Lateral buckling of the stiffening ring for external pressure loading.

[4xeng]

Hello,

I am learning about pressure vessel design for external pressure (vacuum). Just doing the exercise. Not designing the actual vessel.

I came across cautionary note in UG-29 (a) that the stiffening ring may be subject to lateral buckling. And this should be considered in addition to the requirements for Is & Is’.

I understand that the Is & Is’ per UG-29(a) are required for global buckling of pressure vessel.

How the ring will see lateral buckling load? I am wondering how I go about lateral buckling check of stiffening ring itself? Any ideas out there?

Thanks!

 

[saplanti]

The terminology comes from the structural engineering. You need to search for the behaviour of the beam with, let us say, rectangular cross section under uniform loading. The beam under loading will deflect, but under certain loading the compression side of the rectangular plate will move sideway and the beam will loose stabilıty and consequently fail.

The welded rings around the cylindric shell, in case it is outside, will behave similarly under external pressure, it is in the compression side. Therefore structural engineers keep them compact (another structural engineering term) which means the height limited not to change the shape under axial load and do not loose the expected strength.

If you need further information search for local buckling cross sections and lateral torsional buckling of beams.

Hope it helps.

 

[r6155]

See AD 2000 Merkblatt B6 Cylindrical shells subjected to external overpressure
Flat bar. The height of stiffener shall not exceed 8 times the width.

Regards

 

[r6155]

See ASME VIII Div II
(d) Local Stiffener Geometry Requirements for all Loading Conditions - The following equations shall be met to assure
the stability of a stiffening ring.
(1) Flat bar stiffener, flange of a tee section and the outstanding leg of an angle stiffener (see Figure 4.4.3)

h1 /t1 < 0,375 . (sq root (Ey / Sy)) formula (4.4.32)

Regards

 

[4xeng]

Thanks for replies.

I am also looking at stiffening ring size in DIV 2 section 4.4.5. There is a local geometry check (d) but there is also a shear check (f). What would that be for?

 

[r6155]

Read again (slowly) the text of (d) and (f).

Regards

 

[Rob VE]

Hello all,

This is an interesting post to me, we always try to stay or below height to width ratio of 10 for ASME and EN13445 vessels. for AD2000 of course on or below 8.
I immediately entered the formula in Mathcad and checked a few of our most common materials at 3 different temperatures.
For all checked materials I found out that the ratio is higher at higher temperature.
For example 304L:
- 20°C: h1/t1= 12.6
- 350°C: h1/t1= 15.3
Code specifies that yield and E modulus needs to be taken at design temperature, however if vacuum is also applicable at ambient temperature, this case will govern for the height to width ratio.

I did not expect this at all therefor wanted to share my findings.

Regards
Rob

 

[r6155]

Also consider deformation during welding.

Regards