What are the dimensional and shape specifications for EN10296-2 welded steel tube?

When you order welded stainless steel tube for mechanical and general engineering work, the numbers that matter most are the outside diameter, the wall thickness, and how far the finished tube is allowed to drift from those numbers. EN 10296-2 is the European standard that sets those limits. Its full title is “Welded circular steel tubes for mechanical and general engineering purposes – Technical delivery conditions – Part 2: Stainless steel,” and it covers ferritic, austenitic, duplex and heat-resisting grades. For anyone buying or specifying EN 10296-2 welded steel tube, it is the document that tells both the mill and the buyer exactly which dimensional and shape tolerances apply.

How EN 10296-2 dimensions are expressed

Like most European tube standards, EN 10296-2 identifies a tube by its outside diameter (D) and wall thickness (T), with the preferred sizes taken from EN ISO 1127. A typical designation reads EN 10296-2 1.4301 33.7 × 2.0, which means a 33.7 mm outside diameter, a 2.0 mm wall, in grade 1.4301 (304). The standard does not use nominal bore or schedule numbers the way some American standards do, so stating D and T clearly on the order is the first step to receiving the right tube.

Outside diameter tolerance

Outside diameter tolerance is where most of the practical differences show up. For tubes with an outside diameter below 168.3 mm, the tolerance on OD, including ovality, is ±0.75% or ±0.3 mm, whichever is the greater. Above 168.3 mm it loosens to ±1.0%. If your application needs a tighter fit – for example, a sliding fit inside a machined housing – a tolerance of ±0.5% or ±0.15 mm can be agreed at the time of enquiry and order on tubes below 114.3 mm.

Wall thickness tolerance

Wall thickness is held to ±10% or ±0.2 mm, whichever is the greater, for all tube sizes. That is a relatively generous band compared with some precision standards, so if you plan to machine the bore, thread the ends, or form the tube afterwards, it is worth checking that the as-supplied wall is still adequate at the minimum side of the tolerance.

Shape specifications: ovality

Shape is controlled in three ways: ovality, straightness, and weld seam height. Ovality is handled inside the OD tolerance – the standard specifies the tolerance on outside diameter “including ovality,” which means the tube must fit within the stated band even when it is slightly out of round. For thin-wall tubes especially, ovality is worth checking at the receiving end, because it can be exaggerated during handling and storage.

Shape specifications: straightness

Straightness is defined as a deviation over the delivered length. For tubes with an outside diameter of 33.7 mm or larger, the deviation from straightness over any length L must not exceed 0.0020 L. In practical terms, a 6-metre length may bow up to 12 mm. If that is too much for your feed system or guide rails, a tighter limit of 0.0015 L can be agreed at the time of order. For tubes below 33.7 mm, straightness and the method of measurement are agreed between the buyer and the mill.

Shape specifications: weld seam height and finish

The weld seam is the part of a welded tube that most people inspect first. EN 10296-2 defines three weld bead finishes. Finish A leaves both the internal and external weld bead in place, and it is not permitted on high-frequency (HF) welded tube. Finish B removes the external bead and leaves the internal bead; on HF welded tube the outside bead must be removed completely, flush with the outside surface. Finish C rolls or removes both beads, leaving the smoothest surface. The maximum permitted seam heights are set out in the standard – for example, Finish A allows 0.20 T + 0.5 mm on walls below 8 mm, while Finish C holds the seam to 0.15 mm.

Length tolerances

Length tolerances are straightforward. Standard lengths are supplied at 6000 mm with a tolerance of +100 mm / -0. Exact lengths below 6000 mm are held to +5 mm / -0, lengths between 6000 and 12000 mm to +10 mm / -0, and anything longer is by agreement.

Steel grades and delivery condition

Because EN 10296-2 is a mechanical, non-pressure standard, the choice of grade is driven by corrosion resistance, strength and forming behaviour rather than by pressure ratings. Common choices include 1.4301 (304), 1.4307 (304L), 1.4404 (316L), and ferritic grades such as 1.4016 (430) for exhaust and decorative work. Delivery condition also matters: ferritic tubes are supplied as-welded (+AR) or annealed (+A), while austenitic and duplex tubes are supplied as-welded (+AR) or solution annealed (+AT), as specified by the purchaser.

What to include in an enquiry

When you write an enquiry, the information that removes most of the guesswork is: the standard (EN 10296-2), the steel name or number, the outside diameter and wall thickness, the delivery condition, the weld finish, and the length. Adding a straightness or OD option if your application needs it, and stating whether you want a 3.1 inspection certificate, will get you a quotation that matches the tube you actually need.

Getting these details right is exactly what EZ Steel Industrial does every day. As a manufacturer and integrated supplier of industrial metal piping systems, the company supplies EN 10296-2 welded steel tube in a wide range of sizes, together with related mechanical and structural tube such as ASTM A554 welded mechanic tube and other stainless steel tube products. If you are comparing standards or need help turning your application into a clear specification, the team can advise on grade, dimension and delivery condition before you commit to an order.