NEAR STEAM BOILER PIPING

Oyad

Hi all ,
Pls I need second opinion regarding near boiler piping of a steam boiler. We are about to install 2 new steam boilers. 2 Old steam boilers were 2’’ diameter coming out from the boiler to a 4’’ common header and to another 5’’ riser to the attic which circle round the attic area then feed down to radiators. Pls see attached pictures for better understanding. New steam boiler by Weil-McLain LGB6 model come with 6’’ diameter outlet which can be reduce to 4’’. Riser and Header are 4’’ minimum recommendation by Weil-McLian but the supply steam doesn’t have minimum diameter size according to their drawing. However, when I called Weil-McLain tech support am not too convince by their answers I was told they did not test their system for that kind of scenario of mine but they still want to see 4’’ going through the building.
So here is my question can I connect my steam supply coming from the boiler 4’’ to a 2’’ tapping that goes into building existing common header which is 4’’ diameter, also that 4’’ diameter header goes into a riser which is 5’’ diameter ( pls see the pictures with label and attached manufacture drawing) in other word I want to run everything in 4’’ exactly what manufacture show in their drawing but at one point I want to reduce to the existing header which only have 2’’ welded FIP on a 4’’ header. Which is the reason am asking the question because it’s a welded header we don’t want to do extra work of cutting and welding if its not necessary.
By the way the old boiler was same btu size as with the new steam boiler apart from the design that is different. Also, the steam boiler supply 32 units residential apartment.

Jamie Hall

Not good. Saturated steam is funny stuff, and you would find that 2" restriction -- thought short -- will really and truly mess things up. The rest of the sizes are probably OK, but you simply can't have that restriction in there.

If it were mine to do, I'd come out of the boiler at 4 inch, use a drop header with a header diameter of 5 inch, tying into the 5 inch express main to the attic.

Sorry about that...

EBEBRATT-Ed

No it won't work. You need to rip everything out back to the 5" riser. Pipe it per Weil McLains drawing, that why they make those drawings. Separate header for each boiler size it per their recommendations. The common header I would make it 6" with the 5" take off to the building

Oyad

Thanks Jamie and Eberatt. we will follow weil-Mclain recommendation. However, here is my educational thought with my experience working in steam plant. Remember Boyle's law, Charles's law and Gay-Lussac' law etc plus going through my steam table, as well steam table pipe size, I even calculate my velocity ratio. basically reducing to 2'' is fine but nothing less than that because it going into a 4'' which is more or less like'' venturi effect''. obviously it might look weird seen that in mechanical room. one main point weil-Mclain is worry about its building up pressure down stream the boiler side which come down to if am running very short run 2'' diameter length that is going into 4''/5'' diameter pipe there wont be enough time for any pressure to build down stream boiler side and at one point it will equalized.Note if I come out on both end of my boiler outlet going into tee I already created a balance steam head but if i come out on one side only then that might create slight problem. Also the old one we took out is exactly same size in Btu with 2'' and it work well, one main thing Weil Mclain did differently with their LBG is that they created bigger size outlet in what I refer to as 6'' drum this give good accumulation of steam before going into 4'' header and then out to building. Again thanks for shipping in.

Steamhead

EBEBRATT-Ed said:

No it won't work. You need to rip everything out back to the 5" riser. Pipe it per Weil McLains drawing, that why they make those drawings. Separate header for each boiler size it per their recommendations. The common header I would make it 6" with the 5" take off to the building

That's what I'd do, too.

pecmsg

Oyad said:

Thanks Jamie and Eberatt. we will follow weil-Mclain recommendation. However, here is my educational thought with my experience working in steam plant. Remember Boyle's law, Charles's law and Gay-Lussac' law etc plus going through my steam table, as well steam table pipe size, I even calculate my velocity ratio. basically reducing to 2'' is fine but nothing less than that because it going into a 4'' which is more or less like'' venturi effect''. obviously it might look weird seen that in mechanical room. one main point weil-Mclain is worry about its building up pressure down stream the boiler side which come down to if am running very short run 2'' diameter length that is going into 4''/5'' diameter pipe there wont be enough time for any pressure to build down stream boiler side and at one point it will equalized.Note if I come out on both end of my boiler outlet going into tee I already created a balance steam head but if i come out on one side only then that might create slight problem. Also the old one we took out is exactly same size in Btu with 2'' and it work well, one main thing Weil Mclain did differently with their LBG is that they created bigger size outlet in what I refer to as 6'' drum this give good accumulation of steam before going into 4'' header and then out to building. Again thanks for shipping in.

That might work if dealing with dry steam but not with Near Boiler Piping!

Jamie Hall

Uh... problem is that saturated steam doesn't behave that way. Yes, you can reduce -- and increase velocity -- but when you expand again it cools and, being saturated, condenses. Whish is not helpful...

EBEBRATT-Ed

@Oyad

Just keep in mind it will cost more to do it over than it will to do it one time

mikeg2015

Jamie Hall said:

Uh... problem is that saturated steam doesn't behave that way. Yes, you can reduce -- and increase velocity -- but when you expand again it cools and, being saturated, condenses. Whish is not helpful...

That’s a very good point. With superheated stem it would be OK. But cast iron atmospheric boiler has minimal superheat.

With saturated steam, it would act like a piston in a refrigeration system and you’ll condense when you have a pressure drop. Actually it would try and pull heat out of the pipe too, but will instead end up phase changing to give up energy.

Once the system fill with pressure and you have backpressure you are OK. But before that, I wonder if there will be issues.

The book will give you good steady state scenarios, but might not cover startup and shutdown.