BIZOMAT MAKEOS · Strength
Vertical Storage Tank Shell Thickness by Course
How thick must each shell course of this vertical liquid storage tank be, and what does the shell weigh?
Shell plate thickness for an open-top or low-pressure vertical cylindrical storage tank under its liquid head, course by course, by the widely used one-foot method (API 650 style) with joint efficiency, corrosion allowance and a minimum thickness, with tank capacity and shell steel mass — for preliminary comparison.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Tank diameter | m | Nominal tank diameter. |
| Design liquid height | m | Height from the bottom to the design liquid level (top of shell or overflow). |
| Specific gravity of the liquid | Specific gravity of the stored liquid (1.0 for water; use the test water case too). | |
| Allowable stress | MPa | Allowable stress of the shell plate. |
| Joint efficiency | Joint efficiency of the vertical welds. | |
| Corrosion allowance | mm | Corrosion allowance. |
| Minimum shell thickness | mm | Minimum nominal thickness for the tank diameter (from the tank standard). |
| Course (plate) height | m | Height of each shell course. |
| Steel density | kg/m³ | Density of the shell steel. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Tank diameter
- What it is
- The nominal diameter of the cylindrical tank shell. It sets the hoop stress for a given liquid depth and the tank’s capacity.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 200 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Calculated thickness is proportional to diameter; capacity rises with its square.
- Get it right
- The formula takes this in metres while thicknesses are in millimetres; do not type the diameter in millimetres.
What this means: Design liquid height
- What it is
- The height from the tank bottom to the highest liquid level the tank is designed for, usually the top of the shell or the overflow.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 50 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 12 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the liquid head on every course and the number of courses.
- Get it right
- Use the design liquid level, not the normal operating level, which is usually lower.
What this means: Specific gravity of the liquid
- What it is
- How many times denser the stored liquid is than water. It scales the liquid pressure on the shell.
- Units and format
- Enter a plain number with no unit. The form accepts 0.3 to 3. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The calculated thickness before corrosion allowance is proportional to G.
- Get it right
- Type the ratio, not the density in kg/m³. For a liquid lighter than water, check the water test case too.
What this means: Allowable stress
- What it is
- The working stress the tank standard allows in the shell plate for the liquid case, which depends on the plate grade.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 500 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 160 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The calculated thickness before corrosion allowance is inversely proportional to it.
- Get it right
- Take it from the applicable tank standard for the plate grade; it is not the yield or tensile strength.
What this means: Joint efficiency
- What it is
- The strength of the vertical welded joints relative to the plate, set by joint type and the amount of inspection under your standard.
- Units and format
- Enter a plain number with no unit. The form accepts 0.5 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.85 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The calculated thickness before corrosion allowance is inversely proportional to it.
- Get it right
- Type it as a fraction, not a percent.
What this means: Corrosion allowance
- What it is
- Extra thickness added to each course to allow for metal lost to corrosion over the tank’s life.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Adds directly to every calculated course thickness.
- Get it right
- It is added to the calculated thickness before comparison with the minimum, not on top of the minimum thickness.
What this means: Minimum shell thickness
- What it is
- The least nominal plate thickness the tank standard allows for this tank diameter, regardless of liquid load.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 50 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 6 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Any course whose calculated thickness falls below it is raised to it.
- Get it right
- Take it from the tank standard for the diameter; upper courses are often set by this value rather than by the liquid head.
What this means: Course (plate) height
- What it is
- The height of each ring of shell plate, normally the width of the plates bought.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 5 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the number of courses and the liquid head at the bottom of each one.
- Get it right
- Use the plate width actually available; the top course may be shorter and the tool allows for that.
What this means: Steel density
- What it is
- The mass of one cubic metre of the shell plate steel, used only to turn the shell volume into a mass.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 10000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 7850 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Shell mass is directly proportional to it; thicknesses do not change.
- Get it right
- Enter kg/m³, not g/cm³.
Method and formulas
- One-foot method: t = 4.9 D (H − 0.3) G ÷ (S E) + CA (t in mm, D and H in m, S in MPa), with H the liquid height above the bottom of the course.
- Each course thickness is at least the minimum thickness.
- Capacity = π D² ÷ 4 × liquid height; shell mass = Σ π D × course height × thickness × density.
- Example: a 20 m × 12 m water tank needs 9.9309 mm at the bottom course and holds 3,769.9 m³.
Limitations
- Preliminary comparison only; storage tanks must be designed to the applicable standard (API 650, AS 1692, EN 14015) with wind, seismic, roof and bottom design.
- Shell stability and openings are not covered.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate plate thicknesses for a water or oil tank
- Compare tank diameter and height options by steel weight
- Check an existing tank for a heavier liquid
Who it is for
- Mechanical engineers
- Estimators
- Plant engineers
What you get
- Thickness of each course
- Tank capacity
- Shell steel mass
Interpreting the result
- Thickness grows with diameter and depth: a wider, lower tank is not always lighter once the minimum thickness governs the upper courses.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 290–294, 3021–3026. Topic reference; no source tables or recommended settings are reproduced.
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Open the Vertical Storage Tank Shell Thickness by Course calculator