Jack Spanner

Circumferential Guided Waves for Defect Detection in Coated Pipe

Circumferential guided wave propagation behavior in a viscoelastic multi‐layered hollow cylinder is studied to provide a baseline for defect detection in tar coated pipelines. Theoretical work was carried out by developing the appropriate dispersion curves and wave structures for circumferential guided waves in a pipe coated with a viscoelastic material. Parameters that affect wave attenuation were investigated with some initial guidelines being established for improved penetration power. Low frequencies are suggested from both attenuation and detection depth points of view. Under this guidance, experiments utilizing a linear transducer array were conducted at a low frequency for successfully detecting delamination and volumetric defects in tar coated pipe. A study was carried out to find the appropriate features for defect detection in coated pipe and a test protocol based on this study is recommended and summarized.

DEFECT SIZING IN PIPE USING AN ULTRASONIC GUIDED WAVE FOCUSING TECHNIQUE

Defect circumferential location, circumferential length and depth are studied with an ultrasonic guided wave focusing inspection technique. Differently shaped defects, such as a planar saw cut, a volumetric through‐wall hole, and a volumetric spherical shape corrosion are studied. By focusing on 44 circumferential positions around the pipe at a specific distance, the maximum amplitude of the defect echo is recorded with respect to each circumferential focal position. Circumferential lengths of the planar saw cut and volumetric through‐wall hole are then measured by comparing the experimental results with theoretical calculations. It is shown that this measurement technique works well with the planar saw cut and volumetric through‐wall hole defects. In addition, it is shown that reflections from defects with the same cross sectional area (CSA), but different shapes, might be very different.

Sizing Stress Corrosion Cracking in Natural Gas Pipelines Using Phased Array Ultrasound

Gas transmission pipelines are inspected periodically by robotic systems that pass through the pipe. These inspection systems typically use electromagnetic nondestructive evaluation (NDE) techniques to detect flaws such as stress corrosion cracking (SCC). The electromagnetic techniques can detect and measure the length of the cracks, but cannot measure through wall depths. In some cases it would be desirable to excavate down to a cracked area of the pipe, inspect it “in the ditch” to determine the depth of the cracking, and use the depth information to support repair/replacement decisions. The objective of the research was to develop a nondestructive inspection technique capable of measuring the depth of stress corrosion cracks from the outside surface of a gas transmission pipe in the field. EPRI participated in the round robin study by using a linear phased array technique. Field removed specimens were provided by the Gas Technology Institute (GTI) containing SCC for depth sizing. In most cases sizing was difficult to accomplish because of the colony of cracks that existed. This presentation discusses the results obtained and comparing them to destructive analysis results.© 2002 ASME

Further Results on Attenuation of Neutron Embrittlement Effects in a Simulated RPV Wall

A carefully designed irradiation experiment was conducted in which a 190 mm thick reactor pressure vessel (RPV) wall has been simulated using nineteen 10 mm thick slices, 18 of which are made from key RPV steels, and irradiated under test reactor conditions to investigate the through-wall attenuation of neutron embrittlement. Preliminary results for two of the irradiated materials (a low copper content plate and a high copper content Linde 80 flux weld) were reported earlier. The third irradiated RPV steel was the international reference steel designated JRQ, and this paper describes the results for this steel along with updated analyses for the other two steels. Comparisons of predicted attenuation changes in toughness properties with measured fracture toughness and Charpy V-notch results are presented for all three RPV steels. The predictions of through-wall attenuation follow the practice defined in ASTM E900-02 and Regulatory Guide 1.99, Revision 2, in which the attenuation of high energy neutron fluence (E>1 MeV) is projected based upon an approximate displacements per atom (dpa) change through the wall thickness. The resultant degree of material damage using this dpa-based fluence change is estimated using current embrittlement correlation models.

Time Scaling and Frequency Invariant Multiresolution Analysis of Ultrasonic NDE Signals

Nuclear power plant pipes are periodically inspected for possible cracks that occur in the heat-affected zones of welds. Intergranular stress corrosion cracks (IGSCC) are the most common type of cracks encountered particularly in stainless steel piping. Three major factors are required for the formation and propagation of IGSCCs, the tensile stress on the inner diameter of the weld region, a corrosive environment and a sensitized grain structure. When these flaws are not detected early enough, the consequences can be disastrous, and therefore the detection of IGSCCs is of significant interest to the nuclear industry.

