AS1210 - Calculation of Torque and Bending Moment

[iken]

Hi,

Just wondering if someone can confirm (or kick back) my take on the following.

For equations 3.7.5 (1) I need the Bending moment of the vessel, is this simply the maximum I get from the bending moment diagram (for horizontal vessel easy - for vertical vessel seams odd).

For equation 3.7.5(3) i need the torque of the vessel. Is this the torque to rotate (like a spinning top), or to resist topling over. And, as troque is force * distance, the distance is from axis to extreme edge - so would the force be obtained using a simplistic view of the vessel being like a UDL (and taking the UDL value, or is it the force at 1/3 way up etc.

The vessel I am doing calcs for a small, so I don not need these, but I am working on some spreadsheets to make life easire (and have a complete set).

Any help would be great.

Thanks,

 

[EngAddict]

Generally the hoop stress governs the vessel design for shell thickness but sometime under high combined loading the longitudinal stress will govern.

Have you read the first paragraph of 3.7.5, it might answer all your questions. i.e. generally this check is not required since most of the bending stress in a skirt mounted vessel is at the base, which becomes structural design to AS3990. You can still use this method to design the skirt, it is basically the same method as in Bednar, Moss, etc. However for tall vessels or lug mounted vessels or whatever the design calls for which will cause large combined loads to be supported by the shell then you will need to use this method.

To answer your questions:

It is only the maximum bending moment if it happens to be located in the shell. A skirt mounted vessel is a cantilever with maximum bending moment at the base, not in the shell. You could use similar triangles to work back on your BM diagram to check the worst case in the shell. In the case of vertical vessels bending will be caused by wind or seismic, not static weight as in horizontal vessels.

Where did you get torque from?

 

[iken]

Thanks EngAddict,

The tordue (Q) comes from the notation under 3.7, and is used in equation 3.7.5(3) - shear stress.

The need for these loadings will/may be more for a horizontal vessel (shell to withstand the vessel weight including contents), to ensure it doesn't sag/hog. This being so I think the Shear Stress doesn't need to be considered.

Thanks,

 

[EngAddict]

3.7.5(3) is weight stress, not shear. You are using AS1210:1997 without Amendment 3 from 2002. You should be using AS1210:2010, otherwise your spreadsheets may end up being over 10 years old..

However you can get torsional loads from retrained free end displacement of attached piping but is generally negligible for shell sizing.

 

[iken]

Thanks for that.

Still in the dark ages on the standard (I were lead to believe the main difference (from 1997 to 2010) was the material strengths.

Can't justify to the boss to pay for the latest - at the moment.

 

[EngAddict]

"Can't justify to the boss to pay for the latest - at the moment."

$240.. How much do you sell a vessel for?.. Easy justification over the life of the standard revision.

There are heaps of changes, many new appendices added, flange design has changed, MDMT has changed, fatigue changes, Supplement 1 incorporated, etc, etc..

 

[stanier]

iken,

Not buying the latest standards is not supporting an organisation where many volunteers provide their expertise for the greater good.

Suggest you change jobs and get a career where your engineering is supported.

Not having the latest standards puts your company & you at great risk, particularly in the light of the Australian federal government's harmonisation of state OH&S laws. You should be aware that directors and managers in companies will no longer be liable. It is the design engineer who is in the firing line.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/