BS EN 10216-2:2024 Standard For Seamless Steel Tubes

The EN 10216 Series: Five Parts Explained

EN 10216 is published in five parts under the general title "Seamless steel tubes for pressure purposes - Technical delivery conditions". Each part addresses a different service condition and material family, and Part 2 is the one written around elevated temperature behaviour.

The parallel series for welded product is EN 10217, Welded steel tubes for pressure purposes - Technical delivery conditions. Where a weld seam is acceptable to the design code and the end user, EN 10217-2 is the welded counterpart to this part.

Under EN 10020:2000, the three GH grades P195GH, P235GH and P265GH are classified as non-alloy quality steels. Every other grade in the standard is classified as an alloy special steel. That classification is not academic: it determines which test category the tube can be ordered to.

Test Category 1 vs Test Category 2

The 2024 edition uses test categories, not the TR1/TR2 quality levels familiar from Part 1. The test category defines the extent and level of inspection and testing. It is mandatory order information for non-alloy steel, and it must be marked on the tube.

Non-alloy steel tubes are inspected and tested to test category 1 or test category 2 as specified at the time of enquiry and order. Alloy steel tubes are inspected and tested for category 2 only. There is no test category 1 option for an alloy grade.

The practical difference is the volume of non-destructive testing and the number of sample tubes drawn from each test unit. Test category 2 puts every tube through NDT for longitudinal imperfections and doubles the mechanical test sampling, which is why it is the only category permitted for the alloy creep-resistant grades.

BS EN 10216-2:2024 Steel Grades

Steel designation consists of the number of this part of EN 10216 plus either the steel name in accordance with EN 10027-1:2016 or the steel number allocated in accordance with EN 10027-2:2015.

For the non-alloy grades, the steel name is built from the capital letter P for pressure purposes, the specified minimum yield strength at room temperature for wall thickness up to and including 16 mm expressed in MPa, and the symbols GH for elevated temperature. P265GH therefore means a pressure-purpose steel with 265 MPa minimum yield in thin walls, characterised at elevated temperatures. Alloy grades are named from their chemical composition, with the heat treatment symbol appended where the standard specifies one, for example, X11CrMo9-1+NT.

Non-Alloy Quality Steels

Three grades, all supplied normalized, and the only grades in the standard that can be ordered to test category 1.

Low-Alloy Molybdenum and Chromium-Molybdenum Steels

This family carries most of the conventional elevated-temperature pipework in European plants. Molybdenum raises creep strength; chromium adds oxidation resistance and further creep capability as its content rises from 1 % in 13CrMo4-5 to 2.0 to 2.5 % in 10CrMo9-10.

5 % to 12 % Chromium Creep-Resistant Steels

The high-chromium grades cover the hottest duty in the standard. X11CrMo5 and X11CrMo9-1 are offered in isothermally annealed (+I) and normalized and tempered (+NT) conditions, and the yield strength difference between those conditions is substantial: 175 MPa for X11CrMo5+I against 390 MPa for X11CrMo5+NT2 in the same wall thickness.

X10CrMoVNb9-1 (1.4903) is the grade the power industry calls Grade 91, and X10CrWMoVNb9-2 (1.4901) is Grade 92. The 2024 edition specifically revised the creep rupture data for both grades using European Collaborative Creep Committee data sheets issued in 2019.

Manufacturing and Heat Treatment Conditions

All tubes are made by a seamless process. Unless Option 1 is specified, the tubes may be either hot or cold-finished; the terms refer to the condition of the tube before heat treatment. Option 1 requires the tubes to be cold-finished before heat treatment. Tubes are then supplied in the heat treatment condition specified in Table 1 of the standard for the grade concerned.

The steelmaking process is at the manufacturer's discretion, with one exclusion: the open hearth (Siemens-Martin) process is not permitted unless combined with a secondary steelmaking or ladle refining process. Steels shall be fully killed, which excludes rimming, balanced and semi-killed steel.

Selected austenitizing and tempering ranges from Table 1, for the grades most often ordered:

Two footnotes to Table 1 change the delivery condition in the heavy wall. For a number of the +NT grades, it may be necessary, where wall thickness exceeds 10 mm or the T/D ratio exceeds 0,15, to apply quenching and tempering instead in order to achieve the intended structure and properties. For 7CrWVMoNb9-6 and 7CrMoVTiB10-10, the same applies above 16 mm wall or T/D greater than 0,15. The decision has to be stated at the time of enquiry and order, and tubes treated that way are designated with the steel name supplemented by “+QT”.

