Ultrasonic Inspection of Dissimilar Metal Welds for Probabilistic Reliability Assessment of Pipe Welds

2017 ◽  
Author(s):  
Sandra Dugan ◽  
Anne Jüngert
Keyword(s):  
Material Properties ◽  
Ultrasonic Inspection ◽  
Probability Of Detection ◽  
Grain Structure ◽  
Simple Relationship ◽  
Dissimilar Metal ◽  
Flaw Sizing ◽  
Safety Research ◽  
Lifetime Analysis ◽  
Ultrasonic Propagation

There are several sources of uncertainties which need to be considered in a probabilistic reliability and lifetime assessment of safety-relevant components. In addition to the probabilistic distribution of material properties, the size and properties of flaws present in a component contribute to uncertainties in the lifetime analysis. In a current reactor safety research project, a methodology for a probabilistic fracture mechanics assessment of reliability for components with austenitic and dissimilar metal welds will be developed using the combined results from statistical evaluation of material properties and ultrasonic inspection (UT). Dissimilar metal welds present a particular challenge for ultrasonic testing due to the effects of the material anisotropy on ultrasonic propagation and scattering. Evaluation of inspection results is typically done using image-based techniques. As there is no simple relationship between UT response and flaw size, criteria for image evaluation and flaw sizing have to be defined taking into account the influence of various factors such as material and flaw properties on the UT response. In this paper, we present results from a study of the influence of grain structure on the ultrasonic inspection results and discuss the challenges of extracting data for probability of detection (POD) analyses.

Ultrasonic Inspection and Analysis Using the Synthetic Aperture Focusing Technique (SAFT) on Dissimilar Metal Welds With Inter-Granular Stress Corrosion Cracks

2015 ◽  
Author(s):  
Sandra Dugan ◽  
Sabine Wagner ◽  
Hans Rieder ◽  
Martin Spies
Keyword(s):  
Stress Corrosion ◽  
Elastic Anisotropy ◽  
Signal To Noise Ratio ◽  
Ultrasonic Inspection ◽  
Grain Structure ◽  
Synthetic Aperture ◽  
Dissimilar Metal ◽  
Weld Material ◽  
Synthetic Aperture Focusing ◽  
Synthetic Aperture Focusing Technique

Cases of inter-granular stress corrosion cracking (IGSCC) in dissimilar metal welds have led to an increased interest in the reliability of non-destructive testing of these welds and this crack type. The challenges related to ultrasonic testing of dissimilar metal welds (DMW) result from the elastic anisotropy of the material in combination with the grain structure of the weld. The inhomogeneous, anisotropic structure of the weld affects ultrasound propagation and leads to a decrease in the signal-to-noise ratio, thus complicating the interpretation of ultrasonic signals. As a result, cracks located exclusively in the weld material are usually harder to detect. Detection of cracks inside the weld material is particularly important in the case of a circumferential crack in a pipe weld, which could otherwise grow to a critical size before being detected. Studies have shown that the reflected ultrasonic amplitude is considerably smaller for IGSCC than it is for artificial reference flaws. In this paper, we will present the results of ultrasonic inspection and analysis using the Synthetic Aperture Focusing Technique (SAFT) on dissimilar metal welds with IGSCC.

Relationships Between Grain Boundary Structure and Material Properties

1980 ◽  
Vol 38 ◽  
pp. 366-369
Author(s):  
Brian Ralph ◽  
Barlow Claire ◽  
Nicola Ecob
Keyword(s):  
Grain Boundary ◽  
Material Properties ◽  
Main Property ◽  
Grain Structure ◽  
Boundary Structure ◽  
Grain Boundary Structure ◽  
Property Changes

This brief review seeks to summarize some of the main property changes which may be induced by altering the grain structure of materials. Where appropriate an interpretation is given of these changes in terms of current theories of grain boundary structure, and some examples from current studies are presented at the end of this paper.

