Overview
ISO 13971:2012 specifies requirements, design and installation practices for flexible pipe elements, vibration isolators, expansion joints and non‑metallic tubes used in the refrigerant circuits of refrigeration systems and heat pumps. The standard also defines how to qualify the tightness and permeability of non‑metallic tubes (plastic/rubber) on the evaporating and condensing sides. It excludes flexible pipes that are only occasionally overstressed (e.g., during repair) and freely rotating or hinged joints.
Key topics and technical requirements
- Scope and definitions: classification of metallic flexible pipe, metallic flexible tube (bellows), non‑metallic flexible tube, vibration isolator, expansion joint.
- Design & installation:
- Install per manufacturer instructions; use flexible elements only when necessary.
- Respect minimum bend radii and protect against abrasion, freezing and corrosion.
- Prevent static charge accumulation for non‑conductive refrigerants (e.g., antistatic lining).
- Pressure, vacuum and strength testing:
- Must withstand a vacuum of −99 kPa without damage.
- Strength tests: individual strength test at ≥1.43 × P_S or type approval at 3 × P_S or 1 000 kPa (whichever is greater).
- Non‑metallic burst test per ISO 6605:2002 with burst pressure ≥3 × P_S.
- Fatigue and cyclic testing:
- Non‑metallic tubes: cyclic (impulse) test per ISO 6605:2002 - 250 000 cycles at 1.1 × P_S and at operating temperature T_S.
- Permeability (leakage) of non‑metallic tubes:
- Permeability expressed per internal surface area; evaluated at 32 °C (saturated vapour pressure) and 100 °C (P_S).
- Leakage rate classes (examples from the standard):
- Class 1: 10 (at 32 °C) / 200 (at 100 °C)
- Class 2: 100 / 1 000
- Class 3: 1 000 / 5 000
- Test method uses helium leak detection in a controlled climate, sensitivity ≥3 g/year.
- Materials & cleanliness:
- Materials subject to ISO 175 chemical‑immersion tests; low‑temperature ductility required.
- Internal surfaces must be free of foreign matter; protect elements during transport/storage.
Applications and users
ISO 13971 is used to:
- Select and qualify hoses, bellows and non‑metallic tubing for compressors, evaporators and condensers.
- Specify vibration isolators and expansion joints to manage thermal expansion and reduce vibration transmission.
- Establish permeation/leakage limits for low‑GWP and specialty refrigerants.
Primary users:
- HVAC/R designers and system engineers
- Component manufacturers and product testers
- Installers, maintenance and reliability engineers
- Safety, environmental and procurement officers specifying compliance
Related standards
- ISO 5149 (safety and environmental requirements for refrigerating systems)
- ISO 6605:2002 (hose test methods)
- ISO 175 (plastics - chemical immersion tests)
Keywords: ISO 13971, refrigeration systems, heat pumps, flexible pipe elements, vibration isolators, expansion joints, non‑metallic tubes, permeability, leak rate, HVAC/R standards.