US utilities are facing an increasingly deregulated market place in which price competition will be featured. Correspondingly, utilities are aggressively pursuing cost reduction efforts in all phases of electric power production. Power plant operating and maintenance cost reduction efforts must be carefully managed, however, to avoid a potential reduction in operating reliability. To succeed in this effort will require new NDE techniques and decision support tools. Key attributes of such new techniques will be improved measurement speed and accuracy, reduced preparation requirements, automated data acquisition, and computer-based analysis support. Tools will be required to assist power plant personnel in making the best decisions on what, when, and how to inspect plant components to achieve overall economic objectives.

Typical damage mechanisms for the petroleum and utility industries are discussed. Responses to UT and AE are described. Decisions regarding when and where to inspect should be team effort of materials, inspection and stress analysis professionals.

Technological development in inspection technology has occurred rapidly over past 10 years. These developments have allowed users to obtain information on the condition of equipment that was previously unavailable, that is more detailed and comprehensive than previous methods, and that can be done without removing the equipment form service. The benefits to plant operators has been increased reliability and safety. This paper summarizes some recent developments in inspection technology for piping and aboveground storage tanks. The paper also discusses a joint-industry project that is currently underway to develop and commercialize new inspection technology for process industry applications.

Nondestructive examination (NDE) is a key contributor to the management of aging infrastructure at the Savannah River Site. Aging management is performed under a sitewide structural integrity program where NDE engineers function within a multidisciplined team to apply risk informed processes to select facilities and their safety significant structures, systems and components for the aging management program. This paper discusses an engineering approach for integrating NDE into aging management programs. It describes a process for verifying adequacy of existing predictive maintenance programs. It addresses NDE needs and trends for buried piping, a wide range of access constraints and challenges for NDE in facilities and components with hazardous materials, and provides an example of how NDE was used in a structural integrity evaluation that allowed cancellation of scheduled 1.5 million dollar piping system replacement project.

This paper will describe work within the American Society of Mechanical Engineers committee responsible for rules for inservice inspection of nuclear power plants. Work is progressing with the objective of producing proposals for risk-informed inspection programs that will be incorporated by the US Nuclear Regulatory Commission into the Federal Regulations Governing the construction and inservice inspection of al domestic commercial power plants. The paper will describe in detail the two primary proposals now under development and review. Both are directed toward enhancing safety while reducing the expense of periodic examination of piping welds. The first proposal provides a sound technical basis for reducing the number of Class 1 piping weld examinations as much as 60 percent while improving or maintaining equivalent safety. This is accomplished by using risk-informed techniques to re-establish the most important areas to examine. The second is a broader approach addressing all piping systems considered to be important under risk-informed assessment techniques. Both proposals are based on recent insights into risk analysis techniques developed within the pressure vessel industry, and both require evaluation of theoretical analysis and inputs of practical experience related to a wide variety of detrimental conditions. These proposals are being supported by pilot programs in a number of operating nuclear power plants. The authors will also attempt to explain the institutional constraints inherent in the process of obtaining regulatory recognition of proposals developed cooperatively by industry and the regulatory agency.

Predictive maintenance/inspection planning is being applied more frequency to counter the problem of component aging affecting reliability of plant components. Component aging is one of the critical issues in an increasingly competitive environment, especially in plant components built and installed during the 50s and 60s. Drawing the highest value for the predictive maintenance/inspection dollar is key is this issue for the electric utility and other production facilities. This paper discusses the basic idea of using decision analysis to tie the works of fully quantitative probabilistic engineering analysis and economic evaluation together for decision making. To illustrate this idea, specific application examples of this approach will be presented on power plant components. In addition, the concept of prioritization of multiple component maintenance/inspection projects, with maintenance budget and safety constraints for maximum net present value, will be presented.

