Overview
ISO/TR 7468:1981 is a Technical Report that compiles and summarises average stress‑rupture (creep rupture) properties of wrought steels used for boilers and pressure vessels. The data were obtained by cooperative testing among ISO member bodies and served as the experimental basis for the International Standards ISO 2604 parts I–IV (1975). The report provides tabulated rupture stresses and parametric master curves covering long durations (typically 10 000 h to 250 000 h), with metadata on chemistry, heat treatments, product forms and the quantity/duration of test data.
Key Topics
- Average rupture stress tables for many wrought steel grades (carbon steels, carbon‑manganese steels, Mo‑alloyed steels, Cr–Mo types, etc.), given for a range of temperatures and times.
- Parametric master curves and coefficients to relate stress, temperature and time to rupture (creep‑rupture parameter).
- Data quality indicators: the report documents number and duration of test points used to derive values and notes a typical ±20% scatter about the average.
- Extrapolation rules:
- Extended time extrapolation is flagged with an asterisk (*) where tabulated values go beyond reliable test durations.
- Extended stress extrapolation is indicated by parentheses and is acknowledged as more uncertain.
- Material conditions and scope: chemical composition ranges, heat‑treatment states, product forms and sizes for which the values apply.
- Practical correction factors: examples include a 10% reduction in average rupture stress recommended for carbon and carbon‑manganese steels that have been tempered, stress‑relieved or post‑weld heat treated for >3 h at 620 °C.
Applications
ISO/TR 7468 is useful when you need empirically based creep‑rupture data for design, assessment or specification of steels in high‑temperature pressure equipment. Typical uses:
- Preliminary material selection for boilers, pressure vessels and high‑temperature piping.
- Creep life assessment and long‑term strength estimation in engineering calculations.
- Supporting procurement specifications and acceptance criteria when matching materials to ISO 2604 quality requirements.
- Reference for metallurgists and testing laboratories evaluating test programs and extrapolation limits.
Who uses this standard
- Mechanical and pressure‑vessel engineers
- Materials scientists and metallurgists
- Design offices, QA/QC and procurement teams for power and process plants
- Test laboratories and standards committees.
Related Standards
- ISO 2604 (Parts I–IV) - quality requirements for the steel grades covered in this report.
- Relevant ISO/TC 17/SC 10 technical documents (source of the test datasets).
Keywords: ISO TR 7468, stress rupture properties, creep rupture strength, wrought steels, boilers, pressure vessels, master curves, ISO 2604, material selection, long‑term strength.