Operating & Maintenance Procedures For Returning
Submerged Gear Drives To Temporary Service
Step-by-step procedures from Philadelphia Gear to restore mission-critical gear drives following Hurricane Katrina
September 7, 2005 (Norristown, PA) Many of
the pumps needed to de-water New Orleans have gearboxes attached
to them, which have been submerged during the flooding. In
order for these pumps to operate properly, Philadelphia Gear Corporation,
a full-service provider of gearing and power transmission solutions,
offers some basic steps to prevent short-term failure of these mission-critical
gear drives (regardless of manufacturer). Adopting these procedures
will help in preventing any delays in removing floodwaters that
would result from failed, gear driven pumps.
When a gear drive is submerged in seawater,
the primary damage to critical components occurs through corrosion,
specifically to rolling element bearings and gear elements.
Underwater, this corrosion occurs at a relatively slow rate
based on the oxygen content of the water.
However, when the gear drive is drained
of all water and not immediately and properly serviced, exposure
to the atmosphere can result in corrosion damage within a
very short period of time in as little as 24 hours,
notes Jules DeBaecke, Vice President of Engineering, Philadelphia
Gear Corporation. This condition elevates the risk of
premature operational failure to unacceptably high levels.
The step-by-step emergency procedure outlined
below, if followed immediately after the gear drive is drained
of contaminated water, can render the unit operational for
a significant period of time before unit rebuild is required.
Immediately upon draining the gear drive, remove
all inspection covers and thoroughly flush the gear drive
with hot (150-180°F), fresh water. If available, deionized
water is the optimal choice and the unit should be continuously
flushed until acceptable levels (.02 mg/25cm3) of chloride
are obtained. The primary consideration here is to limit accelerated
corrosion damage that occurs when the gear drives critical
components (bearings, gear elements and housing internal surfaces)
are not coated with oil and are exposed to the atmosphere
or chlorides contained in the water.
Immediately following the fresh water flush,
flush the unit again with a low viscosity flushing oil. There
are several flushing products on the market that are relatively
low viscosity products that will penetrate close tolerance
components like rolling element bearings, and remove water
and debris as the fluid is circulated throughout the unit.
Some of these products also include additives that actually
absorb water and remove it during the flushing process.
During both water and flushing oil processes,
maximum exposure of the flushing fluid to all gear drive critical
surfaces and internal housing areas is required. Completely
filling the gear drive with flushing fluid and immediately
draining the fluid is the best way to get maximum benefit
from the flushing process. If this is not feasible due to
gear drive size or location, then the gear drive internals
should be thoroughly lanced through inspection ports. When
lancing, do not direct lance at RTD wires or at hydrodynamic
bearings (sleeve type babbitt bearings). Direct impingement
of flushing fluid under pressure on all accessible rolling
element bearings, gear elements and internal housing areas
should be accomplished.
During flushing, the gear drive input shaft
should be slowly rotated at regular intervals to permit the
draining or lancing operations to dislodge any debris or moisture
pockets that might be trapped in the gear mesh and/or in rolling
In the event that flushing oil is not immediately
available, the unit should be flushed with fresh or deionized
water and then submerged in fresh or deionized water. This
will prevent any rapid corrosive activity due to metal surfaces
being exposed to the air. At such time that flushing oil is
again available, repeat steps one and two above.
The gear drive lubrication system must also
be cleaned and flushed in a fashion similar to the gear drive.
All water-oil coolers, unit piping, relief valves, pumps,
motors and filters should be either disassembled, cleaned
and reassembled or replaced as required. All electrical equipment
including electric motors, switches and any other electrical
devices should be either replaced or serviced in accordance
with equipment manufacturers recommendations to ensure
safety of operation.
Once all cleaning procedures are accomplished,
the gear drive should be operated as soon as is practical.
Prior to operation, lubrication oil should be circulated through
the unit and the unit lubrication system until the filter
elements remain clean since last inspection. If a centrifugal
oil purifier is available, circulating the new oil charge
through the purifier will aid in the removal of any residual
water and/or debris that might be dislodged during the flushing
or oil circulating processes. After the lubrication oil shows
clean in the filters, acceptable minimal levels of both water
and chloride contents should be verified by either taking
an oil sample or replacing the oil charge that was utilized
during the oil circulating process. If the chloride content
level is above acceptable minimum levels, subsequent gear
drive operation at normal operating temperatures can result
in accelerated metallic component corrosion.
Once the system is operational, the unit should
be operated at the lowest possible speed and load conditions,
depending on the nature of the prime mover. Any noted unusual
noise or vibration will indicate that significant damage has
been done and the unit should be shut down immediately and
properly reconditioned by a qualified repair facility. During
initial operation, all regularly monitored parameters (oil
pressures, oil inlet and outlet temperatures, bearing oil
temperatures, vibration levels, etc.) should be monitored
and compared to previously recorded parameters taken under
similar operating conditions. If there is no significant divergence
in previous and current parameter magnitudes, the gear drive
can be operated until such time that the gear drive can be
removed from service and properly inspected and overhauled.
This work should be scheduled at the earliest feasible opportunity.
Gear Drive Operations After Submersion
These procedures are intended to be an emergency
action to be employed when gear drive operation is required
in an emergency situation. During operation following unit
flooding and prior to unit overhaul, gear drive operation
should be closely monitored to ensure that premature bearing
or gear element degradation is not occurring. Periodic
condition monitoring should be performed on an accelerated
schedule to avoid potential equipment conditions that could
result in unscheduled downtime or represent an undesirable
safety condition, comments DeBaecke.
A founding member of the American Gear Manufacturers
Association (AGMA), Philadelphia Gear offers products and
services found in use worldwide; from conveyor gear drives
used in long wall coal mining operations, to emergency repair
services critical to the power generation industries. The
company serves thousands of customers across the globe from
its regional service and manufacturing facilities in New Castle,
DE; Birmingham, AL; Chicago, IL; Houston, TX; and Los Angeles,
CA. Philadelphia Gear is headquartered in Norristown, PA.
For more information on Philadelphia Gear, call
1-800-766-5120, fax 610-337-5637.