Maintenance activities are needed to protect structures from deterioration and preserve their integrity. In turn, improved design is necessary both to reduce the required maintenance as wed as to facilitate it. Nondestructive evaluation (NDE) offers infrastructure man- agers tools which can help them to design, operate, and maintain their facilities in a more cos~effective manner. NDE involves both probing structures, for flaws and other features with techniques which do not damage the structures and evaluating the residual integrity of the structure. This concept has recently emerged from
68 the more generic term, nondestructive testing, which refers to flaw detection. Reliable condition information, coupled with effective mod- els and decmon support tools, can lead to unproved ma~nten~ce management, which ~ turn, offers the potential of reduced costs to m~nt~un our public facilities. An example of this has been demo~tra~ by the use of NDE for cIames of electric power gen- erating plants (Armor, et al, 1981~. Key components in the failure profile of fossil-fuel fired plants are the boiler, turbine, "d stern generator, which lead to 25, 2, and 5 days outage per year of per baseload plant, respectively; these outages total about $30 million annually, since each unscheduled outage costs about $1 million per plant per day. The dominant failure modes of each compm nent ~d fruitful areas for on-~ne nondestructive monitoring have been estabILshed. Specifically, NDE provides information regard- ing the likely impact of Baws on the structural integrity of these components in time for planned maintenance rather than repair during ~ unscheduled outage. NDE can also medicate unexpected and unacceptable plant operating condition that arise, so that appropriate modifications can be implemented. When used as part of an overall reliability strategy, NDE may also allow design and maintenance options not otherwise possible. The interest in design of structural components with nominally brittle ceramics has led to a requirement for NDE dur- ing both processing and service of these components (Katz ~d Lenoe, 1981; Evans, 1981~. An NDEYbased maintenance option ~ the "retirement-for-cause~ program In the Department of DO feme. Implementation of this program would change the basis for replacement of a critical component from an arbitrary time of ser- ~rice to the detection by NDE of a design-critical Eaw; thus NDE will lead to substantially increased time of service and cost effec- tivene" of each component (Thompson and Thompson, 1981~. Because ex~t~g infrastructure systems represent an enor- mous financial investment Ed have extremely long design lives, reliability strategies should emphasize maintenance. The total maintenance in~restment will deepens upon the specific facility en ~ the maintenance strategy. The bases for maintenance strategic include: I. Post-fai~ure repair as needed - repair facilities wicn neces- sary after senous problems develop. It ~ likely that the
~9 repa~r-a~needed strategy wiD result ~ the highest total cost because the extent of deterioration win have proceeded to the point where major and costly rehabilitation will be needed to restore the facility. 2. Continual preventive maintenance - develop routine main- tenance to prcac~vc facilities and apply maintenance con- tinuously. The preventi~re-mamtenance strategy will adroit the costly rehabilitation expense by keeping the facility in sound condition; however, the routine maintenance costs may be significant. Managers need to know the tradeoffs between the routine maintenance costs and rehabilitation costs. 3. Predictive maintenance - monitor facility conditions and maintain facilities based upon condition information and predicted likely future condition. This strategy requires con- stant feedback of reliable information on facility conditions so that managers car' amps the deterioration trends of the facility. As a facility beams to enter a rapid deterioration phase, protective maintenance activities are undertaken. Predictive ma~ntensuce ~ bred on the premise that m~nte- nar~ce should be invested In facilities prior to the onset of accel- crated deterioration. It ~ a cost~effective way for infrastructure managers to mamta~n the facilities ~d prolong their useful lives. Its Widespread use will require techniques such as elective NDE to mo~tor facilibr condition systematicaBy, modem and associated data bases to predict facility detenoration, and Section support methodologies to assist mar~agers in allocating the maintenance and rehabilitation funds. Various NDE methods are already employed within current infrastructure inspection routines, including visual, laser, elec- trocheniical, and acoustic techniques (ManDing, 1985; Burdekin, et al, Ig86; Brown ~d CaldweD, 1984; Wibon, 1985; C~iforma Dept. of Water Resources, 1986~. These have been incorporated maintenance procedures on 8 piecemeal basis. One extremely suc- ce~fu} application of modern NDE technology ~ the correlation leak detector (Califc~rma Dept. of Water Resources, 1986~. This technique malces it possible to use a small hand-held system with two detectors to pinpoint the location of a water leak. Because of its cost benefits, this system has been widely adopted since its inception in 1978.
70 This study discuses opportunities for greater use of NDE In condition assessment arid overall reliability strategies for public works, in order to achieve both better design and more effective managenal strategies for operation of these systems. It is timely to examine these opportunities, since NDE has developed rapidly within the last two decades through ad~r~ncen in instruments tion, understanding of the interaction of radiation tenth defects In materiab Ed components, appreciation of the role of defects in material and structures, and recognition of the economic lever- age of reliable structural performance. Section m of this report discusses the use of and need for NDE techniques ~ three repre- sentative infrastructure systems. The concept of a project with near-term payoff is proposed in Section IV to demonstrate and evaluate the capabilities of NDE for the infrastructure; a specific example ~ given as wed. Section V describes research needs to enhance the role of NDE In infrastructure assessment. In Section V], institutional issues are noted. HL STATUS OF ODE ~ SELECTED PUBLIC WOWS 53YI311:MS A wide range of NDE techniques is available for use in assent ing the condition of the nation's infrastructure. Brief descriptions of some of the more important method now ~ use along with some possible emerging techniques for infrastructure Ferment are presented in the GIomary "d In Table 1. Current applications of these techniques in three specific public works areas ---highways, buildings (mostly above grade), and water supply pipes (below grade) are described In this section; no priority ~ designated. Hi~w"e Definition of Highway System In the context of this review, Highway systems refers to pavements and bridges intended to carry high-speed, high-volume traffic. Typically, the pavements are of concrete, with or without reinforcement. Very often the concrete slabs have been covered tenth asphalt o~rerIays. Bridges are composed of steel or reinforced concrete superstructures, arid bridge decks are typically reinforced concrete. The advances made in the development of NDE methods
71 for the evaluation of highway oysters have been made possible by the concerted efforts of the Fevers Highway Adn~nistration and state highway departments. Little work has been performed directly on NDE inspection techniques suited specifically for city streets which are typically asphalt concrete pavements supported by prepared subgrades. The nature of the deteriorating actions are not identical for these two broad classes of highway systems. However, it may be possible to transfer some of the technological solution Tom state and federal highway programs. Types of Defects or Deterioration For concrete pavements containing steel reinforcement, one of the major forrrm of deterioration ~ cracking due to the disruptive stremes arming from corrosion of the steel. Extensive research has shown that the premature failures here resulted from the exten- sive application of deicing chemical. The chloride ions negate the normally protective (alksdine) environment provided by con- crete for the embedded steel reinforcing elements so that these elements are prone to corrosion in the presence of moisture and oxygen. Chemical incompatibilities among the matenab used to make the concrete or the clisrupti~re action of multiple cycles of freezing and thawing are other causes of concrete pavement d~ terioration. These can only be effectively controBed by proper selection of materials and TIiixture proportioning during concrete production. FmaDy, the disruption of the subgrade can lead to pavement cracking. Bridges are more vulnerable than pavements to deterioration because of the more severe loading and exposure conditions. For example, normal fluctuation ~ ambient temperature cause dif- ferential movements which, if not carefully considered in design, can lead to high stresses. Bridges are aL30 subject to high cyclic stresses, which tend to reduce the strength of the material. BY cause of these factors and the grave consequences of a failure, bridge inspection becomes ~ key element of the infrastructure maintenance program. For steel bridges, the prmcip^1 cause of distress are corrosion and cracking which usually arise from cyclic Joshing in combi- nation with poor design details. For reinforced and prestressed concrete bridges, the major canes of Hatred are environmental deterioration of the concrete and corrosion of embedded steel.
