Last month I concluded the article at the beginning of a discussion on the
This month we will delve deeper into
what some of these impurities are,
allowable limits for proper boiler
operations, how to control them and the
type of damage they cause.
The following are charts listing common
impurities and allowable limits for Fulton
boilers commonly used in
Similar charts are available from all boiler manufacturers although the
allowable limits may vary
from manufacturer to manufacturer.
“Wow,” you say. That’s quite a list of things I know nothing about. Lacking a degree in chemical
engineering what can I do about it?
Well, the answer is not much as far as the chemistry of the new or make-up water
is concerned. It
depends on the local water supply.
However, the good news is that commercially available boiler treatments,
generically called “boiler
compound” and water softening devices, do an excellent job in keeping your boiler in
condition and are readily available.
In most cases providers of boiler compound and water softening services will
take water samples
from your steam system and analyze them in order to set up the proper dosing
schedule to maintain
proper boiler chemistry.
Water testing should be done every few months minimum. If you own a water
softener instead of
using a service, most large swimming pool supply houses will be able to test for
hardness, often at no
OK, we have reached the point where you are aware that boilers need the proper
and there are effective means to treat that water in order to provide that
What could go wrong?
Plenty, and the next paragraphs will suggest how to avoid the dreaded “Pitfalls of Boiler Water
Here’s two most common bad actors found in makeup water that you have the ability to
Dissolved oxygen. Oxygen which is dissolved in feedwater attacks the steel in the boiler and the
feedwater system and causes a condition described as “pitting.”
The pits that are produced can vary from tiny depressions to holes large enough
to penetrate the
boiler metal and are usually covered with pimple-like bumps of rust.
Once pitting starts, it may be extremely hard to arrest and can proceed at a
rapid rate. Sodium
sulfite is used to remove the dissolved oxygen left in the feedwater. It reacts
dissolved oxygen binding it so it is not available to destroy metal.
Dissolved oxygen control is based on maintaining a level of sodium sulfite in
the boiler water
therefore it is important that the feedwater and make-up water are mixed as
thoroughly and as
quickly as possible so that sodium sulfite binds feedwater oxygen before the
oxygen can cause
damage to the boiler.
With this in mind, it is far better to add compound to the return tank using a
metering pump when
new make-up water is added to the return tank or when the return pump is pumping
water into the
boiler than it is to add the compound manually a couple of times a day.
When water is heated, the dissolved oxygen is driven off therefore condensed
flowing back to the condensate return tank is essentially oxygen free.
Only new, untreated make-up (city water) water adds the damaging oxygen.
Constant addition of new water caused by leaky ball float valves (Roberts Valve)
found in almost
every return tank is a boiler killer.
In order to prevent pump cavitation caused by high return tank water
operators sometimes run a stream of new water into the return tank to cool it.
Leaky ball float valves (Roberts Valve) and return tank water cooling using this
method will kill
boilers by overwhelming the capacity of the boiler compound to treat the water — both by adding
large amounts of oxygen and also diluting the boiler treatment chemicals.
Water hardness. Water hardness is the measure of calcium and magnesium content. Calcium and
magnesium carbonates are the major components of scale, which is the hard layer
that forms on the
metal surfaces inside of boilers and pipes.
Its formation is controlled by:
• Removing as much of the scale-forming carbonates before they enter the boiler
which is called
There are water softener services which routinely replace the active components
of the softening
system, or you can own and maintain your own water softener.
Either requires the replenishment of the softening media (most often salt,)
based upon the original
“hardness” of the incoming water and the volume of water treated.
Hardness levels should be monitored regularly by sampling, then testing the
• Chemicals in the boiler compound which keep the carbonates from hardening on
Both of the methods listed above are defeated by excessive volume of new
entering the return tank. Once again the culprit is usually the fault of the
ball float valve (Roberts