Integrity of Weld Overlay of Flexible Joints and Lined Pipe

2015 ◽  
Author(s):  
Petrônio Zumpano ◽  
Alexandre G. Garmbis ◽  
Eduardo V. Oazen ◽  
Luis Guilherme T. S. Leite ◽  
Rafael N. Silva
Keyword(s):  
Carbon Steel ◽  
Ultrasonic Inspection ◽  
Base Material ◽  
Probability Of Detection ◽  
Internal Layers ◽  
Flexible Joints ◽  
Weld Overlay ◽  
Corrosion Resistant ◽  
Alloy 625 ◽  
Sulfide Stress

This paper describes different alternatives to be adopted to assess the integrity of weld overlays of flexible joints and lined pipes in offshore pipeline and riser projects. Protective layers are adopted as an interesting alternative to full thickness corrosion resistant alloys due to the possibility to adopt carbon steel as base material in order to reduce overall material costs. UNS N06625 (alloy 625) is generally selected for internal layers, such as weld overlay steels, lined pipes or clad pipes because of its sulfide stress cracking (SSC) resistance and outstanding weldability. However, unless the long-term integrity of the cladding or overlay as a protective layer can be demonstrated under the intended service conditions, the base material shall also be resistant against sulfide stress corrosion cracking. Due to low resistance of carbon steel to corrosion fatigue in the presence of contaminants in fluid content, the rupture of thickness of CRA (Corrosion Resistant Alloy) layer becomes a failure mode. An Engineering Critical Assessment (ECA) shall be performed in order to assess if circumferential planar flaws in weld overlay regions will not propagate through the CRA layer, thus exposing the base material, when submitted to critical cyclic loads during the service life. Such analysis would involve fatigue crack growth simulation and surface interaction of full circumferential embedded defects to determine the maximum weld overlay pass height to be limited by machining. This limited height of machined layers should guarantee that a full circumferential flaw will withstand the operational fatigue life. However, this is a very time consuming manufacturing process and would implicate additional concerns for long extensions due to out of straightness and out of roundness. Alternatively, the ECA results may be used to determine the flaw acceptance criteria and required probability of detection of volumetric non-destructive testing. Recent developments in ultrasonic inspection were successfully adopted and represent a better solution for alloy 625 weld overlay in terms of project scheduling and manufacturing costs. Radiographic testing may also be used provided it meets the required sensitivity, in terms of image quality indicators (IQI). Anyway, validation tests shall be performed to demonstrate adequate reliability to detect the minimum required flaw height.

Effects of Texture on Thermoelectric Power in Ti-6Al-4V

2006 ◽  
Author(s):  
Hector Carreon
Keyword(s):  
Thermoelectric Power ◽  
Material Properties ◽  
Material Characterization ◽  
Grain Structure ◽  
Power Dependence ◽  
Anisotropic Behavior ◽  
Nondestructive Technique ◽  
Parallel Direction ◽  
Polycrystalline Microstructure ◽  
Power Measurements

Ti-6A1-4V alloy exhibits a very strong anisotropic texture caused by the existence of a preferred crystallographic orientation in the polycrystalline microstructure. This crystallographic alignment can result in anisotropic behavior of the material so that the material properties are different depending on whether they are measured in perpendicular or parallel direction. In addition to this morphological anisotropy, due to the dominantly hexagonal grain structure, the Ti-6A1-4V alloy also exhibited a substantial thermoelectric anisotropy. This study was conducted to investigate the effect of thermoelectric anisotropy on the thermoelectric power measurements in a highly textured Ti-6A1-4V specimen using a completely nondestructive technique based on the Seebeck effect. The result shows the thermoelectric power dependence associated with texturing and the macroscopic grain structure in a rolled Ti-6A1-4V specimen, which was annealed at 710°C for 2 hours and slowly cooled. The measurements clearly demonstrated that the intrinsic sensitivity of the thermoelectric contact technique is a very useful tool that could be exploited for quantitative nondestructive (QND) material characterization.