72 The most serious current problem ~ highway systems ~ pro mature deterioration of reinforced concrete bridge decks as a result of chIoride-ion intrusion and ensuing corrosion of the steel. Cor- rosion causes an expansion of the embedded steel bars which may result in the formation of cracks paraDe! to the top surface of the deck (delimitations). Remedial actions require removal of the chloride contaminated concrete, which often results In serious disruption to normal traffic flow. Application of NDE Techniques visual inspection Is the predom~n~t method currently used for condition assessment In highway systems, and its power and versatility should not be underestimated. However, it has its Obvious limitations. Too often, effective corrective action should be taken before the signs ofd~tre" are observed. Vu inspection is unable to provide information about the conditions below the surface. Finally, the quality of a V~U81 inspection ~ dependent on the experience of the inspector. The use of NDE techniques to supplement Usual inspection in various stages of development. For locating flaws in steel struc- tures, several standardized techniques are available. For example, cracks may be located using ultrasonic, X-ray, eddy current, dye penetrant, or magnetic methods. Ultrasonic thickness gauges per- m~t the measurement of member thicknesses with access from only one side. Sensors are under development which Frill provide continuous monitoring of the structure In order to detect the for- mation and propagation of cracking. The major obstacle in the application clef advanced NDE method to steel structures ~ pr~- marily one of technology transfer including the unfamiliarity of focal officials with NDE methods. For example, the advances in acoustic imaging that have been made in the medical and germ nautical fields could be adapted for use in inspecting structural steel components. In the inspection of concrete highway components, the am plication of NDE techniques has lagged behind that for steel in" spection. The primary reason for this disparity is the complexity of concrete ~ a material. Since concrete is composed of distinct phases (cement pate, aggregates and air voice) traditional ultras sonic pulse echo methods, for example, have not been successful for locating internal groins or cracks. Concrete is not electrically
73 conductive nor magnetic, and so eddy current or magnetic meth- ods are not applicable. Finally, concrete nary exist ~ various moisture conditions, from saturated to dry. The presence of moist ture interferes with the ability of some NDE techniques to probe within concrete. Because of these inherent difficulties, the mu jority of developments ~ NDE methods here been in the area of strength determination rather than Baw detection. Hoverer, within the last ten years significsot progress has been made ~ the application of radar "d infrared thermography (M-nine, 1985) for locating delaminations and other internal defects, and new am preaches are under development utilizing stress wave propagation methods. But before these new techniques can be widely used, additional efforts are needed to develop standards for instrument calibration and data interpretation. Needs for NDE Techniques for Highway Systems One of the most important needs In condition assessment of highway systems deals with the detection of corrosion. The ret queered inspection techniques are related to the conditions required for corrosion of embedded steel. These are (~) a lo" in the prm elective oxide of the steel, (2) a conductive path for current flow within concrete, and (3) a supply of oxygen. Since the presence of chloride ions ~ the principal cause of corrosion of steel, methods are needed for rapid, m-situ determination of chloride contents at the level of the reinforcing steel. Presently, the technique ~ to arid holes in the pavement and perform chloride determinations within the holes. This method ~ time consuming. Art mstru- ment for measuring chloride content using neutron radiation was developed, but procured to be too bulky and expensive for routine impactions. The permeability of concrete is the most important charac- termtic in terrors of long-term per£o~mance because it affects the rate of ingress of undesirable species, such as chloride ions, and it affects the electrical conductivity. Knowing the permeability essential for ameming the remaining life of a concrete structure. Standard methods do not exist for m-situ measurement of concrete permeability. The quantification of corrosion activity is a vital aspect of condition assessment of concrete structures. It is important to know whether the conditions exist for active corrosion, at ~ if they
74 do, corrosion rates need to be determined. Presently, standard test methods exist for making the former determination but not the latter. Recent studies have demonstrated the feasibility of methods to measure corrosion rates, but further development and field verification are needed. The development of advanced NDE methods to detect zones of delarrunations in concrete bridge decks has received significant support from the Fevers Highway Administration. Field demon- strations have shown the ability of ground penetrating radar and infrared thermography to rapidly surrey bridge decks, and private Grins are marketing inspection services based on these methods. However, some advances are needed to put there techniques into coIrunercia1 readiness for local highway departments. For example, objective studies should be performed to develop staDdaz<1 meth- oafs for signal analysis. Presently, different techniques are used by the various equipment (levelopers or research organizations. It would be desirable to determine the best methods of signal analysis and data presentation for different types of flaws. Manufacturers should talre advantage of developments in the microprocessor in- dustry and provide a new generation of led expensive and more portable Reprices. Past research attempts to develop flaw detection methods based on stress wave propagation had limited success and failed to result in a commercially produced test system. Recently, federal laboratories have taken a new look at the problem. By the com- bmed application of computer-based analytical method and new digital signal processing techniques, new insights have emerged. Thus with continued development, field test systems based on stress wave propagation should emerge to compliment the pulse echo system currently available for steel structures. Another area requiring attention is the development of meth- ods for condition abetment of tendons in post-tensioned concrete elements. In contrast to ordinary reinforced concrete, in which reinforcing team are embedded directly In the concrete, in posh tensioned concrete the tendons are contained within ducts which are typically filled tenth grout. NDE method "e needed to d~ terniine whether the tendons are protected by grout and whether corrosion h" occurred. Corrosion of steel used in prestressed structural members is a much more serious concern than corrosion of ordinary reinforcement, because the tendons are highly stressed
