FAILURE ANALYSIS OF WATER TREATMENT PLANT EQUIPMENT
by
Charles C. Roberts, Jr.
Most municipalities have a water and sewage department as part of their
governmental structure. Like any other industrial environment, complex
mechanical and electrical equipment are at work performing various functions such
as water purification, auxiliary power generation, sludge removal and
decomposition of organic wastes. Failure of mechanical or electrical equipment can
result in a substantial monetary loss, giving rise to an insurance related claim. A
review of four case studies involving such claims gives insight into the technical
issues involved.
Figure 1 is a view of a typical clarifier pond showing a rotating boom structure that
sweeps floating solids to discharge openings on the side. The boom gear drive unit
failed, rendering the clarifier inoperative. Figure 2 is a view of the drive base
Figure 1
Figure 2
showing a water mark inside. Figure 3 shows the remains of the large 2 inch
diameter ball bearings, showing evidence of improper lubrication. Apparently the
pond had flooded during a severe rain storm, such that the water level was above
the oil sump, causing contamination of the lubricant. After the water receded, the
unit was allowed to run until the failure occurred. The maintenance department
failed to change the contaminated oil after the flood, a procedure that probably
would have saved the gear drive unit.
Figure 3
Figure 4
Figure 4 is a view of an auxiliary generator unit which is typically required for
emergency power to run a sewage treatment plant. The unit caught fire during a
test cycle, resulting in a total loss. Figure 5 is a view of the diesel engine, showing
Figure 5
Figure 6
severe damage to the oil pan assembly. Figure 6 is a close-up of the oil pan hole,
revealing the remains of a bearing and connecting rod that had failed. The
connecting rod was propelled through the oil pan wall, allowing hot oil to escape
and become atomized by the turbulent air flow from the cooling fan. Hot surfaces
are the likely cause of oil vapor ignition, resulting in the fire that ultimately
destroyed the unit. The cause of the loss was mechanical failure of a connecting
rod bearing.
Figure 7
Figure 8
Figure 7 is a view of a large rotating drum used to accelerate biological
decomposition of effluent from a sewage treatment plant. The main support shaft
failed causing the assembly to settle into its basin. Figure 8 is a view of the shaft
which suffered a metal fatigue related failure (see Insurance Adjuster, March
1983). This failure was design related.
Figure 9
Figure 10
Chlorinator equipment is found in most water treatment operations. A chlorinator
room usually contains the chlorine tanks and apparatus used to feed the chlorine to
the water supply. A unique failure mode of equipment in these buildings relates to
the inadvertent escape of chlorine gas. Although the amount of gas escaping may
be minute, it combines with water vapor causing a corrosive hydrochloric acid
environment. Figure 9 is a view of a chlorinator room where an improperly
installed hose fitting leaked, allowing chlorine solution to enter the area. There was
evidence of severe corrosion as indicated by the arrow. The air vent grill shown in
Figure 10 was badly corroded, additional evidence of chlorine leakage. A motor
controller failed in the chlorinator room as a result of the corrosive environment.
Figure 11
Figure 11 is a view of another chlorinator room showing evidence of severe
corrosion at the ventilation grill. As a result of corrosion from a chlorine solution
leak, the furnace thermostat in the room locked shut, causing the furnace to
overheat. The very high temperature in the unoccupied room most likely exceeded
150F. This caused polymer housings on several pieces of equipment to soften and
sag, rendering the contents a total loss.
The causes of losses in water treatment plants are unique to that environment. As
exemplified in the chlorine leakage examples, the cause of the malfunction may not
be a deficiency in the equipment but leakage of a contaminate that causes a
malfunction. Telltale signs such as rust on ferrous metals and green corrosion on
copper based metals give clues as to the cause of a loss. As always, the cause of
the loss is pivotal in the decision making regarding coverage.
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