Blind thickness Calculation 2

[beercia]

Is there a formula for calculating the thickness of a piping blind (i.e. Flange, Fig 8, line blind, etc) ? If so, what is the appropiate formula for each type?

Carlos

 

[JohnBreen]

Hi Carlos,


Look at B31.3, paragraph 304.5.3:

The minimum required thickness for a blank shall be calculated by the following equation:

Tm = dg * ((3*P /16*SE) + c)^0.5

Tm = mininum required thickness
dg = inside diameter of gasket for raised or flat face flanges
dg = the gasket pitch diameter for ring joint and fully retained gasket flanges
S = the allowable stress from Appendix A
E = the weld quality factor See Tables A-1A and A-1B
P = design pressure (psig)
and the weld strength factor must be applied if there is a weld in the plate.

 

[JohnBreen]

..........and

C = the corrosion allowance. Also use "C" to allow for impingement abrasion or other wasting of the blank thickness.

 

[DSB123]

Carlos,
Just for clarity the formula given by John is for a line blind fitted between two flanges. It does not apply to a Blind Flange which is subjected to bolting moments.

 

[jte]

To summarize, if the blind has bolting going through it, the most likely code to use is B16.5; if the blind is inside the bolt circle, the B31.3 formula may be applied. See also B16.48 which does the calc's for you based on the B31.3 formula.

http://catalog.asme.org/Codes/PrintBook/B1648_2005_Line_Blanks.cfm

The B31.3 formula is based on the solution to the differential equation developed by Poisson a few years ago. Since the situation is actually highly nonlinear from both a geometrical and material perspective, the B31.3 formula is also quite conservative. More reading at

http://store.asme.org/product.asp?c...ponents_PVP2005TCK-3&product_id=PVP2005-71164

jt