Tube, Pipe & Profile Forming calculator
Hydroforming Initial Yield Pressure Calculator
Estimate initial yielding of a round tube with closed ends and no imposed axial feed. Enter initial geometry, tensile yield strength and the approved pressure limit.
What this calculator does
- Estimate the pressure that begins yielding a closed-end, thin-walled round tube before hydroforming calibration.
Formula used
- Inner radius (mm) = outside diameter ÷ 2 − wall thickness
- Initial yield pressure (MPa) = 2 × tensile yield strength × wall thickness ÷ (sqrt(3) × inner radius)
- Pressure headroom (MPa) = process pressure limit − initial yield pressure
- Pressure limit used (%) = initial yield pressure ÷ process pressure limit × 100
- Inner radius to wall = inner radius ÷ wall thickness
Inputs explained
- Initial Outside Diameter: Initial tube outside diameter from the blank drawing.
- Initial Wall Thickness: Initial measured wall thickness before forming.
- Tensile Yield Strength: Material yield strength at the forming temperature.
- Process Pressure Limit: Approved gauge pressure limit for this machine and tooling.
How to use the result
- Best suited to initial tube yielding Estimate, hydroforming feasibility review.
- Does not predict corner filling, strain hardening, wall thinning or bursting. Axial feed, weld properties and die contact need a separate forming model.
Current U.S. benchmarks
- The producer price index for steel mill products stands at 381.162 (BLS, Aug 2026), up 23.4% from a year earlier. Quotes priced off last quarter's material cost miss this move.
Common questions
- Why are closed ends specified? Pressure on closed ends creates axial stress alongside hoop stress. This model assumes that pressure-induced axial stress and no additional axial feed load; different restraint changes the yielding condition.
- Does this give my final forming pressure? No. It estimates initial yielding of the round blank. Final pressure depends on evolving wall thickness, hardening, die geometry and axial feeding, which require a validated process model or trials.
- Why does thick wall block the result? The membrane approximation neglects radial stress and variation through the wall. The cited model requires inner radius at least ten times wall thickness; use a thick-wall analysis outside that range.
- Is the entered pressure limit a burst limit? No. It is your approved machine and tooling operating limit. This calculator does not predict tube rupture or qualify a pressure-containing assembly.
Last reviewed 2026-10-06.