We supply welded precision steel tube to DIN 2393. The strip is formed and welded, the flash is scarfed, and the tube is then cold drawn, which brings the wall back to concentric and gives a bore that machines cleanly at a lower cost than seamless tube. Buyers who write welded steel tube, ERW tube or cold drawn welded are describing the same product under three different names.
Price: quoted per specification. Steel prices move with the raw material market, so every quotation is confirmed at the time of order.
Specifications
- Standard: DIN 2393 welded precision steel tube (superseded by EN 10305-2)
- Steel grade: St34-2, St37-2, St44-2, St52-3; EN E195, E235, E275, E355
- Delivery condition: BK, BKW, GBK, NBK, or the EN symbols +C, +A, +N
- Size range: outside diameter 8-80 mm, wall 0.8-6 mm, or quoted to drawing
- Length: random 4-7 m, fixed length or cut to size on request
- Tolerance: OD +-0.10 mm and wall +-10 percent as standard, closer on the last draw
- Testing: chemical composition, tensile and yield, elongation, flattening, weld expansion or drift test, dimensions
- Documentation: EN 10204 3.1 mill test certificate
Welded, ERW, HREW, CDW: what the drawing says
The name on the drawing tells you how the tube was made, and the price follows the process. Four names cover almost every enquiry we receive.
| Term | How it is made | Drawn after welding | Where it is used |
|---|---|---|---|
| welded steel tube / welded tube | Strip formed and welded, flash scarfed | Not always | General fabrication, low-pressure lines |
| welded steel pipe, steel welded pipe | Same product, sized as pipe | Not always | Plant piping, structure, guards |
| ERW tube / electric resistance welded tube | Resistance or high-frequency welded | Usually not | Mechanical parts, automotive, furniture |
| ERW piping | ERW pipe for process lines | No | Water, air and process piping |
| HREW tubing | Hot rolled strip, ERW, no cold draw | No | Low-cost mechanical tube, frames |
| CDW, cold drawn welded | ERW, then cold drawn over a mandrel | Yes | Precision parts, shock absorbers, bushes |
| weldable steel tubing | Low carbon, made to be welded by the customer | Either | Parts joined after delivery |
Two points are worth clearing up at quotation stage. All ERW tube is welded, but not all welded tube is ERW: strip can also be joined by laser, TIG or submerged arc, and the weld quality differs. And welded pipe is usually the same mill product as welded tube, ordered by nominal bore instead of by OD and wall.
How welded precision tube is made
A coil of pickled strip is slit to width, formed through rolls into a round section, and welded along the seam by high-frequency resistance welding. The outside and inside flash is scarfed off while the seam is still hot, and the tube is then cold drawn over a plug or a mandrel, which consolidates the weld, removes the remaining ridge and brings the wall back to concentric.
The seam does not disappear. What disappears is the raised bead, which is what damages a bore, catches a tool and shows up as an uneven layer after plating. Between draws the tube is annealed, and the last draw sets the tolerance. That is why a cold drawn welded tube can be used for a shock absorber body where a plain ERW tube cannot: the bore is round and the wall is even.
DIN 2393, EN 10305-2 and DIN 2394
DIN 2393 is the German standard for welded precision steel tube that is cold drawn after welding. It has been superseded by EN 10305-2, but drawings written before the change still quote DIN 2393, and the tube is the same.
| Standard | Product | Grades | Note |
|---|---|---|---|
| DIN 2393 | Welded precision tube, cold drawn | St34-2, St37-2, St44-2, St52-3 | German, still written on older drawings |
| EN 10305-2 | Welded cold drawn precision tube | E195, E235, E275, E355 | Current European standard |
| DIN 2394 | Welded precision tube, not cold drawn | St34-2 to St52-3 | As-welded, cheaper, wider tolerance |
| EN 10305-1 | Seamless cold drawn precision tube | E235, E355 | No seam, for pressure and thin walls |
Delivery conditions: BK, BKW, GBK, NBK
| Symbol | Condition | What it means for the part |
|---|---|---|
| BK | Cold drawn, not heat treated after the last draw | Hardest and strongest, lowest ductility, least straight after drawing |
| BKW | Cold drawn and soft annealed | Soft enough to flare, bend or swage; strength drops |
| GBK | Annealed, straightened, then cold drawn | Good surface and straightness with moderate strength |
| NBK | Normalised | Uniform structure for parts that will be welded or machined heavily |
| +C / +A / +N | EN symbols for the same conditions | Written on EN 10305-2 orders instead of BK, BKW, NBK |
On a shock absorber body the usual choice is BK or GBK, because the bore is honed or roller burnished afterwards and the tube has to stay round. On a part that will be flared, swaged or welded, BKW or NBK avoids cracks at the joint.
Typical applications
- Shock absorber bodies: reserve tube and working cylinder
- Gas spring outer tubes and seat damper bodies
- Steering column tubes and steering rack housings
- Machined bushes, spacers and sleeves
- Furniture frames, guards and general fabrication
- Low-pressure hydraulic and pneumatic lines
In all of these the welded route wins on cost: the same part in seamless tube would cost more per metre for a wall and tolerance it does not need.
Sizes and tolerances
| Item | Range | Note |
|---|---|---|
| Outside diameter | 8-80 mm | Larger sizes quoted as a special roll |
| Wall thickness | 0.8-6 mm | Wall to drawing where the OD allows |
| OD tolerance | +-0.10 mm | Tighter after a final cold draw |
| Wall tolerance | +-10 percent | Closer on request for honed bores |
| Length | 4-7 m random, or fixed | Cut to length with deburred ends |
| Straightness | 1 mm per metre | Straightened after the last draw |
FAQ
Is welded tube as strong as seamless tube?
For the same wall and grade, a cold drawn welded tube is close, because the weld has been scarfed, drawn and annealed. It is not identical: the seam remains a line of different microstructure, so for pressure, fatigue or thin walls seamless is still the safer choice.
What does BK mean on a DIN 2393 order?
BK means cold drawn without heat treatment after the final draw. It is the hardest and strongest condition, and it is the one that needs stress relief before welding or heavy machining.
Can welded precision tube be used in a hydraulic cylinder?
For low and medium pressure, and for the outer or reserve tube of a shock absorber, yes. For the pressure barrel of a high-pressure cylinder, seamless EN 10305-1 or EN 10305-4 tube is the normal choice, because the seam is the part that decides fatigue life.
What is the difference between ERW and welded tube?
ERW is one welding method, electric resistance welding, usually high frequency. Welded tube is the wider term and includes laser, TIG and submerged arc. In practice most mechanical welded tube on the market is ERW, which is why the names get used interchangeably.
Does the weld seam still show after cold drawing?
The raised bead is gone and the bore is round, so nothing catches on it. Metallurgically the seam is still there, which is why a welded tube is not sold as seamless and why the pressure rating is quoted separately.
What is HREW tubing?
Hot rolled ERW: tube welded from hot rolled strip and not cold drawn afterwards. It is the cheapest mechanical tube, with a wider wall tolerance and a rougher surface, used for frames and general fabrication rather than for precision parts.
Standard reference: see our DIN 2393 standard page for grades, delivery conditions and tolerances.
Quality and packing: tubes are protected with anti-rust oil and packed seaworthy, in wooden cases where agreed. Each lot is tested for chemical composition, yield and tensile strength, flattening, elongation and dimensions, with visual inspection and NDT available on request.
Request a quotation: send your size list or drawing through our contact page. We reply within one working day with price, tolerance and lead time.