IS 803 is the Indian standard for the design, fabrication, erection, and testing of above-ground vertical, cylindrical, welded mild steel tanks used for oil storage. Often considered the Indian equivalent to API 650, it provides essential guidelines for ensuring structural stability under hydrostatic, wind, and seismic loads, alongside strict welding and NDT protocols.
Code of Practice for Design Fabrication and Erection of Vertical Mild Steel Cylindrical Welded Oil Storage Tanks
Quick Reference Values
Minimum thickness of bottom plates6 mm (excluding corrosion allowance)
Minimum thickness of roof plates5 mm
Minimum thickness of shell plates (D < 15m)5 mm
Minimum thickness of shell plates (15m <= D < 36m)6 mm
Specific gravity basis for hydrostatic test1.0 minimum (water)
Maximum design temperature limit90°C (typically for atmospheric tanks)
Key Formulas
t = (4.9 * D * (H - 0.3) * w) / (S * E) + C — Minimum thickness of shell plates (1-Foot Method)
Practical Notes
Ensure the foundation is well-compacted and leveled; uneven settlement during the mandatory hydrostatic testing can deform the tank bottom and shell.
Wind girders (stiffening rings) are essential for large-diameter open-top or weak-roof tanks to prevent buckling from wind pressure when the tank is empty.
Always apply an appropriate corrosion allowance based on the chemical properties of the stored fluid and environmental exposure, as the minimum thicknesses specified exclude it.