Probabilistic fracture mechanics (PFM) is considered to be a promising methodology in structural integrity assessments of pressure-boundary components in nuclear power plants since it can rationally represent the inherent probabilistic distributions for influence parameters without over-conservativeness. To strengthen the applicability of PFM methodology in Japan, Japan Atomic Energy Agency has developed a PFM analysis code PASCAL4 which enables the failure frequency evaluation of reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and thermal transients. PASCAL4 is expected to make a significant contribution to the probabilistic integrity assessment of Japanese RPVs. In this study, PFM analysis for a Japanese model RPV in a pressurized water reactor (PWR) was conducted using PASCAL4, and the effects of nondestructive examination (NDE) and neutron flux reduction on failure frequencies of the RPV were quantitatively evaluated. From the analysis results, it is concluded that PASCAL4 is useful for probabilistic integrity assessments of embrittled RPVs and can enhance the applicability of PFM methodology.

Creep failure of the pressure equipment operated at high temperatures in power and petrochemical industry is a frequent reason of its collapse. Ultrasonic waves' velocity is sensitive to change of material properties due to thermally induced degradation processes, especially plastic strain. The article demonstrates that measurement of ultrasonic waves' velocity ratio is able to localize plastic strain induced by various means including creep. Results are confirmed by comparison with hardness and metallographic analysis. Furthermore, statistical significance of the results is tested by t -statistics. The proposed application may help with selection of potentially critical areas during routine inspections on pressure equipment in operation.

In pressure vessel and pipe inspection, ultrasonic nondestructive evaluation plays a pivotal role in both in-situ and laboratory examinations. Scanning acoustic microscopy (SAM) has been a well-recognized laboratory tool for both visualization and quantitative evaluation of pressure vessel and piping materials at the microscale since its invention in 1974. While there have been multiple advances in SAM over the past four decades, some issues still remain to be addressed. First, the measurement speed is limited by the mechanical movement of the acoustic lens and the sample stage. Second, a single-element transducer with an acoustic lens forms a predetermined beam pattern for a fixed focal length and incident angle, thereby limiting control of the inspection beam. Here, we propose to develop a phased-array probe as an alternative to overcome these issues. Preliminary studies to design a practical high-frequency phased-array acoustic microscope probe were explored. A linear phased-array, comprising 32 elements and operating at 5 MHz, was modeled using PZFlex, a finite element method software. This phased-array system was characterized in terms of electrical input impedance response, pulse-echo and impulse response, surface displacement profiles, mode shapes, and beam profiles. Details of the construction of the model and the results are presented in this paper. Development of a phased-array acoustic microscope probe will significantly enhance scanning acoustic microscopy techniques for detecting surface and subsurface defects and microstructural changes in laboratory samples of pressure vessel and piping materials.

Many piping networks in processing plants, such as refineries, chemical plants, and electric power generation plants, are operated at elevated temperatures (≥250 °F or 121 °C). Failure of these insulated high temperature pipes can cause a major disruption of plant operation. In addition to inspection during the regular plant shutdowns, processing industries are looking for ways to inspect and monitor these pipelines on-line to ensure safe operation of the plants. Permanent monitoring of high temperature structures would require addressing the following technical problems: supporting the sensor functionality at high temperatures, ensuring the probe durability, and maintaining good coupling of the probe to the structure. In this work, a probe utilizing magnetostrictive transduction was tested on a mockup at 200 °C and produced a steady high amplitude signal over a period of 270 days. Probe performance parameters such as signal to noise ratio, data reproducibility, and sensitivity to anomalies are discussed.

Layered vessels have been in-service for many years which use layered construction. This construction technique has been employed since the 1930's. This generally involved either concentric plates or spirally wrapped plates to manufacture vessels with thick walls that otherwise would require very thick and heavy forgings. Long term asset management of these vessels, including non-destructive evaluation of the vessels welds and life assessment of the vessels due to operational cycling the vessels experience can be challenging. This paper is meant to address some of the challenges in managing these critical assets and provide a discussion on the application of state of the art techniques which are being applied today.

