Discussion

SESSION VIII: DEVELOPMENT WORK

H. D. ROHRIG

How effective an oxide film may be in the low pressure range is shown by Fig. VIII.1. The bottom curve shows the influence of some unintentional oxidation; the upper curves could only be attained after a strong annealing treatment of the specimen in pure hydrogen.

In order to obtain more information on the establishment of oxide scales and their permeation impeding behaviour, we made - as part of the preliminary testing programme - some measurements on Incoloy 800 samples with different oxygen potentials controlled by a defined moisture content of the working gas. The philosophy of the testing procedure was to begin with the highest temperature so that an oxidation would proceed to some near equilibrium that would not change significantly at any lower temperature. Indeed we found a quick decrease of permeation rate by a factor of some hundred.