Used air compressor oil- how much white metal is too much?

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hugerich
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Used air compressor oil- how much white metal is too much?

Postby hugerich » Wed Apr 15, 2015 12:30 am

Hello, got a question regarding air compressors if anyone has some insight.

So today I carried out a service on a 2 cylinder single acting main air compressor, 26 bar discharge pressure. Everything was fine apart from, in my opinion, the oil. I drained it off, opened the crankcase doors for an inspection, and found nothing remarkable. The bottom of the sump looked clean to me, shining a torch in there I didn't see anything that indicated excessive wear. Nothing that looked out of place on the crankshaft either, and from what I could see externally there was no evidence of anything untoward happening on the main bearings.

So, I cleaned up the sump with some rags (quite clean) and took off the oil filter, a disposable type. I replaced it with a new one, then emptied the old one into a container to have a look at the oil. In the oil I could see bright metal, which I can only assume is white metal from the main bearings. We aren't talking huge chunks here, think flat grains of fine salt, no thickness to any of the bits. The concentration wasn't excessive in my opinion, not when considering the surface area of the main bearing shells compared to the amount of metal I saw. Nevertheless, I brought it to the attention of the boss, but didn't really get a helpful answer apart from being told to pour it away and finish boxing the job up, I was told it was paint fragments (which it most definitely was not).

So what do you think to this? This is the first air compressor I have worked on that has had a disposable filter element after the lube oil pump discharge so I have a suspicion that the main reason I have noticed this more is because of the superior filtering. Normally I have just come across a relatively course strainer and a magnetic plug on the sump, also this air compressor has a lot more capacity than most of the ones I have worked on. Is this something a good engineer should take as a sign of imminent bearing failure, or is this something to be expected and can wait until the next scheduled bearing replacement?

Thanks for any help you have.

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Merlyn
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Re: Used air compressor oil- how much white metal is too much?

Postby Merlyn » Wed Apr 15, 2015 5:44 am

Sounds to me that you have a case of " let it develop " here, owners used to say this to me when they were not sure or didn't want to hear it. The obvious place for the White metal is, of course where it was meant to be, ie on the steel backed shell bearings and not collected in the oil filter. I presume your compressor was not subject to a recent overhaul whereby the shells were not replaced recently. Oil pressure drop ( if you have a gauge fitted ) will tell you any damage present firstly besides audible sounds but if it was my problem and you have a quick change filter ie spin on/off type for my money I would get a few more hours on the clock and spin the filter off, up end it and should any more white metal be present then perhaps you have indeed a problem with the crank albeit in early stages of.
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Re: Used air compressor oil- how much white metal is too much?

Postby rodrigger » Wed Apr 15, 2015 6:12 pm

lube oil analysis will tell you if its iron....check the previous oil report.....does your vessel have one in place? any kind of metal in air compressor is a NO, problem should be rectified immediately.

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JollyJack
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Re: Used air compressor oil- how much white metal is too much?

Postby JollyJack » Wed Apr 15, 2015 7:40 pm

Did you take Plastiage clearances in the bearings? If so, compare with the last ones done. (if they ever were.)
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Re: Used air compressor oil- how much white metal is too much?

Postby Revolver » Wed Apr 15, 2015 10:18 pm

Manuals I have read from air compressors have said "excessive wear" regarding bearing checks and changes - but exactly what is excessive.
And trouble shooting the bearings seems to generally come from compressor noise according to the same manuals.

Boss man says box it up, like Merlyn said the 'ol "let it develop" case...

Be cautious, keep good eye on both stage pressures, noises and L.O pressure.
See if there are any trends from daily log readings that could be predictive, and maybe an intermediate filter change between recommended hours to check the state again.

Compressor brand?
Pictures?

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Big Pete
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Re: Used air compressor oil- how much white metal is too much?

Postby Big Pete » Wed Apr 15, 2015 11:28 pm

The original question appears to have been well covered. There is a possibility that the compressor had bearing problems before, and it is old debris that wasn't cleaned out of the system when the bearings were replaced.
It is good practice to change the oil and change/ clean the filters after a short running in period after a major overhaul, particularly if there were a lot of wear particles around.
It is worth looking in the History of the machine to see if there was a bearing failure in the past and if the filter was changed afterwards.
Unfortunately, I find that people are much more willing to lie when writing something in a computer than when writing it by hand, so I don't altogether trust computer based records for that reason.
It is always better to ask a stupid question than to do a stupid thing.

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JK
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Re: Used air compressor oil- how much white metal is too much?

Postby JK » Thu Apr 16, 2015 12:27 am

Really BP? That is a very interesting observation regarding record keeping in computer programs. Though on reflection, it is who the end user of the records is perceived to be and I can see that comments would be carefully phrased in the computer.

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Merlyn
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Re: Used air compressor oil- how much white metal is too much?