75 and prone to fracture from the strew concentrations arming at · · . corrosion sites. Many deterioration problems in pavements result from fail- ures of the subgrade, which lead to uneven pavement sections, extensive cracking, and potholes. Thus condition Segments of pavements should provide information on the subgrade as well as the pavement itself. Limited work has been performed on the use of ground-penetrating radar for this purpose, but additional study is necessary to understand the capabilities and limitations for this application. Other studies have demonstrated that by monitoring the propagation of surface stress waves generated by impact at a point, it is possible to obtain quantitative information about the subgrade stiffness beneath concrete pavements. This is a highly promising technique that merits continued development. The above has dealt with application of NDE to existing high- way structures. For new construction, sensors should be developed which can be embedded In the structure and can be used at a later tune to gain quantitative measures of exulting conditions in struc- tural members. The development of acoustic emission sensors is a step in this direction, but other devices which measure, for exam- ple, internal stress, moisture content, permeability, and corrosion potentials should be investigated. These devices wig have to be ex- traordinarily durable to continue providing meaningful data over the service life of the structure. Building Systems Definition of Building Systems The building system includes the foundation, structural shy tem, internal systems, facade, ~d roof. Different building mate- riab respond differently to their environment. The more common ones include steel, rew forced concrete, wood, aluminum, and com- posite systems (such as a gypsum and reinforced concrete and polymers). Types of Defects or Deterioration The environment of a building system includes various ther- mal, mechanical, and radiative loads, such as: (a) tempera- ture (and temperature changes); (b) solar radiation; (c) natural
76 hazards wind (hurricanes, tornadoes), earthquakes, floods; (d) water (moisture); (e) vibration (impact, steady state); Ed (f) superposed loads (door, occupancy, etc.). The response of the building to these loin may result In structural deterioration. Factors contributing to deterioration, along tenth common NDE techniques used to monitor several of these, are: corrosion visual and electrochemical methods, . defection (strain) induced by pressure electrical resin tance sensors, . cracking and voids-dye penetrants and ultrasonic tech- n~ques, delamination-ultrasonic methods, leak rate correlation leak rate testing, moisture content thermography, dimensional stability (Iocations of inserts and inclusions) ultrasonic methods, motion vibration sensors, chemical reactivity, freeze and thaw cycles, and . wide temperature fluctuations. In addition, several other items need to be addressed. Poor construction workmanship ~ weD as design and construction er- rors exacerbate structural response to the environment,and the responses are not necessarily mutually exclusive. For example, den lamination may be a measure of corrosion promoted by deflection caused by excessive stress. Though all responses are not evident or measurable at once, all should be considered in the building den sign and in the use of NDE methods during building construction and operation. Another major difficulty ~ that buildings are often used for purposes for which they were not arig~naDy intended. For example, the conversion of buildings for technical and scientific ap- plications may involve vibration molation or ~renting and cram age of toxic chemicals; such applications require carefill retrofit design, maintenance and continual evaluation of the building condition. Corrosion is a major problem in the deterioration of building structures. Introduction of chlorides into concrete mixes to accel- erate setting results In corrosion of the reinforcement steel wire or bar in concrete structures. ChIoride-~duced corrosion also occurs in puking garages in areas of the Coventry where deicing chemicals
77 are used. The chlorides penetrate the decks and corrode the rev Force steel. The corrosion product form under pressure and cracks the concrete. Detection of this type of corrosion, its extent, and activity are necessary for maintenance and life prediction of the structure. Electrochemical methods have been used for these tasks. The deterioration of the building facade and roof is a major expense to owners. Water penetration causes corrosion and de- terioration of the facade and interior of the structure. Current practices require extensive visual add destructive methods of am semment. There is considerable demand for more cost effective NDE methods. Long-term serviceable roofs are a rarity. Contin- ued sur~reiDance ~ needed by NDE methods to amen conditions and establish maintenance methods and schedules. Currently, ef- fective NDE methods are not sufficiently developed or applied. Application of NDE Techniques When selecting the NDE method used for building systems, consideration should be given to measurement of both the en~ri- ronrr~ent and of the response to it. For each type of response, severers different NDE method may be applicable. The choice calf the method ~ dependent upon the type of structure, acce - , degree of accuracy desired, cost, and the en~rironTnent in which measurements me made. NDE methods are used to equate thermal movement of building structures. Buildings subjected to solar heating will dim tort if the primary structural members are not shielded. Dim tree can occur ~ the facade if it ~ not designed for this distor- tion. For renovating or replacing facades in existing structures, this deformation sometimes has to be evaluated. Electrmoptical defiection-measunag devices operate at frequencies from zero to several hundred Hertz are a principal meant to measure diurnal thermaDy-induced deformations of masonry structures and to e~ral- uate their serviceable lifetimes. Measurements are normaDy made by placing a receiving telescope in the base of the structure and ~ tracking light in the top arid determining the relative horizontal movements between these two positions. Data on the response to wind pressure of high-nse buildings ~ important to provide design information for facade replacement or repair. The moving of a high-rise building requires that the facade
78 be sufficiently flexible to tolerate this movement without susta~n- ing damage. Electro-optical deflection measuring devices have also been user} to measure relative dedection between the base of a building and its top under infrequent high velocity winds. These measurements are then used to predict movements of the struc- ture at design wired speeds. This method of deflection prediction allows characteristics of the real structure to be used in its ev~u- ation rather than mathematical models that may not adequately simulate the real structure. Signal processing and the details of data acquisition are of prime importance to NDE methods because huge quantities of information are obtained which may obscure the application if not properly acquired in real time. Cradking of joints in metal structures ~ ~ measure of fatigue or overstress. Buildings subjected to cyclic loading and load ret versal often are subject to this cracking. Many fatigue cracks, even if surface defects, may not be visible unIe" highlighted bar NDE methods. Size, shape, direction, and termination point of these cracks are important to evaluate the life of a structure, de- sign of repair, =d clesign of further testing requirements. Dye penetrants and magnetic particle surveys are used effectively with this cracking problem. These provide on-site and rapid methods of evaluation. A disadvantage Is that they do not provide a view of interior cracks that do not penetrate the surface of the metal (which are usually related to manufacturing or fabrication causes). Thermographic surveys can be used to evaluate moisture in roofing systems. In expansive flat roofs, surveillance and subse- quent repair are important to maintain roof serviceability. The roof membrane should not be penetrated during the survey. Ther- mography ~ a technique which can detect relative changes in moist ture content so that moist areas can be identified. This technique should be farther developed to provide I~ expensive surveys and more easily used equipment than currently available. Foundation systems pose problems ~ building amemment. They generally are not accessible from both sides and their extent is generally not known, even if drawings are available. Depths of footage and thickness of retaining waBs generally have to be determined from one side of the building. Ultrasonic or pulse echo methods have been used here. Impact signals, by striking the structure, are passed through the system and resect oE dif- ferent interfaces. These reflections are recorded, proce~ed and interpreted as thicknesses. Positions of reinforcing steel, cracks
