6 replies to this topic

[jawbkk]

I am calculating the stress on a pressure vessel which is 20m tall with 2:1 semi-ellipsoidal heads. The vessel sits on a 2m high skirt.
The wind pressure is 130 kg/m2.
What is the formula for converting this into a stress value?
I cannot seem to find it anywhere!!
I don't need to go into huge detail as this is for a project I am doing at college.
Regards
John

[Bobby Strain]

Keep searching and you will find it.

 

Bobby

[ankur2061]

John,

 

The units of pressure and stress are the same i.e. force per unit area. Wind pressure what you mention as 130 kg/m2 is basically kgf / m2. Converting to any other stress unit can be easily done using an unit conversion calculator such as "Uconeer".

 

Regards,

Ankur.

[kkala]

Your search may be fruitful by looking at Coulson and Richarson's "Chemical Engineering, Volume 6, An Introduction to Chemical Engineering Design", Pergamon Press (I think Elsevier now), several editions from 1983 on. Chapter 13, Mechanical Design of Process Equipment, deals mainly with pressure vessels. Para 13.8.2, Wind loads (tall vessels) give design instructions. Example 13.3 is a  mechanical design calculation of a 50 m tall distillation column, including wind load and resulting bending moment / stresses.

Chapter 13 can be useful in other matters of your design too. It is brief, probably as simplified as possible, needing some knowledge of strength of materials.

[kkala]

It is clarified in addition that wind pressure is not same as stress developed in the vessel wall because of the wind, even though both have same units. E.g. in the example 13.3 (referenced in previous post) wind pressure is 1280 N/m2 (130 kgf/cm2), but bending stress due to wind ±61.1E6 N/m2 (±6.2 E6 kgf/m2).

Similarly between internal vessel pressure and stress in its wall because of it (in the example:10 N/mm2 versus max 55.6 N/mm2).

 

Editing note 4th Mar 13: 130 kgf/m2, not 130 kgf/cm2. Typo corrected after post no 6  by ankur2061

Edited by kkala, 04 March 2013 - 04:05 PM.

[ankur2061]

It is clarified in addition that wind pressure is not same as stress developed in the vessel wall because of the wind, even though both have same units. E.g. in the example 13.3 (referenced in previous post) wind pressure is 1280 N/m2 (130 kgf/cm2), but bending stress due to wind ±61.1E6 N/m2 (±6.2 E6 kgf/m2).

Similarly between internal vessel pressure and stress in its wall because of it (in the example:10 N/mm2 versus max 55.6 N/mm2).

The conversion of 1280 N/m2 is 0.013 kgf / cm2 and not 130 kgf /cm2.

[kkala]

Thanks. As next conversion of 61.1 E6 N/m2=6.2E6 kgf/m2 indicates, this is a typo. It has been corrected.

The essential point for clarification is that pressure is not same as wall stress.