scholarly journals Assessment of Tensile Residual Stress Mitigation in Alloy 22 Welds Due to Laser Peening

2004 ◽  
Vol 126 (4) ◽  
pp. 465-473 ◽  
Author(s):  
Adrian T. DeWald ◽  
Jon E. Rankin ◽  
Michael R. Hill ◽  
Matthew J. Lee ◽  
Hao-Lin Chen
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Compressive Residual Stress ◽  
Base Material ◽  
Corrosion Cracking ◽  
Contour Method ◽  
Laser Peening ◽  
Alloy 22

This paper examines the effects of laser peening on Alloy 22 (UNS N06022), which is the proposed material for use as the outer layer on the spent-fuel nuclear waste canisters to be stored at Yucca Mountain. Stress corrosion cracking (SCC) is a primary concern in the design of these canisters because tensile residual stresses will be left behind by the closure weld. Alloy 22 is a nickel-based material that is particularly resistant to corrosion; however, there is a chance that stress corrosion cracking could develop given the right environmental conditions. Laser peening is an emerging surface treatment technology that has been identified as an effective tool for mitigating tensile redisual stresses in the storage canisters. The results of laser-peening experiments on Alloy 22 base material and a sample 33 mm thick double-V groove butt-weld made with gas tungsten arc welding (GTAW) are presented. Residual stress profiles were measured in Alloy 22 base material using the slitting method (also known as the crack-compliance method), and a full 2D map of longitudinal residual stress was measured in the sample welds using the contour method. Laser peening was found to produce compressive residual stress to a depth of 3.8 mm in 20 mm thick base material coupons. The depth of compressive residual stress was found to have a significant dependence on the number of peening layers and a slight dependence on the level of irradiance. Additionally, laser peening produced compressive residual stresses to a depth of 4.3 mm in the 33 mm thick weld at the center of the weld bead where high levels of tensile stress were initially present.

Reducing Potential for Stress Corrosion Cracking During Design and Fabrication of Small Modular Reactors

2011 ◽  
Author(s):  
Lloyd A. Hackel ◽  
C. Brent Dane ◽  
Jon Rankin ◽  
Fritz Harris ◽  
Chanh Truong
Keyword(s):  
Residual Stress ◽  
Tensile Stress ◽  
Laser Beam ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Compressive Residual Stress ◽  
Cost Effective ◽  
Corrosion Cracking ◽  
Laser Peening ◽  
Corrosive Environment

Reactor designs employ the best materials available such as Alloy 600 and Alloy 690 to resist stress corrosion cracking (SCC); yet the problem has continued to exist. As SCC is driven by three main contributors, susceptible material, corrosive environment and existence of tensile stress, eliminating any one can greatly improve the situation. In this paper we discuss a laser peening process for the nuclear industry that can convert areas of tensile stress to deep levels of compression. Laser peening induces deep levels of plasticity into materials resulting in compressive residual stress to depths of 0.100 inches (2.5 mm) or deeper. This enables increased fatigue strength and lifetimes and greatly enhances resistance to stress corrosion cracking. The deep plasticity closes the inter-granular boundaries and induces a deep layer of compressive stress dramatically improving the stress corrosion cracking (SCC) resistance of components subjected to tensile loading in a corrosive environment. The deeper plasticity generated by laser peening can be contrasted to a depth of only 0.010 inches (0.25 mm) typically achieved with conventional shot peening, a beneficial and widely used technology. Advances in laser technology have enabled highly reliable, high-rate, cost-effective processing that has made a major impact in aerospace; thousands of parts and large scale structures have been and are being treated. Advanced laser beam delivery to components has enabled cost-effective field applications. The peening is done without physical contact with the component. The technology has been approved by organizations such as the FAA, EASA and USAF and deployed to enhance lifetime of key structural components on the F-22 fighter. Component faducials on a structure are first visually detected by a camera and alignment laser and then the main laser beam is automatically aligned to the component. The technology has the potential to serve a broad range of fielded industrial applications including oil and gas lines, on-board ship applications, nuclear power plants, upstream exploration and recovery, and downstream oil refining. We will discuss examples of advanced fatigue and corrosion resistance in steels provided by the laser peening technology as well as the hardware now available for field use. The laser peening technology enables SCC mitigation via engineered compressive residual stress to be considered much more seriously at the design level for reactors.

Laser Peening without Coating to Mitigate Stress Corrosion Cracking and Fatigue Failure of Welded Components

2008 ◽  
Vol 580-582 ◽  
pp. 519-522 ◽  
Author(s):  
Yuji Sano ◽  
Yoshihiro Sakino ◽  
Naruhiko Mukai ◽  
Minoru Obata ◽  
Itaru Chida ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Compressive Residual Stress ◽  
Fatigue Testing ◽  
Corrosion Cracking ◽  
Laser Peening ◽  
Alloy 600 ◽  
Metallic Materials ◽  
Laser Peening Without Coating

The authors have applied laser peening without coating (LPwC) to metallic materials. Compressive residual stress nearly equal to the yield strength of the materials was imparted on the surface. Accelerating stress corrosion cracking (SCC) tests showed that LPwC had a significant effect to prevent the SCC initiation of sensitized materials of SUS304, Alloy 600 and the weld metal, Alloy 182. Push-pull type fatigue testing demonstrated that LPwC drastically enhanced the fatigue strength of fillet-welded rib-plates of SM490A.

