Does a boiler Blowdown tank have to be ASME rated? 1

[BronYrAur]

I have been asked to replace some boiler blowdown tanks in an old hospital. The existing tanks are unique as far as blowdown tanks go. They are 42" diameter vessels with flanged covers.

Blowdown enters the first tank witch then "spills" into the second tank. Discharge from the second tank is hard-piped into the sewer. Each tank has a vent line that go to a common header. One final thing with these tanks is that the joints where the pipes connect are lead joints!!!

I can't imagine that these tanks are ASME rated, especially with the lead joints. Now, I know that these days, cold water is introduced to temper the blowdown, and I'm sure that the discharges are dumped into an open site drain as opposed to hard-piped to the sewer. Since this is a direct replacement, do I need to be concerned with that?

Back to my original question, do I need ASME? I could easily make these tanks out of 42" pipe and weld all the connections, but it would not be ASME. Since the tanks are vented, is ASME required?

 

[brkmech1234]

If the design pressure is more than 1 bar, they fall into scope of ASME VIII Div1

 

[gr2vessels]

Bron,
Just to complement a bit the answer above;- the blowdown tank can see rapid increase of pressure from steam flashing, faster increase rate than the vent could relieve. There is a typical process calculation to estimate the maximum pressure which can rise in the vessel, thus the design pressure should be that maximum operating pressure. Again, the vent does not guarantee the maintaining of atmospheric pressure in the vessel, unless is calculated/sized per the relevant API 2000. Just remember that designing per ASME BPVC, you can still use your 42" pipe, you don't need to U-stamp it, just make it safe and have it certified with the A1 form. Better safe than sorry.
Cheers,
gr2vessels

 

[GenB]

I think the question would be for the Jurisdiction-local boiler inspector for approval of repair or a new one with or w/o ASME stamping.
note that the cost difference these days is not much difference between Code and non-Code. of course you will want to give the job to an ASME certified Shop and not to the muffler shop down the street...

 

[MJCronin]

Bron,

Throw out that old crap from the 1800s......

Purchase tanks with and ASME stamped for 50 psig @450F...it will not cost much more. You will be ensured of a quality engineered product and a good decision when the regulators come a-callin.....

The tank diameters/shell etc should be sized based on the industry accepted criteria of the NATIONAL Board

These people can answer your questions:

http://www.pennseparator.com/brochures.htm

Please be respectful and finish this thread by telling us of your final decision

 

[davefitz]

As I recall, the older design guidelines for dsigning blowdown tanks was to design the vents to ensure the tank never exceeded 15 psig, maybe to avoid asme jurisdiction.

But I had found a fallacy in that approach as the "designer" of the tank never communicated with the "designer" of the vent piping and the blowdown lines to the tank. So MJ Cronin is right- but one should nonetheless calculate the "casualty" flow to the tank thru all drain /blowdown connections to it and ensure the vent pipe is sized large enough to avoid overpressure of the tank. If no silencer is provided, then the Fanno curves shuld accurately predict the pressure needed for choked steam flow thru the vent pipe, knowing the total { sum fL/d}.