What is the difference between EN10312 steel pipe Series 1 and Series 2?

EN 10312 is the European standard for welded stainless steel tubes used to convey aqueous liquids, including water for human consumption. Inside this single standard, however, two parallel "series" of dimensions coexist, and confusing Series 1 with Series 2 is one of the most common reasons for a mismatched fitting, a leaking joint, or a rejected shipment. This guide explains exactly what each series is, how the tolerance tables differ, and which one to specify for your next project.

What EN 10312 Actually Covers

EN 10312, "Welded stainless steel tubes for the conveyance of aqueous liquids including water for human consumption – Technical delivery conditions," was published by CEN in 2002 and is widely adopted across Europe, the Middle East, Southeast Asia, and Latin America. The standard defines:

• Material composition for austenitic stainless steels (commonly 304, 304L, 316, 316L)
• Tube dimensions and tolerances – given in two parallel series
• Manufacturing process (TIG or laser welded, annealed, pickled)
• Mechanical properties and testing requirements
• Surface finish suitable for contact with drinking water

For specifiers, the dimension table is the part that matters most day-to-day, and that is precisely where the Series 1 versus Series 2 question appears. Both series are produced in volume by established manufacturers with EN 10204 3.1 certification and in-house calibrated test equipment.

Where Do Series 1 and Series 2 Come From?

The two series did not appear at random. They are a deliberate harmonization layer that lets the European tube world talk to two very different fitting families that already existed on the market:

• Series 1 – the metric "thin-wall" dimensions used in traditional European stainless press systems. Wall thicknesses run from 0.6 mm up to about 1.5 mm for most common sizes.
• Series 2 – the dimensions matched to the JIS G 3448 / GB/T 19228.2 family of stainless tube, which is the standard size for press fittings widely used in East Asia and, increasingly, in international hotel, hospital, and high-rise residential projects.

In other words, Series 1 is the "European metric" answer, and Series 2 is the "Asia-compatible" answer. Both meet the same metallurgical and testing requirements of EN 10312, but their OD and wall combinations are different, so the fittings are not interchangeable.

Side-by-Side: Series 1 vs Series 2 Dimensions

The clearest way to see the difference is to put the two tolerance tables next to each other. Series 1 uses a maximum/minimum OD pair (asymmetric tolerance), while Series 2 uses a symmetrical ± tolerance on OD and a separate ± tolerance on wall thickness.

Series 1 – Preferred European Thin-Wall Sizes

Series 1 – wall thickness tolerance is typically ±10% of the nominal wall.

Series 2 – Compatible with JIS G 3448 / GB/T 19228.2

Series 2 – tube is matched to the JIS/GB fitting geometry, so the wall is thicker and the OD tolerance is symmetric.

Five Practical Differences Between Series 1 and Series 2

Once the tables are placed side by side, several practical differences jump out.

1. Wall Thickness at the Same OD

Series 1 keeps the wall as thin as the standard allows. For example, a 28 mm tube in Series 1 is 0.8 mm, while the same 28 mm OD in Series 2 is 1.2 mm. The Series 2 tube is roughly 50% thicker at this size, which directly improves pressure rating and mechanical robustness for long vertical risers.

2. Fitting Compatibility

Series 1 tubes are designed to work with European metric press and compression fittings. Series 2 tubes share outside diameters with JIS G 3448 stainless tube and are typically connected using JIS/GB press fittings, including the double-press profile common in Asia. Always confirm the fitting brand and series on the same purchase order.

3. Tolerance Style

Series 1 uses an asymmetric max/min OD window, which is convenient for press-fitting geometry. Series 2 uses a standard ± tolerance, which is closer to ISO pipework tolerances and easier to measure on a generic caliper.

4. Pressure Rating

Because Series 2 carries a thicker wall, its working pressure at the same OD is higher. For a 22 mm tube at 316L, Series 1 (0.7 mm) typically gives around 25 bar working pressure, while Series 2 (1.2 mm) reaches roughly 45 bar. For tall buildings, long risers, or industrial water mains, Series 2 is the safer default.

5. Weight and Cost

Thinner walls mean lighter tubes and lower material cost per metre, which is why Series 1 dominates domestic and light commercial plumbing. Series 2, with its heavier wall, costs more per metre but reduces the number of support brackets, simplifies jointing on site, and lowers total installed cost in demanding applications.

Which Series Should You Specify?

There is no universally "better" series – the right choice depends on the project. The following decision flow works for most specifiers.

