NRC/EPRI Residual Stress Validation Program Phase I: Experimental Specimen Modeling and Measurement

2011 ◽  
Author(s):  
J. Broussard ◽  
P. Crooker
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Phase 1 ◽  
Measurement Techniques ◽  
Corrosion Cracking ◽  
Welding Residual Stress ◽  
Hole Drilling ◽  
Pressurized Water

The US Nuclear Regulatory Commission (NRC) and the Electric Power Research Institute (EPRI) are working cooperatively under a memorandum of understanding to validate welding residual stress predictions in pressurized water reactor primary cooling loop components containing dissimilar metal welds. These stresses are of interest as DM welds in pressurized water reactors are susceptible to primary water stress corrosion cracking (PWSCC) and tensile weld residual stresses are one of the primary drivers of this stress corrosion cracking mechanism. The NRC/EPRI weld residual stress (WRS) program currently consists of four phases, with each phase increasing in complexity from lab size specimens to component mock-ups and ex-plant material. This paper describes the Phase 1 program, which comprised an initial period of learning and research for both FEA methods and measurement techniques using simple welded specimens. The Phase 1 specimens include a number of plate and cylinder geometries, each designed to provide a controlled configuration for maximum repeatability of measurements and modeling. A spectrum of surface and through-wall residual stress measurement techniques have been explored using the Phase 1 specimens, including incremental hole drilling, ring-core, and x-ray diffraction for surface stresses and neutron diffraction, deep-hole drilling, and contour method for through-wall stresses. The measured residual stresses are compared to the predicted stress results from a number of researchers employing a variety of modeling techniques. Comparisons between the various measurement techniques and among the modeling results have allowed for greater insight into the impact of various parameters on predicted versus measured residual stress. This paper will also discuss the technical challenges and lessons learned as part of the DM weld materials residual stress measurements.

NRC/EPRI Welding Residual Stress Validation Program: Phase III Details and Findings

2011 ◽  
Author(s):  
Lee F. Fredette ◽  
Matthew Kerr ◽  
Howard J. Rathbun ◽  
John E. Broussard
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Plant Material ◽  
Welding Residual Stress ◽  
Phase Iii ◽  
Pressurized Water ◽  
Dissimilar Metal

The US Nuclear Regulatory Commission (NRC) and the Electric Power Research Institute (EPRI) are working cooperatively under a memorandum of understanding to validate welding residual stress predictions in pressurized water reactor primary cooling loop components containing dissimilar metal (DM) welds. These stresses are of interest as DM welds in pressurized water reactors are susceptible to primary water stress corrosion cracking (PWSCC) and tensile weld residual stresses are one of the primary drivers of this stress corrosion cracking mechanism. The NRC/EPRI welding residual stress (WRS) program currently consists of four phases, with each phase increasing in complexity from lab size specimens to component mock-ups and ex-plant material. This paper discusses Phase III of the WRS characterization program, comparing measured and predicted weld residual stresses profiles through the dissimilar metal weld region of pressurizer safety and relief nozzles removed from a cancelled plant in the United States. The DM weld had already been completed on all of the plant nozzles before use in the mock-up program. One of the nozzles was completed with the application of the stainless steel safe-end weld to a section of stainless steel pipe. Measurements were taken on the nozzles with and without the welded pipe section. Several independent finite element analysis predictions were made of the stress state in the DM weld. This paper compares the predicted stresses to those found by through-thickness measurement techniques (Deep Hole Drilling and Contour Method). Comparisons of analysis results with experimental data will allow the NRC staff to develop unbiased measures of uncertainties in weld residual stress predictions with the goal of developing assurances that the analysis predictions are defensible through the blind validation provided using well controlled mock-ups and ex-plant material in this program.

Stress Corrosion Cracking (SCC) of Nickel-Base Weld Metals in PWR Primary Water

2013 ◽  
Vol 747-748 ◽  
pp. 723-732 ◽  
Author(s):  
Ru Xiong ◽  
Ying Jie Qiao ◽  
Gui Liang Liu
Keyword(s):  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Surface Condition ◽  
Cold Work ◽  
Corrosion Cracking ◽  
Pressurized Water ◽  
Weld Metals ◽  
Surface Residual Stresses ◽  
Primary Water

This discussion reviewed the occurrence of stress corrosion cracking (SCC) of alloys 182 and 82 weld metals in primary water (PWSCC) of pressurized water reactors (PWR) from both operating plants and laboratory experiments. Results from in-service experience showed that more than 340 Alloy 182/82 welds have sustained PWSCC. Most of these cases have been attributed to the presence of high residual stresses produced during the manufacture aside from the inherent tendency for Alloy 182/82 to sustain SCC. The affected welds were not subjected to a stress relief heat treatment with adjacent low alloy steel components. Results from laboratory studies indicated that time-to-cracking of Alloy 82 was a factor of 4 to 10 longer than that for Alloy 182. PWSCC depended strongly on the surface condition, surface residual stresses and surface cold work, which were consistent with the results of in-service failures. Improvements in the resistance of advanced weld metals, Alloys 152 and 52, to PWSCC were discussed.

