Before the Snow Flies...

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 30^o F increase above 70^o 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