Fulton Ancillary Equipment SteamPac Unfired Steam Generators - Manual (Page 19)

Fulton Thermal Corp.*SteamPac Unfired Steam Generators Manual* Version 2010-0201
Page 19
slightly more than enough sodium sulfite to consume all of the dissolved oxygen that slips
through the deareating equipment. Sulfite as a treatment represents the second line of
defense against oxygen corrosion. Primary protection against this type of attack requires
adequate facilities for mechanical deareation of the feed-water plus a vigorous
maintenance program to safe guard against oxygen leakage into the pre-boiler system.
c) Suspended Solids: Suspended solids are the undissolved matter in water, inc-luding
dirt, silt, vegetation, iron oxides, and any other insoluble matter. Normally suspended
solids are expressed in terms of turbidity. Suspended solids may also deposit in low
velocity areas and create fouling. In line filters, or various types of pretreatment can be
used to lower the suspended solids level. Various polymers assist in holding solids in
suspension. Periodic blowdowns will eliminate suspended solids.
d) Alkalinity: Alkalinity is the capacity of a water to neutralize acids. Common water
alkalinities consist of bicarbonate, carbonates, hydroxide, phosphate, and silicate. These
alkalinities, especially bicarbonates and carbonates, break down to form carbon dioxide
in steam, which is a major factor in the corrosion on condensate lines. High alkalinity also
causes foaming and carry over in boilers. Both foaming and carry over cause erratic
boiler operation. When foaming occurs an antifoam should be added or increased. The
reason for the high alkalinity should be determined. It may result from lack of sufficient
blow off. Quite often the source of alkalinity is an overdose of alkaline internal water
treatment chemical.
e) pH: pH is a measure of the degree of acid or base of solution. pH ranges of 8.0-10.5 will
have little influence on the corrosion rate of carbon steel. A low pH can result in corrosion
of metals, while a high pH can result in scale formation or caustic embrittlement. In order
to control boilers and equipment used for the external treatment of make up water, it is
essential that reliable pH measurements be made. RO/DI water will have a pH of 6.0 -
6.5 and will require neutralization if used in a carbon steel vessel.
f) Chlorides: If chloride levels are high enough to cause severe corrosion, they can be
controlled by limiting the cycles of concentration and increasing boiler blowdowns.
Corrosion from chlorides can also be controlled by increasing the amount of corrosion
inhibitor or changing to a more effective inhibitor. Reverse osmosis is another method of
pretreatment to reduce chlorides. Chlorides are a major concern in a stainless steel
vessel.
g) Oil: Oil is not a natural constituent of boiler water; still it can frequently enter a system
through leaks in a condenser or other heat exchanger. Oil can also enter a system
through the lubrication of steam driven reciprocating equipment. Whatever the source,
the presence of oil in boiler water is undesirable. Oil can act as a binder to form scale. In
high heat-transfer areas oil can carbonize and further contribute to the formation of scale
and low pH. Foaming is one indication of oil in boiler water. Its presence can also be
confirmed by first shaking a bottle containing boiler water. If oil is present foam will