An Analytical Evaluation of the Effect of Weld Material Thickness on Residual Stresses Produced by Structural Weld Overlays on Pressurized Water Reactor Primary Cooling Piping

2009 ◽  
Author(s):  
L. F. Fredette ◽  
Paul M. Scott ◽  
F. W. Brust ◽  
A. Csontos
Keyword(s):  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Intergranular Stress Corrosion ◽  
Pressurized Water ◽  
Weld Overlay ◽  
Water Reactor ◽  
Dissimilar Metal ◽  
Structural Reinforcement

Full Structural Weld Overlay (FSWOL) has been used successfully to mitigate intergranular stress corrosion cracking in boiling water reactor (BWR) welded stainless steel piping for many years. The FSWOL technique adds structural reinforcement, can add crack resistant material, and can create compressive residual stresses at the inside surface of the welded joint which reduces the possibility of further stress corrosion cracking. Recently, the FSWOL has been applied as a preemptive measure to prevent primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR) on susceptible welded pipes with dissimilar metal welds common to PWR primary cooling piping. This study uses finite element models to evaluate the likely residual and operating stress profiles remaining after FSWOL and describes the results of sensitivity studies which were performed to examine the effect of weld overlay thickness on the residual stresses for typical dissimilar metal weld configurations.

An Analytical Evaluation of the Effect of Weld Sequencing on Residual Stresses Produced by Full Structural Weld Overlays on Pressurized Water Reactor Primary Cooling Piping

2009 ◽  
Author(s):  
L. F. Fredette ◽  
Paul M. Scott ◽  
F. W. Brust ◽  
A. Csontos
Keyword(s):  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Cooling System ◽  
Corrosion Cracking ◽  
Intergranular Stress Corrosion ◽  
Pressurized Water ◽  
Water Reactor ◽  
Dissimilar Metal ◽  
Structural Reinforcement

Full Structural Weld Overlay (FSWOL) has been used successfully to mitigate intergranular stress corrosion cracking in boiling water reactor (BWR) welded stainless steel piping for many years. The FSWOL technique adds structural reinforcement, can add crack resistant material, and can create compressive residual stresses at the inside surface of the welded joint which reduces the possibility of further stress corrosion cracking. Recently, the FSWOL has been applied as a preemptive measure to prevent primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR) on susceptible welded pipes with dissimilar metal welds common to PWR primary cooling piping. This study uses finite element models to evaluate the likely residual and operating stress profiles remaining after FSWOL for typical dissimilar metal weld configurations and describes the results of sensitivity studies which were performed to examine the effect of weld sequencing on the residual stresses produced in common configurations of PWR primary cooling system piping.

Residual Stress and Stress Corrosion Cracking of High Pressure Hydrocarbon Transmission Pipelines

2006 ◽  
Author(s):  
Greg Van Boven ◽  
Ronald Rogge ◽  
Weixing Chen
Keyword(s):  
Residual Stress ◽  
High Pressure ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Stress Gradient ◽  
Corrosion Cracking ◽  
Tensile Residual Stress ◽  
Surface Residual Stress ◽  
Residual Stress Gradient

Stress corrosion cracking (SCC) can occur on the exterior surface of high pressure hydrocarbon transmission pipelines fabricated from low carbon steels. Both the initiation of SCC and the ability of SCC to progressively increase in depth is a complex and poorly understood phenomena. Previous empirical evidence suggests that residual stresses may be involved in this initiation and growth process. This paper describes a laboratory research project designed to investigate the correlation between residual stress and SCC. In this project, tensile test specimens with increasing levels of compressive and tensile residual stress on the surface and through the thickness of the specimen were fabricated. These stresses were sufficiently large as to dominate the other slight variations in material properties that may occur on identically formed test specimens. The residual stresses were then mapped across the length and through the depth of the specimens by a non-destructive neutron diffraction technique. A SCC initiation process was applied to the specimens. It was found that the formation of micro-pitting, to a depth up to 200 μm, occurred preferentially in areas where tensile residual stresses were the highest (about 300 MPa). Initiation of SCC, although found all at the bottom of this micro-pitting, occurred with a 71% normalized frequency in locations where the surface residual stress was in the range of 150 MPa to 200 MPa. Experimental data revealed that cracks generated in near-neutral pH environments can be readily blunted, due to both plastic deformation (room temperature creep) and extensive dissolution. As a result, a high positive tensile residual stress gradient is necessary for developing cracks in pipeline steels exposed to near-neutral pH environments. The tensile residual stress represents a large mechanical driving force for initial crack nucleation and short crack growth. Active cracks may become dormant as the near-surface residual stress gradient changes from a high to a low tensile stress or if the stress becomes compressive due to self-equilibration through the wall thickness direction. Special conditions may exist in pipeline steels where crack dormancy may not occur within a short distance to the surface, which may include, for example, the presence of a large tensile residual stress gradient over a longer distance, particular microstructures conducive to galvanic corrosion, and special environmental conditions susceptible to hydrogen-induced cracking.