79 arid groins can be determined. The method has many potential applications in the evaluation of foundation systems. However, currently the equipment ~8 cumbersome, difficult to use, and is operator sensitive. Further technique development ~ deemed nec- essary for widespread adoption of this approach. Needs for NDE Techniques for Building Structures NDE methods are urgently needed to a - let in the amen ment of building structures. Emphasis should be placed on field- portable, rugged, user-friendly equipment that provide an on-site or real-t~me analysm. Equipment needs to be further developed in the areas of pulse echo (ultrasonics), corrosion detection, and measurement of corrosion rate. Innovative applications of other technologies also need to be accelerated such as use of radar (Matzkanin, et al., 1984~. Water Piping Systems Definition of Water Piping Systems Water supply systems consist of transmission and Attribution pipes varying in diameter from 3/4 in. to over 20 ft. The pipes in the water supply transmission system are constructed of steel, prestressed concrete, pretensioned reinforced steel, ductile iron or reinforced concrete. Sewers ~d storm crams are normally designed to use gra~r- ity Bow, and constructed of clay, asbestos cement, ductile iron, masonry, reinforced concrete, or poly~riny} chloride =d generally have larger diameters than water transmission lines. Types of Defects or Deterioration A buned pipeline ~ in a relatively protected environment. For this reason, a perception armes that the service life of a pipeline is virtually indefinite. Nevertheless, pipelines do dete- riorate and some at a very rapid rate. The principal cause ~ corrosion. Pipelines in the United States vary in age and some are more than 150 years old. Many of the major water pipelines, however, were constructed after World War II. Technological ad- vancements permitted refinements in design using higher strength
80 material which increased the susceptibility of the pipes to CO~TO- sion and reduced the margin against failure. It ~ anticipated that an increased rate of failures car occur with age of the pipeline inventory. This could involve many of the larger diameter (~d higher pressure pipes with more serious consequences of failure) unless adequate mew of evaluation are developed to locate ongm ing corrosion so that timely repair can be made. Failures In ~} water Retribution and sewer collection systems are a Ably occurrence. Over 300 failures of large (>Latin. dia~r~e- ter) prestre~ed water transmission muns have taken place ~ the hut 15 years. What is significant In this statistic ~ that the prod- uct was installed in quantity starting approximately thirty years ago. In small (<~in. diameter) pipes, failure ~ usually evidenced by leakage appearing at the surface or a subsidence over the line. Conveniences usually consist of the temporary Irruption of ser- vice and traffic patterns and minor financial effects on a small number of people. In the case of large-diameter pipe, however, a failure is likely to be catastrophic ar ~ can result ~ considerable damage, financial lo-, and inconvenience to the community. The collapse of interceptor sewers and major storm drains ~ roadways endanger traffic and have resulted In injury. Failures of water transniission mains can be explosive in nature, involving huge flows of water =~d resulting in large craters. Current maintenance procedures for buried pipelines are lim- ited. Appurtenances such as valves receive some attention. How- ever, maintenance is not performed on the line itself unIe" dictated by some event which ~ evidence of failure. Lack of maintenance results from an anticipation of troubl~free performance of the pipe, the difficulty of routine inspection, and the limited means of assessing the condition and maintenance requirements of the pipe or fittings. Application of NDE Methods Evaluation method differ radically between gravity flow and pressure pipes. Corrosion of gravity pipes tulles place primarily on the interior of the pipe by virtue of the fluid being carried, or through lo" of bedding support through exfiItration from the pipe. Corrosion of pressure pipe usually proceeds from the exterior.
81 drains ~ currently limited to Aqua] obaervatio=. For the smaDer collection lines a camera cu. be puBed through the pipe to an sist with amemment. Definition of the picture ranges from poor to excellent. For larger pipes, visual inspection is performed by personnel entering active sewers. Need for reps or replacement is made on the basm of measurements and observations. There are no means, at present, for e~raluat~ng the condition of sewer or drain fines by remote instrumentation other than the limits use of cameras. Prce~rc Once: Co~To~on usuaBy takes place from the exte- rior of pipelines operating under pressure and which are entirely full at all times. Since the pipe is generally buried, visual exam- ination ~ not possible, and misdirect means must be used. While many techniques have been used, none of them have been entirely satisfactory. A Locution of the methods employed follows. . Physical Testing pressure greater than the working prep sure is applied to molated sections of the system, and sensual observations "e made to detect failure. Results of the test show only whether the pipes can withstand the pressure applied and do not evaluate the condition of the line. Flow tests are conducted to determine the capacity of the line. Such tests evaluate the condition of the interior surface only. Visual inspection- examination of the surface over the pipeline can be made for subsidence, lush growth, or leak- age Tom the line. Eternal inspection of small pressure pipe can sometimes be made by camera. Larg~diameter pipe can be emptied "d entered for direct visual inspec- tion. Since corrosion invariably occurs on the exterior of the pipe, only instances of incipient failure are detectable by distress seen on the pipe iDtenor. Electric Potential Surveys-corrosion occumng on the ex- terior of a pipe produces electrical potentials in the sur- rounding soil. These potentiab can be detected by use of a half-cell electrode on the surface above the pipe. The effectiveness of the method depends on the construction of the pipe and its exterior coating. In order to conduct a pipe-to-soi} potential survey, the pipeline must be elec- trically continuous. This requirement restricts its use to steel pipelines with welded jolts or to those In which
