ISO 22538-2:2007

Overview

ISO 22538-2:2007 - "Space systems - Oxygen safety - Part 2: Selection of metallic materials for oxygen systems and components" defines a process for selecting metallic materials used in oxygen systems for space applications. The standard applies equally to ground support equipment, launch vehicles and spacecraft and focuses on minimizing ignition and combustion risks in high‑pressure gaseous oxygen (GOX), liquid oxygen (LOX) and oxygen‑enriched environments.

Key topics and requirements

• Scope and applicability: Material selection process for metallic parts in direct or indirect oxygen service across ground and flight systems.
• Design considerations: Treats structural and operational pressures equally with flammability risk; emphasizes geometry, configuration and component design as important mitigations.
• Ignition mechanisms: Identifies credible ignition sources such as particle and mechanical impact, pneumatic impact, galling/friction, electrical arcing, promoted ignition, resonance, and ignition by contaminants (oils/greases).
• Materials testing and limits: Notes there is no single test that provides absolute ignition limits for all materials; selection relies on ignition and combustion testing tailored to the component’s end‑use conditions.
• Material classes covered: Guidance is provided for common metals and alloys (nickel and nickel alloys, copper and copper alloys, stainless steels, aluminium and aluminium alloys, iron alloys and others).
• Materials control and certification: Requires manufacturer material certification and recommends independent confirmation. Stresses strict control of materials used in LOX, GOX and oxygen‑enriched systems.
• Environmental and operational factors: Selection must consider temperature (including low temperatures for LOX), pressure, flow, surface condition, oxide layers, contaminant susceptibility and aging effects.
• Configuration testing: Advises component‑level testing and evaluation under representative operating conditions.

Practical applications

• Use ISO 22538-2 to:
  • Select alloys and surface treatments for oxygen valves, fittings, tanks and piping.
  • Define procurement and certification requirements for metallic parts used in oxygen service.
  • Develop test plans for component‑level ignition testing and LOX/GOX compatibility assessments.
  • Inform cleaning, handling and maintenance procedures to avoid contaminant‑initiated fires.

Who should use this standard

• Aerospace systems designers and engineers (spacecraft, launch vehicle and ground support)
• Materials and metallurgical engineers
• Safety, reliability and quality assurance teams
• Procurement and supplier qualification personnel
• Test engineers responsible for oxygen compatibility and ignition testing

Related standards

• ISO 22538-1: Design of oxygen systems and components
• ISO 22538-3: Selection of non‑metallic materials for oxygen systems and components
• ISO 22538-4: Hazards analyses for oxygen systems and components
• ISO 4589 (Plastics - Determination of burning behaviour by oxygen index) - normative reference

Keywords: ISO 22538-2, oxygen safety, space systems, metallic materials, LOX compatibility, GOX, material selection, ignition mechanisms, materials certification.