Introduction of Hot Isostatically Pressed, Reactor Coolant System Components in PWR Plant

2010 ◽  
Author(s):  
John L. Sulley ◽  
Ian Hookham ◽  
Barry Burdett ◽  
Keith Bridger
Keyword(s):  
Nuclear Reactor ◽  
Structural Integrity ◽  
Full Range ◽  
Ultrasonic Inspection ◽  
Grain Structure ◽  
Reactor Plant ◽  
Strategic Sourcing ◽  
Staged Approach ◽  
Route Cost ◽  
Non Destructive

This paper presents an overview of the work undertaken by Rolls-Royce to introduce Hot Isostatically Pressed (HIP) components into Pressurised Water Reactor plant, and also results of non-destructive and destructive examinations of a thick-walled pressure vessel. It presents the work from a design justification/manufacturing quality assurance perspective, rather than from a pure metallurgical perspective. Although the HIP process is not new, it was new in its application to Rolls-Royce designed nuclear reactor plant. As a consequence, Rolls-Royce has implemented an evolving, staged approach, starting with HIP bonding of solid valve seats into small bore valve pressure boundaries. This was followed by powder HIP consolidation of leak-limited, thin-walled toroids, and has culminated in the powder HIP consolidation of thick-walled components. The paper provides an overview of each of these stages and the approach taken with respect to justification. Mechanical testing and metallurgical examination results of sample material taken from different sections of a thick-walled component are presented. A full range of test results is provided covering, as examples: tensile, charpy and sensitization susceptibility. Differences in weldability between the HIPed and the previous forged form are also documented. The paper describes the benefits that Rolls-Royce has realised so far through the introduction of HIPed component. Structural integrity benefits are described, such as improved grain structure, mechanical properties, and ultrasonic inspection. Project-based benefits are also described, such as provision of an alternative strategic sourcing route, cost and lead-time reductions.

scholarly journals Finite Element Simulations to Predict Probability of Detection (PoD) Curves for Ultrasonic Inspection of Nuclear Components

2014 ◽  
Vol 86 ◽  
pp. 461-468 ◽  
Author(s):  
S. Mohamed Subair ◽  
Krishnan Balasubramaniam ◽  
Prabhu Rajagopal ◽  
Anish Kumar ◽  
B. Purnachandra Rao ◽  
...  
Keyword(s):  
Finite Element ◽  
Ultrasonic Inspection ◽  
Probability Of Detection ◽  
Finite Element Simulations

Validation of Welding Residual Stress Model Using Results From a Pressurizer Surge Nozzle Mockup

2011 ◽  
Author(s):  
Doug Killian
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Residual Stresses ◽  
Crack Growth ◽  
Material Properties ◽  
Welding Residual Stress ◽  
Stress Model ◽  
Dissimilar Metal ◽  
Dissimilar Metal Weld ◽  
Metal Weld

Although numerical welding simulation is now commonly used in the nuclear industry to predict residual stresses in reactor vessels and associated piping components, there are currently no universally accepted guidelines for performing such analysis. Moreover, due to the complexity of the calculations and varying analytical procedures among analysts, there remains a need to validate predictions of residual stress against benchmark studies. As part of an industry initiative to manage the degradation of dissimilar metal welds in pressurized water reactor piping that are susceptible to primary water stress corrosion cracking, the U.S Nuclear Regulatory Commission embarked on a multi-phased program to validate welding residual stress models. The aim of Phase II of this program is to obtain measured residual stresses from a pressurizer surge nozzle dissimilar metal weld mockup for use in comparisons with numerically predicted stresses. This paper presents results of finite element analysis for various stages during the fabrication of a 14–inch pressurizer surge nozzle mockup, including an Alloy 82 dissimilar metal weld between a stainless steel safe end and carbon steel nozzle, an inside surface weld repair (back weld) and fill-in weld (weld build-up), and a stainless steel “field” weld attaching a section of straight pipe to the safe end. The NRC validation program was structured to allow participants to first calculate results using their own material properties, and then tune their welding simulations to thermocouple data. This was followed by reanalysis using NRC-supplied material properties. The program was conducted as a round robin analysis among an international group of participants and formatted as a blind validation project wherein results were submitted to the NRC prior to receipt of thermocouple and material property data. Results were obtained for both kinematic and isotropic hardening rules to study the effect of these two extreme measures of material characterization on the development of residual stress. Predicted stresses are then compared to measured stress data obtained by the deep-hole drilling technique at multiple locations through the thickness of the weld. The NRC residual stress model validation project serves as a valuable contribution to the understanding of how residual stresses are developed in dissimilar metal welds. The correlation of calculated residual stresses with measured data from a relevant mockup also serves to increase confidence in predicting crack growth in these primary pressure boundary welds by removing much of the uncertainty previously associated with residual stress input to crack growth analysis.

