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
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.