ISO 21173:2019

Overview

ISO 21173:2019 specifies a unified hydrostatic pressure test method for the pressure hull and buoyancy materials of submersibles. The standard defines the required test sequence (a prior tightness test followed by the hydrostatic pressure test), optional tests (continuous pressurization/depressurization, long‑term static load and cycling external pressure tests), environmental and equipment conditions, and reporting. It applies to the pressure structure of manned and unmanned submersibles, including accessories such as viewports, hatches and connectors, but is not applicable to submarines or submersibles that park or operate underwater for more than one week.

Key topics and technical requirements

• Test sequence: mandatory tightness test, then hydrostatic pressure test; optional strain, continuous pressurization/depressurization, and buoyancy material long‑term/cycling tests.
• Test pressures:
  • Manned submersibles (max working depth ≤ 6 000 m): test pressure = 1.25 × maximum working pressure.
  • Manned submersibles (> 6 000 m) and unmanned submersibles: test pressure 1.1 × to 1.25 × maximum working pressure.
• Pre-test: newly built pressure hulls are recommended to undergo a pre‑test cycle to relieve residual stresses before formal testing.
• Pressurization/depressurization rates and hold times:
  • Rates must be at least equal to pressure change rates caused by diving and surfacing speeds.
  • Hold time at maximum working pressure must be at least the design operation time at that pressure.
• Test environment and media:
  • Temperature typically 10 °C to 30 °C (viewports tested at their design temperature with tight tolerances).
  • Atmospheric pressure 0.084–0.106 MPa, relative humidity 30–95%.
  • Pressure medium: fresh water or seawater.
• Equipment and calibration:
  • Test equipment must be certified and instruments verified/calibrated.
  • Pressure gauge range: two‑thirds of range must be ≥ maximum test pressure.
• Records and reporting: all checks, measurements and outcomes must be recorded; a formal test report is required.

Applications and users

ISO 21173:2019 is used to verify pressure resistance and leak tightness before assembly or deployment. Typical users:

• Submersible designers and manufacturers (manned and unmanned)
• Test laboratories and certification bodies
• Classification societies and regulators
• Operators preparing new submersibles or replacing pressure‑bearing components
• Materials engineers evaluating buoyancy materials (qualification testing)

Related standards

This standard was prepared by ISO/TC 8 (Ships and marine technology), SC 13 (Marine technology). For comprehensive compliance, use ISO 21173:2019 alongside your organization’s design specifications and other marine/submersible testing and safety standards.