The Reactor Coolant System (RCS) piping of a pressurized water reactor (PWR) plant is probably the best in terms of resistance to known degradation mechanisms of passive components. However, a failure in the RCS piping is extremely important in terms of safety and economic significance. Therefore, an effective management tool is needed to mitigate the potential effects of degradation due to aging or other effects such that plant reliability and availability are not affected. Currently, the RCS piping of all US PWR plants is being subjected to inservice inspection (ISI) based upon certain deterministics criteria set by the ASME code and the NRC regulatory guide. Even though the history of large RCS piping has not shown any degradation, the ISI continues at many locations at greta expense to the plant owners whereas, there can be only a few locations of relatively high vulnerability. A risk based ISI can provide an alternative and cost-effective solution in this situation. Pressurizer surge line is a unique segment in the RCS which is subjected to significant transient loadings due to stratification and striping during the normal heatup and cooldown processes. Therefore, the surge line is considered for illustration. Examples of structural reliability studies of pressurizer surge lines in four PWR units are presented in this paper to demonstrate possible reduction of ISI and significant cost saving without reduction of plant safety or reliability.

Following the catastrophic failures of seam-welded reheat piping at two power stations in 1985/86, the industry, with the assistance of the Electric Power Research Institute (EPRI) embarked on an aggressive inspection and evaluation effort to minimize the apparent risk associated with operating seam-welded hot reheat piping. This effort resulted in the EPRI guidelines for the evaluation of seam- welded stream pipes issued in 1987. Since 1987, more data and plant experience relating to seam weld cracking have become available. The data and experience have furthered our understanding of the inservice damaging process, and have helped assess the field effectiveness of the EPRI- recommended procedure for inservice seam-welded pipe inspection. Based on metallurgical evaluation and mechanical tests of weldments, the factors contributing to failures have been identified to be some or all of the following: excess stress and temperature; pre-existing flaws; nonmetallic inclusions; sharp weld cusps and creep strength mismatch; impurity segregation; weld roof-angle; etc. Since exceptions exist in every case, attempts to develop screening criteria for pipes 'at risk' have been less than successful. This paper presents an overview of the current state-of-knowledge with regard to the integrity of hot reheat seam-welded piping in the USA, with summary guidance on quantitative application of this knowledge of the life prediction of inservice piping.

Conventional ultrasonic inspection techniques may not possess the required attributes to detect early stages of creep cracking, accurately size indications or differentiate between benign and detrimental defects. Typical types of damage are presented and the need for personnel and procedure qualification programs discussed. Training using service damaged reference materials has been found to be necessary.

Increasingly, the detectability limits placed on inspection methodologies applied to the assessment of critical high energy components in fossil fuelled power plants are being forced to lower values. Most notably, recent events involving longitudinal seam welded piping have raised the question of lowering the detectibility limit for ultrasonics to a level necessary for resolving incipient creep damage. Historically, several testing methods were required for the detection of defects over the range of anticipated flaw sizes in an economically and technically acceptable manner. However, unyielding limitations exist for several of these currently used methods. While accepting that the detection of isolated creep cavities is not technically feasible with current conventional ultrasonic methods, the detection of high density cavitation sheets or zones prior to microcrack initiation has been demonstrated and successfully applied to field inspection of critical welds using focused ultrasonics. This paper describes the equipment and verification process used to extend the detectability limit of a field ultrasonic systems for longitudinal seam weld evaluations to approaching that of an acoustic microscope for the identification of incipient creep cavitation.

The project researches results of system for evaluation of oil and gas pipelines bedded in rivers are presented. The existing methods for evaluation of pipelines are analyzed and methods of ultrasonic scanning and videomonitoring are picked out as most perspective of all. The questions dealing with technical realization of system devices, methods of devices carrying to pipelines and methods of pipeline basis erosion place geographical coordinates definition are considered. The structural scheme of one system version is presented.