82 pipe sections have been electrically connected. For those pipes which are electrically discontinuous, only differences in surface potential cam be measured as an indication of corrosion. Potential surreys are useful in delineating the most likely areas of corrosion, but excavation of the line is re- qu~red to determine its actual condition. The results of potential surveys are affected by subsurface conditions and interferences from other electrical sources. . Soil Res~tivity Surveys the rate at which corrosion of exposed steel will proceed when buried in soil can be cor- related with the electrical reactance of the soil. Measure meets are made at regular intervals along a line to locate low reactivity areas where rapid corrosion is most likely to occur. Impedance Surveys- recent developments have resulted in the application of impedance surveys in which an electrical current is applied to the pipeline. Faults In the coating are located by detecting leakage of the current. This tech- nique ~ still under development. An electricaDy continuous pipeline is necessary to apply the method. Needs for NDE Techniques for Piping System Buried pipelines in the United States are deteriorating and will continue to deteriorate. An increasing number of failures can be expected. Accurate NDE techniques are needed for condition assessment of both gravity and pressure pipelines. Corrosion ~ the predominant form of deterioration, and present methods for corrosion detection are limited In scope and objectivity. Existing methods only indicate the possibility of deterioration. Evaluation Of the actual condition of a line requires excavation slid visual examination. Thus there is a need for techniques to determine the rate en cl extent of corrosion so that service life of lines can be estimated. ' Significant advances have been made In techniques for locating pipelines and for leak detection in pressure lines. However, surface survey techniques are needed to locate areas of mfiItration and ex- fiItration In gravity Ares, and techniques are required for detecting small leaks In large pressure lines. The potential of various NDE
83 method for asse - sing the structural integrity of below-grade su~ way tunnel has been recently reviewed (MatzkaDin, et al., 1984), and the needs and applications for NDE may parallel those in e e plpmg systems e a. NEAR-TERM DEMONST1"TION PROJECT Concept The NDE pane} proposes a demonstration project which would involve coordinated field testing of several com~nerciaBy available NDE methods in order to evaluate their capabilities to provide reliable facility condition Information. This approach should be a more persuasive demonstration of the effectiveness of NDE than separate research and development projects or ~ isolated field demonstration of individual techniques. There are several attractive candidates for this project utility systems, highways, Buns (and possibly aquifem), water piping gym terrm and central mans, large pumps for wastewater treatment, and bridge structures. The pane! suggests the city street/utility corridor as the test case for the demonstration project. This case worthwhile not only because of its importance to utility oper- ations, but also because municipalities usually do not have the financial resources to conduct such an evaluation individually. Several one/t~vo block projects should be select for condition assessment. Geographical, construction, material, and weather- relay factors would be considered ~ the selection of the actual study sites to ensure that the study results are representative of conditions across the United States. The city street/utility combos represents a complex ~nfra- structure example which may include (a) street pavement, (b) gas utility line, (c) sewer tine, (~) water line, (e) electric, (f) telephone, (g) steam, and (h) special comrr~unication lines. Individual agencies own these facilities and share the common underground space. The actions of each agency can affect the others 80 that they have a collective need to effectively manage the underground space. Institutional, financial, and technical barriers restrict the flow of facility condition information among the facility owners.
84 Project Objectives The demonstration project should be designed to meet the forgoing study objectives: Provide field level information on the capabilities of ~ter- native commercial and emerging NDE techniques to accu- rately determine the condition of facilities; Compare the results of ~1ternati~re NDE techniques on the same structured; Develop procedures for the comparative equation of NDE techniques for evaluation of infrastructure facilities; Compare the accuracy of these alternati~re commercially available NDE techniques with current practice; and Assess the feasibility of using ex~t~g NDE techniques to define facility conditions. Project Approath The detain of the project should be structured by a Project investigation teams with expertise both In public works inspection and ~ NDE. The team win have to establish criteria for selection of NDE method to be included In the case study, test protocol, etc. It is anticipated that broad participation in the study by various technique advocates would be desirable, as would be wide sponsorship or endorsement by interested utility consortia. AR information general should be made available to the public domain rather than restricted to proprietary interests. OnUine of Project Wow Ply An overview of the proposed study ~ presented to a - let in understanding the intent of the demonstration project. A detmIed work ply must be developed which specifies the criteria to be used in selecting the actual sites, the NDE techniques to be in- vestiga - , the procedures to be used to ~rer~f~r the NDE results, study report requirements, and provisions for recommeIldatiom for future studies. Site selection should include locales representing the ~rariou~ climate, material, age, snd defect characteristics of public works
85 across the United States. Cooperation of city public works depart- ments and utilities will be critical in the success of the demonstra- tions. Standard data collection procedures and recording format pro- cedures should be developed to aid in evaluating and comparing aD baseline and NDE data snd test results. For each test site, municipal and utility infrastructure agen- cies win be requested to provide detailed facility information which will serve as baseline condition information. This information will include (a) base maps which accurately define the location and charactermtics of all infrastructure facilities in the study site, and (b) inspection of each facility by its owner using their norms pros reduces to define current conditions. The results of the individual owner inspections should be graphically depicted as overlays to the base map as well ~ be recorded ~ the standard format. The baseline reflects the ferret of information that the infrastructure agencies would normally hare available using their current tech- nology. This will provide a reference point for comparison with NDE techniques. It ~ not the intent to prescribe here the ~Iternati~re NDE methods to be used in this project. Nevertheless, it is anticipated that method such as ground radar, thermography, and ultrasonic pulse echo wiB be among those included. Suppliers of commer- ciaDy available NDE equipment should be invited to conduct field tests of their equipment ~ the test site. Both the capabilities of the equipment and the level of personnel training needed for its successful usage are of Interest. Results should be documented In a standard format. Field verification of NDE results ~ essential to confirm the accuracy of the NDE technique. This effort may mvolve the use of borage to confirm groins, or the excavation and inspection of buried facilities. For example, sites which are scheduled to have extensive new construction or rehabilitation could be selected so that the facilities can be excavated and inspected In this task. A comparative analysm should be prepared by the project- investigation team of NDE results with the baseline and actual field-`rerified condition information. This analysis should be con- ducted in conjunction with systems reliability strategies (see sec- tion V) or with the goal of mung their development. Condition comparisons should be made between (a) baseline and actual, (b) NDE and actual, and (c) NDE and baseline.
