Overview
ISO/TR 12391-1:2001 is an informative Technical Report that documents the philosophy, background and conclusions for performance testing of refillable seamless steel gas cylinders, especially those manufactured from steels with tensile strength (Rm) greater than 1 100 MPa. It covers cylinders from 0.5 l to 150 l water capacity and provides the technical rationale used to introduce additional manufacturing and test controls for higher‑strength steels. The report summarizes the WG 14 research program, test methods, data collection and final recommendations that informed changes in ISO cylinder design standards.
Key topics and technical requirements
- Scope and intent: Guidance for assessing fracture performance and fatigue behaviour of high‑strength seamless steel cylinders and for updating ISO design and test standards.
- Primary test methods:
- Flawed cylinder burst test - finished cylinders with an exterior machined flaw (~75% of wall thickness) are pressurized (monotonic or cyclic, hydraulic) to observe leak vs. fracture behaviour.
- Flawed cylinder cycle test - shallow machined flaw (~10% of wall thickness) with cyclical hydraulic pressurization to evaluate fatigue life.
- Charpy V‑notch (CVN) impact test - transverse orientation at −50 °C used as a secondary toughness control.
- Standard tensile testing to record mechanical properties.
- Fracture performance focus: Distinguishes between leak‑before‑break (LBB) and running crack fracture modes and addresses the potential toughness reduction at higher tensile strengths.
- Data program and validation: Over 500 standardized tests from multiple manufacturers were compiled in a common data bank (NIST) to validate the flawed cylinder approach and CVN acceptance criteria.
- Conclusions: The flawed cylinder burst test is an effective manufacturing control to predict fracture initiation; CVN at −50 °C supports toughness acceptance. The flawed cylinder cycle test was later adopted in ISO 9809‑2 to control fatigue performance.
Applications and users
ISO/TR 12391-1 is practical for:
- Cylinder manufacturers developing or qualifying high‑strength seamless steel cylinders
- Design and materials engineers evaluating fracture and fatigue safety margins
- Test laboratories and quality control teams implementing flawed burst/cycle and impact tests
- Regulators and certification bodies assessing compliance of new cylinder designs
- Standards committees and researchers updating design rules or creating advanced design standards
Related standards
- ISO 9809‑1:1999 - design and testing for quenched and tempered steel cylinders (Rm < 1 100 MPa)
- ISO 9809‑2:2000 - design and testing for cylinders with Rm ≥ 1 100 MPa (adopts flawed cycle test)
- ISO 6406:1992 - periodic inspection and testing of seamless steel gas cylinders
- ISO/TR 12391 Parts 2–4 - detailed test data and procedures (fracture and cycle tests)
Keywords: gas cylinders, seamless steel, refillable cylinders, flawed cylinder burst test, fracture performance, Charpy V‑notch, fatigue cycle test, ISO 9809‑2, leak‑before‑break, tensile strength >1100 MPa.