Using a SCH STD WT BW Valve in a XS line

[crazypiper]

Due to a mix up in valves (a common occurance), we have had the following suggestions justifying the use of STD WT BW valves in a XS line.

1. The 12.5 % mill tolerance does not apply to valves, therefore it's OK to weld a STD WT valve in an XS strong line (provided that calculations support it). I strongly disagree to this approach, since the pipe you are welding it to still has 12.5% mill tolerance.

2. You can do as suggested in #1 if you weld flanges to the valve, because the 12.5% mill tolerance does not apply to the valve or flange, therefore you're OK with a STD WT valve in an XS line (if calcs support this).

For me, I'm against making any assumptions as suggested in #1 and #2 (it seems like backyard engineering to put a weak link in a chain based upon assumptions).

Opinions?

 

[dcasto]

A valves pressure rateing is on the valve or in the papers with the valve. There is no such thing as an extra-strong valve.

 

[crazypiper]

It's understood that the valve is manufactured to the worst case of any pressure rating/material - that's a given.

I should have mentioned that the pipe is calc wall - the code calculations determine that the pipe wall thickness shall be extra strong. In order to match the pipe, the BW valve is ordered bored to match XS thickness of the pipe. All BW valves are specified this way (STD, XS, XXS, etc). XS refers to the bore that the BW valve is machined too.


In reading 16.5, it states that the hub welding end of a flange is manufactured to the same 12.5% mill tolerance. Therefore #1 and #2 are the same.

Maybe I've answered my own question ... just say NO.