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topic 12460

Alternatives to chromium for passivation of mild steel piping


A potential customer produces LPG "powered" appliances. The appliances are dependent on a contained aqueous ammonia solution that circulates through an elaborate plumbing mechanism. The piping that is currently being used is ordinary mild steel piping. In order to prevent corrosion of this piping, sodium dichromate is added to the aqueous ammonia solution to passivate the mild steel surface and prevent corrosion. The presence of chrome in this solution complicates the effluent treatment process. Does anyone have any suggestions as to an effective passivating agent for a process such as this which would simplify the effluent treatment process? Any suggestions most welcome.

Neil Rein
- Johannesburg, Gauteng, South Africa


Have you removed oxygen and carbon dioxide from this ammonia?

pooky tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania


There is no stringent removal of either oxygen or carbon dioxide. A sodium dichromate solution is premixed (in the open) using distilled water. This solution is then mixed with ammonia in closed holding tanks. This solution is introduced into the plumbing of the appliances under pressure (hydrogen gas is used). I therefore suspect that during the mixing of the dichromate in particular, both oxygen and carbon dioxide are introduced into the solution.

Neil B. Rein
- Johannesburg, Gauteng, South Africa

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