Postby Merlyn » Thu Apr 16, 2015 3:03 am

Had a wag who would whip his brass/ white metal magnet out on this job to suss it out. Non ferrous you say? Exactly. Anything that didn't stick to his magnet was to be put away till the ship docked and off to the scrapyard for beer money. Any iron filings on your job would be picked up instantly and stand to attention on his bar magnet. The real use was retrieving valve collets dropped without a strip down when shakey hands were at work. Earnt a lot of money that brass bar magnet.
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Re: Used air compressor oil- how much white metal is too much?

Postby D Winsor » Thu Apr 16, 2015 3:52 am

I agree with what BP has said about Computer records not being all that reliable sometimes. I have forgotten how many times when I've checked the maintenance records on a piece of failed equipment and found in the comments box "All OK", very little or nothing at all written on what was done or found or outright flogged with remarks copied and pasted from a previous inspection just to get rid of flagged overdue computer generated work orders because that is what the Chief or Office doesn't want to see on the Monthly Overdue Maintenance Report.
With respect to the compressor besides the bearings I would also check the pistons and cylinder liners as well. A piston and or liner damaged by overheating, broken or damaged oil rings, low or loss of lubrication, condensate or cooling water, debris sucked into the compressor or improper assembly during overhaul, could cause white metal from the connecting rod small end bearing, or aluminum from the piston,to be deposited in the crankcase and picked up by the filter.
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Big Pete
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Re: Used air compressor oil- how much white metal is too much?

Postby Big Pete » Thu Apr 16, 2015 7:23 am

As D. Winsor says, I have lost count of the ships I have gone on where every report in the computer says "Job done according to work instruction" doesn't matter if it is a full overhaul of a Gen set, or a weekly inspection of a battery, same comment copied and pasted for years.
On one ship I was on, the Boa Fortune, she had twin azipuls for propulsion and I noticed that a job was coming up to check the operation of the overload alarm on the steering motors, for some unknown reason, it came up for the ETO to do one and the Second Engineer to do the other. They both signed them off, "job done according to work instruction" as it had been every month for 5 years. I then pointed out that this job description was for the Thermal overload on the electric motor of a conventional Hydraulic steering gear, ( the only Thermal overload on a ship that triggers an alarm instead of stopping the Motor) and that our steering was through variable speed drive electric motors, directly geared onto the Azipul, and fitted with all sorts of Bells and whistles, internally, But absolutely no Thermal overloads, (if there had been there should have been 4, not 2).
On another occasion the Second Engineer was reading the jobs due in the planned maintenance and went out of the control room for two minutes and signed off half a dozen pumps as having been inspected, I asked him which pumps they were (they were not individually name in the PM system, you had to look up the asset number in the asset tree to find out which system the pumps were on) and he told me it didn't matter because we had all Polish Engineers on board so they must report everything as being in good condition or the Office would think they were bad Engineers.
I find many of the Engineers I sail with now have no respect for the truth as an abstract concept, they say whatever will keep them out of trouble, without any hesitation or conscience.
I think there is a big Psychological difference between telling hand written lies and telling lies on a computer, the keyboard makes it impersonal.
It is always better to ask a stupid question than to do a stupid thing.

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JK
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Re: Used air compressor oil- how much white metal is too much?

Postby JK » Thu Apr 16, 2015 3:34 pm

Interesting comments. We are mixed on how reporting is done, the older ships are mostly still paper. I
had run into the not reporting the bad stuff because of the " it reflects on us" mentality but didn't realize it was that prevalent.
I know that once we require certain of our reports to be uploaded to the office It is a tough time convincing the submitter that it does not reflect on him, that a 25 or 30 year ship has issues and I know when I am being snowed.
Thanks for answering, I like the handwritten\computer comment especially as it makes sense.

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Big Pete
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Re: Used air compressor oil- how much white metal is too much?

Postby Big Pete » Thu Apr 16, 2015 11:20 pm

I am old style, I am over 62 years old and started at as a Cadet nearly 44 years ago!
There was a time when an Englishman's word was his bond and there were things that "no Englishman would do.."
a relic of the British Empire when children were brought up to " fear God, honour the King and spit in the Devil's eye", we have lost that Moral certainty and courage that goes with it, everything is shades of grey now. Even if the Manager of the ship is an incompetent fool or ignorant, nobody on board will stand up to them and tell them so any more. You would be sacked straight away now. (There was time if you disagreed with your Boss that he would respect your opinion and accept your right to give it, but that appears to have been lost, most of management now see themselves as "Tin Gods", and constructive criticism has become a sacking offence.
The Asians are brought up under the Confucian system of ethics and the appearance of order and cohesion and agreement is fundamentally more important to them than the truth or ability.
The Eastern Europeans survived 50 years or more of Russian Military Occupation, and for the older ones maintaining "Solidarity" against the Foreign enemy is all important to their culture. They will always protect each other against the "Outsiders", regardless of truth, ability, safety or anything else.
It is always better to ask a stupid question than to do a stupid thing.