scholarly journals PERFORMANCE OF PRESSURE TUBES IN CANDU REACTORS

2016 ◽  
Vol 5 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Douglas Rodgers ◽  
Malcolm Griffiths ◽  
Grant Bickel ◽  
Andrew Buyers ◽  
Christopher Coleman ◽  
...  
Keyword(s):  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Material Properties ◽  
Corrosion Behaviour ◽  
Alpha Phase ◽  
Operating Conditions ◽  
Grain Structure ◽  
Candu Reactors ◽  
Hexagonal Close Packed ◽  
Pressure Tubes

The pressure tubes in CANDU reactors typically operate for times up to about 30 years prior to refurbishment. The in-reactor performance of Zr-2.5Nb pressure tubes has been evaluated by sampling and periodic inspection. This paper describes the behavior and discusses the factors controlling the behaviour of these components. The Zr–2.5Nb pressure tubes are nominally extruded at 815 °C, cold worked nominally 27%, and stress relieved at 400 °C for 24 hours, resulting in a structure consisting of elongated grains of hexagonal close-packed alpha-Zr, partially surrounded by a thin network of filaments of body-centred-cubic beta-Zr. These beta-Zr filaments are meta-stable and contain about 20% Nb after extrusion. The stress-relief treatment results in partial decomposition of the beta-Zr filaments with the formation of hexagonal close-packed alpha-phase particles that are low in Nb, surrounded by a Nb-enriched beta-Zr matrix. The material properties of pressure tubes are determined by variations in alpha-phase texture, alpha-phase grain structure, network dislocation density, beta-phase decomposition, and impurity concentration that are a function of manufacturing variables. The pressure tubes operate at temperatures between 250 °C and 310 °C with coolant pressures up to about 11 MPa in fast neutron fluxes up to 4 × 1017 n·m−2·s−1 (E > 1 MeV) and the properties are modified by these conditions. The properties of the pressure tubes in an operating reactor are therefore a function of both manufacturing and operating condition variables. The ultimate tensile strength, fracture toughness, and delayed hydride-cracking properties (velocity (V) and threshold stress intensity factor (KIH)) change with irradiation, but all reach a nearly limiting value at a fluence of less than 1025 n·m−2 (E > 1 MeV). At this point the ultimate tensile strength is raised about 200 MPa, toughness is reduced by about 50%, V increases by about a factor of 6, while KIH is only slightly reduced. The role of microstructure and trace elements in these behaviours is described. Pressure tubes exhibit elongation, diametral expansion, and sag. The deformation behaviour is a function of operating conditions and the material properties that vary from tube-to-tube and as a function of axial location. Semi-empirical predictive models have been developed to describe the deformation response of average tubes as a function of operating conditions. The effect of material variability on corrosion behaviour is less well defined compared with other properties but there are instances where tube orientation and ingot source can be identified as factors that have an effect on hydrogen pick-up.

Sign in / Sign up

Export Citation Format

Share Document