Posted by Tony Conner on November 08, 2001 at 05:08:53:
In Reply to: PITTING ON TUBES posted by MIKE on November 07, 2001 at 14:58:07:
The upper layer of water in the idle boiler will gradually absorb oxygen from the air, and cause pitting at the water line. If the boiler is laid-up wet, you need to add extra sulphite to the water, and check it a couple of times a week, and/or fire the boiler to a few PSI, as the boiling will drive off any dissolved oxygen. Very often, boiler are filled with water right to the non-return valve as well. On large boilers, a few PSI of nitrogen is sometimes used to blanket the steam space, keeping air (and oxygen) out. These methods all require someone to keep an eye on things, though. It's pretty easy for things to slip though the cracks.
If this was my boiler that was being laid-up for an extended period, though, I'd drain it, flush it, and leave the manhole/handhole covers out. Not much to go wrong with this method.
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