Relief valve on main steam outlet nozzle

[arvi]

Freinds,

Is it acceptable to put a relief valve on the main steam outlet nozzle. We have a rental boiler for emergency heating steam requirements during the winter period. Boiler supplied is 300 psig rating and our existing system is 150 psig. Vender has offered to put a relief valve @150 psig on the steam outlet nozzle before the stop valve by providing a tee on the outlet nozzle.

Boiler is designed to section I. As per section I PG-71.2 and PG-71.7 an independent connection is required for RVs. Can this be considered as an indepenedent connection beacuse as such there is no obstruction in the steam path to RV.

Other issues like BFP etc. we are resolving separately.

This boiler is for Ontario, Canada.

Thanks a lot in adavance for your advise.

Arvi

 

[unclesyd]

Come back with a little more information.
Like:
Are you going to derate the boiler (300psig-150psig)?
Is this to protect the existing system from the 300 psig?
What type boiler is it?
Is the other PSV 300 (psig)still in place?
Any other information.

 

[TBP]

arvi - contact the TSSA - Boilers & Pressure Vessel Safety Division. They are the authority that will have to approve this.

http://www.tssa.org

 

[arvi]

Thanks unclesyd for responding.

De-rating the boiler to 150 psi was the first option we thought of but since that requires re-registration we are trying to avoid that.

Two PSVs @300 will stay. Additional RV at 150 is to protect the existing system.

The boiler is oil fired (start up with propane).

My thoughts were that if we install the additional RV after the stop valve then we have to follow 31.1 which means 1 RV at 150 psi for the maximum flow is enough (Max capacity would be with the steaming capacity at 150 psi which will be more than the steamning capacity at 300 psi which can be calculated). BUT if the RV is before the stop valve probably we have to follow the rules of sec I which means 2 RVs and again if adding the RV on the outlet of main steam is acceptable.

Please let me have your expert advise.

Thanks a lot

Arvi

 

[unclesyd]

As "TBP" stated you will have to get the jurisdictional authority and you insurance carrier on board. Get your AI in the discussion loop. Also the boiler providers AI should be appraised of this proposal.

As you stated you are going to design the PSV for the maximum heat input of the boiler and the boiler is still protected at its’ design pressure. I can see no problem other than an operational one if the stop valve is closed. The only other thought is the location on the run of a tee. Though I’ve never seen this on a fired boiler I still see nothing wrong as it’s not protecting the boiler.
In discussions with our AI the only problem he has seen in such a system is people using the PSV as pressure control valve. What you are proposing is to operate the boiler at a high turndown.

One important point is that make sure the nozzle on the boiler is capable of carrying the additional load of the valve and its’ reactive load on same.

Have written information from the boiler provider that all his controls and associated safety devices will operate at the reduced pressure. Also that the additional valve will not interfere with any of these systems.

We operate several vaporized oil heating systems where we have a similar condition in that the tubular heater is designed and rated for 150 psig and is protected as such, but we operate the flash drum at 70 psig (designed for 150 psig but rated a 90 psig)dictates the system pressure of both heater and drum. The relief valves on the drum are sized for the max fire condition of the heater.


Let us know how it is resolved.

 

[unclesyd]

One question:
Is this outlet nozzle flanged?

 

[arvi]

Thanks Unclesyd

Yes the nozzle is flanged.

We will get the approval from the jurisdictional authority (CNSC and TSSA)before installing the boiler.

Proposal is to put a Tee on the nozzle so that the RV can be installed in vertical direction. On the branch side of the tee stop valve will be installed.

Since this steam line goes to a common header double block (gate) valve will be installed with a drain valve in between (Code requirement: ASME BPVC section I, PG-58.3.2 and B 31.1 -122.1.7). Since both the valves are gate additional check valve will be installed after these two block valves before connecting to header.

I was trying to paste a sketch for clarity but it does not work.

I will keep updated on the final outcomes. It will be a real interested case.

Thanks

Arvi

 

[unclesyd]

The first flange may govern the limits of the boiler. I don't know the current Canadian Code but you should check on this. If the flange governs then its an engineering consideration. Still get the jurisdictional folks involved though.

Good luck with the project.