FILLING AND WATER TREATMENT : NOTES ON PREVENTING CORROSION, COMMON TYPES OF CORROSION, AND WATER QUALITY
COMMON TYPES OF BOILER CORROSION:
GENERAL SURFACE CORROSION - this is similar to the rust you would find on bare steel that has been outdoors for a period of time. Surface rust without pits is not critical. Monitor over time and note any abnormal changes. UNDER DEPOSIT CORROSION - occurs where water treatment chemicals are not able to directly contact steel. This will occur under sludge that may form on the floor of the tank or other horizontal surfaces. NOTE: Sludge can only be removed mechanically by hand scraping or pressure washing. Filtration will not remove existing sludge. The GARN unit must be drained to properly remove sludge. Clean any corrosion to bare steel after the sludge is removed. BACTERIOLOGICAL CORROSION - occurs when a bacteria is introduced into the tank water. As the tank water expands and contracts with heat, it “breathes”, drawing air into the tank as the water cools and pushing air out as the water expands. This breathing can draw in bacteria from the air (sources of airborne bacteria include: animal confinement buildings, agricultural waste, and industrial chemical processing). Bacteriological corrosion is highly unpredictable; however, once active it can corrode through a tank in a few months. Bacteria that cause corrosion can be common in rural water wells. Visual inspection, periodic testing and periodic cleaning coupled with ongoing chemical treatment is one of the most effective methods for bacteriological corrosion prevention.
If bacteria are found to be present in the GARN® unit, biocide agents can be ordered and used in conjunction with the normal water treatment program.
BLISTERS OVER PITS - is pitting type corrosion and it is not always apparent what causes this to occur at a particular location. Note any corrosion and wire brush or sand blast to bare steel.
GALVANIC CORROSION/ELECTROLYSIS - results from a “noble” metal (i.e. copper, bronze, brass, etc.) in close proximity to steel (a sacrificial material). It can also result from improperly grounded/isolated equipment or an improperly grounded electrical service to a building. No water treatment can prevent this form of corrosion. Connect only non-galvanized steel pipe to GARN® WHS and ETS units, and install dielectric couplings where copper pipe connects to steel pipe. APPEARANCE OF CORROSION Blisters formed by bacteriological action will have either: a shiny, dime color or charcoal color underneath, with a slimy substance within the blister. Oxygen pits are characterized by a black powder inside a blister. Corrosion underneath sludge may be of either type. Shiny dime colored pitting (especially in the vicinity of a tank seam or pipe fitting) is generally electrolysis.
GARN WHS 1000 and WHS 2000 Manual © HY-C Company LLC - September 2024
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