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Maintaining spares and redundant machinery in a prime state, ready for operation, can be a daunting proposition, particularly given that most of the planet is covered with a substance that tends to attack these stored and standby machines.
We call the substance water. It is vital to life, health, happiness and keeping the wheels turning in the wide world of manufacturing. Water also has the distinct potential to wreck idle industrial machines.
Machinery can be idle from intermittent use, stand-by (redundancy), storage for spare parts, or for temporary decommissioning. This article looks at practices that protect equipment characterized as decommissioned, short-term storage or storage of stand-by capacity.
Preserving or inhibiting corrosion of inactive process machinery depends on the type of equipment, expected length of inactivity and the time required to restore the equipment to service.
Petrochemical companies usually develop their standards based on such criteria. One recent typical mothballing program for indefinite storage in a northern climate zone was planned and executed as follows and forms the basis for the author’s recommendations.
The probability of equipment failure is high following commissioning of equipment, whether for initial operation or following rebuild. Machines can often sit at a new industrial site for months while the arduous process of site construction creeps along. Unless the buyer clearly specifies storage measures in the contract, it is likely that the machine would be shipped without provision for storage. Onsite storage preparation for the three to 12 months at a construction site is usually termed a preventive maintenance (PM) program. Storage protection plans would look like the following, again in a northern, dry climate:
Rotate all motors, turbines, compressors, pumps (excluding deep well pumps with rubber bushings), fin fans, blowers, aerators, mixers and feeders every two weeks.
When rotating exposed machined surfaces, check shafts and couplings to see that a protective coating has been applied and has not been removed. Reapply if needed.
Check all lubricating lines to see if any tubing, piping, tank or sump covers have been removed. Retape ends and cover. If flanges are open on machinery, notify pipe fitter general foreman or other designated personnel.
Inspect the interior of lube oil consoles on a six-week schedule. Check to see if the reservoir is clean and rust- and condensate-free. Clean and dry if needed, then fog with rust-preventive concentrate.
Drain condensation from all bearing housings, sumps and oil reservoirs on a once-per-month schedule. If an excessive amount of condensation is found, recheck once a week, or at two-week intervals depending on condensate present.
Fill all bearing housings that are oil-lubricated but not force-fed with rust-preventive concentrate, bringing the oil level up to the bottom of the shaft. For force-fed bearings, the upper bearing cap and bearing must be removed. A coat of heavy, inhibited oil can be applied to the journal and bearing surfaces. This should be reapplied as needed.
Spot-check turbines by removing the upper half of the turbine case and visually inspect. Plan to open a sampling of these turbines, selecting from the first preserved and those in the worst condition. This should be done on a three-month schedule. Other turbines may be inspected by the manufacturer’s field service engineer on his monthly visits. Small, general-purpose turbines should be fogged with rust-preventive concentrate through the opening in the top case as the rotor is being rotated. This should be done on a three-month schedule.
Manufacturers’ representatives should inspect the compressors during monthly visits. Preservatives needed can be applied under their supervision. Fog centrifugal process compressors, and consider placing desiccant bags in these machines. Inspect these compressors on a two-month schedule. Inspect high-speed air compressors on a three-month schedule. Inspect and fog axial compressors on a three-month schedule.
Open reciprocating pumps and inspect on a two-month schedule. Fog centrifugal and in-line pumps with rust-preventive concentrate. Volute cases need not be filled unless it is anticipated that they will remain out of service for longer than one year.
Electric motors with greased bearings need not be lubricated. If received with a grease fitting it should be removed and plugged or capped. For other lubrication type bearings, see bearings section of this article.
Fog the interior of the housing with rust-preventive concentrate. Coat tooth contact points with an inhibited grease or heavy, tacky oil. Remove inspection plates on gears and visually inspect interiors on a three-month schedule.
Inspect blowers for rust on a three-month schedule.
Fill mixers with rust-preventive concentrate.
Drive belts should stay on. Run several minutes at least every two weeks or whenever snow load dictates.
Lubricate miscellaneous equipment as applicable and rotate on a two-week schedule.
In a warm, high-precipitation climate it is wise to look for alternate solutions to the problem of field storage during construction and prior to start-up. If oil-mist lubrication is not already part of the original design, it should be seriously considered as in many cases it provides the best protection against contaminant ingression.
Figure 1. Temporary Oil Mist Lines and Generator Used
to Protect Equipment Prior to Installation
Figure 1 shows temporary field tubing that supplies oil mist to the bearing points of a turbine drive pump row.
Figure 2. Open Storage Yard with Oil Mist Tubing
Protecting Pump and Motor Bearings
Figure 2 shows a similar installation, feeding oil mist to pump and motor bearings.
Figure 3. 15,000-hp Electric Motor Stored with Oil Mist
Preservation on the Bearing Housings
Figure 3 illustrates construction site storage oil mist supply lines that run to a vertical mechanical drive turbine as well as to a large feed pump motor.
The third and last case of machinery storage protection arises when standby capability of inactive equipment is desired. Reference 1 describes such a case. It appears as though there are no limits to the ingenuity displayed by operators, as long as a “do nothing and take your chances” stance is not taken. In addition, best practice dictates that all preventive maintenance be logged by item number in the maintenance log.
While the case of extended standby protection does not seem to present a problem for process pumps and other general-purpose equipment, especially where oil-mist lubrication is installed and operating, it might well be a challenge to operators of steam and gas turbines as well as reciprocating engines and compressors. One company has had excellent success with a program it developed in-house for standby storage of critical machinery, particularly gas turbines. Following is one manufacturer’s recommendations for the standby protection of gas engines or gas engine-driven compressors:
Drain the water jackets and then circulate the proper compound (see Table 1) through the jackets making sure that all surfaces in the jacket are reached. Drain the system and plug all openings.
For engine lubrication systems, the following procedure is recommended:
Drain the lubricating oil system, including filters, coolers, governors and mechanical lubricators. Flush the complete system with standard petroleum solvent that will take the oil off the surfaces. Use an external pump to force solvent through the system. Spray the interior of the crankcase thoroughly, then drain.
Refill with Product 4 to the minimum level, just enough to ensure pump suction at all times, in each case. Crank the mechanical lubricator by hand until all lines are purged. Where compressors are used, be sure to flood the compressor rod packing.
Using air pressure or any other convenient means, turn the engine at sufficient speed and for a sufficient length of time to thoroughly circulate the compound through the engine.
Stop and drain the engine sump, filters, coolers, governor, lubricators, etc. Plug all openings.
Remove the spark plugs or gas injection valves and spray with Product 2 inside the cylinders, covering all surfaces. At the same time, rotate the engine by hand so that each piston is on bottom dead center when that particular cylinder is being sprayed.
After this operation the engine should not be turned or barred over until it is ready to be placed in service. Tag the engine in several prominent places with warning tags.
Where compressors are involved, including scavenging air compressors, remove the valves and spray inside the cylinder to cover all surfaces. Dip the compressor valves in Product 1 and drain off the excess. Reassemble valves in place.
Bloch, H. and Shamim, A. 1995. Oil Mist Lubrication: Practical Applications. Lilburn, G: Fairmont Press.
This article excerpted, by permission, from Practical Lubrication for Industrial Facilities, 2000.
Photos courtesy of Lubrication Systems Company in Houston, Texas.