Tank, Vessel & Pressure Equipment Fabrication worked example

Shell Thickness Allowance with available shell thickness of 63 units: a worked example

Here is what the math looks like when conditions slip. We hold every other input steady and drop available shell thickness to 63 units, then walk the calculation through step by step. Shell Thickness Allowance is the margin between the plate thickness you actually have and the minimum the pressure code requires for the design conditions.

The inputs for this scenario

  • Available shell thickness: 63 units (the input this scenario stresses; the baseline uses 125)
  • Code-required minimum thickness: 100 units (held at the documented default)
  • Reference nominal thickness: 100 units (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Shell Thickness Allowance margin = available value - required value.
  • Margin works out to -37 % at these inputs, and this is the headline figure for the scenario.
  • Absolute margin works out to -37 value at these inputs.
  • Available amount works out to 63 value at these inputs.
  • Required amount works out to 100 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where available shell thickness sits at 125 units and the headline result is 25 %, this scenario comes in 248% below the baseline at -37 %.
  • The practical read: the gap between this scenario and the baseline is entirely attributable to available shell thickness, so recovering it is worth quantifying in dollars before considering equipment or staffing changes. It is a straight thickness comparison and does not itself perform the ASME t = PR/(SE-0.6P) minimum calculation — you must supply a correctly derived required thickness.

Results at a glance

  • Margin: -37 % (headline result)
  • Absolute margin: -37 value
  • Available amount: 63 value
  • Required amount: 100 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Shell Thickness Allowance calculator, set available shell thickness to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.