Wall Thickness on Bend ASME 31.3 para 304.2.1
Wall Thickness on Bend ASME 31.3 para 304.2.1
(OP)
According to the calculations related in 304.2.1 the minimum wall thickness on the extrados of the bend can be thinner than the minimum wall thickness required for a straight of the same length (section 304.1.2) , conversely on the introdos the wall is required to be greater than that of the straight for the same design pressure.
Can anyone explain a) why inner wall should be thicker and outer wall can be thinner. Note the calculations are for required thickness not actual thinning that occurs.
Although fairly irrelevant the figures used for the formulas are as below.
Straight minimum wall thickness by Calculation 3a (para 304.1.2)
Bend minimum wall thickness by calculation 3c, using 3d and 3e for intrados and extrados I value.
c = 0
P = 5500 psi
D = 0.75"
S = 16700
E = 1
W = 1
Y = 0.4
R1 = 2.2"
This provides a straight section min wall thickness of 0.1091, Extrados mwt of 0.1079, Intrados MWT 0.126.
How can the required thickness on the outside of the bend require to be less than that for a straight? Conversely opposite is true for inside wall?
Can anyone explain a) why inner wall should be thicker and outer wall can be thinner. Note the calculations are for required thickness not actual thinning that occurs.
Although fairly irrelevant the figures used for the formulas are as below.
Straight minimum wall thickness by Calculation 3a (para 304.1.2)
Bend minimum wall thickness by calculation 3c, using 3d and 3e for intrados and extrados I value.
c = 0
P = 5500 psi
D = 0.75"
S = 16700
E = 1
W = 1
Y = 0.4
R1 = 2.2"
This provides a straight section min wall thickness of 0.1091, Extrados mwt of 0.1079, Intrados MWT 0.126.
How can the required thickness on the outside of the bend require to be less than that for a straight? Conversely opposite is true for inside wall?





RE: Wall Thickness on Bend ASME 31.3 para 304.2.1
Some of the hoop stress is directed into the pipe's axial direction as you go around a curve.
RE: Wall Thickness on Bend ASME 31.3 para 304.2.1
To confirm I understand; If (imaginary) hoops are at spacing x on a straight as they sweep around the bend the you have >x spacing on the outside and <x spacing on the inside and thus the axial load less per unit (length) outside and greater per unit (length) inside (and at R1 is as per straight) thus requiring less/more material to cope with the axial load outside / inside respectively.
Is that right? Sorry I am electrical engineer by training so trying hard to understand this mechanical magicary!
RE: Wall Thickness on Bend ASME 31.3 para 304.2.1
RE: Wall Thickness on Bend ASME 31.3 para 304.2.1
Thanks for the time explaining this as it seemed completely counter intuitive to me, I did ask some of my Mechanically trained colleages and got no satisfactory answers, but this seems good. I will enlighten them and then move onwards with finding correct sized tubes and fittings!
RE: Wall Thickness on Bend ASME 31.3 para 304.2.1
https://pure.strath.ac.uk/portal/files/15555068/Ch...
For mitered bends,
https://plasticpipe.org/pdf/mitered-elbow-fea-repo...