Effect of Internal Pressurization on the Creep-Fatigue Performance of Alloy 617 Based on Simplified Model Test Method

Abstract

The Simplified Model Test (SMT) is an alternative approach to determine cyclic life at elevated temperature and avoids parsing the damage into creep and fatigue components. The original SMT concept [1] considered that the effects of sustained primary stress loading could be safely neglected because the allowable local stress and strain levels were much higher than the allowable sustained primary stress levels. This key assumption is critically evaluated on Alloy 617 using internal pressurized cylindrical SMT specimens at 950 °C. The impact of combined internal pressurization and displacement-controlled creep-fatigue loading on the SMT cycle life is demonstrated at different strain ranges. The effect of primary load on the SMT design method is discussed.

Reference constitutive model for Alloy 617 and 316H stainless steel for use with the ASME Division 5 design by inelastic analysis rules

“…The ART program developed the pressurized SMT test geometry to assess the combined effects of axial cycling, elastic follow up, and internal pressure/multiaxial load on the cyclic life of high temperature reactor materials. The program completed several tests of this kind for Alloy 617 at 950 • C [24]. Comparing finite element simulation results using the Alloy 617 model to the experimental data validates the model for complex multiaxial loading conditions, representative of actual component service conditions.…”

“…However, one test had an internal pressure of 2 psi while the other test had an internal pressure of 150 psi. Compared to the experimental data [24] the model captures the influence of pressure on the ratcheting rate and the follow up correctly. However, it does not…”

Report on FY 2020 Testing in Support of the Development and Extension of ASME Code Rules for Grade 91

“…The improved techniques enable the use of standard CF specimens and significantly simplify the testing program. The new techniques were successfully verified in Wang et al 2018aWang et al , 2018bWang et al , 2019aWang et al , 2019bWang et al , 2019c. In FY 2020, analysis was performed to evaluate the hold time effect on the SMT CF life.…”

“…The original SMT key-feature article testing provides critical information in developing the SMT-based CF evaluation methodology. Among the key feature article tests, pressurized tubular SMT was used to evaluate the effect of the primary load (Wang et al, 2019c). In the original SMT concept proposed by Jetter (1998), it was argued that the effects of sustained primary stress loading could be safely neglected because the local stress and strain levels for cyclic loading at peak stress locations were much higher than the allowable sustained primary stress levels.…”