Performance of Nickel base alloys in Chlorine based environments

Dry chlorine is not specifically corrosive at ambient temperatures. Chlorine gas interacts with water to develop equal parts of hypochlorous and hydrochloric acid in the bleaching reaction. This combination of an oxidizing and non-oxidizing acid is responsible for the corrosive effect of most chlorine on metals.

Nickel  200, Monel 400, Inconel 625, Hastelloy C27 and Incoloy 800 and Incoloy 825 are resistant to dry chlorine. Monel 400 is a standard material for trim on chlorine cylinder and tank car valves, orifice plates in chlorine pipe lines and for different parts of chlorine dispensing systems. Wet chlorine at temperatures lower than dew point or aqueous solutions comprising of significant concentrations of free chlorine, are highly corrosive to these alloys, excluding Hastelloy C276 that is used in valve stems to prevent the effects of the ingress of moisture.

Inconel alloy 600 in dry chlorine, shows that longer test runs showed lower corrosion rates, feasibly due to influence of time on the development of security layers. Temperature limits are supposed to be conservative as longer testing durations are anticipated to offer lower corrosion rates for various materials that create security chloride layers.

Nickel 201 and Inconel 600 are the most practical alloys for use in chlorine and hydrogen chloride at high temperatures. When the major factor is resistance to corrosion at temperatures below the dew point, however provision against high temperature corrosion is also required, the specific order of use of materials for development is Hastelloy C276, Inconel 625, Monel 400, Nickel 201 and Inconel 600. Performance of Hastelloy wire is excellent in chloride media.

In choosing materials for use in high temperature chlorine or hydrogen chloride application, specifically at temperatures above 700oF or 371oC, not just the corrosion rate of material, however the influence that temperature can have on the mechanical properties of the material should be taken into consideration. The influence of moisture in hydrogen chloride at high temperature has been evaluated. It is found that 0.25% moisture in hydrogen chloride doesn’t considerably change the corrosion rate of Nickel 201 at 1000oF or 538oC.

In the production of hydrogen chloride from hydrogen and chloride, the recommended combustion unit design makes use of metal construction, with temperature of metal controlled in the specific limits by water jackets. It seems that the danger of corrosion by condensed hydrochloric acid at some temperature near the dew point is higher than by dry hydrogen chloride at high temperatures.

The permitted temperature limit for any metal or alloy may reduce at its lower end due to hydroscopic nature of the chloride of the metal considered. For instance, iron is not recommended to use at temperatures below 54oF or 30oC above then HCl-H2O point while copper can be used upto temperature 9oF or 5oC above the dew point. Considering the hydroscopic nature of nickel chloride, it would be prudent to consider that hydrochloric acid may condense on a nickel surface at temperature as much beyond the dew point as in the case of iron that is 54oF or 30oC.