ISO 3821:2019

Overview - ISO 3821:2019 (Rubber hoses for welding and allied processes)

ISO 3821:2019 specifies requirements for rubber hoses (including twin hoses) used in gas welding, cutting and allied processes. It covers hoses for normal duty (2 MPa / 20 bar) and light duty (max working pressure 1 MPa / 10 bar, limited to bores ≤ 6.3 mm), intended for use at temperatures −20 °C to +60 °C. The standard applies to gas welding and cutting, gas-shielded arc welding, heating, brazing and metallization, but excludes thermoplastic hoses and hoses for high-pressure acetylene (>0.15 MPa). ISO 3821 does not cover hose assemblies (see ISO 8207).

Key topics and technical requirements

• Hose construction and materials
  • Minimum lining and cover thicknesses and acceptable reinforcement techniques.
  • Flux fuel gas hoses include an additional inner plastic layer (max 0.5 mm) under specified conditions.
  • Twin hoses: two hoses joined longitudinally during manufacture but separable for fitting.
• Pressure and duty classification
  • Designation for light vs. normal duty tied to maximum working pressure and bore sizes.
• Dimensions and tolerances
  • Inside/outside diameters, wall thickness, concentricity, and cut-length tolerances.
• Performance and type tests
  • Mechanical: tensile strength, elongation, adhesion.
  • Durability: accelerated ageing, hydrostatic testing.
  • Flexibility: ambient and low-temperature bending tests.
  • Environmental: ozone resistance, resistance to incandescent particles/hot surfaces.
  • Gas-specific tests: non-ignition for oxygen hoses; chemical resistance (e.g., acetone, dimethylformamide for acetylene hoses; n‑pentane for propane; trimethylborate/methanol for flux fuel gas); permeability to LPG, MPS and natural gas.
• Identification and marking
  • Colour coding and marking rules to identify gas service (oxygen, fuel gases, universal, fluxed fuel gas) and hose designation.

Applications and practical value

• Ensures safe selection and use of rubber welding hoses in:
  • Gas welding and cutting shops
  • Industrial fabrication and maintenance
  • Welding equipment manufacturers and suppliers
  • Gas distributors and safety compliance teams
• Helps specify hoses for particular gases (oxygen, acetylene, propane, LPG, natural gas) and for equipment design, procurement and inspections.
• Reduces risk of incompatibility, ignition in oxygen service, chemical attack, gas permeation and premature hose failure.

Who should use ISO 3821:2019

• Welding and cutting equipment manufacturers
• Hose manufacturers and testers
• Safety engineers, procurement and maintenance teams in fabrication shops and industry
• Regulatory and conformity assessment bodies

Related standards

• ISO 8207 - Hose assemblies (fittings and assemblies)
• ISO 1402 - Hydrostatic testing of hoses
• ISO 4080 - Gas permeability of hoses
• ISO 11114-3 - Autogenous ignition test for oxygen compatibility
• ISO 10619-1 / -2, ISO 8033, ISO 188, ISO 1817 - Test methods referenced by ISO 3821

Keywords: ISO 3821:2019, rubber hoses, welding hoses, twin hoses, gas welding, hose requirements, oxygen hose, acetylene hose, flux fuel gas hose, hose marking, hose testing.