Michael T. Anderson

Preliminary Assessment of NDE Methods on Inspection of HDPE Butt Fusion Piping Joints for Lack of Fusion

Studies at the Pacific Northwest National Laboratory in Richland, Washington, are being conducted to evaluate nondestructive examination approaches for inspecting butt fusion joints in high density polyethylene (HDPE) pipe for lack of fusion (LOF). The work provides information to the United States Nuclear Regulatory Commission on the effectiveness and need for volumetric inspection techniques of HDPE butt fusion joints in Section III, Division 1, Class 3, buried piping systems in nuclear power plants. This paper describes results from preliminary assessments using ultrasonic nondestructive techniques and high-speed tensile impact testing for determining joint integrity. A series of butt joints were fabricated in 3408, 12-inch IPS DR-11 material by varying the fusion parameters in attempts to provide good joints and joints containing LOF. These butt joints were visually examined and volumetrically examined with time-of-flight diffraction (TOFD) and phased-array (PA) ultrasound. A limited subset of pipe joint material was destructively analyzed by either slicing through the joint and visually examining the surface or by employing a standard high-speed tensile impact test. Initial correlation of the fusion parameters, nondestructive, and destructive evaluations have shown that areas with gross LOF were detected with both TOFD and PA ultrasound and that the tensile impact test showed a brittle failure at the joint. There is still some ambiguity in results from the less obvious LOF conditions. Current work is targeted on assessing the sensitivity of the ultrasonic volumetric examinations and validating the results with a destructive analysis. It is expected that on-going and future work will lead to quantifying the ultrasonic responses in terms of joint integrity.Copyright

An Assessment of Visual Testing

In response to increasing interest from nuclear utilities in replacing some volumetric examinations of nuclear reactor components with remote visual testing, the Pacific Northwest National Laboratory has examined the capabilities of remote visual testing for the Nuclear Regulatory Commission. This report describes visual testing and explores the visual acuities of the camera systems used to examine nuclear reactor components. The types and sizes of cracks typically found in nuclear reactor components are reviewed. The current standards in visual testing are examined critically, and several suggestions for improving these standards are proposed. Also proposed for future work is a round robin test to determine the effectiveness of visual tests and experimental studies to determine the values for magnification and resolution needed to reliably image very tight cracks.

Review of Literature for Model Assisted Probability of Detection

This is a draft technical letter report for NRC client documenting a literature review of model assisted probability of detection (MAPOD) for potential application to nuclear power plant components for improvement of field NDE performance estimations.

Experimental validation of ultrasonic NDE simulation software

Computer modeling and simulation is becoming an essential tool for transducer design and insight into ultrasonic nondestructive evaluation (UT-NDE). As the popularity of simulation tools for UT-NDE increases, it becomes important to assess their reliability to model acoustic responses from defects in operating components and provide information that is consistent with in-field inspection data. This includes information about the detectability of different defect types for a given UT probe. Recently, a cooperative program between the Electrical Power Research Institute and the U.S. Nuclear Regulatory Commission was established to validate numerical modeling software commonly used for simulating UT-NDE of nuclear power plant components. In the first phase of this cooperative, extensive experimental UT measurements were conducted on machined notches with varying depth, length, and orientation in stainless steel plates. Then, the notches were modeled in CIVA, a semi-analytical NDE simulation platform develope...

Ultrasonic phased array sound field mapping through large-bore coarse grained cast austenitic stainless steel (CASS) piping materials

A sound field beam mapping exercise was conducted to further understand the effects of coarse-grained microstructures found in cast austenitic stainless steel (CASS) materials on phased array ultrasonic wave propagation. Laboratory measurements were made on three CASS specimens with different microstructures; the specimens were polished and etched to reveal measurable grain sizes, shapes, and orientations. Three longitudinal, phased array probes were fixed on a specimens outside diameter with the sound field directed toward one end (face) of the pipe segment over a fixed range of angles. A point receiver was raster scanned over the surface of the specimen face generating a sound field image. A slice of CASS material was then removed from the specimen end and the beam mapping exercise repeated. The sound fields acquired were analyzed for spot size, coherency, and beam redirection. Qualitative analyses were conducted between the resulting sound fields and the microstructural characteristics of each specimen.

Ultrasonic Evaluation of Two Dissimilar Metal Weld Overlay Specimens

Two dissimilar metal weld (DMW) pipe-to-nozzle specimens were implanted with thermal fatigue cracks in the 13% to 90% through-wall depth range. The specimens were ultrasonically evaluated with phased-array probes having center frequencies of 0.8, 1.0, 1.5, and 2.0 megahertz (MHz). An Alloy 82/182 weld overlay (WOL) was applied and the specimens were ultrasonically re-evaluated for flaw detection and characterization. The Post-WOL flaw depths were approximately 10% to 56% through-wall. This study has shown the effectiveness of ultrasonic examinations of Alloy 82/182 overlaid DMW specimens. Phased-array probes with center frequency in the 0.8- to 1.0-MHz range provide a strong coherent signal but the greater ultrasonic wavelength and larger beam spot size prevent the reliable detection of small flaws. These small flaws had nominal through-wall depths of less than 15% and length in the 50-60 mm (2-2.4 in.) range. Flaws in the 19% and greater through-wall depth range were readily detected with all four probes. At the higher frequencies, the reflected signals are less coherent but still provide adequate signal for flaw detection and characterization. A single inspection at 2.0 MHz could provide adequate detection and sizing information but a supplemental inspection at 1.0 or 1.5 MHz is recommended.