• Choose Series 1 when the project uses European metric press fittings, when wall thickness must be minimised for tight ceiling voids, or when the design follows traditional European plumbing practice.
• Choose Series 2 when the project uses JIS or GB press fittings, when higher working pressure is required, when the installation is in a high-rise riser, when the system also feeds a heat exchanger tube or boiler header, or when the end client is in East Asia, the Middle East, or Africa where JIS/GB fittings are more readily available.
• Specify both when a large campus or mixed-use development has multiple contractors: a clear drawing note such as "DN 15, 18, 22 mm – EN 10312 Series 1 for domestic; DN 28, 35, 42, 54 mm – EN 10312 Series 2 for risers" avoids mistakes at goods-in.

For buyers who also need a corrosion-resistant general-purpose stainless steel tube for chemical, food, or process service, the same Series 1/Series 2 logic applies: pick the geometry that matches the fitting system already on site, not the cheapest tube on the offer sheet.

Material Grades That Go With Each Series

Both series are produced in the same stainless families listed in EN 10312. The most common stock grades are:

For drinking water projects, 316L is increasingly preferred for hot water recirculation loops, while 304 remains the workhorse for cold supply. Where the same pipework transitions into a heat efficiency tube section, 316L is recommended for the heat-affected zones.

Testing and Documentation You Should Ask For

EN 10312 requires a defined set of tests on every delivery. When sourcing, request the mill certificate and confirm that the following tests are actually performed – not just listed on paper:

• Dimensional inspection (OD, wall, length, ovality, straightness) – covers both series
• Intergranular corrosion test per EN ISO 3651-2, especially important for 304/316 after welding
• Positive Material Identification (PMI) on every batch to avoid 304/316 mix-ups
• Eddy current or hydrostatic test on 100% of tubes for leak detection
• Tensile test and, where required, flattening or flaring test for ductility
• Surface roughness measurement for sanitary applications (typically Ra ≤ 0.8 µm)

Buyers ordering to an en10312 steel pipe line item should also ask for a third-party witness such as SGS, TUV, or BV when the project is funded by an international lender, since the documentation pack is often audited months after delivery.

Common Mistakes When Ordering EN 10312 Tubes

Across many EN 10312 sourcing projects, a few mistakes keep appearing. Avoiding them is often faster than reworking an order.

• Specifying only "EN 10312" without series. Suppliers have to guess, and guesses on a 40-container order are expensive.
• Mixing Series 1 and Series 2 on the same drawing. If 28 mm in one place is 0.8 mm (Series 1) and 1.2 mm (Series 2) elsewhere, the press fittings will not match.
• Forgetting the test pressure. EN 10312 requires a hydrostatic test; confirm the holding pressure and time on the PO.
• Ignoring end finish. Series 1 tubes are often supplied with plain ends for press fittings, while Series 2 may be ordered with grooved or threaded ends – state this on the order.
• Overlooking the matching fittings. The tube and the press profile must come from compatible systems. If you are switching fitting supplier, retest the joint.

Sourcing Considerations for EN 10312 Tubes

A reliable mill with multi-decade experience should be able to deliver both Series 1 and Series 2 from the same production line, with documented capacity for sizes from 6 mm up to 267 mm OD in 304, 304L, 316, and 316L. Look for an EN 10204 3.1 certificate, an in-house hydrostatic test rig, online eddy current testing, and a PMI station – these four items together cover most quality concerns on a project order.

Third-party inspection by SGS, TUV, BV, or the customer's own engineer can be arranged at the mill before shipment, and multilingual documentation (English, Spanish, Arabic, Russian) helps EPC contractors and regional distributors keep the documentation pack consistent. Confirm the typical lead time, the standard mill test certificate format, and the packaging (plastic caps, wooden cases, seaworthy wrapping) before issuing the purchase order so that goods-in inspection goes smoothly.

For project-specific quotations on either series, send the size list, quantity, grade, and the fitting system you are connecting to. A documented offer with tolerance tables, test plan, and delivery schedule is usually returned within two working days.

FAQ

Are Series 1 and Series 2 metallurgically different?

No. Both series are made from the same EN 10312 material families (304, 304L, 316, 316L, etc.). The difference is purely dimensional – OD, wall, and tolerance.

Can I press Series 1 and Series 2 tubes with the same tool?

Generally no. Press tools are matched to a specific OD and wall. Some manufacturers offer adjustable tools that cover both, but the operator must verify jaw profile before each shift change.

Which series is used more in Europe today?

Series 1 remains the default for residential and light commercial plumbing. Series 2 is gaining ground in hospital, hotel, and high-rise projects where JIS/GB press fittings are already specified by the consultant.

Is EN 10312 the same as DVGW W 270?

No. EN 10312 is the product standard. DVGW W 270 is a German hygienic approval that many European water utilities require on top of EN 10312. Ask the mill for the W 270 certificate if the project is in Germany, Austria, or a German-speaking market.

Can EN 10312 tubes be used for gases?

EN 10312 is written for aqueous liquids, including water for human consumption. For gas service, refer to EN ISO 1127 or local gas standards; do not substitute EN 10312 blindly.