P&T rating of Safety Valves on Power Boiler 4

[Ltrujillo]

Hi,
I have three ASME Section I Safety Valves, rated for saturated steam service, with an ASME "V" stamping.
- 1st. valve is set 1,128 psi (drum) size 3"-600#RF X 6"-150#RF
- 2nd. Valve is ser 1,163 psi (drum) size 4"-600#RF X 6"-150#RF
- And 3rd. valve is set 934 psi (outlet of super heater) size 3"-900#RF X 6"-150#RF

The rated boiler is 250,000 Kg/h @ 1,040 psig @ temperature saturated steam on the Drum and the outlet of super heater is 880 psig @ 905°F approx.

My doubt is, the P&T rating by ASME select for these valves is the correct? Because this inlet flanged is of 600#RF and not of 900#RF for the 1st and 2nd valves (on Drum). The base material flanged is WC6 and temperature class B & D how it are indicated.
All valves are Dresser with the follow models;
1st. 3-2745B-1-X-1WSC
2nd. 4-2765B-1X-1WSC
3rd. 3-2746D-1-X-1WSC

I wait for their soon answer
Thanks

 

[ApC2Kp]

Ltrujillo,

The valves have flange rating established by the flange classes, per ASME B 16.5 which now has new release 2009.

Each material also has established rating with each pressure class. The WC6 material is used for superheat steam conditions with de-rated allowable pressures at the temperatures above 700 deg F. The WC6 material at 900 degF. might have only half of its room temperature strength.

The Boiler documents should show the relief valves have been selected correctly, and the AI would also provide confirmation to your questions on the safety valves.

 

[GenB]

check the tables for pressure and temp of the flange material
if the s.v. set pressure excedes that you are okay.
Usually the valve mfr is correct

 

[skearse]

Is the 1,040 psi the MAWP or an operating pressure? Secttion I requires at least one valve to be set at the MAWP of the boiler and any subsequent valves to be set no higher than 3% of MAWP.

 

[boilerone]

Hello Ltrujillo,

I sized safety valves for many boilers. I checked your data against ASME B16.34 P&T ratings plus Dresser's catalog page 2700.19 for set pressur limits and all of the inlet and outlet flange ratings look good.

I did notice that if the same valves are used for B31.1 applications(not your case) then the 2nd and 3rd valve's outlet flanges do not satisfy table on 2700.21 which considers also B31.1 Appendix II. 300# flanges are needed.