Valve Wall Thickness 1

[bhuat34]

API 6D standard does not touch on the minimum requirement for valves. ASME/ANSI B16.34 provides table for minimum valve wall thickness and formula for calculating valve body wall thickness.
However, B16.34 formula does not include corrosion allowance (CA). Based on comparasion with carbon steel (CS) pipe wall thickness with high corrosion allowance (6mm) on specific flange pressure rating (eg.150#,300#,600#), some small valves minimum wall thickness per B16.34 are insufficient (in fact less than CA).
Does that mean that we have to specify corrosion allowance in valve specification/data sheet? Is valve manufacturer going to custom-make the valve to cater for the CA? Ball may not fit if body is too thick. Or we have to change to corrosion resistance alloy valve (such as SS or Duplex SS?

 

[monofm4m]

In response to your query :

(1) The mimnimum wall thickness per ASME B16.34 includes the additional wall thickness of approx 0.01 inch as specified in F1.4 "Additional Considerations" of ANNEX-F.

(2) If valves required with 6.0mm corrosion allowance, the purchaser is to specify so as to make suppliers verify their standard wall thickness based on B16.34. This means that some suppliers have the heavier wall thickness of their standard design than that specified in ASME B16.34.

(3) For reference : API 600 stipulates the minimum wall thickness of gate valves and those values are heavier than ASME B16.34. Consequently, gate valves per API 600 might satisfy the required wall thickness per ASME B16.34 with C.A.=6mm. You are possible to verify this by means of F1.3 of ANNEX-F.

 

[TerryOsser]

It is always best to specify your required CA and get the vendor to either conform compliance or state his offered CA. Bear in mind a high CA can reek havoc around sealing areas unless CRA overlay is used to ensure sorrect sealing.
6mm CA might mean you need to reselect body material, use overlays, or it may be more economical to accept that the valve will last 1/2 the time and ensure that it is replaced. Often 6mm CA is a figure that is used if it is over 3mm. May be worth revisiting the metallurgists to check out the 'real' CA.