Overview
ISO 23467:2020 - "Ice plug isolation of piping in nuclear power plant" defines requirements and safe practices for using the ice plug technique to temporarily isolate metal piping in nuclear power plants. The standard covers ice plug generation, formation judgment and removal, measures before/during/after ice plugging, personnel qualifications, equipment, and non‑destructive testing. It applies to cryogenic refrigerants such as liquid nitrogen and dry ice, and to freezing liquids (e.g., water or boric acid mixtures). Pressure testing and cladded or internally coated pipes are principally excluded.
Key topics and technical requirements
- Personnel & training
- Qualified, professionally trained staff only; specialized contractors recommended.
- Equipment & safety
- Use purpose-designed ice plug jackets, liquid nitrogen/dry‑ice chambers, hoses, PPE, oxygen meters and calibrated thermometers/pressure gauges; provide anti‑asphyxia protection.
- Preconditions
- Pipes must be filled with a freezable liquid and free of air; flow rate should be minimized (ideally near zero).
- Ambient and pipe surface temperature limits and mock‑up tests for validation are required in some cases.
- Material and structural limits
- Applicable to metallic pipes (carbon or stainless steel); cladded pipes, internal coatings, cast iron/copper and lining pipes are excluded.
- Avoid ice plugging over welds unless validated; vibration and mechanical shock must be prevented.
- Refrigerant selection and size limits
- Liquid nitrogen (≈ −196 °C) recommended up to DN 400 (ferritic) or DN 300 (austenitic) unless mock‑up validated.
- Dry ice (≈ −78 °C) suitable up to DN 100.
- Other refrigerants (e.g., freon) only for very small diameters.
- Positioning rules
- Maintain distance from fittings, valves or welds (greater than 20 × outer diameter or 600 mm, whichever is larger), and provide pressure‑relief arrangements between ice plugs.
- Testing & QA
- Non‑destructive testing methods referenced: penetrant (ISO 3452), magnetic particle (ISO 9934), ultrasonic (ISO 16810), visual weld inspection (ISO 17637) and radiographic inspection (ISO 20769).
- Quality assurance before, during and after ice plugging; record keeping and reports required.
Applications and users
- Practical for on‑line isolation during maintenance, outages and component replacement where permanent isolation fittings are not available.
- Main users: nuclear plant maintenance and outage planners, piping engineers, NDT specialists, safety officers and qualified contractors involved in cryogenic pipe isolation.
Related standards & next steps
- Normative references within ISO 23467 include ISO 3452, ISO 9934, ISO 16810, ISO 17637 and ISO 20769 for NDT methods.
- For implementation: obtain the full ISO 23467:2020 text, consult referenced NDT standards, run mock‑up validation tests, and align procedures with local regulatory requirements.
