Cylinder Thickness Equation - why does it have an extra term?
Cylinder Thickness Equation - why does it have an extra term?
(OP)
According to PD5500, the min cylinder thickness, e = p x Di / (2 x f - p)
where p is pressure, Di is inner diameter and f is design strength
Re-arranged to give stress:
f = p x Di / (2 x e) + p / 2
However, according to standard thin cylinder theory, the stress is:
f = p x Di / (2 x e)
Anyone know why the extra p / 2 factor is added in PD5500?
Is it an additional safety factor? (I thought the reductions applied to obtain the design strength were sufficient to not require extra safety factors)
where p is pressure, Di is inner diameter and f is design strength
Re-arranged to give stress:
f = p x Di / (2 x e) + p / 2
However, according to standard thin cylinder theory, the stress is:
f = p x Di / (2 x e)
Anyone know why the extra p / 2 factor is added in PD5500?
Is it an additional safety factor? (I thought the reductions applied to obtain the design strength were sufficient to not require extra safety factors)





RE: Cylinder Thickness Equation - why does it have an extra term?
RE: Cylinder Thickness Equation - why does it have an extra term?
f = p x(Di+d)/ (2 x d)
RE: Cylinder Thickness Equation - why does it have an extra term?
I note that it gets more conservative as e/Di increases.
RE: Cylinder Thickness Equation - why does it have an extra term?
As this stress is negative (compressive), it adds up to the hoop stress to form the stress intensity, or the difference between the maximum principal stress and the minimum one. So the Tresca failure criterion is used (as expected).
prex
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RE: Cylinder Thickness Equation - why does it have an extra term?
You can also use the outside diameter:
= p x(Do-d)/ (2 x d)
Hence:
e = p x Do / (2 x f + p)
And it is for relatively thin walled cylinders. The design code will mention in what thickness/diameter ratio this formula is applicable.
RE: Cylinder Thickness Equation - why does it have an extra term?
However, I'm not sure why the average (-p/2) of the radial stress is used rather than the maximum (-p).
RE: Cylinder Thickness Equation - why does it have an extra term?
prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads
RE: Cylinder Thickness Equation - why does it have an extra term?