When spare parts arrive, maintenance practices begin

by John C. Robertson

Good maintenance practices begin when parts first arrive.  Too often, parts are received and accepted with the stroke of a pen and are later found to be defective when they're needed most.  The maintenance department should be informed when spares and replacement parts are received, particularly where major components are concerned.  They should then test the equipment to ensure it meets the clients design specifications before acceptance.

Note: During the contract negotiations for the equipment, the buyer should insist that the manufacturers warranty doesn't start until the equipment is operating to the clients satisfaction.

Often, during new plant construction, equipment will lie in the storeroom without any maintenance for months, which negates the warranty even before installation and operation.

When a major component or complete piece of equipment is tested at the manufacturers site, it's virtually guaranteed to pass the acceptance inspection because it is set up under ideal conditions.  However, when the equipment is delivered, it's often subject to abuse during transportation.  Abuse is usually unintentional.  However, during transport, the equipment is subject to vibration, false brinnelling of bearings or improperly placed lifting slings.

Brinnelling is a fretting-type phenomenon normally caused by vibration while the bearing is not rotating, or by an oscillating motion of very small amplitude).  Improperly placed lifting slings allow bending of the frame or bed plate.  This can take place two or three times before the equipment is finally lifted into position.

The only guarantee left is for the client and the manufacturers representative to perform a quality control audit at each step of the receipt and installation process.  If this type of control is not practiced, you can expect the equipment to experience problems that will place it in a reactive maintenance mode over its operational lifetime.

When spare parts and components must be stored for a lengthy period, the storeroom should have a maintenance program in place and a maintenance schedule set to perform periodic tasks to ensure that those components and parts are always ready 
for use.

The following guidelines are based on manufacturers storage instructions and my past experience.

Motors
Motors should be rotated at least 4 1/2 turns every two weeks to prevent false brinnelling of the bearings.  This ensures the bearings rolling elements are lubricated during rotation.  The extra half-turn takes the rotor shaft off its last standing position, thus preventing further loading at the previous rotor location.

To ensure that grease is suitable for use in certain bearings, all recommended greases should be color-coded and the grease guns suitably colored to match that particular grade of grease.  The amount of grease that is delivered from one stroke of the grease gun should be weighed and inscribed permanently on the barrel of the gun for future reference.

Before greasing bearings, ensure the correct grade of grease will be used and determine how much must be applied.  Check bearing grease at least twice a year to ensure there are no signs of separation or contamination.  Also, check that the grease nipples are clean.  As an added precaution, install plastic caps over the nipples.  Color-code these to match the grease guns.  Plastic caps protect the grease nipple ports and prevent ingress of dirt into the bearings during greasing operations.

Add makeup grease to each bearing cavity with its vent drain plug removed to permit excess grease to vent.  During greasing operations, turn the shaft by hand to ensure even distribution of grease within the cavity.  When the excess grease stops venting, replace the drain plug and wipe the area clean with a lint-free rag.

The lower half of a bearing should be one-third to one-half full when the bearing cavity is correctly greased.

Check motor heaters (if fitted) on a monthly schedule to ensure the heaters are energized and no condensation exists on the windings.  Perform insulation tests at least every six months.

Store motors in a controlled environment.  Keep them off concrete floors to avoid dust collecting in the vents and windings.  Avoid areas of dampness and direct exposure to fans or vents.

Bearings
Always consider bearings precision products and, as such, store them in a clean, temperature-controlled environment.

Users often stock bearings in fairly large quantities.  However, even though the manufacturer takes precautions to deliver quality products that are properly packaged to withstand long periods of time, damage often occurs in the storeroom.  New bearings can be damaged if they get too hot, are stored in damp or extremely dirty locations, if packing boxes are opened and then improperly resealed, or someone drops them.  Once these protective properties are lost, the bearing can rust from having lost its protection against dampness.

New bearings are shipped in plastic, sealed bags or wrapped in moisture-resistant paper. Do not use newspaper or ordinary untreated paper.  These products have a blotting effect and will soak up oil or grease; they also have an affinity for moisture and should never be used to protect new or used bearings in long-term storage.

The following precautions must be observed to prevent bearings from getting dirty and rusty:

Never store bearings next to steam lines, a furnace or in unusually warm areas within the storeroom.

Never store bearings where direct sunlight hits them. This will melt factory-protective coatings.

Never let bearing boxes or wrappings become excessively dirty or wet.

Never handle bearings with bare hands if boxes or wrappings are opened and improperly resealed.  The natural pH balance 
of the human body is very acidic and can cause corrosion 
in bearings.

Never use untreated paper to wrap bearings that will be returned to stock.

Never return bearings to stock that have not been properly lubricated with grease.  Grease should be worked in between the balls or rollers to coat every surface, including the inside and outside of the races to prevent rust formation on non-coated surfaces of the metal.

Never use compressed air to blow-dry bearings after cleaning.  This is a dangerous practice that can cause the rolling elements to spin at high speeds.  This can shatter the brittle outer race and potentially maim or kill someone.

Never use cotton waste or dirty clothes to wipe or handle bearings.  Lint and other foreign matter can cause serious damage.

Never polish out nicks and abrasions with emery cloths.

Never bump or drop bearings, even on soft wooden surfaces, as this will jolt the rolling elements against the cages, causing minute indentations.  This is usually referred to as false brinnelling.

