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# Discrepancy in the pressure

## Discrepancy in the pressure

### RE: Discrepancy in the pressure

Flanges used to be described as 150lb, 300lb, 400lb, 600lb and so on and you may still hear that terminology.

The more accepted terminology today is class as in class 300 flanges because the actual allowable pressure rating is a function of the temperature and material the flange is constructed of.

The pressure rating of either a 'class' 150 set of flanges or a 150 'lb' flange would, for the same material, be exactly the same and is set per ANSI B16.5.

### RE: Discrepancy in the pressure

The classes (300#) are dimensions not pressure ratings.
As Bimr said, material, temp, and service will determine the actual pressure rating.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

### RE: Discrepancy in the pressure

Ed,

They are both dimensions and pressure and temperature ratings which vary by material type of the flange.

However if this is indeed a class 600 valve someone has gone a bit berserk in changing the higher temperature rating as group 1.1. materials (LF2) is good for 1360psi at 200F. Class 300 is 680!

SO my guess is that the valve is rated at 284 psi up to 38C and someone has decided to de rate it at 80C in line with the flange rating tables. Madness.

But why they've gone for such a strange rating I just can't tell.

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

### RE: Discrepancy in the pressure

Someone just went a bit mad wit the process data sheet and took what the computer said as gospel from the simulation.

It's right on the boundary of class 150 so 300 maybe, but class 600 for a 14" valve with an MOP of 280 psi??

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

### RE: Discrepancy in the pressure

It is possible for a valve to be designed per ASME B16.34 Class 600. Class 600 wall thickness, end flange dimensions, bolting, etc. and have internal trim parts only rated for Class 150 shut-off pressures. That appears to be the case here. Not sure why there would be such a large difference between the body rating and shut-off differential pressure rating. Most likely a mistake by the person putting the data on the tag. For safety sake, this needs to be checked with the manufacturer.

### RE: Discrepancy in the pressure

600 surely must be a mistake. Check the hydrotest pressure. Call the mfgr, verify whatever it should be and get a new tag for it.

### RE: Discrepancy in the pressure

(OP)
Thanks for all the replies.

My guess is that instead of 264 psi it should be 1264, and instead of 285 psi it should be 1285.

I did have the opportunity to look in the valve documentation, but I let you know if I find the answer.

### RE: Discrepancy in the pressure

What was the hydrotest pressure?

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