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Posted by Vern on January 25, 2002 at 07:49:44:
In Reply to: Corrosion in Deaerator & Feed Tank posted by Ramesh R. on January 24, 2002 at 05:21:47:
: Im having this problem in the Dearaerator(Pressure type)working temp.70C.Just opened up & found heavy pitting all over.
: My heating coils( made of schedule 40) in Feed Water Tank is heavily pitted.
: Temp.50c. pH 7-7.5.Alkalinity is around 80ppm.any idea of this problem?
Tony is right, you need to get your temp up over 100C(212F) or your
Deaerating feedwater tank is nothing more than a hotwell. D/A tanks have
to get the temp up that high to scrub the oxygen and other gases out. Have your
chemical vendor check the dissolved oxygen level in the tank. If you continue
running at your low temp. you will have to put bunches of pounds of sulfite or
another oxygen scavenger in the d/a tank to remove the oxygen and stop the pitting.
But when you do that you increase the level of sulfites in the boiler, which isn't a problem
in low pressure boilers about 125 psi or so, but is in higher pressure boilers around 600 psi or higher.