storing motors

Two references regarding PM requirements for motors in Storage:
1 - EASA Principles of Large AC motor, Section 23 - Motor Storage
2 - EPRI Report 1009698 - Shipping and Storage of Electric Motors

An outline of recommendations from the EASA document:
2 - Storage Preparation:
2A - Store indoors in a clan dry area when possilbe
2C - Store away from vibration. Lock shaft if vibration is present.
2D - Keep the critters out.
2E - Inspect and reapply rust preventative coating on all external machined surfaces including shaft extensions.
2F1 - Fill grease cavities completely full at beginning of storage (will repack before putting in service)
2F2 - Oil bearings - drain while moving, refill to max after moved. Oil should include roust and corrosion inhibitors.
2G - Energize space heaters if present.

3 - Period Maintenance
3A - Oil should be inspected monthly and replaced if contaminated or every 12 months.
3B - Grease lubd bearings should be inspected monthly for moisture/oxidation by purging a small quantity of grease through the drain. If any contamination is present, the grease must be completely removed and replaced.
3C - Rotate shafts once a month to ensure the lub film on the bearing surfaces.
3D - Insulation resistance and P.I. or D.A.

4. Installation preparations:
4A - Thoroughly inspect and clean.
4B - If had been subjected to vibration, disassemble and inspect bearings for damage.
4C - Change oil or grease. After changing grease, run with drain plug removed.
4D - Check insulation resistance and PI or D.A.

Their recommendations vary by length of time in storage.
Out of service less than one month - 2G
Out of service 1 - 6 months - 2A, 2B, 2C, 2D, 2E, 2F, 2G, 3A, 3B, 3C (NO 3d)
Out of service > 6 months - all recommendations.

Note this is an aggressive schedule and applies to large motors. For smaller and less critical motors, these may not all be necessary.

Some thoughts about reasons to rotate motors:
1 - Long slender shaft machines need to be rotated to prevent bowing. This is probably more a concern for some pumps than for motors.
2 - Keeps the bearing surfaces well coated with lubricant to prevent corrosion. More an issue for oil-lub'd bearings than for grease-lub'd bearings.
3 - Prevent damage to bearing surfaces from prolonged load in one place. More a concern if there is vibration or for anti-friction bearings.

Also there have been isolated reports of sleeve bearing motors possibly damaged by rotation during storage (I have a confidential report of one such event though the nuclear network - I could tell you more but I'd have to kill ya'). Part of the reason as far as I know... it is well know that most of the damage in sleeve bearing machines occurs while the machine is moving slowly during start before the oil film estalbishes. When rotating by hand you might keep it moving slowly for a long period of time without any oil wedge (oil wedge only occurs at higher speeds). Additionally, one source recommended adding oil on top of shaft through the slinger ring viewer port before starting to rotate since slinger rings might not be effective, but in my opinion that gives bigger chance for contamination. I just mention these items for completeness. I think since rotating shafts is such a widespread recommendation by industry standard groups, that any hazards are minimal.
The shaft rotation interval is set in order to prevent false brinelling. I have been involved in a number of instances where the lack of shaft rotation has ended up in poor bearing reliability or bearing noise. This is of particular concern when there is traffic or machinery vibration in the area.

During my recent class, a 75hp motor was taken from the shelf for MCSA/ESA testing on a dyno. There had been shrink wrap on the motor including the shaft, so we were aware that the shaft had not been turned, and the storage date on the motor identified that it had been on the shelf for over a year. The bearings were just audible and bearing signatures (outer/inner race) showed up in current.

In general, ball bearing machines should be rotated quarterly, at a minimum, and babbit bearing machines semi-annually. One of the better systems that I have seen uses a two color tag with yellow on one side, red on the other. Each month, a storeroom worker will rotate machines and flip the tags so that they know which ones have been rotated.

Part of the reason that babbit bearing machines are supposed to be rotated is to ensure that an oil film remains on the inner race (shaft) of the bearing. The problem occurs when the shaft is not rotated and you have metal-to-metal contact with the shaft and the babbit material. Damage results when the machine is actually started.

