Boiler pipe problem? 1

[mejia198021]

A 400 HP boiler steam outlet connection. A pipe connection of 6" diameter with a pressure of 150 psi and 366 F. I am trying to find out if sch 40 will be resist the pressure it will be given or should it be switched to a sch 80.

Thank you

 

[pmover]

without knowing the details, i highly recommend using the ASME Boiler Pressure Vessel Code be used to determine suitable nozzle requirements for boiler. i trust the ASME code does apply in this matter.

good luck!
-pmover

 

[NozzleTwister]

Refer to Section 104 in ASME B31.1 for the equations for calculating your minimum wall thickness for 'Boiler External Piping.' You'll also need to know if you have any design conditions that exceed what you stated above, corrosion allowance and of course your pipe material. You'll get your allowable stresses from the tables in the back for your specific pipe material. It's easy, good luck.

NozzleTwister
Houston, Texas

 

[mejia198021]

NozzleTwister, I found the formula's for the min. thickness and the Pressure. What is the best way to find the max. allowable stress in the material (SF). Thanks

 

[NozzleTwister]

You get your allowable stress from Appendix A, Table A-1 in the back of ASME B31.1. If you have welded pipe, make sure you select the values for the correct class of pipe that you have. I forgot to mention earlier, you need to consider mill tolerance as well.

Good Luck

NozzleTwister
Houston, Texas

 

[gmorin]

I agree with everything said to this point. As with any design change, you need to do a calculation to verify the pipe wall thickness vs the allowable stress, corrosion allowances, mill tolerances, etc.

That being said, if you're using steel piping, chances are sch 40 piping will handle your pressure requirements with a lot to spare. The flange rating is generally the limiting factor in this pressure range.

A heads-up. If this is boiler external piping make sure you get the right pipe - SA-106 gr. B vs A-106 gr. B, etc.

One more thing - why is the pipe wall being questioned in the first place? Did you have a failure of some kind?

Good luck

Greg

 

[PAN]

majia198021,

It seems that your condition is condensate near saturated steam. Please check the design condition.

 

[TBP]

Pan - Are you perhaps looking at 150 PSIA on the steam tables, and not 150 PSIG? 150# (gauge) saturated steam is 366*F, and is a very common design condition for industrial steam systems.

 

[PAN]

TBP,
You are right. I worry for mechanical design. Normally for the design and operating conditions are difference. I always use the slightly superheated condition for the design.

Thanks for your advice.

 

[TBP]

PAN - It's an easy mistake to make. I'd suspect that mejia198021's boiler operates to maintain a header or system pressure of 125. The percentage of systems with boiler safety valves set for 150, but filled with Class 125 valves, strainers & traps is HUGE. There's some scary stuff out there.