Papers by Keyword: Omega Method

Abstract: This paper is concerned with the creep life prediction of cast 20Cr32NiNb alloy, an alternative candidate material to wrought Inconel alloys for use in the gas collector pipes of CO reformers which suffer from long-term creep damage due to high temperatures and stresses. Uniaxial creep tests of 20Cr32NiNb alloy were performed at 890 °C and 950 °C for different stresses. The Omega method for creep life prediction is applied to the 20Cr32NiNb tests and shown to give reasonably accurate prediction, particularly at low stress levels. A new method, based on the use of a hyperbolic sine function for stress correlation at specific temperatures for identification of the characteristic Omega parameters is presented and validated.

Abstract: Creep testing of Alloy 718 has been carried out at various loads in the temperature range near 650°C in constant load control mode in order to understand how to predict the creep behavior including tertiary creep. The test results have been used for evaluating the existed models, such as Theta projection and Omega method that have been widely used for predicting long term creep strain and rupture time. After determining variables and material parameters of each method with the test results, estimated creep data from each model have been compared with the each measured creep data from the creep tests. The root cause of the discrepancy between estimated and measured data has been analyzed in order to improve the existed methods. The reliability of the improved model has been evaluated in relation to creep data.