Stress Corrosion Cracking of Nickel Weld Metals in PWR Primary Water

2013 ◽  
Author(s):  
Ru Xiong ◽  
Yuxiang Zhao ◽  
Guiliang Liu
Keyword(s):  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Cold Work ◽  
Corrosion Cracking ◽  
Pressurized Water ◽  
Weld Metals ◽  
Surface Residual Stresses ◽  
Primary Water ◽  
Water Reactors

This discussion reviews the occurrence of stress corrosion cracking (SCC) of Alloys 182 and 82 weld metals in primary water of pressurized water reactors (PWR) from both operating plants and laboratory experiments. Results from in-service experience show that more than 340 Alloy 182/82 welds have sustained SCC, and Alloy 182 with lower Cr have more failures than Alloy 82. Most of these cases have been attributed to the presence of high residual stresses produced during the manufacture aside from the inherent tendency for Alloy 182/82 to sustain SCC. The affected welds were not subjected to a stress relief heat treatment with adjacent low alloy steel components. Results from laboratory studies indicate that time-to-cracking of Alloy 82 (with Cr up to 18%–22%) was a factor of 4 to 10 longer than that for Alloy 182. SCC depends strongly on surface conditions, surface residual stresses and surface cold work, which are consistent with the results of in-service failures. Improvements in the resistance of advanced weld metals, Alloys 152 and 52, to SCC are discussed.

scholarly journals Bounding Surface Flaw Configuration Susceptible to Stress Corrosion Cracking Under Welding Residual Stress in a Multiple-Purpose Canister

2017 ◽  
Author(s):  
Poh-Sang Lam ◽  
Robert L. Sindelar ◽  
Andrew J. Duncan ◽  
Joe T. Carter
Keyword(s):  
Residual Stress ◽  
Stress Intensity ◽  
Stress Corrosion ◽  
Nuclear Fuel ◽  
Stress Corrosion Cracking ◽  
Spent Nuclear Fuel ◽  
Management Program ◽  
Corrosion Cracking ◽  
Surface Flaw ◽  
Welding Residual Stress

The part-through-wall crack perpendicular to the circumferential weld on the outside surface of a spent nuclear fuel (SNF) multiple-purpose canister (MPC) can be shown to be the most limiting fracture configuration driven by the welding residual stress (WRS). A series of semi-elliptical cracks of various sizes is chosen to calculate the stress intensity factors (K) under a bounding residual stress (i.e., the stress distribution that bounds all WRS in a canister). The threshold stress intensity factor (KISCC) of the canister material in the storage environment is used to determine a critical flaw size, below which the stress corrosion cracking would be unlikely to take place. This result can be considered as the flaw disposition criterion should a surface flaw be detected during the inservice inspection as required by the aging management program (AMP), and can be proposed to American Society of Mechanical Engineers (ASME) Section XI Code Case N-860, “Examination Requirements and Acceptance Standards for Spent Nuclear Fuel Storage and Transportation Containment Systems.”

Finite Element Modelling of Transgranular Chloride Stress Corrosion Cracking in 304L Austenitic Stainless Steel

2008 ◽  
Author(s):  
Mark Wenman ◽  
James Barton ◽  
Kenneth Trethewey ◽  
Sean Jarman ◽  
Paul Chard-Tuckey
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Chloride Ions ◽  
Corrosion Cracking ◽  
General Corrosion ◽  
Premature Failure ◽  
Welding Processes