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Re: Used air compressor oil- how much white metal is too much?

Postby hugerich » Sat Apr 18, 2015 1:18 am

Wow, a lot of responses to this, thank you all. I appreciate all the comments so I I'll try and respond to all of them.

No recent major overhauls on this compressor. I believe it was last done over 3000 hours ago so there should have been at least 2 oil changes before I got to it since then.

As for noise levels, nothing unusual. I even went one step futher, we have a very expensive piece of kit on here that can read vibrations and transmit to a cimputer, so I did this and all readings were in the green. This is for multiple points on the compressor and motor, all fine.

All other parameters are in range, even topping up time for the receivers is the same as it has always been (apparently).

We do not carry out LO analysis on the compressor oil, I guess because someone high up decided that it wasn't cost effective. I expect they would be much more likely to just tell us to replace the bearing, which I expect is why certain people would rather cover up the problem.

In all honesty, I have no idea what a Plastiage clearance is. Unless it is the same thing I've been doing on the main engine bearing clearances but having not known the proper term for it.

Compressor brand is Sperre, unfortunately no pictures.

I completely agree with the observation that people have a tendancy to lie on computer forms. I don't trust a single thing I read because it is more than likely a fabrication. I know because senior engineers are forever trying to get me to just ok everything in the planned maintenance system even though I haven't carried out any work, things such as carry out an investigation or clean something. So far I have stood firm and refused, which has gained me no friends I can tell you. However, since it is known I won't forge anything they now just get a more willing engineer to fill out the forms I refuse to do and tell a pack of lies. I wish I could say this is an isolated incident but even though I am very green (7 vessels from cadet till now) and 3 different companies, I have seen it on every vessel. Some worse than others, but it is always there. Be it measurements or readings, or full job tasks, there is always some forgery going on to avoid having to carry out a bigger job.

Even handover notes, enough times now I have been given quite an impressive set of notes only to do some digging and find that they are years old and have just had the names changed, with no recent information on plant operation or maintenance inside. As I always start from scratch with mine I am just waiting for the day that someone trys to give me back my own notes! Which is when I will tell them to sit down and write me a new set.

Anyway, thanks again everyone. I will continue to monitor the situation and see what happens.

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Merlyn
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Re: Used air compressor oil- how much white metal is too much?

Postby Merlyn » Sat Apr 18, 2015 2:44 am

Plastiage is what used to be known as taking leads. Off with the main top cap, ( or big end ) and lay lead wire across the journal complete width. These rolls were not unlike a roll of fuse wire, and were in different diameters. Box it up, torque it up and let it all go. Out with your micrometer ( still got mine from 1960 Brown and Sharpe 1-2 inch imperial,) no mm (Mickey Mouse ) then and Mike it up. You could do the same with a vernier. Clearances were specified by the engine manufacturer and shell bearings replaced/ crank grind carried out as necessary. Back in the old steam days when I started out in 1960 taking leads on a big old up and downers it was a long job with brass shims sometimes half an inch thick downwards fitted. Mains and big ends were flogged off, caps chain blocked off, several leads laid many times before getting to the final scrape in using engineers blue to perfect the job. Any blow holes exposed during scrape ins of the 2 inch plus thick whitemetal of the cap spelt trouble, unless they could be half round chiselled into a nearby oil-way the job was scrap. This would mean a complete strip down, back to workshops and into the plumbers shop, melt out all the bearing caps both top and bottom, black casting sand with a wooden centre mandrel made up and the whole lot recast. Up on a large faceplate on the lathe and bore it out to size. If the casting process was not stirred/ vibrated correctly and any further blow holes exposed back to square one. Often a long and tedious job. Don't forget all the shims had to be present when boring so as to facilitate future scraping etc. Hold your breath jobby alright here on the final cut or what . This was just one of the things you were taught back then along with lots of other work.Back to the ship, reassemble, flog it up, further leads taken, maybe thin shims taken out, engineers blue out and appliedand in with the turning gear, off with the caps and so on and so on. Long job indeed. Used to have to achieve so many high spots from the crank on the White metal surface, can't remember how many, apprentices would get fed up and falsify the blue markings but the charge hand would have to check it over before the final box up, he had seen it and done it all before and would not be fooled. So there it is, sorry for the long drawn out explanations but you have to say I did own up to " taking leads ) and not perhaps attempt to hive years off my age by saying The perhaps more modern " plastic approach " ?
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JK
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Re: Used air compressor oil- how much white metal is too much?

Postby JK » Sat Apr 18, 2015 5:05 am

A couple of points, I have run into poor lube oil management which lead to contaminates being added with the fresh oil, this might be what you are seeing.

Secondly, A lot of times it is cheaper to replace air compressors then to rebuild them. I have replaced many Hamworthies specifically because of the cost of overhauling them as opposed to replacing at 5 years surveys.
Saying that, to not manage them properly in operation is negligent


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