Experimental study of low-cycle fatigue of pipe elbows with local wall thinning and life estimation using finite element analysis

Fracture behaviors of pipes with local wall thinning are very important for the integrity of power plant piping system. In this study, monotonic bending tests without internal pressure are conducted on 1.91-inch diameter Schedule 80 STS370 full-scale carbon steel pipe specimens. Fracture strengths of locally wall thinned pipes were calculated by elasto-plastic analysis using finite element method. The elasto-plastic analysis was performed by FE code ANSYS. We simulated various types of local wall thinning that can be occurred at pipe surface due to coolant flow. Locally wall thinned shapes were machined to be different in size along the circumferential or axial direction of straight pipes. We investigated fracture strengths and failure modes of locally wall thinned pipes by four-point bending test. From the test results, failure modes could be divided three types, ovalization, local buckling and crack initiation. And, the allowable limit of pipes with local wall thinning was investigated. In addition, we compared the simulated results by finite element analysis with experimental data. The failure mode, fracture strength and fracture behavior obtained from the tests showed well agreement with analytic results.

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Low cycle fatigue analyses of open-celled aluminum foam under compression–compression loading using experimental and microstructure finite element analysis

Journal of Alloys and Compounds ◽

10.1016/j.jallcom.2019.05.158 ◽

2019 ◽

Vol 797 ◽

pp. 231-236 ◽

Cited By ~ 1

Author(s):

Behrang Hamidi Ghaleh Jigh ◽

Hossein Hosseini-Toudeshky ◽

Mohammad Ali Farsi

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Aluminum Foam ◽

Low Cycle Fatigue ◽

Cycle Fatigue ◽

Element Analysis ◽

Compression Loading

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A Nonlinear Dynamic Reduced-Order Model for a Large Gas Turbine Outer Casing Low Cycle Fatigue Prediction

10.1115/gtindia2021-76056 ◽

2021 ◽

Author(s):

Aditya Dubey ◽

Rishi Relan ◽

Uwe Lohse ◽

Jaroslaw Szwedowicz

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Gas Turbine ◽

Nonlinear Dynamic ◽

Low Cycle Fatigue ◽

Reduced Order Model ◽

Cycle Fatigue ◽

Order Model ◽

Element Analysis ◽

Reduced Order

Abstract The secondary stresses that result from nonlinear and transient thermal gradients during the start-up and shut down of the large gas turbine engines drive low-cycle fatigue at specific locations of the outer casing. Typical service inspection of the outer casing is primarily based on finite element analysis estimates, considering various safety factors. However, as finite element analysis includes the worst possible combination of loading scenarios and operating conditions any engine may encounter in actual operation, this results in a conservative estimation of the service interval. Therefore, a generic preventive maintenance plan for the whole fleet often underutilises the casing capability and added cost. Hence, this paper proposes a data-driven nonlinear dynamic reduced-order model developed using the temperature data from low-cycle fatigue critical casing locations, ramp rates, and the percentage load of operation to predict the stresses. As a result, a reduced-order model can assess the damage for low-cycle fatigue critical locations in real-time using the operational data and propose an appropriate service intervention plan for each casing in a fleet.

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