86 tions: This comparative aD~y8 - shoed ~ the foQ~g quad Are current mapection practices accurate (baseline ve ac- tual)? Are exiting NDE techniques able to ~ infrastructure conditions (NDE ve actual? Do NDE techniques offer accuracy, coat effecti~rene - , stan- dardization, or management advantages over current prac- tices (baseline ve NDE)? Does coordinated use of several NDE techniques unprove the eEecti~rene" of individual methods? V. 1tE:SE"CH CONCEPTS Many features In different types of system can be detected by ~ variety of NDE techniques (Table 13. Several new and promise ing technologies "e beginning to be used for NDE ^~d medico testing applications. Four of these technologies are discus In this section, as is needed development of software and statisti- cal techniques to give a better understanding of the experiment data. Improved NDE hardware and software for infrastructure system, along with greater knowledge of the physical phenomena controlling deterioration of these systems, make it timely to d~ develop a systems strategy for using NDE within an overall reliability framework. Many of these new ideas could be tried out In the laboratory on concrete samples and in the field. Concrete is a material with widespread use ~ public works. It provides ~ extemely good and relatively simple example on which to develop sad demonstrate new NDE method for finding and recognizing cracks, void, inhm mogeneities, porosity, and serious del~ninations. New HO - are Ultrasomc Techniques Ultrasonic pulse echo and measurements of ultrssomc precocity and attenuation have been used In metals to measure the presence and size of cracks, determine grain structure, porosity, ~nhomo- geneities and groins. Similar techniques are now berg used in
87 concrete. However, further development of the traducer tech- nology and of the signal processing technology to make faults easily recognizable and to provide a better quantitative charactenzation of them ~ baby needed. Thermography Thermogrsphic methods have been demonstrated to provide good information on dela~r~ination ~d on the presence of voids within structures, but often the information abtamed does not readily yield a flaw distribution. By using some of the develop meets in the field of photoacoustics and more sophisticated unage processing than has been applied to thermography heretofore, it may weD be possible to provide better quantitative information to the operator than has been al fable so far. Ground Radar Ground radar System are now commercially al table, and have been wed developed by the military for min - searching am plications. The technique has the major advantage that it can provide information at extremely high speed the concomitant problem ~ that the signal measured ~ not easily interpreted. It is apparent that the results obtained with such systems need to be evaluated on known structures, and better proce~mg of the information ~ required. Fiber Optics Fiber optic semors have the great ad~rantage that they car be up In an environment In which there ~ strong electromagnetic and vibrational interference. They con be up to sense tempera sure, pressure, strew add strain vanation, as wed as the presence of different types of liquids or gases. In some applications the phase delay of the light pa"mg through the fiber ~ changed by the straining of the fiber which ~ bonded to a structure. ~ an- Other example, light is emitted from the end of the fiber and passes through a sensing material, such as polyethylene, to another fiber. ~ this case the transparency of the polyethylene changes when immersed in oil. Thus the device senses the presence of oil. In
88 other cases the sensors can be USA to determine a liquid level, the temperature, or the presence of a gas. Since the fibers are relatively inexpensive, can extend over lengths of several kilometers, and are unpervious to destruction by corrosion, they hare a wide range of applicability. They lend them~el~res to berg embedded ~ a structure during construction, and to being used to determine the presence of leaks, large stresses, and the development of cracks tenth the breaking of the fiber). It might be hoped that such fiber semora could be interrogated Mom time to time, and left permanently In place for the life of the structure (~tern. Soc. for Optical Engineering, 1984; GiaBorenzi, et al., 1986~. Development of Us - -friend} 878t~8 It ~ of marital importance to simplify sophisticated NDE systems for use by relatively unskilled operators. The more information that the machine provides, the more it must be absorbed "d sort out by the engineer or operator. The cheer volume of m- formation soon becomes too much to be used ~nteDigently without some preliminary sorting by the system itself. Therefore, it wiR become unperati~re to make use of some proce - ring of the data to effectively use NDE. It ~ ~ ~mport~t for the system to be capable of carrying out some predictions of both useful life and the need to repair. Such applications lend themselves to the use of ar- tificial ~nteHigence techniques. But first, a better system strategy or framework for failure analysis, NDE usage, and determination of the reliability of venous types of infrastructure components needed. ondestroctne E~a~ati~ Widen a Systens B.eliabilit~r Strategy The most effective manner for incorporating NDE into in- spection routines is to start from an opera reliability strategy for promoting continuous service or product availability from pub kc works. Such a strategy would evaluate optiom for design, manufacture, and product support from the viewpoints of detec- tion of defects, failure analysis, add accep~reject decisions. This approach requires information on system performance, improver meets, and alternatives, e.g.:
89 frequency of system failure; · key components leading to system una~r~ability; underlying failure mechanizers; · major mechanisms of Manage accumulation leading to fail- ure; · cost of system ~mpro~remente; and . cost add mailability of alternative system for the same service or product. The example of fomil-powered electnc~ generating oysters given in Section I! indicates that a reliability strategy for public works based on NDE could be succes~Dy formulas "d un- plemented on a cost~eEecti~re bash. For cost effectiveness to be calculated for a brow] range of public works, standards for cont~n- ued delivery of service and products win need to be established. It is anticipated that unproved reliability strategies would be justi- fied for several cases~amm, central crater mans ~ water delivery systems, streets ~d underground utility comport ~ urban areas, among others. VL ~3T1TUTION" NE1:DS Several Dues anse in the diffusion of the status ~d future directions of nondestructive evaluation for specific infrastructure projects. These mclude central organization roles, personnel tra~n- ing, and standardization. ~ d. ]~ ~ Organ~ati~ At present, the NDE capability in the Unit-States is ~ tnbuted throughout several institutions in industry, government, and scademe (see Table 2~. Though public works improvement has not been a major force ~ NDE development, it could be a beneficiary. However, no institution has responsibility to promote NDE for public works, even though several are conducting re- se~ch and development in this area. The Customers" for NDE the public works arena are the may operating utilities. Though some of these are large enough to justify ongoing research and development on NDE, most coot. One example of a central research and development laboratory set up for an maustry or group of compames, which m~ividuaRy cannot support state o£th~art expertise, is the NDE laboratory
go (the EPRI NDE Center of the J.A. Jones Applied Research Com- pany, Charlotte, North Carolina) funded by the Electric Power Research Institute. This laboratory conducts research, qualifies techniques for engineering application, used conducts training of personnel for field testing. It is generally recognized that these capabilities far exceed those which could be justified by m~i~ridual electric utility complies. Another example ~ the American Welding Institute (Knox- grille, Tennessee) which was formed in 1984 under the premise that welding technology is critical to the reliability of many systems, but that it ~ not an area of focus for corporations designing and manufacturing these systenm. Therefore, amiable and emerging capabilities have not been brought into application as quickly possible, sometimes comprom7R=g the effectiveness of the welding technology actuaBy used. It is the opinion of this study pane} that the use of NDE in public works mirrors the above two examples and that a central organization ~ needed to provide leadership In research and devel- opment capability, in engineering qualificatioII of NDE techniques, and In personnel training. This organization Should aLso serve as a central source for dissemination of information on techniques add standards as weD as for trar'rfer~g Formation on research to utilities and other interested parties. Fir' ally, this organization should also participate ~ establishing standard and be able to compare the standards used In different NDE public works groups throughout the country. Most public works utilities win have some resident or m-house NDE expertise. However, the level of expertise required for some specialty NDE methods, and the equipment for these methods, may be provided more effectively by personnel operating out of regional centers rather than within each utility. Such regional groups would genre as a conduit of information to and from the central organization descnbe.d above to brag both problems and solutions to the attention of appropriate persons. Personnel Faming Greater emphasm has been placed on engineering system ret liability now than ever before. Thus, there is a great demand for persons with knowledge of NDE methods. Only a few universities offer multiple courses and multifaceted research programs in NDE,
91 ar ~ their graduates are sought by firms ~ industries (or research and development areas) supporting the university research. A pa=- alle} shortage of termed emaciate engineers or technicians exists as well. It ~ unlikely that this shortage will be relieved ~ the near future, so that infrastructure systems will have to compete for ND~trmned personnel. In contrast to the deficit ~ initial training programs, there appears to be ample number of refresher courses on NDE methods. ODE Standards in order to consistently apply NDE methods, standards have to be established for their use. Though many elements of the standards process already emit, they are inadequate for compre- hensive application of NDE methods to public works and for broad acceptance of information provided by NDE. Standards should be established in the areas of methodoic)gy, analysis, And pass/fai} rules or criteria. Methodology includes the type of NDE equipment add the process by which it is am plied. The NDE equipment should accurately measure quantities required. Necessary response ranges, safety,, and ruggedn-A need to be established. The process should be established which cons~ tently applies the NDE equipment. This Cures that comparative results can be consistent. Appropriate calibration of the equip ment to laboratory standards and to field conditions should be included ~ the methodology standards requirements. Analysis of NDE data ranges from very simple counts to com- plex signal proce-ins. Because of this, method need to be em tumbled through standards for consistent data interpretation and comparison. As application of NDE methods expand, more em- phasis is placed on user-friendly equipment which puts the method in more hands for greater use. The establishment of standards for methods of analysis would a - let ~ this opportunity. NDE method provide the data for interpretation and decision making. In many Stances the data and resulting analysm provide information which cannot be classed as pa" or fail, In other ~n- stances it does. Standards or guidelines should be provided which include rules for use of the information resulting from aneurysm. Some rules are already established by existing standards which can be cros~referencetl. In the process of establishing rules, the need would be revealed for new ones.
