Overview
EN ISO 21003-3:2008/A1:2021 - "Multilayer piping systems for hot and cold water installations inside buildings - Part 3: Fittings - Amendment 1" is a CEN-endorsed amendment (approved October 2021) to ISO 21003-3:2008. It updates requirements for fittings used with multilayer piping systems for potable hot and cold water inside buildings, clarifying material, dimensional, corrosion and test requirements and adding a new tightness test and minimum wall thickness criteria for metallic (mainly copper-alloy) fittings.
Key topics and technical requirements
- Scope of fittings: Revised definition of a fitting as a component that connects two or more pipes/fittings; examples include compression, radial/axial press, flanged, push‑fit and fusion fittings.
- Metallic materials: Metallic fittings for ISO 21003 systems shall be copper alloys or stainless steels, defined by an appropriate standard or regulatory document. Copper-alloy fittings must meet specified corrosion resistance rules.
- Corrosion and dezincification:
- Resistance to stress corrosion required for copper-alloy fittings. Certain alloys (CuSnZnPb, CuZn‑Si ≥2% Si) and CuZn alloys with hardness HBW 2,5/62,5 ≤ 110 are deemed resistant without additional testing.
- Other copper alloys with ≥10% Zn require ISO 6957 testing (pH 9.5 ammonia test) with no cracking allowed.
- Dezincification testing per ISO 6509-1 is required where a fitting is declared dezincification‑resistant; acceptance: max depth ≤ 200 µm, average ≤ 100 µm.
- Appearance and dimensional control:
- Plastic fittings: surfaces must be smooth/clean; dimensions measured per ISO 3126.
- Metal fittings: clean, no sharp edges; dimensions measured per ISO 2768-1 and/or ISO 22081.
- Minimum wall thickness: Annex B (normative) defines measurement points (A, B, C) and a table of minimum wall thickness values for machined/wrought and cast copper-alloy fittings across nominal diameters.
- Tightness test for cast fittings: New Clause 12 requires leak-tightness testing of cast fittings after machining - e.g., compressed air ≥ 0.5 MPa (5 bar) while immersed in water (bubbles = leak). Alternative methods may be applied.
- Sealing elements: Materials must not harm pipes/fittings and shall conform to ISO 21003-5 and EN 681‑1/2 as applicable.
Applications and users
This amendment is essential for:
- Manufacturers of multilayer piping fittings (compression, press, push-fit, fusion)
- Product designers and R&D ensuring material selection and dimensional compliance
- Testing laboratories and certification bodies performing corrosion, dezincification and tightness tests
- Plumbing engineers, specifiers and installers who require compliant fittings for hot/cold water systems in buildings
- Regulators and standards committees harmonizing national adoption (CEN members to implement by April 2022)
Related standards (normative/important references)
This amendment helps ensure robust, corrosion-resistant fittings and consistent dimensional and testing practices for safe, long‑lasting multilayer hot and cold water installations.
