The component is a two-stage centrifugal drip pump driven by a 3000 HP 4 pole motor. The process fluid is 370 degF water at 170 psia. The OB pump mechanical seal has developed a 2 gpm leak. The pump location is in a pit with limited access and escape. We are collecting additional oil samples from a tap that is real close to the leaking seal, as well as routine vibration surveys. Escape from that area, should it be necessary, would have to pass an area radial from the leaking seal.

So...to my point...is this dangerous? Our engineering staff has evaluated it as OK...but with little detail of explanation. I'm looking for 1st or 2nd hand knowledge of what such a seal failure would look like...how dangerous could it be to somebody performing a vibe survey at the pump? I suspect that the leakage would increase as a result of tripping the pump or otherwise taking it out of service due to additional delta-P across the seal? Comments?

Thanks in advance,
George

George, you state that the "process fluid is 370 degF water at 170 psia". This of course means it flashes to steam upon exiting to atmospheric pressure. I'm no safety engineer, but I would be concerned that someone would be present in the immediate area when the seal could perhaps totally blow out. Depending on the proximity of the person to the seal area, serious burns could be the result.

John from PA

About the only thing I know for sure about mechanical seals is that I don't know much. I'm pretty sure there is one style where the seal flow is fed from pump discharge through an orifice. The orifice would limit leakage in event of a complete seal failure and the max flow can be computed knowing the orifice size and the dp. But I am pretty sure there are a wide variety of seals and failure modes.

I would recommend to keep asking the question until you are satisfied that it is safe.

It is NOT ok. Burns are painful, slow to heal and can be disfiguring. It's not worth it chancing getting someone burned or maybe even worse. If your engineering staff still says it's ok, hand THEM the data collector and oil sample bottle and tell them to go in the pit. What does your safety department say about this? They should have the final and legal say so.

"in pit" is this an enclosed space? Limited access what rescue plans are in place in case of an accident?

Is this your own site or a customer, has a risk assessment and method statement been carried out.
what are your/customer control measures?

Any doubt fit sensors and hard wire for safety

Have you checked OSHA regulations on Confined Space? California is even tougher than many Federal Regulations, so check to see if there are any State Regs preempting the Federal Regs.

It doesn’t have to be very deep to be classified as confined space. There’s also some definition around one escape route and ease of escape. Check it out for your own good. Company Safety Departments don’t truly have final legal say so if they are wrong. If company decisions don’t match regulations, CHALLENGE AUTHORITY!

I believe that if it does meet the definition of Confined Space, there must be a published Rescue Plan in place at the Company Level.

This message has been edited. Last edited by: Wally,

quote:

process fluid is 370 degF water at 170 psia. The OB pump mechanical seal has developed a 2 gpm leak

So I assume the leakage rate has been measured? That implies the leakage is in a fluid state, right? The leakage is not flashing to steam, at present....correct?

This suggests the seal does not directly "see" process fluid. Your engineers may be correct. It all depends on how the seal is arranged. I suggest that you research this. Why not just call the pump manufacturer. I'm sure they have seen seals "fail" on this type pump before.

If the pump has been provided with disaster bushing to prevent flow from leaking seal in the form of jet, then it is safe to a reasonable extent.The bushing will divert the flow to a leakage collection area. But , of course, if flashing is there, it may cause burn. Kindly have a look at API 682 for mechanical seals.

Forgive my ignorance. I can't say I've ever heard of one before, and a quick Google search brought up nothing useful. What is a drip pump?
Is the 170psia suction pressure, or seal chamber pressure?

I'm with MCDM here guys - If it looks like, sounds like and smell like something that can cause you an injury then it probably is classed as dangerous.
Sounds to me it is classed as a confined space(not a normal place of work). If this is the case then you would need too follow your country's rules on entering and working within a confined space. If you identifiy a potential risk such as this the eliminate the problem or engineer it out. A simple gaurd over the seal area or remote monitoring may be required.
We have several areas on my plant in which access is limited/dangerous and these items will not be surveyed by anybody untill it is deemed safe by our team made up of the people doing the work as well as the supervisors etc.

YOU ONLY HAVE THE ONE BODY LOOK AFTER IT!

Hooch

George, I've noticed that the original post was two months ago. Has the seal failed yet? There are a couple of points, the first is that some mechanical seals have throttle bushes in their internals which limits the amount of product which can pass through the seal in the case of a total failure, however, there is still a fair amount of product which can escape, in the case of your pump, as has been pointed out, it would become steam and therefore very dangerous to personnel. The second point is, don't believe word of mouth safety procedures. Ask to see the procedure then you can judge for yourself if the conclusions are sensible. I have been asked to do work in dodgy circumstances, and when I asked for the safety procedure I only got mumbling and red faces.
Be careful and good luck
Joe Mc Cormack