ASME SECTION 1 PG 61.5 interpretation 2

[dipaeng]

Hello everyone,
This is my 1st post in this forum.can anyone please explain it.

1) Does para.PG 61.5 of ASME section 1, also applicable to Once Through Steam Generator (Oil/Gas /GT exhaust fired) OTSG that has also dry running capabilities for short duration.)
2) Does para.PG 61.5 of ASME section 1, requires maximum feed flow corrosponding to maximum sustained pressure at boiler inlet or it is silent about feed flow requirement. Only feed pump should be capable of supplying feed at maxium sustained pressure.

Regards,
dipaeng

 

[Fizza453]

Hello Dipaeng,

PG-61.5 is also applicable to OTSG. To support my answer, please see following interpretation

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Interpretation: I-01-10
Subject: PG-61.5, Sizing Criteria of the Boiler Feed Water Pumps
Date Issued: September 25, 2001
File Number: BC01-619
Related Documents:

Question: Do the requirements in PG-61.5 apply to all forced flow steam generators with no fixed steam or waterline (once through steam generator)?

Reply: Yes.
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Regarding your second question, Designer is responsible for feed water flow rate, feed water pressure, feed water pump selection etc. He should do all these selections that must be in line with the intent of PG-61.5. The requirement of 3% of PG-61.1 is not applicable to OTSG.

Please also eighth paragraph of the Preamble that discusses a little about OTSG.

Hope it helps.



Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[davefitz]

As I read PG 61.5,the boiler mfr is to determine the max sustained pressure that will be present at the inlet to the steam generator ( ie economizer inlet) when the unit is generating maximum design steam flow AND the final element of the steam generator ( ie main steam outlet header) is at its MAWP.

The forced flow steam generator also has a design pressure that varies over the length of the steam generator; there is not one "master stamping pressure" for all of the pressure parts as is done for a drum-type boiler, so there is an incentive to minimize the design pressure of the main steam outlet header to allow minimizing the specified design pressure of the upstream components and of the BFP.

There is one other unusual aspect to this:
===> in the old days, before the use of the "combined oxygenated feedwater treatment " method became prevalent, the pressure drop thru the furnace waterwall tubing would increase quickly due to accumulations of deposits of magnetite that was spalled off from the carbon steel tubed feedwater heaters. For some units, the pressure at the economizer inlet would increase rapidly over time due to this progressive increase in furnace frictional pressure drop. Annual acid cleaing of the furnace was common for one brand of forced flow steam generator ( 0.75" ID tubes) , but other brands with larger ID turbes could wait as long as 3-5 years between acid cleanings. As the boiler mfr rarely provides the BFP, the boiler mfr would primarily be obligated to advsie the EPC the max performance requirements for teh BFP and assocaited piping , and advise the operator when the unit would need to be scheduled for acid cleaning due to excessive pressure at the BFP outlet.