Long Term Stability Evaluation of Stress Improvement Effect on Ni-Based Alloy Welds by Various Residual Stress Improvement Methods

2021 ◽  
Vol 1016 ◽  
pp. 819-825
Author(s):  
Li Na Yu ◽  
Kazuyoshi Saida ◽  
Masahito Mochizuki ◽  
Kazutoshi Nishimoto ◽  
Naoki Chigusa
Keyword(s):  
Residual Stress ◽  
High Temperature ◽  
Stress Relaxation ◽  
Compressive Residual Stress ◽  
Alloy 600 ◽  
Pressurized Water ◽  
Residual Stress Relaxation ◽  
Temperature Environment ◽  
Water Reactors ◽  
High Temperature Environment

Stress corrosion cracking (SCC) is one of serious aging degradation problems for the Alloy 600 components of pressurized water reactors (PWRs). In order to prevent SCC, various methods such as water jet peening (WJP), laser peening (LP), surface polishing have been used to introduce compressive stresses at the surfaces of the PWR components. However, it has been reported that such compressive residual stress introduced by these methods might be relaxed during the practical operation, because of high temperature environment. In this study, the hardness reduction behavior of the Alloy 600 processed by LP, Buff and WJP in the thermal aging process has been investigated to estimate the stability of the residual stress improving effect by each method, based on the fact that there is a correlation between the compressive residual stress relaxation and the decrease of hardness. The behavior of the residual stress relaxation in the processed materials in the high temperature environment has been discussed with kinetic analysis.

Long Term Stability of Compressive Residual Stress Introduced in Alloy 600 by Water Jet Peening Under Elevated Temperature Environment

2011 ◽  
Author(s):  
Tadafumi Hashimoto ◽  
Yusuke Osawa ◽  
Masashi Kameyama ◽  
Shinro Hirano ◽  
Naoki Chigusa ◽  
...  
Keyword(s):  
Residual Stress ◽  
Elevated Temperature ◽  
Stress Relaxation ◽  
Compressive Residual Stress ◽  
Water Jet ◽  
Target Area ◽  
Pressurized Water ◽  
Plastic Deformations ◽  
Term Operation

Primary water stress corrosion cracking (PWSCC) in the weld metal of alloy600 is an issue of concern in a pressurized water reactor (PWR). As a countermeasure against PWSCC, water jet peening (WJP), which can change tensile residual stress into compressive residual stress, has been applied to welded joints. Microstructure in the target area of WJP has an influence of not only WJP but welding and machining. Especially machining introduces severe plastic deformations to the materials. So microstructure in the target area might lack thermal stability due to severe plastic deformation. Additionally the region that compressive residual stress by WJP is nearly up to 1mm from the surface of the target material. As PWRs are operated at about 596K for long term, the compressive residual stress by WJP may be relieved due to creep. In order to keep operating PWRs safety, the stability of the compressive residual stress by WJP at elevated temperature has been clarified. In this work, the results were obtained written below. As a result of thermal aging test, a relaxation of compressive residual stress at specimen surface layer occurred due to recovery of the plastic deformations by machining. This stress relaxation behavior followed Johnson-Mehl equation. However residual stress relaxation due to creep was very few. Therefore it has suggested that the compressive residual stress introduced in Alloy600 by WJP is confirmed to remain stable during long term operation under elevated temperature.

scholarly journals Small–Scale Experimental Investigation of Fatigue Performance Improvement of Ship Hatch Corner with Shot Peening Treatments by Considering Residual Stress Relaxation

2021 ◽  
Vol 9 (4) ◽  
pp. 419
Author(s):  
Jin Gan ◽  
Zi’ang Gao ◽  
Yiwen Wang ◽  
Zhou Wang ◽  
Weiguo Wu
Keyword(s):  
Residual Stress ◽  
Surface Roughness ◽  
Fatigue Life ◽  
Stress Relaxation ◽  
Stress Field ◽  
Shot Peening ◽  
Compressive Residual Stress ◽  
Fatigue Performance ◽  
Residual Stress Field ◽  
Residual Stress Relaxation

Ship hatch corner is a common structure in a ship and its fatigue problem has always been one of the focuses in ship engineering due to the long–term high–stress concentration state during the ship’s life. For investigating the fatigue life improvement of the ship hatch corner under different shot peening (SP) treatments, a series of fatigue tests, residual stress and surface topography measurements were conducted for SP specimens. Furthermore, the distributions of the surface residual stress are measured with varying numbers of cyclic loads, investigating the residual stress relaxation during cyclic loading. The results show that no matter which SP process parameters are used, the fatigue lives of the shot–peened ship hatch corner specimens are longer than those at unpeened specimens. The relaxation rate of the residual stress mainly depends on the maximum compressive residual stress (σRSmax) and the depth of the maximum compressive residual stress (δmax). The larger the values of σRSmax and δmax, the slower the relaxation rates of the residual stress field. The results imply that the effect of residual stress field and surface roughness should be considered comprehensively to improve the fatigue life of the ship hatch corner with SP treatment. The increase in peening intensity (PI) within a certain range can increase the depth of the compressive residual stress field (CRSF), so the fatigue performance of the ship hatch corner is improved. Once the PI exceeds a certain value, the surface damage caused by the increase in surface roughness will not be offset by the CRSF and the fatigue life cannot be improved optimally. This research provides an approach of fatigue performance enhancement for ship hatch corners in engineering application.

