Material strength : SS316 for class 2500 valves

[gazman2]

Hello everybody.

I am a valve designer and I am facing a concern about the use of SS 316 (or other material whith the same strength) for class 2500 valves (or higher). When I use a FEA software to compute the body, I often reach stresses which overgo the 316 yield strength, for sizes bigger than 2 in.

Is it common to choose such a material for such a pressure ?
Has anybody ever faced such a problem ?

Or other materials, with higher strength, have to be advised ?

Thank you

 

[rzrbk]

What pressures are you using?
Typically, allowable pressures for SS flanges are lower than for other materials.
(see B16.5)

 

[gazman2]

class 2500 correspond to 431 bars as working pressure

 

[Sircrashalot]

In the offshore market for ANSI 2500# and API 10,000#, I've used a number of materials. Good options for strenght vs. weight seems to be 6Mo material (ANSI A182-F44). Also the Duplex and Super duplex grades of stainlees steel (F51 & F53/F55) are also common. I have also used A350-LF2 with an inconel 625 weld overlay on whetted areas for large valves.

The other thing you will likely have to look at is increasing the wall thickness of your valves considerably if you need to continue to use 316.

Andy

 

[gazman2]

Thank you both.

I know that I have to increase the wall thickness. It is possible radially. But in the other direction I am limited by the face to face... Perhaps have I to fix a bigger face to face.

 

[Sircrashalot]

What kind of valve are you designing? For ball valves at these pressures, I haven't noticed any problems with face to face.

Andy

 

[gazman2]

A trunnion mounted ball valve.

 

[xcrosby]

Are you using the wall thickness per ANSI/ASME B16.34?

 

[gazman2]

Yes. But is it sufficient to guarantee the resistance ?

We always verify the stress thanks to FEA. And depending on the material used, the stress can be too high... even if the minimum wall thickness is repected.

 

[joethemetallurgist]

I think that for most applications, especially in chlorides, the use of duplex materials offers substantial improvement in yield strength. With the present price of nickel, etc. the use of 2205 duplex may make sense - however, I would carefully check qualifications of suppliers. The material is prone to sigma phase embrittlement if incorrectly heat treated.