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Magnetite build-up in boiler tubes

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Posted by Andy Ryder on November 10, 2004 at 04:33:46:

In the cast iron steam heated pressure vessels which we manufacture, we use a condensate removal system, part of which includes stainless steel tubes of around 1/4" bore thickness. These tubes remove condensate from the vessel bore using steam blow- through i.e. a stream of steam carries drops of condensate up though the tubes and exits the vessel. When our customers get their water treatment wrong, black oxide is carried around through the system and a build-up of magnetite is formed at each end of the tube bores, which enentually blocks them. The stainless steel tubes are attached to a mild steel bracket at one end and a small cast steel (coated with titanium nitride) bracket at the other.

I have a theory that the chromium oxide coating on the stainless steel tubes is attracting the particles of magnetite due to the 'magnetoelectric effect' of the chromium oxide. For this to occur the chromium oxide needs to be in the presence of an electic field. Could the electode potential between the tube and the brackets at each end be providing this electric field? Where else could the electric field be coming from, bearing in mind that this is a steam atmosphere with a high velocity liquid/steam mixture? Does my theory sound likely?

Any help would be greatly appreciated!

Andy Ryder

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