Tank Shell Plate Thickness Calculator
Calculate tank shell plate thickness accurately for your build. Get material quantities, waste allowances, and project cost breakdowns.
Formula
t = (P x R) / (S x E - 0.6 x P) + CA
Where P is the design pressure (kPa), R is the tank inner radius (mm), S is the allowable stress (MPa), E is the joint efficiency factor (0-1), and CA is the corrosion allowance (mm). This formula derives from the ASME thin-wall pressure vessel equation and is widely used in API 650 tank design for calculating required shell course thicknesses.
Worked Examples
Example 1: Atmospheric Storage Tank
Problem: Calculate shell thickness for a tank with 5 m radius, 15 kPa design pressure, 137.9 MPa allowable stress, 0.85 joint efficiency, and 3 mm corrosion allowance.
Solution: t = (P x R) / (S x E - 0.6 x P) + CA\nt = (15 x 5000) / (137.9 x 0.85 - 0.6 x 15) + 3\nt = 75000 / (117.215 - 9) + 3\nt = 75000 / 108.215 + 3 = 0.69 + 3 = 3.69 mm\nMinimum per API 650 = 5 mm
Result: Required thickness = 5 mm (minimum governs)
Example 2: High Pressure Vessel Shell
Problem: Calculate shell thickness for a vessel with 2 m radius, 1500 kPa pressure, 138 MPa allowable stress, joint efficiency 1.0, and 1.5 mm CA.
Solution: t = (1500 x 2000) / (138 x 1.0 - 0.6 x 1500) + 1.5\nt = 3000000 / (138 - 900) + 1.5\nNote: For high pressures, use thick-wall formula\nt = 3000000 / 137.1 + 1.5 = 21.88 + 1.5 = 23.38 mm
Result: Required thickness = 23.38 mm
Frequently Asked Questions
What standard is used for tank shell plate thickness calculations?
The most common standards are API 650 for atmospheric storage tanks and ASME Section VIII for pressure vessels. API 650 provides specific formulas for calculating shell plate thickness based on hydrostatic loading, wind, and seismic conditions. The formula considers design pressure, tank radius, allowable stress of the material, and joint efficiency factor. A corrosion allowance is always added to the calculated thickness to extend service life.
What is joint efficiency in tank design?
Joint efficiency is a factor (typically 0.7 to 1.0) that accounts for the strength reduction at welded joints compared to the base material. A joint efficiency of 1.0 means the weld is as strong as the parent metal, which requires full radiographic examination. Lower values like 0.85 or 0.7 correspond to spot or no radiographic examination. The choice of joint efficiency directly affects the required plate thickness and overall tank cost.
Why is corrosion allowance added to the calculated thickness?
Corrosion allowance accounts for material loss over the design life of the tank due to chemical attack, erosion, or environmental degradation. Typical values range from 1.5 mm to 6 mm depending on the stored product and operating conditions. For mildly corrosive services, 3 mm is standard, while highly corrosive environments may require 6 mm or more. Without corrosion allowance, the tank could lose structural integrity before its intended service life ends.
What is the minimum shell plate thickness for storage tanks?
Per API 650, the minimum shell plate thickness depends on the tank diameter. For tanks up to 15 m diameter, the minimum is 5 mm. For tanks between 15 m and 36 m, the minimum is 6 mm. Tanks between 36 m and 60 m require at least 8 mm, and those over 60 m need 10 mm minimum. These minimums apply regardless of the calculated thickness to ensure structural rigidity during fabrication, transport, and erection.
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