92 VIL GLOSSARY Acoustic Erni~ion: When strew ~ applied to a body and cracks or faults propagate through it, acoustic wares are emitted. Thus, acoustic emission can be an indicator of the onset of structural faults. The direct obeenration of the sound emitted Tom a water or gas leak con be a very powerful and simple nondestructive evaluation technique. Acoustic Resonance Methods: A common method for finding structural flaws, such as the presence of delaminations or of cracks in metal structures, ~ to tap the structure with a hammer and listen for the resonant vibration. The sound wild change when there ~ a fault present. A chain can be dragged scrod a structure to carry out this measurement on a Isrger scale. It ~8 also possible to determine the frequency content of the recorded vibrations, so as to carry out a more detailed quantitative analysm. This technique, although an extremely powerful one for showing up the presence of a fault, does not readily pinpoint its location. Chemical Techniques: The presence of moisture Ed acidity or al- lcalinity can be detected by change ~ color of certain chemical semors such as litmus paper. Correlation Water Leak Testing: An extremely powerful method for locating a leak ~ to use two microphones to measure the acoustic emotion Tom a leak. The recorded signals are subject to a signal processing method known ~ correlation analysis which can be determined by the position of the leak tenth respect to the microphone locations. Displacement Gages: Tlnese are used to measure the relative mo- tion between two reference pointy Vanous techniques are available depending on the magnitude of displacements that must be measured and the distance between reference points. For relatively large displacements between Extant points on a structure, electro~optical gages are a~railable. For measunng small displacements between closely spaced points, mechanics and electrical gages are a~railable. Dye Penetrants: A structure can be coated with a simple or fluorescent dye whith glows under ultraviolet light. This is a simple and quick technique for recreating the presence of small surface cracks.
93 Eddy Current Techniques: Ecidy current testing involves mew surement of the impudence of a small coil excited by a radio frequency current, when it is moved along the surface of a metal conductor. If there ~ a crack or flow near the surface of the conductor, an impedance change ~ obeer~red. This tech- ~uque ~ most useful for obse~r~g small near surface cracks in metal. Electrochemical Methods: Measurement of the frontage potential between a copper/copper suEate half-cell, placed on the sur- face of concrete, and the embedded reinforcement can be used to deliniate regions of corrosion activity. Polarization tech- niques are under development that would glare indications of corrosion rate. The latter method will be extremely useful in the prediction of remaining life. Fiber Optic Sensors: Optical fibers can be buried In the ground. In building structures and so on during the course of co~truc- tion. Sensors for various types of liquids, gases, temperature measurement, pressure, displacement, strain and so on can be either part of the fiber itself or care be attached to the fiber. The fiber optic semore can ~ In prmc~ple, be interrogated from time to time, even many yeam after ~rmtaBation. The fibers tales up very little room, are impervious to electromagnetic interference, and their presence does not affect structural m- te~ty to any great degree. Fiber optic semors here not been used in inhastructural application, and are still very much in the reteach stage. However, they may be widely up ~ the future as they become more fully developed. Gas Leak Detection with Lacers: This technique uses sensors which are sensitive to certain tracer gases. Such tracers are inserted into a pipe under pressure, and their leakage ~ used to detect the presence of cracks. Ground Radar: Short pulse radar techniques have been developed for detecting delamination In bridge decks for locating buried pipes, and for detecting flaws ~ concrete. Holography: By recording a photographic image of the optical hinges caused by interference between an optical beam ret fiected from a surface and a reference beam, it ~ possible to obtain a Lenitive measure of surface displacement. Such tech- zuques can be USA to look at changes of shape tenth time of a structure, or to measure vibration amplitudes of a structure.
94 Magnetic Field Measurements: When there are ferromagnetic ma- terials, such as pipes, buried in the ground, measurement of smug anomalies of the magnetic field with a detector moored over the surface of the ground can show up the presence of buried structures. This technique can also be used to detect cracks in steel components. Neutron Absorption: The absorption of neutrons pawing through maternal can be used to measure density. Changes ~ absorb tion can be employed to measure the moisture content. Nuclear Magnetic Resonance (NMR): This relatively new tech- nique has been applied mainly In medical applications. Its application to structural components has been demonstrated at Southwest Research Institute. It ~ useful for determ~n- ing the moisture content in materiab. At the present tune, the large magnets it needs, along with the sophisticated com- puter proce - sing required makes the system too sophisticated, bulky ~d expensive to be applied to infrastructure amen meet. However, this may change. Odor Sensing: This technique ~ useful for determining the prep ence of leaks of certain gases =d vapors. It is subjective, and erratic as a testing method because it relies on the judgment of the Spector. Radiography: X-ray, gamma ray and other penetrating radiation can be used to detect cracks, voids and foreign materiak In stmctural components. Although it can be effective, the apparatus is bulky, and requires personnel access to be limited while the work ~ in progre - . It ~ unsuitable for use ~ the field to examine components which are more than one foot thiclt. Stereo Photography: Stereo photography is a simpler and less sensitive technique than holography for measuring the shape and size of structures. It can determine whether distortions in the shape of a structure have taken place ogres a period of time. Strain Gages: A strain gage measures the change In reactance of a small wire or foil when it ~ stretched. When this gage is bonded to a structure such as a bridge member, it can measure the strain produced by applied loads. Television Inspection: This technique is like direct visual inspec- tion. A TV camera can be inserted in, for instance, a sewer pipe to determine the conditions inside the pipe.
