ASME B16.34 minimum wall thickness 3 pieces trunnion ball valve.

[CATVALVE]

Dear all,

When designing a 3 piece trunnion ball valves the point 6.1.2 part c point 1. Says:
for the central core piece, the value of d shall be the inside diameter of the core piece. If the core piece wall has axial holes, whether through- or partial threaded, then the inner and outer ligaments shall also meet the requirements of dimensions f and g of Fig. 2.

This is very clear f and g have to be minimum 25% of the minimum wall thickness t.

But the questions is.

Does it apply in this type of valve the point 6.7 ( wafer and flangeless valves) part e that says that the sum of inner and outer ligaments f+g shall not be less than t?


Thanks

 

[PeterIgg]

Correct. It means that the bolt hole can be in a range of positions such that the minimum distance from either the outer or inner walls is not less than 0.25 tm (the wall thickness) BUT that the sum of the two ligaments must be equal or greater than the required wall thickness.

 

[CATVALVE]

Thanks PeterIgg,

What I don't see clear is if the sum of the 2 ligaments really apply because point 6.7 refers to wafer or flangeless valves. And a center piece of a 3 pieces ball valves is not a waffer design.

Any other opinion?

Thanks

 

[bcd]

The wall thickness requirements will change back to previous editions in the next revision of B16.34. Most likely sometime in 2016.

The committee added the extra wall thickness and ligament requirements for the center section of 3 piece ball valves about 2 revisions ago. Since then, there have been a lot of complaints about the extra weight it caused. Especially when there was not a problem in the first place. So the next revision will allow the wall thickness to be determined by the end port connection diameter, not the center body bore.

 

[CATVALVE]

Thanks bcd,

Its good to know that this will change during this year, but do you know if with the actual revision, the sum of the ligaments f+g>t apply to the 6.1.2 (c) point 1?

Thanks

 

[bcd]

The ligament distances in part (c) will be optional, not required.