Overview
ISO 23208:2017 - "Cryogenic vessels - Cleanliness for cryogenic service" specifies minimum cleanliness requirements for all surfaces of cryogenic vessels and associated accessories that contact cryogenic fluids under expected operating conditions. The standard sets acceptance criteria to reduce equipment malfunction and to ensure safety against ignition when components contact oxygen or oxidizing fluids.
Key topics and requirements
- Scope and purpose: Defines acceptable levels of surface and particle contamination for cryogenic service, with special provisions for oxygen/oxidizing fluids (see ISO 10156).
- General cleanliness:
- Foreign matter (chips, oxide scale, weld spatter) is not acceptable.
- Particles visible under daylight/white light without magnification are unacceptable.
- Free water must not be detectable by visual examination.
- Weld root passes shall be protected (e.g., forming gas) to avoid gross porosity.
- Oxygen and oxidizing fluids:
- Hydrocarbon contamination, paints, adhesives, sealants and protective coatings shall not be detectable by visual white‑light inspection unless oxygen‑compatible per ISO 21010.
- A guidance value for maximum hydrocarbon contamination is 500 mg/m² (taken from CGA G‑4.1); lower limits may be required based on application.
- Cleaning procedures:
- Any cleaning method is acceptable if it meets the requirements. Solvents/agents must be compatible with materials (particularly plastics) and removed if not oxygen‑compatible.
- Cleanliness evaluation and inspection:
- Inspection and sampling methods must ensure compliance and be documented. Annex A lists practical methods: direct visual (daylight/white light), ultraviolet (UV) inspection, wipe tests, water‑break tests and solvent contamination tests (mass, volume, light transmission).
- Post‑cleaning protection:
- Items must be protected (packaging, purging, sealing) to maintain cleanliness. Protective gases must be dry, oil‑free and dust‑free. Packaging must be removable without leaving residues. Purge/pressurizing gas pressures >0.5 bar require a warning tag.
- Identification and documentation:
- Conformity evidence via certificate or label: use “ISO 23208 – cleaned oxygen” for oxygen service, or “ISO 23208” for other cryogenic fluids. Indicate protective gas type and pressure when used.
Applications - who uses this standard
- Manufacturers and fabricators of cryogenic vessels and accessories
- Quality assurance and inspection teams in cryogenic engineering
- Plant operators, maintenance and commissioning personnel handling liquid oxygen or other cryogenic oxidizers
- Procurement and safety engineers specifying cleaning acceptance criteria and documentation
- Testing laboratories performing cleanliness verification (wipe tests, solvent analysis, water‑break)
Related standards
- ISO 21010 (cryogenic gas/materials compatibility)
- ISO 10156 (oxidizing ability and fire potential)
- ISO 21029‑1 / ISO 21009‑1 (related cryogenic vessel design/fabrication standards)
- CGA G‑4.1 and EIGA guidance are referenced for hydrocarbon contamination guidance
Keywords: ISO 23208, cryogenic vessels, cleanliness, oxygen service, oxidizing fluids, cleaning procedure, inspection methods, wipe test, water break test, hydrocarbon contamination.