Rotating shafts should be done on all stored motors. It relates to the few seconds to turn the shafts versus the time to install then have to remove a motor.

And, large and small motors is a relative term, even in IEEE standards.

Sincerely,
Howard
I agree some people may tend to use the term "large motor" differently.

Reading the EASA large motor maintenance book, the very first standard excerpted is NEMA MG-1 Section 20.1 which defines large motors as follows. From the context it seems clear they are establishing the scope of the book.

Per NEMA MG-1 section 20-1, induction motors above the following hp ratings are considered large:

For 1800-3600 rpm - 500hp
For 1200 rpm - 350hp
For 900 rpm - 250hp
For 720 rpm - 200 hp
For 600 rpm - 150 hp
For 514 rpm - 125 hp
<=450 rpm - all motors at this speed considered large.

That is also the definition embraced by Nailen in his book Managing Motors and in EPRI documents.

I am aware of IEEE standard 56 (Guide for Insulation Maintenance of Large AC rotating machinery 10,000 kva and large). I don't think it was the intent of this standard to redefine "large motor".

Just to clarify which part is EASA's and which part is mine... I gave you the EASA recommendations almost word for word. They make no statement about applicability but the title of the book is large motors. I added the statement (my opinion) that "this is an aggressive schedule and applies to large motors. For smaller and less critical motors, these may not all be necessary"
Doc/Pete,
The EPRI 1009698 also mentions rotation of vertical motors and to jack the shaft off of the thrust collar to prevent damage.
In my opinion, shaft rotation is a good idea and generally more benefit for motors with anti-friction bearings.
There comes a point however due to physical size of some motors that the ability to rotate some of motors is near impossible.
What should be the upper cut off point?
Regards,
James
Guys:

Excellent discussion of one of the most overlooked items in motor reliability. The EASA recommendation is very good and at our facility we agree that shaft rotation and insulation resistance should be performed and documented monthly for trending. In addition due to the high humidity in our area we feel dehumidification (approximate RH 30-35%) is critical. We also feel that for our area the best way to accomplish dehumidification is by heating (approximately 5 C) a storage facility above the ambient temperature and controlling with a humidistat. This system works well to prevent condensation if a motor is called for in summer time.

Max Texas Gulf Coast
Being a mechanical guy, guess I look at large motors differently. I call any motor I can not pick up by hand a LARGE motor!!!!!!!!! We used to rotate the shafts monthly, but that was when the electrical reliability group managed the motor inventory. Now that Sorbanes-Oaxley got into the mess, the motors belong to the stores group and I don't think they even know where the storage building is. Fortunately, it is a long ways from the machine buildings and vibration is low. Time will tell if we are still doing a good job of avoiding false brinelling.

How about them Gators??? (got to be one by default, 3 kids and >$100,000 invested)

Gary B
You used to rotate the shafts but now you are not doing that because the motors are under another organizational unit jurisdiction?

I do not understand, what difference makes who supervise the storage area vs the need that certain pieces of property has for proper maintenance?

In my plant most air handling units are under the Utilities department and another small group are under Manufacturing department ownership; we do the maintenance for all.
It is now locked with access only with a stores person. We are trying to work something out. The stores personnel were given all the tasks of managing a motor inventory, but they are not maintenance people. We hope to get the management of the motors back in our hands soon.

Gary B.
A maintenance order from the CMMS should be enough authorization for any "equipment owner" to the "right" of Maintenance to do its job. The equipment owner manage his/her equipment; Maintenance manage the maintenance programs for the whole plant equipment, regardless of actual equipment/asset location: stores warehouse, production room, packaging line, machine room, external utilities field area, office building roof, etc.

The stores supervisor (in the same way of all other supervisors "owning" equipment requiring maintenance at the plant) shall coordinate with Maintenance when their area is available for maintenance orders execution. Management of the motors does not have to return to Maintenance for the PMs be done. If Maintenance Technicians can not be left alone with the motors during the order execution then the coordination between the Maintenance Planner (or Maintenance Scheduler) and the stores area shall include that the stores supervisor provide one of his/her employees to escort the techcnician while performing the tasks.
GaryB/Eugene,
I guess it's all about philosophy and ignorance. In my previous company being the plant maintenance engineer I was the owner of parts for all the rotating equipment on the plant and stores. This meant I had to track the status of all critical rotating elements and stationary parts to ensure we had the right parts and adequate quantities required for turnarounds. The stores personnel were responsible providing the environment to preserve the parts.