Attenuation of Neutron Radiation Damage Through a Simulated RPV Wall

An experiment has been conducted in which a 180-mm thick reactor pressure vessel (RPV) wall has been simulated using eighteen 10-mm slices and irradiated under test reactor conditions to investigate the through wall attenuation of neutron embrittlement. Attenuation of neutron radiation damage through the wall of an RPV is a process that involves a changing neutron flux spectrum. The effect of the changing spectrum has not been fully studied to define the change in fracture toughness properties through the RPV wall. One low copper content base metal and one high copper content Linde 80 weld metal have been irradiated in various positions through the simulated wall to allow quantification of an improved experimentally-based embrittlement attenuation model. Comparisons are made of predicted attenuation changes in toughness properties with measured fracture toughness and Charpy V-notch results for the high copper content weld metal and the low copper content plate. The predictions of through-wall attenuation follow the practice defined in ASTM E 900-02, in which the attenuation of high energy neutron fluence (E >1 MeV) is projected based upon displacements per atom (dpa) change through the wall thickness. The resultant degree of material damage (Charpy V-notch 41 J transition temperature, T41J) using this dpa-based fluence change is estimated also using the ASTM E 900-02 embrittlement model. The irradiation-induced shift in T41J (ΔT41J) is typically assumed to infer the shift in fracture toughness transition temperature to be used for structural integrity assessments for the reactor pressure vessel. This assumption will be checked by measuring Master Curve fracture toughness properties for the high copper content weld metal and the low copper content plate.

Effectiveness of Substituting Ultrasonic Testing for Radiographic Testing for Repair/Replacement

Technical justifications and demonstrations are needed by utilities to substitute ultrasonic examinations for radiographic examinations during repair/replacement activities. This paper provides technical justification and demonstration results for using this alternative inspection method. It also provides a potential demonstration process that could be acceptable to regulators and authorized nuclear in-service inspector agencies.Copyright

Insights Arising From a Comparison of the tanh and Exponential Fitting Methods for Charpy V-Notch Energy Data

In the 1960s and 1970s when the surveillance programs for currently operating commercial nuclear reactors were established state of knowledge limitations resulted in the use of Charpy-V notch (CVN) specimens rather than fracture toughness specimens. Reasonable success has since been achieved in correlating CVN and fracture toughness parameters. Such correlations provide an important part of the technical basis for both current regulations and ASME codes. These correlations imply that trends manifest in CVN data must also appear in fracture toughness data even though empirical evidence demonstrates that this is not always true. For example, the temperature dependence of CVN energy (CVE) in transition is thought to be a unique feature of each specific sample of ferritic steel that is tested, a view in sharp contrast with the now widely accepted view of a “Master Curve” for transition fracture toughness (KJc ). Also, effects of product form on CVE temperature dependence and property correlations are widely reported despite the fact that product form effects are absent from KJc properties. These observations suggest that the mapping of CVE behavior onto fracture toughness implicit to correlation-based regulations and ASME codes may produce erroneous trends in estimated values of fracture toughness. In this paper we investigate the hypothesis that the apparent differences between CVE and fracture toughness arise due to differences in how the temperature dependence of CVE and KJc data have historically been modeled. Our analysis shows that when CVE data are analyzed in a manner consistent with KJc data (i.e., transition and upper shelf data are partitioned from each other and analyzed separately rather than being fit with a continuous tanh function) the apparent differences between CVE and toughness characterizations are minimized significantly, and may disappear entirely. These findings demonstrate the differences between CVE and fracture toughness data to be an artifact of the tanh analysis method rather than an intrinsic property of CVE.

Artmap Networks for Classification of Ultrasonic Weld Inspection Signals

Inverse problems in Nondestructive Evaluation (NDE) involve estimating the characteristics of flaws from measurements obtained during an inspection. Several techniques have been developed over the years for solving the inverse problem [1]. These techniques range from calibration approaches to numerical methods based on integral equations. Signal identification and classification is one of the more popular approaches for inverse problems encountered in many practical NDE applications.

Mechanical Property Changes Related to Through-Wall Attenuation of Neutron Irradiation Embrittlement

The through-wall attenuation of neutron fluence of reactor pressure vessel (RPV) steels is often expressed using an exponential decay function based on some estimate of displacements per atom (dpa). In order to verify this function, an irradiation project was performed in which 18 layers of Charpy specimens and one central temperature control layer were stacked in a block to simulate a 190 mm thick RPV wall. Three western-type RPV steels (medium and low copper plates and a high copper Linde 80 flux weld) were irradiated in this project. Mechanical property tests of these materials have been performed under a consortium of EPRI, CRIEPI, NRI-Rez and ATI Consulting to fully characterize the mechanical properties in terms of Charpy transition temperature and upper-shelf energy, as well as reference fracture toughness using the Master Curve. These results have been published and presented previously. Recent hardness measurements were made on the three materials at various thickness levels and the results are summarized in this paper and compared to the previous mechanical property results. This paper has a related paper on microstructure characterization of these same irradiated materials at different thickness levels.Copyright