All non-destructive testing activity has to be carried out by qualified and competent level 1, 2 or 3 personnel authorised in writing by the employer. Level 1 and 2 qualifications follow ISO 11484:2019 or EN ISO 9712:2022; level 3 qualification follows EN ISO 9712:2022. NDT operations are authorised by a level 3 individual approved by the employer.

Chemical Composition of BS EN 10216-2:2024

Chemical composition is specified as cast analysis in Table 2 of the standard, expressed in % by mass. The cast analysis reported by the steel producer applies. Elements not included in Table 2 shall not be intentionally added without the agreement of the purchaser, except for elements added to finish the cast, and measures must be taken to prevent undesirable elements from entering from scrap.

GH Grades and 20MnNb6

The three GH grades are the non-alloy quality steels of the standard. 20MnNb6 is classified as an alloy special steel, but sits close to them in composition and is shown alongside for comparison.

Two conditions attach to the GH grades. The minimum total aluminium of 0,020 % is not applicable where the steel contains a sufficient amount of other nitrogen-binding elements, which then have to be reported; and the ratio Al/N shall be at least 2, except that where nitrogen is fixed by niobium, titanium or vanadium, the requirements for total aluminium and for Al/N do not apply. The contents of Nb, Ti and V need not be reported unless intentionally added to the cast. Sulfur is capped at 0,010 % across all three GH grades, a tighter limit than the room-temperature grades of Part 1 carry.

Low-Alloy Mo and CrMo Grades

For 16Mo3 and 13CrMo4-5, the upper carbon limit may be increased by 0,02 % for both cast and product analysis where wall thickness is 30 mm or greater.

5 % to 12 % Chromium Grades

For X20CrMoV11-1, the upper carbon value of 0,23 % shall not be exceeded on product analysis. For 7CrWVMoNb9-6, the standard sets a minimum Ti/N ratio of 3,5, and offers an alternative route: instead of the minimum ratio, the material may show a minimum hardness of 275 HV in the hardened condition, tested at mid-thickness on two samples per heat treatment lot, with the results reported.

Product Analysis Deviations

Option 3 calls for product analysis. Table 3 of the standard sets the permissible deviations from the cast analysis limits of Table 2, and the allowance widens as the specified level of the element rises.

Option 2 works in the other direction. Where subsequent forming operations need it, an agreed maximum copper content lower than the tabulated limit, together with an agreed maximum tin content, can be specified at enquiry and order.

Mechanical Properties of BS EN 10216-2:2024

Mechanical properties at and below room temperature are given in Table 4 and apply irrespective of whether they are verified on the order or not. Yield strength is banded by wall thickness, and the number of bands a grade carries depends on the thickness range the standard supports for it.

Yield Strength by Wall Thickness

Values are upper yield strength ReH, or the 0,2 % proof strength Rp0,2 where no yield phenomenon is present. Unlike the low-alloy grades, most of the 9 to 12 % chromium grades hold a single yield value across every thickness band the standard covers for them, which simplifies design in heavy wall header and main steam pipework.

Impact Properties

Minimum average absorbed energy KV2 is 40 J longitudinal and 27 J transverse, on the mean of three standard Charpy V-notch test pieces. What varies between grades is the test temperature and whether verification is mandatory or optional.

The standard divides the grades into two groups for impact testing. Group A covers tubes of wall thickness 16 mm and above made from 14MoV6-3, 25CrMo4, 20CrMoV13-5-5, 15NiCuMoNb5-6-4, X10CrSiCuMoNi9-2-1, X10CrMoVNb9-1, 7CrWVMoNb9-6, 7CrMoVTiB10-10, X10CrWMoVNb9-2, X11CrMoWVNb9-1-1, X20CrMoV11-1, X13CrCoWMoVNbBN11-2-2 and X10CrMoVNb11; the impact test at 20 °C is a mandatory test for Group A in both test categories. Group B covers those same grades below 16 mm wall plus all thicknesses of the remaining grades, and impact verification for Group B is an optional test invoked through Option 4.

Three practical rules govern specimen preparation. Impact tests are not required for specified wall thickness below 6 mm. Where standard 10 mm test pieces cannot be produced without flattening, narrower pieces down to 5 mm are used, and the measured energy is converted by KVc = 10 × KVp / w; where 5 mm cannot be obtained, the tubes are not impact tested at all. Test pieces are taken transverse to the tube axis unless Dmin, calculated as (T − 5) + [756,25 / (T − 5)], is greater than the specified outside diameter, in which case longitudinal pieces are used.

