Tank, Vessel & Pressure Equipment Fabrication worked example

Head Forming Allowance with blank plate diameter or size available of 310 in: a worked example

Push blank plate diameter or size available up to 310 in and the picture changes. This example computes every intermediate figure at that operating point. Use it when head forming allowance in tank, vessel and pressure equipment fabrication needs a clean margin number for a tank, vessel and pressure equipment fabrication go / no-go review.

The inputs for this scenario

  • Blank plate diameter or size available: 310 in (raised for this scenario; the documented default is 125)
  • Finished head dimension required: 100 in (unchanged)
  • Nominal head diameter reference: 100 in (unchanged)

Working through the calculation

  • Applying the documented formula (Head Forming Allowance margin = available value - required value) to the inputs above produces each figure below.
  • At this operating point the engine returns 210 % for margin, the number this scenario is built around.
  • At this operating point the engine returns 210 value for absolute margin.
  • At this operating point the engine returns 310 value for available amount.
  • At this operating point the engine returns 100 value for required amount.

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 740% above the baseline at 210 %.
  • It subtracts the required finished dimension from the available blank size and expresses that margin as a percentage of the nominal head reference. The value of this scenario is the size of the gap it exposes: that gap, priced out over a year, is the budget you can justify spending to close it.

Results at a glance

  • Margin: 210 % (headline result)
  • Absolute margin: 210 value
  • Available amount: 310 value
  • Required amount: 100 value

Run it with your numbers

  • Every input above is editable in the live Head Forming Allowance calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.