Hydraulic Runner Design Method for Lifetime

Sabourin, Michel; Thibault, Denis; Bouffard, David-Alexandre; Lévesque, Martin

doi:10.5293/ijfms.2010.3.4.301

Cited by 6 publications

(3 citation statements)

References 15 publications

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“…e present findings corroborate well with the maximum residual stresses of 136 MPa and − 152 MPa reported, respectively, for the longitudinal and normal directions in multipass arc welded ASTM A743M Grade CA6NM after PWHT [42]. In consideration of the damage tolerance design approaches for welded CA6NM in hydroelectric turbines [43][44][45], reduction in the residual stresses to levels between 10 and 25% of the YS [46] through PWHT have been reported to decrease the fatigue crack growth rate through plasticity-induced crack closure during dynamic loading [47]. Hence, the effective reduction in the tensile residual stresses in the HAZ after PWHT of the CA6NM EB welds is expected to improve the fatigue crack resistance, the extent of which needs to be validated through future work aimed at advancing a damage tolerant design, so as to understand the fatigue behaviour of high energy density welds in 13% Cr-4% Ni martensitic stainless steels.…”

Section: Residual Stress Distribution In Eb Welded Ca6nm Aftersupporting

confidence: 87%

Through‐Thickness Residual Stresses, Microstructure, and Mechanical Properties of Electron Beam‐Welded CA6NM Martensitic Stainless Steel after Postweld Heat Treatment

Sarafan

Wanjara

Lévesque

et al. 2020

Advances in Materials Science and Engineering

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In this study, the integrity of electron beam- (EB-) welded CA6NM—a grade of 13% Cr-4% Ni martensitic stainless steel—was assessed through the entire joint thickness of 90 mm after postweld heat treatment (PWHT). The joints were characterized by examining the microstructure, residual stresses, global mechanical properties (static tensile, Charpy impact, and bend), and local properties (yield strength and strain at fracture) in the metallurgically modified regions of the EB welds. The applied PWHT tempered the “fresh” martensite present in the microstructure after welding, which reduced sufficiently the hardness (<280 HV) and residual stresses (<100 MPa) to meet the requirements for hydroelectric turbine assemblies. Also, the properties of the EB joints after PWHT passed the minimum acceptance criteria specified in ASME sections VIII and IX. Specifically, measurement of the global tensile properties indicated that the tensile strengths of the EB welds in the transverse and longitudinal directions were on the same order as that of the base metal (BM). Evaluation of the local tensile properties using a digital image correlation (DIC) methodology showed higher local yield strengths in the fusion zone (FZ) and heat-affected zone (HAZ) of 727 MPa and 740 MPa, respectively, relative to the BM value of 663 MPa. Also, the average impact energies for the FZ and HAZ were 63 J and 148 J, respectively, and attributed to the different failure mechanisms in the HAZ (dimples) versus the FZ (quasi-cleavage consisting of facets and dimples). This study shows that the application of PWHT plays an important role in improving the weld quality and performance of EB-welded CA6NM and provides the essential data for validating the design and manufacturing process for next-generation hydroelectric turbine products.

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Section: Residual Stress Distribution In Eb Welded Ca6nm Aftersupporting

confidence: 87%

Through‐Thickness Residual Stresses, Microstructure, and Mechanical Properties of Electron Beam‐Welded CA6NM Martensitic Stainless Steel after Postweld Heat Treatment

Sarafan

Wanjara

Lévesque

et al. 2020

Advances in Materials Science and Engineering

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“…Apart from cold cracking that normally occurs in the first 48 hours after the repair is completed, fatigue is the other cause of cracks appearing in a turbine runner weld. The mechanisms leading to fatigue cracks in hydraulic turbine welds are complex and involve a lot of parameters [4][5][6][7][8]. One of these many parameters are the residual stresses left in the welds after fabrication and after repair.…”

Section: Introductionmentioning

confidence: 99%

An Experimental Comparison of Weld-Induced Residual Stresses Using Different Stainless Steel Filler Metals Commonly Used for Hydraulic Turbines Manufacturing and Repair

Godin

Thibault

Lévesque

2013

MSF

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CA6NM and UNS S41500 martensitic stainless steels are widely used for manufacturing and repair of hydraulic turbine runners. They offer good mechanical properties and superior cavitation resistance when compared to mild steels. They are also relatively easy to weld. However, when welded homogeneously, they require a post-weld heat treatment (PWHT) in order to temper the as-welded martensite. This PWHT is also beneficial for residual stresses reduction as it effectively lowers the stress peaks. To avoid this PWHT, austenitic filler metals are often used for repair. But omitting PWHT inevitably leaves weld-induced residual stresses in the assembly. In order to better understand the impact of the weld filler metal choice on the importance of residual stress, an experimental study has been conducted on three different filler alloys. The chosen alloys were: • 410NiMo, a martensitic grade having the same composition as the base metal (13%Cr-4%Ni-0.5%Mo) ; • 309L, an austenitic grade widely used for repair (24%Cr-13%Ni) ; • A proprietary low transformation temperature (LTT) martensitic grade (13%Cr-6%Ni). This paper compares residual stresses in the as-welded condition on welds of UNS S41500 (13%Cr-4%Ni) made using these filler metals. Residual stresses were measured using the contour method. Microstructural analysis was performed to identify the phases in the weld and the heat-affected zones (HAZ). Microhardness maps were done to see the hardness distribution of each weldment.

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“…We used an initial value of 2 m MPa , representing the proposed value in the British Standard BS7910 [10]. This lower bound value was then increased to [3,[11][12][13][14]. The resulting effect on reliability can be seen in Figure 4a.…”

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confidence: 99%

The effect of materials properties on the reliability of hydraulic turbine runners

Thibault

Gagnon

Godin

2015

International Journal of Fluid Machinery and Systems

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The failure of hydraulic turbine runners is a rare event. So in order to assess the reliability of these components one cannot rely solely on the number of observed failures in a given population. However, as there is a limited number of degradation mechanisms involved, it is possible to use physically-based reliability models. Such models are often more complicated but are able to account for physical parameters in the degradation process. They can therefore help provide solutions to improve reliability. With such models, the effect of materials properties on runner reliability can be highlighted. This paper presents a brief review of the Kitagawa-Takahashi diagram which links the damage tolerance approach, based on fracture mechanics, to the stress or strainlife approaches. Using simplified response spectra based on runner stress measurements, we will show how fatigue reliability is sensitive to materials fatigue properties, namely fatigue crack propagation behaviour and fatigue limit obtained on S-N curves. Furthermore, we will review the influence of the main microstructural features observed in 13%Cr-4%Ni stainless steels commonly used for runner manufacturing. The goal is ultimately to identify the most influential microstructural features and to quantify their effect on fatigue reliability of runners.

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Hydraulic Runner Design Method for Lifetime

Cited by 6 publications

References 15 publications

Through‐Thickness Residual Stresses, Microstructure, and Mechanical Properties of Electron Beam‐Welded CA6NM Martensitic Stainless Steel after Postweld Heat Treatment

Through‐Thickness Residual Stresses, Microstructure, and Mechanical Properties of Electron Beam‐Welded CA6NM Martensitic Stainless Steel after Postweld Heat Treatment

An Experimental Comparison of Weld-Induced Residual Stresses Using Different Stainless Steel Filler Metals Commonly Used for Hydraulic Turbines Manufacturing and Repair

The effect of materials properties on the reliability of hydraulic turbine runners

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