Conventional nondestructive inspection (NDI) of steel components, using magnetic particle, flux-leakage or near surface ultrasonic methods, is rendered difficult by the presence of protective coatings such as paint or stainless- steel cladding. Thick-section nuclear reactor pressure vessels (RPVs), having as-welded cladding up to 0.25 inches thick are a case in point. Here, magnetic particle techniques do not work and ultrasonic techniques are difficult to apply because of cladding roughens and variable elastic properties in the cladding and the weld interface. An NDI technique that is essentially unaffected by standard thicknesses of protective coatings would be a major advance. Magneto-optic imaging is one such technique. While conventional magneto-optic/eddy current imagers (MOIs) are a proven technology in the NDI of nonferromagnetic conductors, they do not possess a self-contained method for magnetizing steel. The purpose of this work was to develop methods for producing rotating, in-plane magnetization and then combine this technology with magneto-optic imaging to produce a self-contained instrument capable of real-time imaging of cracks in steel through protective coatings. We successfully demonstrated rotating in-plane magnetization using special 'quadrature' magnetic-yokes designed to accommodate both flat and cylindrical steel surfaces. The yokes were attached one at a time, to an MOI of reduced size, and the combined system was placed on a sample of the appropriate curvature containing cracks. A two-channel power amplifier was used to drive the yoke coils in quadrature. The resulting crack images were found to be much less sensitive to liftoff than conventional magnetic particle or flux-leakage NDI. In particular, cracks in steel were successfully imaged through 0.125 inches of stainless-steel cladding, making it likely that images of cracks in steel under even thicker cladding should be possible after further development of the technology. Unlike conventional magnetic particle or flux- leakage NDI, where crack orientation is important, rotating in-plane magnetization renders crack orientation irrelevant. Finally, because of these successes, the new NDI technology for steel should find many important applications.

Although acoustic emission testing is generally grouped with other nondestructive evaluation techniques (NDE) such as magnetic particle testing, it differs fundamentally in the way it detects defects. While common NDE methods seek to illuminate a defect using some sort of energy source, acoustic emission detects deformation processes as they occur. That is to say, only so called 'active' cracks are detected. In other words, acoustic emission testing is sensitive to sharp, process related defects and insensitive to fabrication or other blunt defects at normal service or test loads. It is this property, sensitivity to service related damage, that makes AE a good candidate for detection and monitoring of inservice equipment.

Although failure of the seam weld on reheat steam piping has been an infrequent occurrence, such failure is still a major safety concern for fossil plant operations. EPRI has provided guidelines for a piping management program base don periodic inspection. More recently, EPRI has also sponsored research to develop inspection techniques to both improve the quality and reduce the cost of piping inspections. Foremost in this research has been the use of acoustic emission (AE) techniques to detect crack damage in seam welds. AE has the substantial cost advantages of both allowing inspection without full removal of the thermal insulation on the reheat piping and making short-re- inspection intervals practical. This paper reviews the EPRI guidelines for performing an AE inspection on seam-welded hot reheat piping.

The need for AE monitoring electric power piping is discussed. An extensive laboratory program explored the feasibility of detecting crack propagation during isothermal, constant load tests. Emissions consistent with creep crack growth were detected. Test methods, specimen preparation and data obtained are described.

Up to 50 percent of the German sewer system is damaged. The estimation for the restoration costs is about 100 milliards DM. Respective to the German environmental laws the technical state of sewers have to be checked regularly be means of suitable inspection technology. At the present state of art the inspection will be carried out by color video turn-stewing cameras mounted onto remotely controlled vehicles. Thus, depending on the experience and the capability of the operator diagnosis failures can not be avoided. An exactly quantitative measuring coverage of pipe damages such as cracks, fractures, inrised connections is not feasible by means of conventional inspection techniques. Compared with most TV-based systems on the market, RODIAS LMK200 is equipped with a high resolution CCD matrix camera and an integrated laser distance measurer, by which a more qualified detection of damage sizes, type and volume can be achieved. The geometry measuring can be carried out by means of triangulation techniques without optical distortion and with precision of 0.1...0.5 mm. The position of the TV- camera head relative to the object plane is of secondary minor. The measured values will be displayed in the form of line or surface scans. The technical test of the RODIAS prototype in real municipal sewage systems is the object of on-going research.

