Components under water conditions typically suffer more damage than such in an air environment. To estimate the difference quantitatively, strain-controlled fatigue tests in water and in air are carried out with strain amplitudes of 0.3 %, 0.4 %, 0.5 %. The temperature is in both 280 °C, the pressure in the water is 80 bar. The materials investigated are AISI 321 (1.4541) and ER 308L (1.4316) (weld material). 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 (HTW).
In the tests it could be shown, that the specimens tested in water fail at a lower number of cycles than those in air. Also, a higher strain amplitude leads to higher stresses and to a shorter lifetime. Stresses in ER 308L are lower than those in AISI 321. Moreover, there is a low scatter in the tests, especially when compared with the literature.