How to pressurize autoclaves for corrosion testing under carbon dioxide and hydrogen sulfide pressure

All the methods presently used for pressurizing autoclaves have advantages and disadvantages. Pressurizing with pure gases is undoubtedly the surest method, since it is insensitive to the autoclave filling rate, and the influence of temperature stability readily can be controlled. The only limitation is the impossibility of accurately reproducing very low hydrogen sulfide (H2S) partial pressures (< 30 mbar) at high temperatures (> 150degreesC). Conventional pressurizing with gas mixtures is not at all practical, since it demands either excessively large autoclaves or the bubbling of prohibitive volumes of gas. To overcome these fundamental difficulties, alternative methods are proposed, such as high-temperature bubbling using a cooled reflux condenser or presaturation of the autoclave at 60degreesC at a fraction of the test pressure, enabling the latter to be attained during subsequent heating by the natural increase in pressure with temperature.