Solution to Problem 138 Pressure Vessel

Problem 138
The strength of longitudinal joint in Fig. 1-17 is 33 kips/ft, whereas for the girth is 16 kips/ft. Calculate the maximum diameter of the cylinder tank if the internal pressure is 150 psi.



Solution 138


Why do you need to assume 1ft of length when the length is left out from the formula? Also, can I ask if the "ft" from the "kips/ft" the thickness of the thin-walled vessel? I'm only assuming from the formula.