300 Series Flange 2

[Wayne Falco]

Greetings,

I have been assigned to change our 150 psi for 1-1/4" pipe to 300 psi. I have near zero knowledge of piping.

I am attaching what I am now using for 300 psi flanges. My real question currently is what the dimension currently at .298 should be? How much compression? I can't seem to locate that detail. Currently I show line to line nominal.

Thanks,

Wayne

 

[racookpe1978]

Were not the "original" pressure classes named for the saturated steam pressures the "basic steel" fittings of that size and thickness could hold?

Thus, I thought a "150 lb fitting" could hold 150 psig saturated steam, but much higher air or liquid pressures, if those fluids were at room temperature?

 

[LittleInch]

That's what I once thought, but if you look at the intro to ASME B 16.5 it's not that clear where the "lb" term appeared other than hasn't appeared in the official standard since about 1975. 150 psi is about 575C I think nowadays (group 1.1 materials). That's quite a bit higher than "steam". Class 300 - 300 psi is about 870C so no consistency.

However its confusing terminology is hard wired into the industry so hard that I've seen some official company specifications which refer to "150 lb" instead of the official Class 150 designation.

Mc Master though quote the same ( reduced) pressure rating at both 50F and 300F... Madness.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[racookpe1978]

Thank you.

The source may be lost in the vernacular twists and turns, like the "10d" and "16d" nails: "How many pennies (in the older English (pre-metric currency), "d" came from the Latin "denerius" term for 1/100 of a coin, which became an Old English "penny") did it take to buy 100 of the nails?

So "d" stands for a "penny" from a term from a language no longer in use, for an English coin no longer in use, based on paying a blacksmith no longer used in Medieval rates for a nail measured in English units based on the width of a Medieval thumb to hold 2x4 lumber - which aren't 2 nor 4 in any measurement system used anywhere!

 

[LittleInch]

Had a look at the B16.5 intro and it doesn't say anything about the history. There are a numbe rof theories if you google it, but in Appendix A (method for establishing P-T ratings), it uses the class rating as pressure in A-1.2 and A-1.3. A-1.2 uses a max bolt stress of 7000 psi (pretty low) and also the same 7000 psi for strength of flange material in hoop stress.

So the origin seems to be that based off possibly something like Cast Iron or Grey Iron from the 1920's when the standard first appeared for boilers?? Maybe??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.