What EN 10255 Defines
EN 10255 is the European specification for non-alloy steel tubes suitable for welding and threading, with the full title of non-alloy steel tubes suitable for welding and threading and technical delivery conditions. It covers the tube itself, its dimensions and tolerances, the steel grades permitted, and the end finishes in which the tube may be supplied. The standard superseded the earlier national and international documents used for the same product, notably DIN 2440 and ISO 65, so a specification written to those older documents is normally re-issued against EN 10255.
EN 10255 tube is manufactured only by welding processes. Seamless tube is not within the scope, and a requirement for a seamless product must be placed against the appropriate seamless tube standard instead.
Grade S195T: Chemical and Mechanical Properties
S195T, steel number 1.0026, is the grade most frequently ordered for water, gas, liquid and general low-pressure service. It is a low-carbon, fully killed weldable steel with a deliberately restricted analysis that keeps carbon, manganese, phosphorus and sulfur within limits suited to welding and to galvanizing.
| Property | Requirement for S195T |
|---|---|
| Carbon, % max | 0.20 |
| Manganese, % max | 1.40 |
| Phosphorus, % max | 0.035 |
| Sulfur, % max | 0.030 |
| Minimum yield strength, ReH, MPa | 195 |
| Tensile strength, Rm, MPa | 320 to 520 |
| Minimum elongation, A, % | 20 |
Specifications issued by other standards organisations for the same product family, such as the S235JRH grade, follow the same tabular format. Where a project calls for a higher grade, the composition and property table of that grade applies instead, and the change should be confirmed against the standard rather than assumed from the S195T figures.
Series, Dimensions and End Finishes
EN 10255 tubes are supplied in three wall thickness series, designated light, medium and heavy, which are differentiated by wall thickness and therefore by pressure capacity. Light series tube is used for the least demanding duties, medium series for normal water and gas distribution, and heavy series where higher pressure capacity or greater mechanical robustness is required.
Outside diameters range from roughly 10 mm up to about 165 mm, corresponding to nominal sizes from DN 6 to DN 150.
Wall thickness follows the selected series, typically about 2.0 mm to 5.4 mm in the commonly used sizes.
Standard lengths are 5.8 m and 6.0 m, with other lengths supplied to agreement.
End finishes are plain end, threaded, or threaded and socketed, with the thread form and socket dimensions in accordance with the relevant pipe thread standard.
Ends and threads are protected against damage and corrosion for transport, and threads are supplied with a protective covering.
Manufacturing Routes and Corrosion Protection
Because only welded tube is permitted, two production families are used. Electric resistance welding is the standard route for smaller sizes, on the order of 219 mm outside diameter and below: the strip edges are heated by high-frequency current and squeezed together, producing a forged weld that typically achieves at least 90 % of the base metal strength and is suited to high production rates and municipal water and gas lines. Arc welding processes, principally submerged arc welding and plasma arc welding, are used for larger diameters above about 219 mm, where submerged arc gives deep, consistent penetration and plasma arc gives a precise, clean weld suited to low-pressure fluid service.
For external corrosion protection the tube is commonly supplied hot-dip galvanized in accordance with EN ISO 1461. The coating mass is specified by wall thickness class rather than as a single figure, so a minimum local coating thickness of roughly 45 micrometres applies to thin walls, about 55 micrometres to medium walls and about 70 micrometres to heavier walls, with a corresponding minimum local coating mass. Alternative protection for buried or wet service includes factory-applied epoxy, polyethylene or polyurethane coatings, chosen against the corrosivity category of the installation.
Testing and Inspection
Appearance inspection requires a sound surface free from cracks, folds, scars and laminations, with weld reinforcement kept within the limit set by the standard for the relevant welding process. Dimensional inspection covers outside diameter, wall thickness, ovality and length, with tolerances taken from the standard.
Mechanical testing is carried out on samples taken from each inspection lot and comprises the tensile test plus a bend test in which the specimen is bent through 180 degrees around a former with a diameter of three times the wall thickness, acceptance being the absence of cracks in the bent zone. Leak-tightness is verified on every tube, either by hydrostatic testing at the pressure calculated from the wall thickness and grade, or by an equivalent non-destructive method permitted by the standard. Weld quality on resistance welded tube is normally verified by an eddy current test applied to the full weld length, while arc welded tube is examined by radiographic testing on a sampling basis. The design pressure used for the test is calculated from the wall thickness and the steel grade, not from a nominal product table.
The selection logic is straightforward: match the series to the working pressure, the end finish to the jointing method, and the coating to the environment. A tube that is correct in diameter but one series too light for the line pressure, or galvanized without the coating mass being specified, is a common source of field problems.
FAQ
Q: What does the T in grade S195T stand for?
It identifies a tube grade suitable for threading, which is why S195T is the grade most often ordered for screwed water and gas services. The designation also carries the steel number 1.0026 for unambiguous ordering.
Q: Can EN 10255 tube be supplied seamless?
No. The standard covers welded tube only, produced by resistance welding for smaller sizes and by arc welding for larger sizes. Seamless tube must be ordered against the corresponding seamless tube standard.
Q: What are the light, medium and heavy series?
They are the three wall thickness series defined by the standard. The series is selected according to the required pressure capacity and mechanical strength, with medium series being the normal choice for water and gas distribution.
Q: How is the galvanized coating specified?
By coating mass or minimum local coating thickness for the applicable wall thickness class under EN ISO 1461, rather than by a single thickness figure. Thin walls receive a lighter coating than heavy walls, and the requirement should be stated on the order.
Q: What tests accompany an EN 10255 delivery?
Appearance and dimensional inspection, tensile testing and a 180 degree bend test on samples from each lot, a leak-tightness test on every tube, eddy current examination of the full weld on resistance welded tube, and radiographic examination on a sampling basis for arc welded tube.
Q: What ends can be supplied?
Plain ends for welding, threaded ends for screwed joints, and threaded and socketed ends where a coupling is fitted at the mill. The thread form and socket dimensions follow the pipe thread standard referenced by the order, and threads are protected for transport.