On the acceptance rule, the mean of three test pieces has to meet the specified value, and one individual value may fall below it, provided it is not less than 70 % of that value. If that fails, a second set of three may be tested; the unit then conforms only if the average of all six meets the minimum, no more than two of the six fall below the minimum, and no more than one of the six falls below 70 % of it.

Proof Strength at Elevated Temperature (Option 6)

This is the data that distinguishes Part 2 from Part 1. Minimum Rp0,2 values at temperature are tabulated in Table 5 of the standard, and Option 6 makes verification by tensile test at elevated temperature part of the order, with the test temperature specified at enquiry.

Values are a minimum of Rp0,2 in MPa. Table 5 in the standard runs from 100 °C to 400 °C in 50 °C steps; the columns above are a subset. For strength data above 400 °C, see the informative creep rupture strength values in Annex A (100 000 h basis), which is a different property (creep rupture strength, not proof strength).

Creep Rupture Strength (Annex A)

Annex A is informative and gives creep rupture strength values at 10 000 h, 100 000 h, 200 000 h and 250 000 h for each grade over the temperature range where that grade is characterised. The 100 000 h figure is the one most design codes work from.

The progression through that table is the whole argument for the standard's grade range. At 500 °C, P265GH holds 32 MPa for 100 000 h, while Grade 91 holds 241 MPa. At 600 °C, 10CrMo9-10 has fallen to 35 MPa where Grade 92 still holds 112 MPa. Grade selection under EN 10216-2 is a creep decision before it is a room-temperature strength decision.

Dimensions, Masses and Tolerances

Unless Option 11 is specified, tubes are delivered by outside diameter D and wall thickness T. Preferred dimensions are selected from EN 10220:2002 and listed in Table 6, covering outside diameters from 10,2 mm to 711 mm and wall thicknesses from 1,6 mm to 100 mm. Dimensions outside Table 6 may be agreed upon.

Table 6 sorts diameters into three series: series 1 covers diameters for which all the accessories needed to build a piping system are standardized, series 2 covers those for which not all accessories are standardized, and series 3 covers special-application diameters for which very few standardized accessories exist. Specifying a series 3 diameter usually means sourcing non-standard fittings alongside it.

Alternative Dimension Sets (Option 11)

Option 11 lets the purchaser order to a set of dimensions other than D and T, which matters where the bore has to be held rather than the outside surface:

Where tubes are ordered by d, dmin or Tmin, calculated values Dc, dc and Tc are derived from the ordered dimension plus half the applicable tolerance and used in place of D, d and T for the requirements that depend on them, including the flattening test, the hydrostatic test pressure, dimensional inspection, NDT acceptance levels and marking.

Tolerances on Diameter and Wall Thickness

Out-of-roundness is included in the tolerance on diameter, and eccentricity is included in the tolerance on wall thickness. Which of the five tolerance tables applies depends on how the tube was ordered.

Two points follow from those tables. Cold finished tube to Table 11 is roughly twice as tight on diameter as hot finished tube and holds ± 10 % on wall regardless of T/D ratio, which is why cold finished product is specified where fit-up tolerance is critical. And for outside diameters of 355,6 mm and above, Tables 7 to 10 permit the upper wall thickness to be exceeded locally by a further 5 % of T, with no restriction to a particular T/D band.

Mass

Mass per unit length follows EN 10220:2002, with grade-specific density corrections in place of the usual value:

These are not rounding differences. On a large-bore header run, using the EN 10220 default instead of 7,67 kg/dm³ for X10CrSiCuMoNi9-2-1 overstates the theoretical mass by more than 2 %, which shows up directly in a weight-based purchase price.

Lengths, Straightness and End Preparation

Unless Option 12 is specified, tubes are delivered in random lengths, with the delivery length range agreed at the time of enquiry and order. Option 12 calls for exact lengths, and the tolerances are over-only:

Deviation from straightness shall not exceed 0,0015 L over any tube length L, and deviation over any one metre length shall not exceed 3 mm.

Tubes with a wall thickness of 3,2 mm and above are delivered with square-cut ends, free from excessive burrs. Option 10 calls for bevelled ends instead: a bevel angle of 30° (+5° / −0°) with a root face of 1,6 mm ± 0,8 mm, except that for wall thickness greater than 20 mm an agreed alternative bevel may be specified.