In North America, most of the water mains pipes have been fabricated with either cast or ductile iron. It is well known that unprotected iron water mains are prone to corrosion resulting sometimes in serious metal loss and even major water leaks. At present time, water utilities have thus to replace parts of their water distribution pipes ont he basis of their average age, the number of breaks per kilometer per year, the hydraulic efficiency and water quality. In this paper, an ultrasonic technique which will enable the in-situ measurement of the pipe wall thickness is presented as an alternative to these inaccurate criteria. Such a technique can be used to map the defects along a water main and to evaluate their severity even if a mortar lining has been used to avoid the formation of tubercles. This technique uses water as the ultrasonic couplant and will not notably disturb the flow. The novelty of the approach relies on the use of a specialized model for ultrasonic propagation in multilayers coupled with a variable gain amplifier which increases significantly the dynamic range of the ultrasonic measurement systems. This system has been successfully used to produce images of corroded or graphitized areas in cast iron pipes of 6 inches nd 8 inches in diameter. The ultrasonic images agree well with the corresponding optical images. Thickness measurements have been also performed on water mains specimens around the defects found. The results indicate that the remaining iron thickness in the corroded regions can be estimated, in most cases, after proper signal processing.

Results of inspection of creep damage by magnetic hysteresis measurements on Cr-Mo steel are presented. It is shown that structure-sensitive parameters such as coercivity, remanence and hysteresis loss are sensitive to creep damage. Previous metallurgical studies have shown that creep changes the microstructure of he material by introducing voids, dislocations, and grain boundary cavities. As cavities develop, dislocations and voids move out to grain boundaries; therefore, the total pinning sources for domain wall motion are reduced.This, together with the introduction of a demagnetizing field due to the cavities, results in the decrease of both coercivity, remanence and hence, concomitantly, hysteresis loss. Incorporating these structural effects into a magnetomechanical hysteresis model developed previously by us produces numerical variations of coercivity, remanence and hysteresis loss consistent with what is measured. The magnetic model has therefore been used to obtain appropriately modified magnetization curves for each element of creep-damaged material in a finite element (FE) calculation. The FE calculation has been used to simulate magnetic detection of non-uniform creep damage around a seam weld in a 2.25 Cr 1Mo steam pipe. In particular, in the simulation, a magnetic C-core with primary and secondary coils was placed with its pole pieces flush against the specimen in the vicinity of the weld. The secondary emf was shown to be reduced when creep damage was present inside the pipe wall at the cusp of the weld and in the vicinity of the cusp. The calculation showed that the C- core detected creep damage best if it spanned the weld seam width and if the current in the primary was such that the C- core was not magnetically saturated. Experimental measurements also exhibited the dip predicted in emf, but the measurements are not yet conclusive because the effects of magnetic property changes of weld materials, heat- affected material, and base material have not yet been sorted out experimentally form the effects of creep damage.

Corrosion in pipework is a major problem in the oil, chemical and other industries and there is an urgent need for the development of a quick method for the detection of corrosion under insulation. An attractive inspection method would be to use cylindrical Lamb waves which will propagate along the pipe wall from a transducer placed in a 'keyhole' cut in the insulation, echoes returning to the transducer indicating the presence of defects. This paper describes the results of an extensive set of field trials using the technique, together with the results of systematic laboratory and theoretical investigations of the reflection and mode conversion of the waves from part-circumferential defects. It is shown that propagation distances of over 50 meters in 3, 6 and 8 inch diameter pipes can be obtained using a dry coupled piezoelectric transducer system, and defects around half the wall thickness deep and there times the wall thickness in diameter can be detected. The method shows great promise for the rapid inspection of pipework for corrosion under insulation, and is also equally applicable to the detection of internal defects. Furthermore, it is shown that the mode conversion of the waves can be exploited in order to discriminate between part-circumferential defects and axially symmetric features such as welds.

To verify and maintain the integrity of duplex stainless steels currently in service, we conducted a study in order to develop a method to nondestructively estimate their Charpy-impact energy at room temperature. Hardness of the ferrite phase was found to be a reliable indicator of the process of embrittlement during long-term heating for duplex stainless steels, but further information on the ferrite phase and the austenite phase is required for the estimation of Charpy-impact energy. An equation involving the hardness values of the ferrite and austenite phases,the ferrite content, and the average spacing of ferrite phase islands was found to be applicable in the nondestructive estimation of Charpy-impact energy at room temperature.

