Collapse Pressure

Standard: API TR 5C3 (formerly API Bulletin 5C3), Technical Report on Equations and Calculations for Casing, Tubing, and Line Pipe Used as Casing or Tubing — equivalent methodology to ISO TR 10400. The tension correction is the biaxial (von Mises ellipse) method these standards describe for combining axial load with collapse resistance.

Formula basis: API’s collapse rating is piecewise — four regimes (yield strength, plastic, transition, elastic collapse), selected by the pipe’s D/t ratio, each with its own theoretical or empirical formula. Axial tension reduces the yield strength used in these formulas (compression technically increases it slightly) via the biaxial correction, producing a reduced yield strength Ypa in place of the pipe’s actual minimum yield strength Yp. Leave axial load at 0 to get the standard, unreduced API collapse rating for the pipe.

Scope and limitations: This is collapse resistance under axial load only — it does not include the effect of internal pressure (the full triaxial/von Mises envelope combines collapse, axial load, and internal pressure together), temperature derating, or connection rating. Axial stress should reflect the true stress at the point of interest in the string (pipe weight above, buoyancy, bending, shock loads) — not just static surface weight.

For preliminary screening only. Not a substitute for a full triaxial (von Mises) load-case analysis or a certified engineering assessment.

Need the pipe body’s burst-pressure capacity too? Try the Internal Yield (Burst) Pressure calculator.