Fatigue Tests of the Weld Metal ER 308L in Air and High Temperature Water Environment

Due to corrosive effects, components in high temperature water conditions typically suffer more damage than such in an air environment. These components usually come with weld joints. For this reason, the effect of environmental assisted fatigue must also be investigated for the weld material. To estimate the difference between fatigue in air and high temperature water (HTW) quantitatively, strain-controlled fatigue tests in water and in air were carried out with strain amplitudes of 0.3%, 0.4%, 0.5%. The temperature in air and water was 280 °C, the pressure in the water was 80 bar. The weld material investigated is ER 308L (1.4316). In order to keep the strain amplitude in water and in air identical, the global displacement in air is measured with a linear variable differential transformer (LVDT). Out of this recorded LVDT signal, an analytical function for approximation of local strain is formed and then used for control in the associated fatigue test in high temperature water. In the tests it could be shown, that the specimens tested in HTW failed at a lower number of cycles than those in air. Also, a higher strain amplitude leads to higher stress and to a shorter lifetime. Furthermore, the weld material shows hardening and softening material behavior, comparable to the austenitic stainless steel base metals.