ASME 1 rules for overpressure protection in HRSG

[ATsampalas]

Dear Sirs,
Can someone explain where to find, within ASME 1 Code (or additional rules to ASME), the requirements about the necessity of safety valves and their capacity with a view to protect against overpressure :
a) Steam Turbine Side ;
b) Cold Reheat Side ?
We guess that the existence of an isolation valve is of importance.
Please confirm the same and consider all known cases .


Sincerely,

A. TSAMPALAS

 

[metengr]

Yes, you can review the following paragraphs in Section I (2004 Edition) - steam tubine side is superheater outlet;

PG-67
PG-68

Cold reheat is reheater inlet to the boiler from the HP turbine, and this would not be addressed in the Code.

 

[ATsampalas]

Dear Mr Metengr,
Thanks for your reply.

Sincerely,

ATsampalas

 

[davefitz]

An interesting historical summary of why reheater components are not covered by section I is found in "Power Boilers" by MD Bernstein and L. Yoder, p3, - they claim that the 2 major US turbine vendors have successfuly prevented the inclusion of that piping in section I, although neither of those vendors have supplied that piping system since the 1950's.

 

[davefitz]

Regarding the max capacity of the reheater relief valves, some unusual scenarios can arise for the case of multiple HRSG's on a header system:

a) If the STG has tripped and the HRSG is on a bypass system , the max steam flow to the reheater may need to include the add'l steam flow from the HP bypass spary attemporator

b) Such a reheater could be considered as a "separately fired superheater" in that it has isolation valves at both inlet and outlet ( since it is downstream of the IP boiler bank on a HRSG, it cannot avoid code inclusion). The code clause that proportions the relief valve capacity to the "separately fired superheater" surface area has been interpreted to mean all the steam the reheater can generate if it is blocked, and there may be a code case or interpretation that formalizes this.

c) some plants have included an "overload valve", bypassing some HP main steam directly to the hot reheater, to avoid overpressuring the GE STG that has a low throttle pressure limit. This design must add add'l releif capactiy in the hot reheater piping near the intercept valve to account for the max casualty flow thru the overload valve.

 

[samctu]

Hi,

Sorry to add a question to this thread, but what does ASME 1 cover exactly?

Thanks.

 

[ATsampalas]

Dear Mr Metengr,
Following your reply dated 30 March 2006 and due to an inappropriate answer, my message had been truncated.
To see our problem, please have a look at the link hereafter:

http://users.skynet.be/fb248691/03042006_1.pdf

Sincerely,

A_Tsampalas

 

[ATsampalas]

Dear Mr Samctu,
Please find hereafter a file showing what does ASME 1 cover.

Sincerely,

A. Tsampalas

http://users.skynet.be/fb248691/ASME_1.pdf