All bearings should be stored flat on the shelves and clearly labeled with their respective identifiers such as:
Job identifier (pump, motor, fan, etc.)
Bearing manufacturer (SKF, Fafnir, Timken, etc.)
Bearing type (SKF series SDAF 230 KA spherical roller bearing pillow blocks, etc.)
Number and type of rolling elements (ball, roller, needle, etc.)

The bearings should be grouped together by manufacturer, type and size in isolated cubicles with the above information clearly posted in front of the cubicle or shelf.

Place Babbitt-lined cylindrical sleeve bearings flat on wooden bases.  Ensure the protection covers are in place over the openings to protect the Babbitt faces and edges from damage.

Establish a minimum/maximum set of numbers and post them to inform people of stock levels so those levels will be maintained.  This should take into account what the manufacturers lead times are for part deliveries.

Pumps
Receiving inspection of new pumps is critically important to the overall health of the machine.  When new pump units (complete with motor and/or gearbox) arrive, carry out an immediate onsite inspection.  Often, a pump unit may have three different manufacturers equipment on a skid (bed plate), a motor, and a gearbox and pump that a fourth member then assembles.  Each of the three principle suppliers may have different ideas component installation and then, in many cases, the fourth member installs the equipment on the skid to their standards.  Their standard practices may not be in compliance with the original manufacturers standards.  This scenario may cause problems for the receiving client when it comes to warranty repairs.

Sometimes, the main parties won't honor any warranty agreements because they did not sell their equipment direct to the user.  The assembler is then responsible but may not have the skills or carry appropriate spares to resolve problems.  The assembler may even have their own parts identifiers, which may be totally different from those of the original equipment manufacturer.  Therefore, the user should initiate a receipt inspection program for all equipment by looking at the following key points:

1.) Ensure the bed plate is level and not twisted.

3.) Remove the protective covers from the suction and discharge nozzles, and check single-stage pumps for signs of internal damage or contaminants.  Replace and secure the protective covers after competion of the inspection.  Note: Heavy-duty and multi-stage pumps require a more in-depth inspection program (removal of casing covers, etc.), but use the same inspection techniques described in this section.

4.) Check the shafts for total indicated runout (TIR) to ensure shafts are straight. TIR should not exceed +/- 0.002 inches (verify the TIR specification from the manufacturer).

5.) Examine the shafts for surface damage that may indicate the unit was improperly slung when handled in transport.

6.) Check the rotation of the shaft by hand or a strap wrench.  Never use a pipe wrench to turn the shaft as this will damage the shaft surface and probably negate the manufacturers warranty.

7.) Because of transportation hazard laws, there is no oil in the equipments bearing wells.  The bearings are lightly oiled or greased to prevent damage from dirt and any slight movements experienced in transit.  Therefore, fill the oil wells to the appropriate working level with the recommended grade of oil.  At this point, rotate the shafts three or four turns to ensure the lubricant gets to the working surfaces of the bearings.

8.) Inspect the gland/mechanical seal area to ensure there are no problems.  Standard packing glands should have the gland follower inserted into the stuffing box to a depth of one-third the thickness of a packing ring.  Note: It is often a good practice to remove the pump manufacturers packing from the glands (and valves) and repack the gland with packing proved to be satisfactory in service for that pump and the system it will be used in.  Depending on the reputation of the manufacturer, it has been found that the cheapest grade of compatible packing has been installed and will not perform very well for any appreciable period of time.

9.) Keep vertical pumps stored in the upright position. If stored in the horizontal position, the shaft may bend during lifting operations.  As the lifting tackle is usually placed on the motor, the weight of the pump acts on its own swivel point, namely the casing of the pump where it is resting on the floor, and tends to bow the center of the pump during the lifting process.  The shaft that is the weakest component will also bend and may not return to its original straightness.  Note: Always check the shaft TIR (plus or minus 0.002 inches) after moving a vertical pump into the upright position, especially on pumps more than 4 feet in length.

10.) Include each new piece of rotating equipment in the storeroom maintenance schedule.

In conclusion, avoid substituting spare parts, as they are often the unwitting source of major problems.  In most troubleshooting cases, a substituted part is overlooked because it has been newly installed and, being new, is viewed as perfect.  For example, if a cast-iron motor is being replaced, it's often replaced with a lighter-weight motor because of the materials used in its construction.  This factor may be the cause of resonance, which can be destructive.  The natural frequency of the unit is now changed due to the lighter weight and may cause a machine to destruct because its natural frequency is within plus or minus 500 cycles per minute.  Ball and roller bearings are also a major source of resonance when the substitute bearing meets the physical dimensions but has a different number of rolling elements, which can put it outside the design specifications for vibration tolerances.

Never let the purchasing department decide which parts are to be bought for replacement when their purchasing power is limited to the lowest of three bids.  Maintain your equipment to the specifications that were calculated for the machine in question.  If it's not, the substituted parts will eventually destroy the machine with resonance.

John Robertson is the maintenance reliability specialist for Strategic Work Systems, a consulting firm with offices in Greenville, S.C., and Mill Spring, N.C.  For more information, call , e-mail or visit www.swspitcrew.com.

MRO Today.  Copyright, 2000.

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