ISO/TR 10771-2:2008

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

• ISO 10771-1:2002 - Test method (mandatory reference)
• ISO 4413 - Fluid power - General rules for piping (exclusion scope)
• ISO 5598 - Fluid power vocabulary

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.