Reliability of oil mist lubrication 1

[ponderer]

We encounter a dangerous fire in our refinery recently.

The direct cause is the failure of the pump mechanical seal which cause the crude oil to leak.

After the fire, when we check the bearing, we find that pump bearing(ball type) also is damaged.

The bearing balls are no loner spherical and some balls disappear.

We use oil mist lubrication for all the rotating machine in our refinery.

What could be the root cause of the fire?

Oil mist fail -> Bearing fail -> Mechanical Seal fail ?

 

[EnglishMuffin]

Are you asking "is my proposed failure sequence a possible one" ? If so - answer is apparently yes.
If you are asking what the actual cause was, its obviously impossible to say without an on site investigation, which will no doubt occur and probably involve insurance investigators, legal experts etc.
If you suspect the oil mist system - there are many possible things that can go wrong, as simple as such systems are, such as :

1. Tank ran dry
2. Loss of air pressure
3. Clogged nozzle(s)
4. Pipe break
5. Poorly designed sytem leading to puddling

etc etc

You haven't indicated whether you know why the oil ignited.
I won't make any other posts on this topic.

 

[Hippo41]

If the oil mist failed, the bearing would heat up enough to ignitet he remaining lubricant and start the fire. It happens more often than you think!

Lester Milton
NBC Group Ltd, Telford, Shropshire, UK

 

[EnglishMuffin]

Hippo41
I know I said I wouldn't be replying to this post again - but just this once - I've seen an awful lot of marginally lubricated bearings that have got red hot and burnt up, (probably hundreds) mostly in the machine tool field - mist lube and oil air - and never once have I seen that lead to a fire - there just wasn't enough oil around for that. But I humbly bow to you superior experience!

 

[Texaco]

There are in excess of 20,000 pumps in USA refineries that are lubricated with pure oil mist (this does not count pumps in other businesses or in other countries). There is no know case in which oil mist has caused a fire.

 

[electricpete]

What is the principle by which fire is avoided in presence of oxygen, heat, and oil mist?

 

[Texaco]

Oil mist is one part oil and 200,000 parts air. That is far below the lean limits of flammability. Concentrations of 1::250 is required to support combustion.

 

[ponderer]

The fire is caused by the hot crude oil (140 C) leaking from the damaged mechanical seal, not the oil mist itself.

What I am saying is that poor oil mist distribution may cause failure of pump bearing which then induce a seal failure, and let crude oil leak to the air.

It is surely very easy to make a big fire when hot crude oil contact with air.

 

[electricpete]

Texaco - thx, that makes sense now.

ponderer- is there any other equipment fed by same oil mist system? (if so then one would think the other machines would have been affected by system failure as well).

 

[ponderer]

All the process pumps in this refinery are serviced by the centralized oil mist system.

 

[Texaco]

No matter what the lubrication mode, bearings will eventually fail from fatigue. Having said that, there is one refinery in the NW that uses oil mist and claims a MTBR of 10-11 years. I don't think that this recored is possible without oil mist lubrication.