API 650 Storage Tank Shell Thickness (1-Foot Method) Calculator

Determine minimum nominal shell plate thickness (td & tt) for each course of welded atmospheric storage tanks per API Standard 650 Section 5.6.

Tank Geometry & Product Properties

Tank Nominal Diameter D (m):

Max Design Liquid Height H (m):

Liquid Specific Gravity G: Crude ~ 0.85-0.90 | Water = 1.0

Corrosion Allowance CA (mm):

Shell Steel Grade (API 650 Table 5.2):

Shell Course Evaluated:

Plate Thickness & Governing Case

Governing Nominal Thickness:

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Governing Condition:

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Operating Thickness (t_d):

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Hydrostatic Test Thickness (t_t):

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Tank Storage Volume & Plate Weight:

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Frequently Asked Questions

What is the API 650 "1-Foot Method" for shell plate design?

The 1-foot method calculates circumferential hoop stress at a point 1 foot (0.3 meters) above the bottom weld of each course. This offset accounts for the bending moment restraint offered by the rigid bottom-to-shell joint or adjacent course.

When is the 1-foot method permitted versus the Variable-Design-Point method?

The 1-foot method is permitted for tanks up to 60 meters (200 ft) in diameter. For larger tanks (D > 60 m), the Variable-Design-Point method (Section 5.6.4) must be used to optimize plate thickness and save steel weight.

Why is hydrostatic test thickness evaluated without corrosion allowance?

Hydrostatic testing is performed with clean water prior to commissioning when the tank shell is in pristine, brand-new condition. Therefore, no corrosion allowance is needed, and higher allowable stresses (St ≈ 0.75·Y) are permitted.