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ASME Section I, forced-circulation boiler and Design Pressure and MAWP

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fjallraven

Mechanical
Jan 20, 2015
1
Hello

I have a question about forced-circulation boiler and pressures (DP and MAWP).

If I had a forced-circulation boiler with a steam drum and the steam drum had a feed water inlet and saturated steam outlet (to superheaters), would it be possible to use two Design Pressures and two MAWPs for the system? The boiler would be designed according to ASME Section I.

Feedwater pipe, steam drum and superheaters would have lower Design Pressure and lower MAWP but forced-circulation would have higher Design Pressure and higher MAWP after the pump. Is this kind of situation allowed by ASME BPVC SI or does it have to be one Design Pressure and MAWP for whole boiler?

PG-21.1 says "No boiler, except a forced-flow steam generator with no fixed steam and water line that meets the special provisions of PG-67, shall be operated at a pressure higher than the maximum allowable working pressure ..." Does the "forced-flow steam generator with no fixed steam and water line" mean once-thourgh boilers only or are forced-circulation boilers (with a steam drum) considered to be in this group also?
 
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An ASME sect I drum type boiler has one MAWP for the evaporator and superheater. The fact that you are using a recirculation pump does not make it a once-thru steam generator. In some cases ( such as some HRSG's) the economizer may have a higher DP than the MAWP if the feedwater control valve is located at the outlet of the economizer.

"Whom the gods would destroy, they first make mad "
 
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