Full structural weld overlays (FSWOLs) have been used extensively as a repair/mitigation technique for primary water stress corrosion cracking in pressurizer nozzle dissimilar metal (DM) welds. To support an approved FSWOL design and safety submission for British Energy pressurized water reactor (PWR) nozzles, an in-depth evaluation was performed to assess the effects of a FSWOL on the through wall residual stress distribution in safety/relief pressurizer nozzles. Two safety/relief pressurizer nozzle mockups were fabricated based on British Energy’s PWR nozzle design. One mockup included the nozzle to safe-end DM weld and the safe-end to stainless steel weld, while the second mockup included the DM weld, the stainless steel weld, and a Westinghouse designed structural weld overlay. The mockups were fabricated utilizing materials and techniques that represented the plant specific nozzles as closely as possible and detailed welding parameters were recorded during fabrication. All welds were subsequently nondestructively evaluated (NDE). A thorough review of the detailed fabrication records and the NDE results was performed and several circumferential positions were selected on each mockup for subsequent residual stress measurement. The through wall residual stress profiles were experimentally measured through the DM weld centerline at the selected circumferential positions using both the deep-hole drilling (DHD) and incremental deep-hole drilling (iDHD) measurement techniques. In addition to experimental residual stress measurements, the through-wall residual stress profiles were simulated using a 2D axisymmetric ansys™ finite element (FE) model. The model utilized the application of temperature constraints on the weld elements to simulate the thermal welding cycle which greatly simplified the simulation as compared with detailed heat source modeling methods. Kinematic strain hardening was used for material modeling of the weld and base metals. A range of residual weld stress profiles was calculated by varying the time at which the temperature constraints were applied to the model. The simulation results were compared with the measurement results. It was found that the effects of the FSWOL were principally threefold. Specifically, the FSWOL causes a much deeper compressive stress field, i.e., the overlay shifts tension out toward the outside diameter (OD) surface. Furthermore, the FSWOL reduces tension in the underlying dissimilar metal weld, and finally, the FSWOL causes higher peak compressive and tensile residual stresses, both of which move deeper into the nozzle wall after the overlay is applied. Relatively good agreement was observed between the FE results and the measurements results.

This paper describes the use of an eddy current testing (ECT) method for the inspection and detection of impact damage in carbon fiber-reinforced composites (CFRP). ECT method is a nondestructive testing (NDT) method where electric induction is used. This method is widely used for detecting cracks and corrosion in metals, or checking their electric conductivity. Because carbon fiber in CFRP has electric conductivity, ECT method has a potential to inspect the defects. However, electric conductivity of CFRP is much smaller than that of metals. Moreover, from the view of the eddy current probe, CFRP to be checked looks as a inhomogeneous conductive materials where conductive fibers are bundled and laid up, and this is completely different situation comparing with metal samples that are homogeneous. Therefore, there are several problems to be solved for applying ECT method to CFRP such as proper selection of test frequency, shape of probe, or signal processing.

Destructive tests are generally applied to evaluate the fixed strength of spot-welding nuggets of zinc-plated steel (which is a widely used primary structural material for automobiles). These destructive tests, however, are expensive and time-consuming. This paper proposes a nondestructive method for evaluating the fixed strength of the welded joints using surface electrical resistance. A direct current nugget-tester and probes have been developed by the authors for this purpose. The proposed nondestructive method uses the relative decrease in surface electrical resistance, α. The proposed method also considers the effect of the corona bond. The nugget diameter is estimated by two factors: RQuota, which is calculated from variation of resistance, and a constant that represents the area of the corona bond. Since the maximum tensile strength is correlated with the nugget diameter, it can be inferred from the estimated nugget diameter. When appropriate measuring conditions for the surface electrical resistance are chosen, the proposed method can effectively evaluate the fixed strength of the spot-welded joints even if the steel sheet is zinc-plated.

This paper describes preparing mockup tubesheet specimens for visual examination using a digital microscope to determine that tube-to-tubesheet joint welds are of the specified size and that expanded joints are satisfactory for the intended purpose. It discusses nondestructive examinations (NDE) of the tubesheets and tube joints intended to assure achieving sufficient tightness and strength to satisfy the uses to which the exchangers will be put. This paper refers to the ASME Boiler and Pressure Vessel Code (Code) paragraphs that apply to tube joint welds and expanded joints including shear load testing when the Code requires it [1]. The discussion also addresses the need for manufacturers to have qualified tube joining procedures and personnel qualified to use the qualified procedures. The work concludes with a summary of ways to assure tube joint tightness and strength.

