Page 22 - Chemical Process Equipment - Selection and Design

RULES OF THUMB: SUMMARY XiX
4. For vacuum operaition, design pressures are 15psig and full VESSELS (STORAGE TANKS)
vacuum.
5. Ivlinimum wall thicknesses for rigidity: 0.25 in. for 42 in. dia and 1. For less than 1000 gal, use vertical tanks on legs.
under, 0.32 in. for 42-40 in. dia, and 0.38 in. for over 60 in. dia. 2. Between 1000 and 10,000ga1, use horizontal tanks on concrete
6. Corrosion allowance 0.35 in. for known corrosive conditions, supports.
0.15 in. for non-corrosive streams, and 0.04 in. for steam drums 3. Beyond 10,000 gal, use vertical tanks on concrete foundations.
and air receivers. 4. Liquids subject to breathing losses may be stored in tanks with
'7. Allowable working stresses are one-fourth of the ultimate floating or expansion roofs for conservation.
strength of the material. 5. Freeboard is 15% below 500 gal and 10% above 500 gal capacity.
8. Maximum allowable stress depends sharply on temperature. 6. Thirty days capacity often is specified for raw materials and
products, but depends on connecting transportation equipment
schedules.
-20-650 750 850 1000 7. Capacities of storage tanks are at least 1.5 times the size of
TernperatLire (OF)
Low alloy steel SA203 (psi) 18.750 15,650 9550 2500 connecting transportation equipment; for instance, 7500 gal tank
Type 302 stainless (psi) 18,750 18,750 15,900 6250 trucks, 34,500 gal tank cars, and virtually unlimited barge and
tanker capacities.