Ultrasonic inspection is frequently used to detect defects in structures during manufacturing, maintenance, and service. Traditionally the inspection is performed by manually or robotically scanning the surface with a single ultrasonic transducer. A flexible ultrasonic transducer array represents an innovative solution to many of the problems associated with traditional ultrasonic inspections. The flexible array consists of hundreds of ultrasonic pulser-receivers in a 2D arrangement that can be tailored to the geometry of the part to be inspected. The inspection is performed by placing the array on the inspection surface and activating each pulser-receiver in turn under computer control. Advantages of the flexible array include ease of use, rapid automated inspection, vacuum coupling to the surface, and ability to conform to curved surfaces. Since the array elements are at fixed locations, the inspection results can always be displayed as easy to interpret C-scan images. This paper describes the flexible ultrasonic array inspection systems and discusses potential piping inspection applications.

Due to failures in power plant feedwater piping, inspection of these components has become a priority item. The major reason for the failures is wall loss due to flow-accelerated corrosion on the inside diameter (ID) of the pipes. It can be very costly to use standard nondestructive testing (NDT) techniques for a comprehensive inspection due to the need to remove large areas of insulation. Guided UT waves can travel through the pipe over long distances and detect cross- sectional changes in the pipe wall with minimal insulation removal. This makes the guided UT wave an excellent candidate for locating significant wall loss due to corrosion and pitting. Southwest Research Institute (SwRI) has developed a simple and robust technology for generating and receiving guided UT waves based on magnetorestrictive sensors. Signals are generated and detected in the pipe via multi-turn coils acting as transmitters and receivers. Insulation removal is only required where the coils are attached to the pipe and this allows many meters of pipe to be inspected from a single location. Guided UT waves detect cross-sectional changes from corrosion on both the ID and outside diameter of the pipe and can also be used to map weld locations. This paper describes SwRIs systems and the preliminary results from testing on a feedwater pipe mockup containing simulated flow-accelerated corrosion.

There have been several failures in power plant feedwater piping systems due to wall thinning caused by flow- accelerated corrosion of the inner surface. Detection of wastage in susceptible pipes is costly as traditional NDE methods such as ultrasonic testing entail removal and reinstallation of insulation over many meters of pipework. Radiography is one solution to this problem, but it is slow to apply and requires careful attention to safety. The RTD Incotest system uses pulsed eddy current technology to measure pipewall thickness through insulation and external cladding. The technology has been licensed from Arco, Inc., who originally developed the technique for large diameter pipelines and storage tanks where the area interrogated was made deliberately large. This paper describes an optimized Incotest systems which can detect and measure internal or external wall wastage which is more localized and typical of flow-accelerated corrosion. Improvements have also been made to the inspection and data acquisition in order to increase the inspection rate and overall productivity. Ultimately the performance of the optimized Incotest system has been verified on samples which contain artificial and real corrosion.

In order to create a method to monitor the structural integrity of aerospace systems that can utilize current technology, effectiveness of processing data produced by current instrumentation is desired. Utilizing modal vibration methods to measure the dynamic characteristics of a structure, an ANN's ability to discern patterns and then interpolate similar patterns from information it is unfamiliar with, creates an appropriate vehicle for developing a damage assessment system that performs, in a manner, with relatively low computational time. In this study, two ANN paradigms were utilized to create neural network systems to identify, quantify, and locate damage to an ideal three-degree-of-freedom system. Damage was defined as a percentage reduction in the properties of the elements comprising the three-degree-of-freedom system. An artificial neural network damage assessment system based on the back- propagation paradigm was created and then compared against an artificial neural network damage assessment system based on the radial basis function paradigm. Both systems utilized the same data, consisting of resonant frequencies and modes of vibration, to evaluate the condition of all the elements of the three-degree-of-freedom system. Results show that the radial basis function network performed with a greater efficacy and robustness in assessing damage for this system.

The nondestructive eddy current methods are commonly used for automated defect inspection to detect cracks in materials which are used in cars, power and aircraft industries. The eddy current signal from a infinitely long crack can be classified with the help of the fuzzy logic and the neural network techniques. A rule based fuzzy logic classification guarantees better results than fuzzy-cluster- means algorithm, because the classification results can be increased in this case step by step. By using the neural network for the classification of the crack signals it is very important to have a good 'learning pattern.' The advantage of time-delay networks in this application is the fact that the network can 'learn' the eddy-current time signal; a signal preprocessing is not necessary.

