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Posted by Vern on January 10, 2002 at 07:37:56:
In Reply to: Thanks for replies; followup question: posted by Gern Blanston on January 10, 2002 at 06:28:25:
: Thanks for the help guys. Vern, you indicated that something besides disolved oxygen might be causing the localized pitting? The holes we have developing in these tubes are very pretty little things, they almost look like they were machined into the tube. We only found three of them, several feet apart, and the rest of the tube metal and the boiler looks like brand new.
: What else should I look for? Thanks again.
Hello. Inside the pipe where the holes are, did they have what looks
like miniature volcanoes over them? These are called tubercles, and is
a buildup of corrosion over the hole. That would be oxygen pitting.
Other possibilities might be localized corrosion under a deposit.
Another possibility could be process contamination of the boiler water.
Some years ago I saw a guy with a 30 hp Parker Boiler. He had the same
problem as you. We ran with high sulfite levels, changed blowdown procedures,
but the ultimate solution was when he changed one of his plant processes.
He was getting a weak acid back into the system on shutdown. The boiler would
sit idle for several days, causing his problem. But keep checking on the oxygen
because that is probably the culprit here. Hope this helps. Vern
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