Fire Pump with Long Exhaust Run

[hgordon]

Hi all,

We are working on a hotel job and need to install 2x diesel driven pumps for sprinkler and hydrant. The pump room is becoming enclosed by the new hotel extension, which makes things difficult for the exhaust route for the diesel engines. There is one micky mouse way to get it outside with many elbows and a seismic flexi required between the original building and new building. But I am looking at the option of going straight out of the pump room and up the small gap between the original building and new building (which will be enclosed at the front and top) so if the exhaust went this way it would not be accessible again. This point alone could make it a big no no.
But this route requires minimum elbows and with stainless steel it would not corrode and should have a long life. It would need to rise 10 floors up which is about 30m elevation. However the backpressure is still OK compared to what the manufacturer requires.
I am wondering if it is a workable idea - will I need thermal flexible connections on the vertical for thermal movement between every pipe hanger?
I think I would need a water trap and valve at the bottom to drain any water.

Thanks,

 

[LittleInch]

Sounds more like a piping question to me.

I would hang this from the top support and just have guides along the way so long as the pipe can stand the 30m static weight then install a single flexible / bellows at the bottom.

Maybe oversize it first time around so that if it corrodes you can drop a liner down it from the top later on.

The devil is in the detail here and we have no drawings or sketches so rather difficult to add anything....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TugboatEng]

Expansion joints need to be used between every pair of pipe supports that is axially rigid.

For your long vertical run you only need one expansion joint at the bottom. You will use a single axially rigid support at the top of the pipe and the rest will hang. If the pipe is too heavy to be supported by a single axially rigid support then an expansion joint will be required above each axially rigid support.

What are your plans for thermal management? A diesel engine exhaust can easily exceeded 1000°F. While more of a problem with generators, what if you have a stack fire due to wet stacking?

 

[Lou Scannon]

If you go between the two buildings, I would design it to be serviceable somehow. E.g. access panels at each support and joint, and a way to extract the entire pipe or pieces thereof vertically - I assume it goes vertically to the roof so this would be doable. If the pipe is in several lengths that must be removed individually, you would want to think of a way to grab on to each individual piece from the roof, with a cable.
To prove the design is serviceable, build it by installing the pipes through the roof and making the connections through the access panels.
Don't forget about the thermal load. Double wall pipe? Insulation? Refractory lining? Forced air cooling?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[TugboatEng]

I also don't think I would bother with stainless steel on an exhaust, either. I have never seen deterioration of sch40 steel pipe on tugboats within the engine room. Some of our vessels are upwards of 50 years old and have close to 100,000 hours of run time on the engines.

 

[hgordon]

thanks, it makes good sense to hang it from the top with guides.

 

[EdStainless]

And with carbon steel there will be less thermal expansion.
I would look to see if the bottom portion could be sch40 and the the upper sch10 to reduce the hung weight.
The worst corrosion is likely to either be the upper portion where it cool enough to have condensation, or the very bottom where that acid condensation runs down and pools. Make sure that it can drain out the bottom.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[gruntguru]

What about the exterior of the pipe and exposure to the elements?

je suis charlie

 

[TugboatEng]

The pipe should be well insulated. This will prevent condensation on the inside of the pipe and the jacket on the insulation should protect the outside.

 

[hgordon]

Carbon steel exhuast pipe is just black steel pipe with no corrosion coating or other inhibitors?

Thanks,

 

[TugboatEng]

No coatings or inhibitors, the insulation protects the outside of the pipe. Ideally the engine gets run under load regularly which keeps the moisture on the inside of the pipe under control as well.

 

[EdStainless]

Just make sure that during the monthly tests it runs long enough to reach full operating temp in the stack.
The OD will be insulated and clad, and the flashing at the top needs to be maintained to assure no water gets under the insulation.
Yep, plain carbon pipe, make sure that no idiot tries to use use galvanized.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[MikeHalloran]

In exhaust pipe sizes, sch40 and even sch10 are very heavy. Sch5 may be available.

Resist the temptation to run both engines' exhausts through one stack. ... ever.
Hot condensate from the running engine will destroy the idle engine's valves, cylinders and rings.
... even with check valves.
... even with soft seat ball isolation valves.
... even on short infrequent duty cycles.
Irrecoverable damage happens in mere minutes.


Mike Halloran
Corinth, NY, USA

 

[Compositepro]

It might be a good idea to have an exhaust blower on the roof and draw excess air through the pipe to cool it and prevent condensation. It will also keep the pipe at negative pressure so the danger posed by leaks would be reduced. There would have to be suitable safety interlocks.
The chimney effect could make a blower unnecessary. Gas-fired water heaters use an air gap and chimney.

 

[hgordon]

Thanks for feedback, we are looking at the vertical and another horizontal run option. I specified sch10 stainless or sch40 carbon steel. Stainless thinwalled tube may also be Ok? Have noted to insulate the pipe in the pump room but not when it exits. The specs will he confirmed by the construction company and consultants. Have allowed for thermal expansion.