EN 10312 Welded Stainless Steel Water Tube Guide

EN 10312:2002+A1:2005 is the European standard specifying technical delivery conditions for light-gauge welded stainless steel tubes intended for the conveyance of water and other aqueous liquids. Approved by CEN under committee ECISS/TC 29, the standard covers straight-length tubes from 6 mm to 267 mm outside diameter (OD) engineered for ambient-temperature plumbing, building service risers, and press-fit or compression jointing systems.

1. Standard Scope, Applications, and Jointing Methods

EN 10312 establishes requirements for longitudinally welded stainless tubes:

• Application Scope: Light-gauge tubing primarily designed for building water systems and aqueous liquid conveyance at ambient temperatures. It is not intended for high-temperature pressure service (for industrial pressure piping, consult the EN 10217-7 welded tube guide).
• Size Coverage: Outside diameters from 6 mm to 267 mm in straight delivery lengths of 5 m or 6 m.
• Fittings and Jointing: Tube geometries are engineered for compression fittings, press fittings, adhesive bonding, silver brazing, or inert gas welding of capillary fittings.
• Allowed Materials: Stainless steel grades conforming to EN 10088-2, excluding martensitic and precipitation hardening grades. Annex A provides a preferred alloy list.
• Companion Standard: For non-alloy steel water pipes, the European companion standard is EN 10224.

2. Dimensional Series: Series 1 vs. Series 2

EN 10312 specifies two dimensional series:

• Series 1 (Table 1): Light-gauge tubes with outside diameters from 6 mm to 159 mm, wall thicknesses from 0.6 mm to 2.0 mm, and unilateral OD tolerances. Suitable for capillary, compression, and press fittings.
• Series 2 (Table 2): Heavier-gauge tubes with outside diameters from 12 mm to 267 mm and wall thicknesses from 1.0 mm to 3.0 mm. Suitable for compression and press fittings, but not capillary fittings.

Table 1: Dimensions and Tolerances for Series 1 Tubes

*Parentheses denote non-preferred sizes. Out-of-roundness is included within outside diameter limits (Clause 8.8.4).

Table 2: Dimensions and Tolerances for Series 2 Tubes

For standard metric tube tolerance classes across broader applications, see EN ISO 1127 stainless steel tube dimensions and tolerances.

3. Fitting Suitability and Jointing Guidelines (Annex B)

Annex B details fitting suitability for each series:

Press-fit systems crimp an external fitting with an elastomeric seal over the tube end. The lighter wall of Series 1 requires precision pressing tools to ensure leak tightness without bore distortion.

4. Manufacture and Delivery Condition (Clause 7)

EN 10312 mandates specific manufacturing rules:

• Welding Route (Clause 7.2): Formed from flat-rolled stainless strip, longitudinally welded without the addition of filler material. No transverse strip-joining welds are permitted.
• Delivery Condition (Clause 7.2): Tubes are supplied in the as-welded condition as standard. Under Option 1, tubes are supplied solution annealed (for austenitic/duplex grades) or annealed (for ferritic grades), with hardness criteria agreed upon ordering.
• Weld Seam Finish (Clause 8.8.6): The external weld bead shall be removed flush with the tube profile. The internal weld bead remains as-welded unless Option 5 is specified.
• Surface Quality (Clause 8.5.1): Tubes must feature a smooth, bright surface free from visually detectable defects. Heat discoloration in the weld area must be kept to a minimum.
• Fire Classification (Clause 8.9): Classified as Class A1 reaction to fire per Commission Decision 96/603/EEC without requiring testing.

5. Mechanical, Technological, and Leak-Tightness Testing (Clause 11)

Testing is conducted per test unit (≤400 tubes of identical grade and size, Clause 10):

• Tensile Test (Clause 11.2, EN 10002-1): Verifies Rm, Rp0.2 (and Rp1.0 for austenitic grades), and elongation A on gauge length 5.65√So.
• Drift Expanding Test (Clause 11.3.1, EN 10234): Austenitic and duplex tubes are flared over a 60° cone until outside diameter expands by +25% without cracking.
• Flattening Test (Clause 11.3.2, EN 10233): Austenitic and duplex tubes are flattened between parallel platens to 5T (5 × wall thickness) with the weld at 90° to load direction, showing no cracks.
• Leak-Tightness Testing (Clause 11.4): Each tube must be verified by one of three methods:
  • Eddy Current Test (Clause 11.4.2): Per EN 10246-1 (ferromagnetic) or EN 10246-2 (austenitic/duplex).
  • Hydrostatic Test (Clause 11.4.3): Minimum 50 bar for OD ≤ 76.1 mm; minimum 30 bar for OD > 76.1 mm (leak-tightness test, not a strength test; no leakage or visible deformation).
  • Pneumatic Test (Clause 11.4.4): Air under water at minimum 6 bar with no bubble leakage.
• Full-Length Weld Seam NDT (Clause 8.5.2 & 11.5): The entire weld seam undergoes non-destructive testing per EN 10246-3 level E4(H) or EN 10246-8 level U4.
• Material Identification (Clause 11.9): Each tube is verified by positive alloy testing to confirm correct grade.
• Intergranular Corrosion (Clause 8.4): Performed per EN ISO 3651-1 or -2 only when Option 2 is ordered.

