O'B OX™ Series
Since all natural surface waters are normally saturated with air, the
presence of dissolved oxygen in make-up waters is to be expected. Where a good feedwater
heater is used, the major portion of the oxygen will be removed, yet sufficient will
remain in the water to cause damaging corrosion.
Inside the boiler the water is heated above its normal boiling point, and the corrosive
action of the dissolved oxygen is greatly increased. Then too, as the water is vaporized
the dissolved oxygen will be evolved and pass into the steam line. When the steam is later
condensed, the oxygen dissolves in the condensate and will cause corrosion in the return
system. Most corrosive action which can be attributed to dissolved oxygen occurs in the
form of pits although this is not always the case.
The most effective means of combating dissolved oxygen under the conditions met with in
a power plant is to add a chemical to the water which will react readily with the oxygen,
forming a non-corrosive product.
O'B OX™ Series
treatments
are designed for this specific purpose. They will not volatilize at any pressure
nor will the reaction product formed with oxygen volatilize. The basic active ingredient
of the O'B OX™ Series is sodium sulfite. However, the effectiveness of the product is dependent upon
the presence of catalytic agents which promote an instantaneous reaction between
the sulfite and oxygen. The boiler metal and sulfite are competing to react with the
oxygen, hence if an effective catalyst is not used with the sulfite some boiler metal
corrosion will then take place.
If the treatment is added directly into the boiler, or if it is fed intermittently at
any point in the system it will only provide protection for the boiler, steam, and return
lines. In order to protect the feed pump and feed lines the material must be fed
continuously into the suction side of the feed line. Where comparatively cool
feedwater is pumped, the pump and feed lines do not normally corrode to any appreciable
extent. For this reason most users will prefer to feed this along with the regular
treatment as a matter of convenience.
A daily sulfite test should be run in order to insure that the proper amount of
treatment is being used. There is positively no other method of determining this.
Furthermore, the test must be run on a freshly drawn (but cool) sample, hence the sample
cannot be sent into the laboratory for analysis. Periodic spot checks by the field
engineer should be made but this will not supplement the daily test. A sulfite
residual of at least 20 ppm must be maintained in order to insure an adequate
concentration of catalyst and to provide sufficient chemical for reaction with the
dissolved oxygen.