Polyethylene (PE) pipes are widely used in transporting natural gas since 1960s. However, there are few published literatures on method for safety assessment of PE pipes. This paper introduces recent work in developing ultrasonic nondestructive testing (NDT) equipment and research on safety assessment of electrofusion (EF) joints of PE pipes. According to the geometrical characteristics and ultrasonic response, defects in EF joints can be divided into four categories, i.e., poor fusion interface, voids, structural deformity, and over welding. The defect of the poor fusion interface includes three typical forms, i.e., cold welding, unscraped oxide skin, and contamination of the fusion interface. Cold welding, which is the most common and dangerous defect, has been successfully detected by using ultrasonic NDT equipment and assessed with a patented cold welding Eigen-line method.

There is growing interest in life extensions to enable longer term operation (LTO) for both existing nuclear power plants (NPPs) and proposed new NPPs. In order to justify an initial license extension for the 40–60 yr period, new nondestructive examination (NDE) approaches have been developed and deployed by NPP operators in their aging management programs. However, to achieve the goals of even longer term operation, and specifically for the United States in looking at methodologies to support subsequent license renewal periods (i.e., 60–80 yr and beyond), it is necessary to understand the capabilities of current NDE methods to detect, monitor, and trend degradation and hence enable timely implementation of appropriate mitigation and corrective actions. This paper discusses insights from past experience, the state-of-the-art, and current activities in the move toward providing a capacity for proactive management of materials degradation to support NPP LTO.

Tube-to-tube-sheet (TTS) welds, occurring in heat exchangers, condensers, and steam generators, are exempted from volumetric nondestructive examination, such as radiography or ultrasonic tests, due to their geometry. An approach of stricter quality control at qualification stage is adopted, apart from tests like liquid penetrant test and leak test applied to production welds. For qualification purpose, a mock up block is destructively examined for weld quality by microscopy and/or macroscopic examination. This paper shows that it is possible to carry out radiography of TTS welds using microfocal x-ray unit with back-throw type rod anode attachment, which sends radiation in nearly radial direction. It demonstrates the use of the same technique for the qualification weld block also. It further shows that the qualification weld slices can be radiographed in axial direction to enable 100% volumetric examination. Besides, it will make metallography more effective and meaningful; instead of a random section, it can then address the plane with a flaw using the help from radiography test. The paper suggests that the code adopt radiography in addition to metallography during qualification for better quality assurance.

Infrared thermography is a nondestructive evaluation method with an increasing span of applications. In this paper the pixel-level image fusion of infrared light and visible light image for infrared thermography and its application in nondestructive testing (NDT) of pressure vessel are studied. First in the image fusion, different mode image registration has been done based on feature corners. The corners and curves relative to each corner are extracted using the curvature scale space method. A new shape context descriptor for each corner is computed as the criterion to match the corners. Marks can then be added to pick up the corners, especially if there are no distinct matching feature corners between the different mode images. Two fusion methods, contrast modulation and transparent fusion, are introduced to fuse the visual and infrared light images. The experimental results show that the methods are good for pixel-level image fusion. Finally the method is applied to inspection of pressure vessel. The research indicates that image fusion for infrared thermography can facilitate defect location and interpretation of inspection results.

This paper describes the “thermal opening technique” for enhancing the ultrasonic response of a tightly closed crack. In this approach, thermal stress is generated by cooling the part locally to reduce the crack closure stress in stainless steel plate, which improves sensitivity to detect the scattering wave from the crack surface; this has however not been successful by the usual ultrasonic inspection technique without introducing the thermal stress. It has been observed that the enhancement of the scattering wave continues for several hours after removing the thermal stress. This valuable and unique characteristic of the scattering wave is related to the change in the contact condition between the mating crack surfaces. Finally, a method is proposed for the evaluation of the depth of tightly closed crack from the difference in the time-of-flight between the scattering wave and the corner echo. The quantitative characteristic of the method is also verified experimentally.

Pressurized vessels such as a steam drum in a typical power plant can often experience in-service cracking. Structural integrity assessment methodology can be a useful tool to determine the suitability of a vessel for service. This methodology may include fitness-for-service and remaining useful life analyses of a vessel based on the nondestructive examination (NDE) results and operating conditions. In this paper, the structural integrity assessment methodology applied to a steam drum case study is described. The analysis procedure, material property determination, stress analysis, limiting flaw size evaluation, and remaining useful life evaluation for the drum are discussed. A thermal shock design tool is briefly introduced. Recommendations for appropriate action are also presented. The assessment methodology employed in this paper can be applied to other similar pressurized vessels and structures in power plants.

