Tank, Vessel & Pressure Equipment Fabrication worked example

Head Forming Allowance with blank plate diameter or size available of 63 in: a worked example

This worked example runs the head forming allowance numbers for a tougher week than the baseline: blank plate diameter or size available of 63 in instead of the typical 125 in. The Head Forming Allowance calculation compares the blank plate size you have available against the finished head dimension you need, expressing the surplus as a margin percent of the nominal head diameter.

The inputs for this scenario

  • Blank plate diameter or size available: 63 in (the input this scenario stresses; the baseline uses 125)
  • Finished head dimension required: 100 in (held at the documented default)
  • Nominal head diameter reference: 100 in (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Head Forming 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 blank plate diameter or size available sits at 125 in and the headline result is 25 %, this scenario comes in 248% below the baseline at -37 %.
  • Use it when checking whether a plate blank is adequate before releasing it to a head-forming press or spinning lathe. A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

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 Head Forming Allowance calculator, set blank plate diameter or size available to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.