I can see the situation GaryB describes arising more frequently as more companies outsource the stores/warehousing. Management should differentiate what the roles are, the roles did not change with outsourcing but some managers think they did.

My company now do not have an in-storage maintenance programme for motors but we are acutely aware of the need.
Stores management recognize that they do not have the skill set to perform the inspection/meggering etc of any programme so it will be up to the Pdm group to perform this maintenance.

Regards,
James
quote:

What do they fear? the mechanic pick up one motor, hide it in his pocket and walk away without register the inventory "transaction"?


Yes exactly, extensive research has been done on the subject: inventory
It is the duty of the stores to watch that the companies money is not wasted in inactive parts, this money could be spend somewhere else and generate revenu. (From the accounting Bible..)

Thus the "New Generation Stores People" are guarding their stores better like forth Knox, complete with extensive Stock Value Monitoring by people who cannot distinguish a bearing from a fuse.

In this environment, you cannot enter the store room and just walk-around.

Every transaction is backed by e-mail, and CYA politics is a must to survive. Big Grin
Let's get the fundamental right ie The materials & services dept incl warehouses or stores exists to provide services to Maintenance dept & other depts. (have anyone reversed this relationship?) At the same time, materials will highlight any areas for improvement eg slow-moving stocks, min-max levels to Maintenance who will decide based on proper knowledge of inventory management, at least to the minimum.

However, having said that, there could be danger when Maintenance wants everything to have spares even for eqpt on breakdown strategy. Why? Because the sapre inventory & purchasing process cannot keep up with maintenance requirements. Therefore, making ready a purchase agreement or consignment stocks with suppliers seem to be an option.

The interaction between maintenance & materials is a major area to be managed properly & where excellent comminication is required. Towards this end, one area which appears interesting is to rotate some maintenance people into the materials & services. By doing this, hopefully the maintenance staff in materials will certainly know both the maintenance & materials requirements. And let's some materials staff become materials coordinators under maintenance dept eg for shutdown.

Materials without maintenance experience won't know the storage requirements and Maintenance should have storage procedures written for implementation.

With materials mgmt practices right, even outsourcing this function won't change much.
You guys are talking about storing the motor with its shaft and bearing. I have seen rotating eqpt rotors stored in a nitrogen-filled vessel with a PG to monitor no pressure drop and turn the vessel with the rotor inside upside down every 6 monthly. Is it necessary to store the whole motor in nitrogen environment to prevent corrosion etc? I have not seen any requirement for this nitrogen in above posts.
Hm, not that I have something against MBA's (I actually now some excellent MBA's), but where do you think they are concentrated right now? People who only look at numbers, but do not know what is the story behind those numbers.

There was a post in this forum "good lubrications practices, boost price of shares"
quote:
The materials & services dept incl warehouses or stores exists to provide services to Maintenance dept & other depts



Wrong, the materials etc.. exist to provide service to The Business

In most "plants" Operations is The Business at least that is the way they think Big Grin

If The Business stops, end of business, period

Maintenance just provide service
Stores/Procurement provide services
HRM...
HSE or SHE...
Acounting...
etc...

And everybody trying to protect his own kingdom.

In small places, this will not be that obvious, because one man calls the shots.

If the Stores/Procurement organization does not desire to allow maintenance technicians into the store room to rotate motor shafts and measure insulation resistance periodically, then they must be trained and tasked to do so. The "maintenance" being done in this case is the preservation of the value of the stored asset, and the Stores organization is directly responsible for that by maintaining proper storage environment/conditions and doing what is necessary to ensure the stored spares are usable for the organization. Financially, any spare motor that is not properly maintained becomes worthless to the maintenance organization. My guess is, that once you propose that the stores people perform the maintenance, that maintenance technicians will be allowed in the stock room again with less hassle. 

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