Sensors are now becoming available that can be embedded in concrete or asphalt, or attached to steel structures for monitoring structural performance over significant periods of time. For the most effective use of these sensors, a monitoring strategy has to be developed for each specific application, which can range from heavy impact detection to modal analysis to concrete shrinkage. Among the tradeoffs that must be considered is the type of sensor. Other factors include the frequency range, the number and location of the sensors and the duration of the data collection. Data collection, transmission and storage systems are also significant components of the overall system.

Fracture mechanics can be applied to assess the safety of cracked bridge members. If crack length and stresses are known, the crack driving force (stress intensity factor, K) can be calculated. K was calculated for hot-rolled beams, as a function of crack length. K eventually becomes negative, indicating not further crack propagation. However a cracked girder will become compliant and 'shed' load to uncracked neighboring members. Our calculations show that the changes in both compliance and load-carrying capacity of the cracked girder are small until the girder is deeply cracked. A finite-element analysis of a cracked girder showed that by determining the bending stresses at about one beam depth from the crack it is possible to determine K. Measurement of these stresses was simulated in a field test. The method used small changes in sound speed to determine stress. The ultrasonic transducers used required no couplants and no surface preparation. They were also used to measure stresses in an integral backwall bridge.

The Coast Guard is responsible for the safety of thousands of vessels which carry passengers and cargo throughout the US. The Research and Development Center has had several projects with the objective of identifying advanced technologies that can increase the safety and efficiency of vessel inspections, especially structural surveys. The aim is to find technologies which will increase inspection coverage while still providing a complete and accurate condition of the vessel. One project focused on the basic technology items such as improved lighting, improved monitors to determine air quality, and use of visual enhancements such as binoculars and night-vision equipment which the inspectors could use directly. It continued on to more advanced nondestructive and visual methodologies which may not find the actual damage, but will indicate the most likely location to the inspector. These included magnetic climbers, robotics, advanced video camera systems and fiber- optic videoscopes, laser ultrasonics and climbing inspectors which utilize mountaineering techniques. Most of these advanced methods are more likely to be used by independent surveyors, classification societies or others hired by the vessel owners and operators. The Coast Guard needs to evaluate the effectiveness of these techniques to ensure the reliability of the information received and to bring some of the technology to the attention of owners and operators. Another project begun this year is investigating the nondestructive evaluation of metal fasteners in wooden boats. This paper provides an overview of these projects.

Standards are available for all NDT methods, but not many can be used for aircraft maintenance inspection, whether it is for aging aircraft or not. An ultrasonic standard for aluminum to calibrate the instrument for contact inspection is overdue. There is lack of requirements for visual inspection, except for the yearly eye examination. The inspectors should have a better understanding of the nature and origin of fatigue failures, corrosion and where, why and how it can occur.

The following propounds a simple way to predict the appearance of cracks. When plane carbon steel reaches the yield point, Lueder's line appear. When stress exceeds yield stress the Lueder's lines change into an orange peel texture. These phenomena are in all cases visible. Therefore it is possible to use the visible change in the appearance of the Lueder's lines that accompanies the increase in loading as a simple device to predict the appearance of cracks. Since the visible surface conditions are used as the predictor, it is unnecessary to use any special instrument. All one has to do is to make the surface that is to be observed flat and smooth. It is an extremely simple technique. Observation was made of the change of state on the flat, smooth surface of a basic material undergoing cyclic loading. Investigation was made of the relation between Stretcher Strains, or the orange peel texture, and the S-N diagram. It was possible to apprehend the process by which the state of the flat, smooth surface changed from the moment that the Stretcher Strains developed until the appearance of cracks. The utilization of the results of this experiment render a concrete example of the possibility of predicting the appearance of cracks by visual observation of stretcher strains. One may consider the use of Lueder's lines or the orange peel texture to be a reliable method for experimental stress analysis.