METHODS FOR THE IN‐SITU CHARACTERIZATION OF CAST AUSTENITIC STAINLESS STEEL MICROSTRUCTURES

Cast austenitic stainless steel (CASS) that was commonly used in U.S. nuclear power plants is a coarse‐grained, elastically anisotropic material. Its engineering properties made it a material of choice for selected designs of nuclear power reactor systems. However, the material manufacturing and fabrication processes result in a variety of coarse‐grain microstructures that make current ultrasonic in‐service inspection of components quite challenging. To address inspection needs, new ultrasonic inspection approaches are being sought. However, overcoming the deleterious and variable effects of the microstructure on the interrogating ultrasonic beam may require knowledge of the microstructure, for potential optimization of inspection parameters to enhance the probability of detection (POD). The ability to classify microstructure type (e.g. polycrystalline or columnar) has the potential to guide selection of optimal NDE approaches. This paper discusses the application of ultrasonic and electromagnetic methods...

The Capabilities and Limitations of Remote Visual Methods to Detect Service-Induced Cracks in Reactor Components

Since 1977, the U.S. Nuclear Regulatory Commission (NRC), Office of Nuclear Regulatory Research has funded a multiyear program at the Pacific Northwest National Laboratory (PNNL) to evaluate the reliability and accuracy of nondestructive evaluation (NDE) techniques employed for inservice inspection (ISI). Recently, the U.S. nuclear industry proposed replacing current volumetric and/or surface examinations of certain components in commercial nuclear power plants, as required by the ASME Boiler and Pressure Vessel Code Section XI, with a simpler visual testing (VT) method. The advantages of VT are that these tests generally involve much less radiation exposure and examination times than do volumetric examinations such as ultrasonic testing (UT). However, for industry to justify supplanting volumetric methods with VT, an analysis of pertinent issues is needed to support the reliability of VT in determining the structural integrity of reactor components. As piping and pressure vessel components in a nuclear power station are generally underwater and in high radiation fields, they need to be examined by VT from a distance with radiation-hardened video systems. Remote visual testing has been used by nuclear utilities to find cracks in pressure vessel cladding in pressurized water reactors, core shrouds in boiling water reactors, and to investigate leaks in piping and reactor components. These visual tests are performed using a wide variety of procedures and equipment. The techniques for remote visual testing use submersible closed-circuit video cameras to examine reactor components and welds. PNNL has conducted a parametric study that examines the important variables that affect the effectiveness of a remote visual test. Tested variables include lighting techniques, camera resolution, camera movement, and magnification. PNNL has also conducted a laboratory test using a commercial visual testing camera system to experimentally determine the ability of the camera system to detect cracks of various widths under ideal conditions.Copyright

Ultrasonic Evaluation and Imaging

Ultrasonic evaluation of materials for material characterization and flaw detection is as simple as manually moving a single-element probe across a specimen and looking at an oscilloscope display in real time or as complex as automatically (under computer control) scanning a phased-array probe across a specimen and collecting encoded data for immediate or off-line data analyses. The reliability of the results in the second technique is greatly increased because of a higher density of measurements per scanned area and measurements that can be more precisely related to the specimen geometry. This chapter will briefly discuss applications of the collection of spatially encoded data and focus primarily on the off-line analyses in the form of data imaging. Pacific Northwest National Laboratory (PNNL) has been involved with assessing and advancing the reliability of inservice inspections of nuclear power plant components for over 35 years. Modern ultrasonic imaging techniques such as the synthetic aperture focusing technique (SAFT ), phased-array (PA) technology, and sound field mapping have undergone considerable improvements to effectively assess and better understand material constraints.

Using Phased Array Ultrasonic Testing in Lieu of Radiography for Acceptance of Carbon Steel Plate Welds

The Pacific Northwest National Laboratory (PNNL) is conducting studies for the U.S. Nuclear Regulatory Commission (NRC) to assess the capability, effectiveness, and reliability of ultrasonic testing (UT) as a replacement method for radiographic testing (RT) for volumetric examination of nuclear power plant (NPP) components. This particular study focused on evaluating the use of UT on carbon steel plate welds. Welding fabrication flaws included a combination of planar and volumetric types, e.g., incomplete fusion, lack of penetration, cracks, porosity, and slag inclusions. The examinations were conducted using phased-array (PA) UT techniques applied primarily for detection and flaw type characterization. This paper will discuss the results of using UT in lieu of RT for detection and classification of fabrication flaws in carbon steel plate welds.