Thick vs. Thin walled pressure vessel 2

[ADNPD]

Could someone please explain the criteria for what constitutes as a thick walled and thin walled pressure vessel. Also, is the hoop stress and longitudinal stress formulas valid for both?

 

[Bobfromoh]

The ASME Section VIII Code, Division 1 is intended for thin shell vessels. In UG-27 the shell thickness is not to exceed one half of the inside radius. In the "Pressure Vessel Design Handbook" by H. H. Bednar in section 3.1 states that a shell is treated as thin if R/t >10. This is also a limit in the ASME Code for thin shells with external pressure.

I would have to say that the design equations do not apply equally for thin and thick shells. Thin shells assume a constant membrane stress through the thickness. In a thick shell vessel, the largest stress will be at the ID. Divison 3 of the ASME Code Section VIII covers thick wall vessels. I don't have that part of the code but maybe it contains additional information that defines thick wall vessels.

 

[PVGuy]

Check out ASME VIII-1 Appendix 1-2 and 1-3 for thick cylindrical and spherical shells.

 

[bmoorthy]

A 19 mm dia tube with 2.5mm thk is used in a Heat exchanger. Should we consider this as thick cylinder or a thin cylinder.

 

[ab1234]

The basic difference between the two is that in Thick wall Raidal stresses are also there in addition to Hoop and longitudinal stresses. Lame's equations are used for determination of various stresses in Thick shell.

Please note that as mentioned above generally thin walled vessels are classified as one where R/t>10. But the ASME Code formula given in UG-27 takes care upto R/t > 2. It means upto some extent Thick wall vessels can also be computed using ASME Code Formula. In fact the modification factor 0.6*p in the denominator of ASME code formula brings membrane stress thin wall formula more close to Lame's Equation for Thick walled Vessels.

If You want to check in Depth, please refer Chapter-14 of Process Equipment Design Book by Brownel & Young.

bye