Valve wall thickness

[Wintechcad]

Hi,

Does anybody know of a definitive standard or method for calculating the thickness of a WOG rated ball valve? I have purchased ASME B16.34 which seems to only give class ratings and associated thicknesses, but it does not cover WOG.

I have a 1000 WOG valve with ANSI 150 flanged ends and wonder how it relates to ASME B16.34 or whether it is acceptable as a class 150 ball valve under the terms of ASME B16.34? It seems that the max. pressure (1000 psi per WOG rating) is higher than that of class 150.

Many thanks.

 

[reverman]

The maximum pressure for the valve is in this case limited to the flanges you have on the valve. So the maximum pressure will be the class 150 100° rating of whatever material the valve is.

You would need class 600 flanges on the valve in order to rate it 1000 psi WOG

 

[gerhardl]

...and I assume the flanges are an integrated part of the body (eg. not loose flanges of 150 of a body constructed, rated and (note!) validly tested higher, with mechanical suited and allowed ends for higher classes).

If yes for first part, you are almost certainly stuck with ANSI 150.(Of practical reasons and cost for reconstructing and retesting.)

 

[Wintechcad]

My question is how is the WOG rating determined? It does not seem to follow ASME B16.34 - I realise that the flanges are the limiting factor, but we have the same valve with socket weld ends. Higher rated flanges from the manufacturer are not an option for this valve. I need to find out if there is a relationship between WOG and ASME as my initial findings are that a 1000 WOG ball valve does not meet ASME B16.34.

Thanks.

 

[bcd]

No, the WOG rating does not meet B16.34. Usually the WOG or CWP (cold working pressure) ratings are established by testing to a percentage above the rating value. ASME BPVC section UG-101 is a common method where a sample valve gets pressurized to 2.5 times it rated pressure to prove the strength of the design.

As soon as flanges are added, and the flanges are calimed to meet class 150, the valve rating cannot be higher than B16.34 allows for the material. Even the MSS standard (SP-72) for flanged ball valves state this. What may be happening is that an unknowledgeable valve supplier has modified their thread or socket weld end design to add flanges and continued to use the 1000 CWP rating designation. This is not correct.

 

[reverman]

In order for a valve to meet B16.34 the manufacture must have "B16.34" on the nameplate and the pressure class and 100°F pressure rating must be listed. If it does not have those markings then it does not meet B16.34