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.

A Development of the Technical Basis for the New Code Case “Mitigation of PWSCC and CISCC in ASME Section III Components by the Advanced Surface Stress Improvement Technology”

2019 ◽  
Author(s):  
S. W. Cho ◽  
W. G. Yi ◽  
N. Mohr ◽  
A. Amanov ◽  
C. Stover ◽  
...  
Keyword(s):  
Residual Stress ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Surface Stress ◽  
Compressive Residual Stress ◽  
Corrosion Cracking ◽  
Chloride Salt ◽  
Spent Fuel ◽  
Term Operation ◽  
Technical Basis

Abstract It is necessary for nuclear power plant operation and spent fuel canisters to provide a sound technical basis for the safety and security of long-term operation and storage respectively. A new code case for mitigation of Primary Water Stress Corrosion Cracking (PWSCC) and Chloride Induced Stress Corrosion Cracking (CISCC) in Section III components by using an advanced surface stress improvement technology (ASSIT) is being developed by Task Group ASSIT which is one of the task groups under the ASME (The American Society of Mechanical Engineers). The necessary technical reports supporting this code case are being developed as part of joint research projects conducted by Doosan Heavy Industries and Construction (DOOSAN), Electric Power Research Institute (EPRI) and Sun Moon University (SMU). A well-known approach to prevent PWSCC and CISCC are to be performed using materials resistant to PWSCC and CISCC. The objective is to eliminate residual tensile stresses, or to induce compressive residual stress using ASSIT methods such as laser peening, water jet/cavitation peening, ultrasonic peening and ultrasonic nanocrystal surface modification (UNSM). Performance and measurement criteria for mitigation of PWSCC by ASSIT will be established based on the magnitude of surface stress and depth of compressive residual stress, sustainability, inspectability and lack of adverse effects. Additionally, for mitigation of CISCC by ASSIT, the evaluation of chloride induced corrosion pitting, the depth and density of corrosion pits and stress corrosion crack initiation and growth under chloride salt chemistry conditions are also being examined. This paper explains the approach, and progress of testing and analysis. The results and details from testing and analysis will be presented in a future PVP paper upon completion.

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.

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.

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.

Weld Residual Stresses and Primary Water Stress Corrosion Cracking in Bimetal Nuclear Pipe Welds

2007 ◽  
Author(s):  
Frederick W. Brust ◽  
Paul M. Scott
Keyword(s):  
Water Stress ◽  
Residual Stresses ◽  
Weld Metal ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Pressure Vessel ◽  
Large Diameter ◽  
Corrosion Cracking ◽  
Primary Water

There have been incidents recently where cracking has been observed in the bi-metallic welds that join the hot leg to the reactor pressure vessel nozzle. The hot leg pipes are typically large diameter, thick wall pipes. Typically, an inconel weld metal is used to join the ferritic pressure vessel steel to the stainless steel pipe. The cracking, mainly confined to the inconel weld metal, is caused by corrosion mechanisms. Tensile weld residual stresses, in addition to service loads, contribute to PWSCC (Primary Water Stress Corrosion Cracking) crack growth. In addition to the large diameter hot leg pipe, cracking in other piping components of different sizes has been observed. For instance, surge lines and spray line cracking has been observed that has been attributed to this degradation mechanism. Here we present some models which are used to predict the PWSCC behavior in nuclear piping. This includes weld model solutions of bimetal pipe welds along with an example calculation of PWSCC crack growth in a hot leg. Risk based considerations are also discussed.

Strategies for Treating Weld Residual Stresses in Probabilistic Fracture Mechanics Codes

2011 ◽  
Author(s):  
Frederick W. Brust ◽  
R. E. Kurth ◽  
D. J. Shim ◽  
David Rudland
Keyword(s):  
Fracture Mechanics ◽  
Residual Stresses ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Power ◽  
Power Plants ◽  
Degradation Mechanism ◽  
Welding Process ◽  
Corrosion Cracking ◽  
Uncertainty Sources

Risk based treatment of degradation and fracture in nuclear power plants has emerged as an important topic in recent years. One degradation mechanism of concern is stress corrosion cracking. Stress corrosion cracking is strongly driven by the weld residual stresses (WRS) which develop in nozzles and piping from the welding process. The weld residual stresses can have a large uncertainty associated with them. This uncertainty is caused by many sources including material property variations of base and welds metal, weld sequencing, weld repairs, weld process method, and heat inputs. Moreover, often mitigation procedures are used to correct a problem in an existing plant, which also leads to uncertainty in the WRS fields. The WRS fields are often input to probabilistic codes from weld modeling analyses. Thus another source of uncertainty is represented by the accuracy of the predictions compared with a limited set of measurements. Within the framework of a probabilistic degradation and fracture mechanics code these uncertainties must all be accounted for properly. Here we summarize several possibilities for properly accounting for the uncertainty inherent in the WRS fields. Several examples are shown which illustrate ranges where these treatments work well and ranges where improvement is needed. In addition, we propose a new method for consideration. This method consists of including the uncertainty sources within the WRS fields and tabulating them within tables which are then sampled during the probabilistic realization. Several variations of this process are also discussed. Several examples illustrating the procedures are presented.

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