Overview
ISO/TR 10771-2:2008 - Hydraulic fluid power - Fatigue pressure testing of metal pressure-containing envelopes - Part 2: Rating methods - defines statistical rating methods for verifying the fatigue pressure capability of metal pressure-containing envelopes in hydraulic components. It is a companion to ISO 10771-1 (test method) and is intended for steady internal cyclic pressure loading only. The report provides a universal verification approach based on material variability, statistical assurance/verification levels and calculation of the cyclic test pressure required to demonstrate a rated fatigue pressure.
Key topics and requirements
- Scope and applicability
- Applies to metal pressure-containing envelopes where fatigue is the dominant failure mode.
- Excludes piping (see ISO 4413), operating regimes causing creep or low-temperature embrittlement, and strength loss from corrosion or chemical action.
- Core definitions
- Rated fatigue pressure (PRF) - maximum pressure verified for a rated cycle life.
- Assurance level - probability that a randomly selected specimen’s fatigue strength exceeds PRF (nominally 90%).
- Verification level - probability that fatigue strength is not less than the cyclic test pressure (nominally 90%).
- Coefficient of variation (ko) - material fatigue scatter (std. dev. / mean).
- Variability factor (KV) - ratio of cyclic test pressure to rated fatigue pressure.
- Determining cyclic test pressure
- Select material ko (from tests or Annex A material database).
- Choose assurance and verification levels, and specimen counts.
- Determine variability factor KV (see Table 1 and Annex B).
- Calculate cyclic test pressure: PCT = KV × PRF.
- Conduct and acceptance
- Perform fatigue tests per ISO 10771-1 for the chosen cycle count (1×10^6 to 1×10^8 cycles).
- Test is successful if selected element specimens do not fail (see Clause 6.3).
- Supporting material
- Annex A: material factor database (ko values).
- Annex B: calculation of KV.
- Annex C: proposal for acceleration factors.
- Annex D: statistical basis and worked examples.
Applications and users
- Who benefits
- Hydraulic component manufacturers (cylinders, valves, pump housings), test laboratories, design engineers, certification bodies and maintenance engineers.
- Practical uses
- Verifying fatigue ratings for product datasheets and safety assessments.
- Establishing test programs to demonstrate lifecycle performance under cyclic internal pressure.
- Extending verified ratings to similar component variants when geometry and strength are not reduced.
Related standards
Keywords: ISO/TR 10771-2:2008, fatigue pressure testing, hydraulic fluid power, pressure-containing envelope, fatigue rating, cyclic test pressure, variability factor, assurance level, verification level.
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