The Effects of Ultrasonic Nanocrystal Surface Modification Technique Temperature on Microstructure and Wear of Alloy 600

2016 ◽  
Vol 879 ◽  
pp. 926-931
Author(s):  
Jun Hyong Kim ◽  
Auezhan Amanov ◽  
Young Sik Pyun
Keyword(s):  
Residual Stress ◽  
Corrosion Resistance ◽  
Surface Modification ◽  
High Temperature ◽  
Compressive Residual Stress ◽  
Wear Behavior ◽  
Treatment Temperature ◽  
Alloy 600 ◽  
Term Operation ◽  
Superior Corrosion Resistance

Alloy 600 (UNS N06600) is an austenitic nickel-based alloy with superior corrosion resistance and high-temperature endurance, which determines its widespread applications in aeronautical, aerospace, marine and nuclear industries. Particularly, a number of nuclear components used Alloy 600 as their structure materials due to their high corrosion resistance, high-temperature endurance and excellent fabricant characteristics. Many failures have occurred in Alloy 600 with various forms of environmental degradations during long-term operation. In this study, an ultrasonic nanocrystal surface modification (UNSM) technique was applied to Alloy 600 at a room and a high temperature of 500 OC. The effects of UNSM treatment temperature on the microstructure and wear behavior including a compressive residual stress were investigated. The hardness, compressive residual stress with respect to depth from the top surface were measured. Also, the wear behavior of UNSM-treated at a room and a high temperature Alloy 600 specimen was compared to that of the untreated specimen. The increase in wear resistance by UNSM technique was discussed in terms of increased hardness, refined grain size and induced compressive residual stress.

Weld Residual Stress Predictions in Reactor Vessel Head Penetrations: FE Simulation

2009 ◽  
Author(s):  
Anne Teughels ◽  
Rodolfo L. M. Suanno ◽  
Christian Malekian ◽  
Lucio D. B. Ferrari
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Element Model ◽  
Mechanical Analysis ◽  
Welding Residual Stress ◽  
Alloy 600 ◽  
Residual Stress Field ◽  
Pressurized Water ◽  
Weld Residual Stress ◽  
Water Reactors

The penetrations in the early Pressurized Water Reactors Vessels are characterized by Alloy 600 tubes, welded by Alloy 182/82. The Alloy 600 tubes have been shown to be susceptible to PWSCC (Primary Water Stress Corrosion Cracking) which may lead to crack forming. The cracking mechanism is driven mainly by the welding residual stress and, in a second place, by the operational stress in the weld region. It is therefore of big interest to quantify the weld residual stress field correctly. In this paper the weld residual stress field is calculated by finite elements, using a common approach well known in nuclear domain. It includes a transient thermal analysis simulating the heating during the multipass welding, followed by a transient thermo-mechanical analysis for the determination of the stresses involved with it. The welding consists of a sequence of weld beads, each of which is deposited in its entirety, at once, instead of gradually. Central as well as eccentric sidehill nozzles on the vessel head are analyzed in the paper. For the former a 2-dimensional axisymmetrical finite element model is used, whereas for the latter a 3-dimensional model is set up. Different positions on the vessel head are compared and the influence of the sidehill effect is illustrated. In the framework of a common project for Angra 1, Tractebel Engineering (Belgium) and Eletronuclear (Nuclear Utility, Brazil) had the opportunity to compare their analysis method, which they applied to the Belgian and the Brazilian nuclear reactors, respectively. The global approach in both cases is very similar but is applied to different configurations, specific for each NPP. In the article the results of both cases are compared.

Residual Stress Stability in High Temperature Fatigued Mechanically Surface Treated Metallic Materials

2006 ◽  
Vol 524-525 ◽  
pp. 57-62 ◽  
Author(s):  
I. Altenberger ◽  
Ivan Nikitin ◽  
P. Juijerm ◽  
Berthold Scholtes
Keyword(s):  
Residual Stress ◽  
High Temperature ◽  
Stress Relaxation ◽  
Plastic Strain ◽  
Low Cycle Fatigue ◽  
Plastic Strain Amplitude ◽  
Metallic Materials ◽  
Loading Conditions ◽  
Cycle Fatigue ◽  
Residual Stress Relaxation

Different classes of metallic materials (aluminum alloys, steels, titanium alloys) were mechanically surface treated by deep rolling and laser shock peening and isothermally fatigued at elevated temperature under stress control. The fatigue tests were interrupted after different numbers of cycles for several stress amplitudes and residual stresses and FWHM-values were measured by X-ray diffraction methods at the surface and as a function of depth. The results summarize the response of the surface treatment induced residual stress profiles to thermomechanical loading conditions in the High Cycle Fatigue (HCF)- as well as in the Low Cycle Fatigue (LCF) regime. The effects of stress amplitude, plastic strain amplitude, temperature and frequency are addressed in detail and discussed. The results indicate that residual stress relaxation during high temperature fatigue can be predicted for sufficiently simplified loading conditions and that thermal and mechanical effects can be separated from each other. A plastic strain based approach appears to be most suitable to describe residual stress relaxation. Frequency effects were found to be not very pronounced in the frequency range investigated.

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