body and neck valve thicknesses 2

[FernandoL]

hello colleagues,

I am used to making thickness calculations according to codes like ASME VIII div 1 for pressure vessels, and now I have the challenge of evaluating if a new valve body design meets the thickness requirements defined by the ASME B16.34 standard.

I am correct in affirming that the methodology for obtaining the minimum thicknesses for valves derives from tables 3A and 3B, but also very related to the calculation by finite elements and accumulated experience of the engineer?

I mean, depending on the geometry and pressurized internal surfaces, the only use of these tables or mandatory appendix VI, for the determination of body thickness can lead to permanent deformations in the hydrostatic test or even rupture of pressurized parts.

Am I right?

any help will be very useful.

 

[gerhardl]

Hi Fernandol

I am no expert here, but if I am correct this is minimum thickness we are talking about(?).

In the good old days, when I got my education, the professor wiped out all factors less than one hundred-parts of the strength factor number he had calculated on the blackboard, paused, and added: 'And then we multiply by a safety factor of five!'

Nothing wrong about adding (a sensible) safety factor, not necessarily five!

 

[bcd]

Hello,

Rules for designing pressure vessels and valve bodies are different. ASME B16.34 has an Appendix that explains the basis for establishing the wall thickness. Because a valve is a mechanical instrument where critical dimensions must remain stable over long periods of time to reliably operate and contain pressure, valve body wall thickness is based on material creep strength. If you perform FEA and use allowable stress as your acceptance criteria, you are not meeting the intent of B16.34.