Offshore pipeline failure statistics have been collected for more than 30 years now and illustrate that the riser predominantly fails as a result of corrosion. The consistent wetting and drying in the splash zone combined with defects in the coatings are the usual contributors to the problem. Risers are inspected at some determined frequency and can be done by internal and external methods. Inspecting by either means brings into account caveats and limitations from the technology used as well as human factors. For example, external inspections can be inefficient and inaccurate with some tools missing defects in areas of coating disbondment. In addition, internal inspections sometimes create false positives and can miss defects. These inaccuracies in the technologies or the techniques used may miss defects that eventually lead to failure. On the other hand, using corrosion mapping and fitness-for-service (FFS) assessment from the data collected, along with the inherent conservatism of this data from limited measurement accuracy, may result in the premature replacement of risers. A literature search is being conducted to review existing riser inspection methods and identify candidate nondestructive methods for riser inspection. These methods should be capable of detecting and monitoring general corrosion, localized corrosion pitting, and stress-corrosion cracking (sulfide or hydrogen induced) as external or internal corrosion damage. Thus far, this search has found that assessing the remaining service life of aging risers is largely dependent on the accuracy of analyzing corrosion damage to the riser surface in the atmospheric, splash (tidal), submerged, and buried environmental zones. The accuracy of each technology was analyzed. The capabilities and limitations of each method/technique used for riser inspection are summarized. The investigation is focused on long- and short-range ultrasonic techniques used for initial screening and corrosion mapping. These techniques can be deployed to detect a significant reduction in wall thickness using guided and torsional waves or to map accurately a corrosion damage using single/multiple transducers and phased-array probes in manual or automated mode. A pulsed eddy-current technique that uses a stepped or pulsed input signal for the detection of corrosion areas under insulation (CUI) is also being evaluated. This allows the detection of wall-thinning areas in the riser without removing the outside coatings. In addition, it is found that filmless, real-time, and digital radiography can be used to find internal and external corrosion defects in an insulated splash zone while the riser remains in service. A survey of nondestructive evaluation (NDE) manufacturing companies, NDE inspection companies, and operating companies was completed to collect information about current instrumentation and inspection/operators’ experience for riser inspection. Examples of advanced riser inspection instrumentation and field results are included. The ability of the candidate technologies to be adapted to riser variations, the stage of standardization, and costs are also discussed.

Circumferential guided ultrasonic Shear Horizontal (SH) wave Electromagnetic Acoustic Transducer (EMAT) pairs mounted on a mobile fixture in a through-transmission mode were used for detection and characterization of mechanical dents on the outer surface of a pipe wall from inside the pipe. The dents were created on a 12 in. diameter standard seamless steel pipe by hydraulically pressing steel balls of various sizes into the pipe wall. n 1 mode SH wave was directed through and along the wall of the pipe. Multiple measurements were obtained both from the dents and from the no-flaw region of the pipe using the EMAT pair. Dent features were extracted with a Principal Component Analysis (PCA) technique and classified into “cup” and “saucer” types using Discriminant Analysis (DA). The overall approach is able to detect and classify dents of depth 25% through wall or deeper, which should meet the needs of the pipeline safety inspection community (U.S. Department of Transportation, Research and Special Program Administration). Preliminary dent depth estimation potential is also shown via an amplitude correlation approach.

This paper addresses implementation of ultrasonic (UT) process qualification by performance demonstration as imposed by the ASME Boiler and Pressure Vessel Code Section XI, Appendix VIII. The intended audience for the present paper is an engineer with a good knowledge of NDE, but a limited knowledge of the ASME Codes and Standards. The starting point for application of UT performance demonstration is described in a paper published in this journal just over a decade ago by Cowfer and Hedden. That paper addressed the application of ultrasonic performance demonstration to qualify an examination process for ASME Code Section XI inservice inspection. The present paper provides a brief summary of papers specifically selected to provide the reader with a concise update of progress in UT performance demonstration since the earlier paper. Given that qualification, the reader should not expect new information in this present paper. The papers selected have been mostly selected from those presented at ASME Pressure Vessels and Piping Conferences, from 1995 to 2002, addressing the subsequent development and application of the UT performance demonstration process. The emphasis is on work performed for nuclear utilities under the Performance Demonstration Initiative (PDI), for application to Section XI inservice inspection. However, material also is included describing parallel work in the European Community, and applications of UT performance demonstration in Sections I and VIII of the ASME Boiler and Pressure Vessel Code, for use of UT in place of RT for new construction, are included.