95 Thermography: An infrared camera m USA to observe small maria tion in surface temperature. When a pavement, for example, is heated by the sun, the presence delamination causes aroma lies In the surface temperature which are detected by the camera. In other applications, by using pulsed heat sources, more detailed information on the depth and location of inter- nal structures can be obtained. Ultrasonic Testmg: In the pull technique a high frequency strew puke ~ introduced into an object and the reflection from interfaces are recorded. Pulse echo method are commonly used for finding faults such as Roil and cracks In metal struc- tures. Such techniques are being developed with relatively low frequency pulses for ex=TnT.~ng concrete. Measurements of the attenuation and precocity of acoustic warren can also pros vice "formation on the porosity of material, delamination, and the quality of bond between the two different materi- ~. ~ this case the through transaction method ~ USA in which the tra~it time between a tr~m~tting and a receiving traducer ~ measured. Visual Inspection: V]BU^1 inspection ~ the supplest aDd most commonly used technique for evaluating amide range offaulta. It ~ often the only NDE technique available, but it ~ labor intermive, and only shows up surface anomalies. The quality of visual inspection is highly subjective and is dependent on the experience of the inspector.
96 Table 1. Features Measured by Vanous NDE Methods Features Voids & Cracke Strain Location of R~inforcement Densit~r Motion ~ Interfaces Radiography G F G N G Neutron Scattering ~ Reflection N N G N N Visual G (surface) N N G N Tele~rision G (surface) N N G N Photography (stereo) G F N N N Holography F G N G N Fiber optic Sensor G G N N N Thermog~phy F N N ~N Ultrasonic Testing G F F N G Acoustic Resonance (semmic) G (in concrete) N F N F Acoustic Emission E. (dynamic) N N N N Correlation Water Leak Testing N N N N N Eddy current G (surface) N N N N Ground radar G N N N G Magnetic Field Measurements F N N N F Displacement (Gage) F G N G N Strain gage F G N G N Dye penetrant G (surface) N N N N Odor eensor N N N N N Chemical N N N N N Le~ detection N N N N N Electrochemical Methode ~N N N N NMR N N N N N Note: Letters in Table indicate relative detectability of {eature by each technique. Key: G = Good F = Fair N = Not Detectable
97 Table 1. Features Measured by Various NDE Methode (continued) Dimensional Location Stability of Embedded Features Corrosion Moisture ~ Warpa~e . 13tn~ctures . Radiography E. N N G Neutron Absorption ~ Reflection N G N N Visual G G G N Tele~rision N N N N Photography (stereo) G (outaide) N G N Holography N N G N Fiber optic Sensor N N G N N Thermography N G N F G Ultr~onic Testing F ~N G N Acoustic . . [esonance (seioniic) N N N F N Acoustic Emission N N N N G Correlation Water Leak Testing N N N N G Eddy current N N N G N Ground radar N N N G F Magnetic Field Measurements N N N F N Displacement (Gage) N N G N N Strain gage N N G N N Dye penetrant N N N N N Odor sensor N F N N G Chemical N G N N F Le~c detection N N N N G Electrocheniical Methode G F N N N NMR N G N N N N G G N N
98 Table 2. Representative Examples of U.S. Institutiom Conduct~g R - earch and De~relopment in Nondestnactive E`raluation Areas of Effort - Representati~re Examules of NDE Technioue De~relonmcnt Institutions Grou~d Conductin ~Penetrat~g R&D on NDE Acoustic Electroma~rneticThermo~raDhic Radar Rockwell Science Center X X Jones Associates X United Tech. Research Center X Schlumberger X Southwest Research Institute X XX Concrete Technology Laboratory X Wiss, Janney, Eletner Assoc. Inc. X XX Johns Hopkine University X X Ohio State Uni~rersity X X Stanford Uni~rersity X X National Bureau of Standards X X X X Ames Lab (Iowa State Uni~reraity) X X X Argonne Natl. Lab X X Batelle Pacific Northwest Lab Idaho National Engrg. Lab Oak Ridge National Lab Waterways Exper. Station Na~ral Constr. Engrg. Lab X X X X X X t X
99 Table 2. Representative Examplce of U.S. Institutione Conducting Research and De~relopment in Nondestructi~re E,raluation (continued) Areas of Effort Representati~re Examples of Institutions Materials Charactensation ~rith NDE Methods Conductin~r Pobmer Geotechnical R&D in ND E Met ale Ceramice C'omPosites Concrete _S tructure Rockwell Science X X X Center Jones Associates X United Tech. Research Center X Schlumberger Southwest Re~search Institute X X X X X Concrete Technology Laboratory X Wi", Janney, Eletner ~oc. inc. X X X Johns Hopkins Uni~r. X X X Ohio State Uni~rersity X X X Stantord University X Natl. Bureau of Standarde X X X X Ames Lab (Iowa State Uni~remity) X X X Argonne Natl. Lab X X Batelle Pacific Northwest Lab X Idaho National Engrg. Lab O~k Ridge National Lab Waterways Exper. Station Na~ral Constr. Engrg. Lab X X X X X X X
100 Table 2. Representati~re E:,camples of U.S. Institution Conducting Research Ad De~relopment in Nondestnacti~re Evaluation (continued) Areas of Effort Reoresentati~re Examples of Institutions Conducting R&D on NDE Aircraft Enemy Plants Infrastructure Building Component _S~rstem Characterization with NDE Methods Rockwell Science Center X Jones Associates X United Tech. Research Center X Schlumberger Southwest Research Institute X X X Concrete Technology Laboratory X X X Wise, Janney, Elatner A"oc. Inc. X X X Johns Hopkins University X X Ohio State University X X Stanford IJni~rersity Natl. Bureau of Standards Ames Lab (Iowa State University) Argonne Natl. Lab Batelle Pacific Northwest Lab X X X X X X X X Idaho National Engrg. Lab X Oak Ridge National Lab X Waterways Eloper. Station X Natural Constr. Engrg. Lab X X
