As we transition from Summer into Fall, those facility management teams who use their
steam boilers for heating find this a particularly challenging time of the year
to maintain proper chemical levels in their boilers. Some days are rainy and
cool, then we get an occasional warm spell going from needing to not needing
that heat. Similarly we may have cool mornings - requiring heat, and sunny
afternoons with no additional heat demand.
The challenge is to keep enough oxygen scavenger in the
boiler feedwater as well as in the boilers. Failure to maintain proper chemical
levels can lead to costly failures - in the boiler feedwater tank and piping,
in the boiler tubes, and in the steam and condensate piping system.
To prevent these failures we strongly encourage you to feed
more oxygen scavenger than typically necessary. A common chemical used for this
purpose is sulfite (SO3). Normal maintenance levels are 20-40 ppm of
sulfite. During the fall months, you may need to maintain sulfite levels at
80-100 ppm to ensure that there is enough sulfite in the system to prevent oxygen
pitting.
The reason for this recommendation is as follows: as the
boiler and boiler feedwater cool down when not in use, a partial vacuum can
develop in the feedwater tank, drawing air into the feedwater. Similarly this
can occur out at condensate receivers throughout the facility. This oxygen
becomes very corrosive when heated.
In fact, for every 30o F
increase above 70o F, that oxygen doubles in its corrosiveness.
True, this process will cost a little more than normal. Also true is that it will add TDS (frequently referred to as conductivity) to the boiler, but
these issues are minimal compared to the costs and downtime for pipe and tube
replacements.
Posted on behalf of Fred Lattin
