API TR 5C3 and ISO/TR 10400 both show up as the cited basis for casing and tubing burst, collapse, and tension calculations, and it’s a fair question whether picking one over the other actually changes anything. The short answer: for the core equations, no — ISO/TR 10400 was developed specifically to be the internationally-recognized equivalent of API’s document. But “functionally equivalent” isn’t quite the same as “identical,” and it’s worth knowing where the two actually line up and where the practical differences show up.
Same origin, different governing body
API TR 5C3 (formerly Bulletin 5C3) is API’s technical report covering the standard equations for calculating burst, collapse, and tension ratings of casing and tubing — the same collapse-regime and biaxial-tension-correction equations behind our own Collapse Pressure and Internal Yield (Burst) Pressure calculators. ISO/TR 10400 was developed under ISO’s petroleum and natural gas industries technical committee to provide the same design equations in an ISO-governed document, for use in jurisdictions and organizations that specify ISO standards as their baseline rather than API’s.
Where they genuinely line up
The core technical content — the API 5C3-derived collapse regime equations (yield, plastic, transition, elastic), the burst pressure formula, and the biaxial (von Mises ellipse) axial-tension correction to collapse resistance — is the same underlying method in both documents. A pipe’s calculated burst, collapse, or tension rating shouldn’t come out meaningfully different depending on which document you cite, because both are drawing on the same body of API-developed empirical and analytical work.
Where the practical differences actually show up
- Which one your contract or regulator specifies. An operator, a regulatory body, or a client contract may name one document explicitly as the required design basis, in which case the choice isn’t really a choice — it’s whichever one governs the job.
- Edition and revision timing. The two documents aren’t necessarily updated on the same schedule, so it’s worth confirming which edition of whichever standard applies is current, rather than assuming “API 5C3” or “ISO 10400” alone fully specifies the calculation basis without a revision date attached.
- What a reviewer expects to see cited. A design package reviewed by an API-standard-oriented body will expect to see API TR 5C3 referenced explicitly; an ISO-oriented reviewer will expect ISO/TR 10400. Citing the “wrong” one for your reviewer’s context, even with an identical correct calculation behind it, can slow a review down for no technical reason.
The practical takeaway
For the actual engineering — the formulas and the numbers they produce — API TR 5C3 and ISO/TR 10400 are the same calculation under two different governing bodies, and neither is more “correct” than the other. Which one to cite in a given design package comes down to what your client, regulator, or contract specifies, not which one gives a different answer, because for the core tubular design equations, they don’t.
Our burst and collapse calculators are built on the shared API TR 5C3 / ISO TR 10400 equations. Try the full calculator set, browse more terms in our Glossary, or talk to an engineer about which standard your project needs to cite.