6. Straightness, Length, and End Tolerances

Dimensional controls ensure compatibility with plumbing fittings:

• Overall Straightness (Clause 8.6): Deviation across total length L must not exceed 0.0015 × L (0.15% of length).
• Local Straightness: Over any 1 m span, deviation is ≤ 3 mm for Series 1; for Series 2, ≤ 2 mm for 12 mm < D < 128 mm and ≤ 2.5 mm for D ≥ 128 mm.
• Delivery Lengths (Clause 8.8.3 & 8.8.7): Standard lengths are 5 m or 6 m with a tolerance of ±20 mm (Option 4 allows custom lengths).
• Tube Ends (Clause 8.7): Square cut and free from harmful burrs.
• Diameter Measurement (Clause 11.7): Outside diameter is measured ≥ 10 mm and ≤ 3D from the tube end.

7. Preferred Stainless Steel Grades (Annex A)

Annex A lists preferred European grades from EN 10088-2:

• Ferritic Grades: X3CrTi17 (1.4510), X3CrNb17 (1.4511), and molybdenum-alloyed X2CrMoTi18-2 (1.4521). Ferritics provide resistance to chloride stress corrosion cracking in hot water.
• Austenitic Standard Grades: X2CrNi18-9 (1.4307), X2CrNi19-11 (1.4306), and X5CrNi18-10 (1.4301).
• Austenitic Molybdenum Grades: X2CrNiMo17-12-2 (1.4404), X5CrNiMo17-12-2 (1.4401), stabilized X6CrNiMoTi17-12-2 (1.4571), X2CrNiMo17-12-3 (1.4432), X3CrNiMo17-13-3 (1.4436), and X2CrNiMo18-14-3 (1.4435).
• High-Alloy Austenitics: X2CrNiMoN17-13-5 (1.4439), X1NiCrMoCu25-20-5 (1.4539), X1CrNiMoCuN20-18-7 (1.4547), and X1NiCrMoCuN20-20-7 (1.4529).
• Duplex Grades: Lean duplex X2CrNiN23-4 (1.4362) and standard duplex X2CrNiMoN22-5-3 (1.4462).

For dairy and food processing lines, compare these with the DIN 11850 food and beverage tube standard.

8. Purchaser Options 1–9 and Ordering Specification

Clause 6.2 provides 9 standardized options:

Example Order Line (Clause 6.3)

Specifies 1,000 meters of Series 1 tube, 76.1 mm OD × 1.5 mm wall, grade X5CrNi18-10 (1.4301), in 6 m lengths, with bundle label marking per Option 8.

9. Inspection Documents: Test Report 2.2 vs. Certificate 3.1.B

Clause 9 governs inspection documentation per EN 10204:

• Default Non-Specific Inspection: Deliveries are covered by a Test Report 2.2 per EN 10204, confirming compliance based on non-specific factory production control.
• Option 6 Specific Inspection: When Option 6 is specified, an Inspection Certificate 3.1.B (EN 10204:2004 3.1) is issued with verified chemical analysis, tensile, drift expansion, flattening, and NDT test records. For compliance details, see our EN 10204 3.1 mill test certificate guide.

10. TeCarve Supply Range

TeCarve is the exclusive factory-direct export channel for two dedicated manufacturing plants in Foshan (welded & decorative tubing) and Wenzhou (seamless & precision tubing):

• Production Scope: EN 10312 is among the standards listed on our welded stainless steel pipe and tube product page.
• Water Treatment Plant Sourcing: System guidance is detailed in our guide on stainless steel pipe for water treatment industry.
• Size Range: The welded product page lists TIG, plasma, laser and ERW welded pipe and tube with outer diameters from 6 mm to 4200 mm, wall thicknesses from 0.5 mm to 120 mm and lengths up to 12 m.
• Testing: Hydrostatic or nondestructive electric testing, with eddy-current or radiographic examination where required, as listed on the welded product page. For EN 10312 orders, the leak-tightness method and weld seam NDT follow Clauses 11.4 and 11.5.
• Quality Certification: EN 10204 3.1 inspection certificates are provided with shipments; EN 10204 3.2 witnessed inspections (SGS, BV, TÜV) are available upon request.
• Plant Accreditations: Quality management and pressure equipment approvals (ISO 9001/14001/45001, PED/AD 2000-Merkblatt W0, and marine classification society type approvals) are held by the plants — see https://tecarvepipes.com/verify-our-factories/.
• Regulatory Clarification: Generic tubing stock does not carry unilateral European potable certificates (e.g., WRAS, DVGW); local potable compliance must be verified per project regulations.

Frequently Asked Questions (FAQ)

Summary based on EN 10312:2002+A1:2005; refer to the purchased standard for the full text.