Austenitic stainless steels (ASS) have excellent resistance to general corrosion. However, these steels can be susceptible to localised corrosion such as pitting and crevice corrosion. In the presence of a tensile stress they can also exhibit stress corrosion cracking (SCC). In pressurised water reactor (PWR) nuclear plant incidents of SCC, especially chloride-induced SCC (CISCC), have been observed. Chloride ions which can lead to CiSCC of even low carbon austenitic grades can be introduced from many sources including the atmosphere and materials introduced into the reactor environment. Stress can result from primary loading or introduced as secondary stresses, such as residual stress, through machining or welding processes. Residual stresses are internal self-balancing stresses that can act alone or together with a primary stress to cause premature failure of a component. 15 mm lengths of 304L ASS tube were subjected to an in-plane compression of between 1–10 mm before unloading. This created regions of plasticity and on relaxation the specimen contains a complex state of residual stresses that can be modelled by finite element (FE) methods. The tube specimens were then boiled in MgCl2 for 14 days before metallographic examination. A FE model of transgranular CISCC has been created by writing a VUMAT user subroutine implemented into the commercial FE code ABAQUS. The model is based on simple rules which include the initiation of surface corrosion pits from which, under mechanical control, SCC cracks may propagate. The model includes rules for SCC growth, based on hydrostatic stress state, and can incorporate the idea of grain orientation effects. Cracks created interact with and modify the residual stress field in the tube. Test results were then compared with model outputs. Crack morphologies and to a certain extent crack positions matched well with experiment. Attempts were made to calculate the crack tip driving forces from the model. The results also highlight the need to consider the importance of triaxial stress states, created by pits and cracks, and stress as a tensor rather than a scalar property. The effect of grain misorientation is also investigated, but so far, found to be of more limited importance for modelling transgranular CISCC.

scholarly journals Role of Crack-Tip Residual Stresses in Stress Corrosion Behavior of Pre-stressing AA7020

2019 ◽  
Vol 9 (03) ◽  
Author(s):  
Ashish Thakur
Keyword(s):  
Residual Stress ◽  
Aluminum Alloy ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Corrosion Behavior ◽  
Stress Corrosion Cracking ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Compressive Residual Stresses

This paper analyzes stress corrosion cracking (SCC) of pre-cracked samples in the presence of compressive residual stresses generated in the vicinity of the crack tip during fatigue pre-cracking. Research focuses on the role of cracktip residual stresses of compressive nature, generated by fatigue loading, in stress corrosion cracking of pre-cracked samples of medium high strength aluminum alloy 7020 subjected to localized anodic dissolution and hydrogen assisted cracking. Fatigue pre-cracking load on the samples generates compressive residual stresses in the vicinity of the crack tip which improve the stress corrosion behavior of the aluminum alloy by delaying either the metal dissolution or the hydrogen entry, thus increasing the fracture load in an aggressive environment. The rice model of the residual stress distribution in the vicinity of a crack tip may be usedto explain these retardation effects by estimating the stress level and plastic zone size. Microscopically, compressive residual stress produce a transition topography between the fatigue pre-crack and the cleavage-like (unstable) fracture mode.

Numerical Simulation of Screw Manufacturing Process for the Assessment of Surface Integrity

2015 ◽  
Author(s):  
Vincent Robin ◽  
Philippe Gilles ◽  
Benoît Bosco ◽  
Louis Mazuy ◽  
Frédéric Valiorgue
Keyword(s):  
Residual Stress ◽  
Stainless Steel ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Manufacturing Process ◽  
Cold Work ◽  
Water Environment ◽  
Corrosion Cracking ◽  
Pressurized Water ◽  
Transition Radius

Stress corrosion cracks have been observed on screws made of stainless steels grade 316 after some years of service in Pressurized Water Reactor (PWR) water environment. Grade 316 of stainless steel is not sensitive to corrosion unless it has been sensitized and/or subjected to a complex combination of factors including an important level cold work at the surface and in the bulk of the material. The tightening of the screw induces tensile stresses. This preload cannot explain the Stress Corrosion Cracking (SCC) defect appearing in the transition radius between the screw shank and its head. Thus, the question has been raised of the initial state of the screws after manufacturing. The simulation of the manufacturing processes has been carried out to have a better understanding of manufacturing process consequences on material degradation: solution annealing, cold drawing and machining. The dedicated “hybrid method”, specifically set up to simulate finish turning has been applied to obtain stress and strain states close to the surface. This method is detailed in the paper. The manufacturing process of these bolts is likely to induce high strain hardening since they have been cold drawn and then machined. It is suspected that tensile residual stress and cold work play a major role in the initiation of stress corrosion cracking of austenitic stainless steel grade of 316 type in PWR water environment. Simulation chaining method and results are highlighted in the paper with comparison with experiments. The main achievements are: the smaller the screw the less the cold work, the residual stress on the surface is mainly due to machining and the location of crack in the transition radius is well explained.

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