BS EN 10216-4:2013 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". Selecting the wrong part is the most common specification error with this series, because four of the five parts cover overlapping material families and are separated by service condition.

The parallel series for welded product is EN 10217, Welded steel tubes for pressure purposes - Technical delivery conditions. Part 3 also offers low temperature qualities in its NL and QL grades, and the two parts overlap around − 50 °C. The distinction is range and material: Part 3 stops at − 50 °C in alloy fine grain steels reaching 690 MPa yield. Part 4 carries a short option list: 14 options in total. The options Part 4 does not have are as informative as the ones it does: there is no option for alternative dimension sets, none for elevated temperature verification, and none for impact testing at an additional temperature.

Test Category 1 vs Test Category 2

The test category indicates the extent and level of inspection and testing. It is mandatory order information for non-alloy steel, and it appears in the tube marking for those grades.

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. Alloyed steel tubes are inspected and tested to test category 2 only. Since only three of the nine grades in this standard are non-alloy quality steels, test category 1 is available on a minority of the range.

BS EN 10216-4:2013 Steel Grades

Under the classification system of EN 10020, the grades P215NL, P255QL and P265NL are classified as non-alloy quality steels. The other six grades are classified as alloy special steels.

Designation follows two different rules depending on which group the grade belongs to. Non-alloy steel names are built from the capital letter P for pressure purposes, the specified minimum yield strength at room temperature in MPa, the symbol of the heat treatment, and the symbol L for low temperature - so P265NL reads as a pressure-purpose steel, 265 MPa minimum yield, normalised, low temperature. Alloy steel names are built from the chemical composition plus the heat treatment symbols, which is why 12Ni14 and X10Ni9 carry no P prefix and no yield figure in the name.

Minimum yield and tensile values apply for wall thickness up to and including 40 mm. The lowest test temperature column is the temperature at which the mandatory impact test is carried out under Clause 11.7.1, for the thinner of the two wall bands where a grade has two.

Manufacturing and Heat Treatment Conditions

All tubes are manufactured by a seamless process. Unless Option 1 is specified, the tubes may be either hot or cold finished at the manufacturer's discretion; 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 for the grade concerned.

Where the delivery condition is +QT, the temperature shown is the hardening temperature; where it is +N or +NT, it is the normalising temperature.

Six footnotes qualify that table, and three of them change what a purchaser receives. Where two types of heat treatment are specified for a grade, the choice depends on wall thickness and T/D ratio; the decision rests with the manufacturer but has to be reported in the inspection document. For 11MnNi5-3 and 13MnNi6-3, tempering can occasionally be necessary after normalising - the decision again rests with the manufacturer but has to be stated to the customer at enquiry and order, and tubes treated that way are designated by the steel name supplemented by "+NT". For X10Ni9 in the +QT condition, an additional prenormalizing treatment in the range 880 to 930 °C may be necessary, and the manufacturer then has to inform the purchaser.

On the cooling medium, the standard notes that the influence of other parameters such as dimensions and quenching temperature on properties and crack susceptibility should be taken into account, and that other cooling media such as synthetic quenchants may also be used.

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

All NDT activities are carried out by qualified and competent level 1, 2 or 3 personnel authorised to operate by the employer, with qualification in accordance with ISO 11484 or at least an equivalent. The standard recommends that level 3 personnel be certified in accordance with EN ISO 9712 or at least an equivalent, the operating authorisation follows a written procedure, and NDT operations are authorised by a level 3 individual approved by the employer.

Chemical Composition of BS EN 10216-4:2013

Chemical composition is specified as cast analysis in Table 2, expressed in % by mass. The cast analysis reported by the steel producer applies. Elements not included in the table shall not be intentionally added without the agreement of the purchaser, except for elements which may be added for finishing the cast. All appropriate measures shall be taken to prevent the addition of undesirable elements from scrap or other materials used in the steelmaking process.

Four footnotes qualify the composition table. Aluminium may be replaced by other elements having a similar effect, by agreement between purchaser and manufacturer. Option 2 allows an agreed maximum copper content lower than tabulated, together with an agreed maximum tin content, to facilitate subsequent forming operations. And for 11MnNi5-3 and 13MnNi6-3, the lower limit for nickel may be reduced to not less than 0,15 % for tubes with wall thickness not exceeding 10 mm.

The sulfur limits are the clearest signal of what this standard is for. The six grades rated to − 60 °C and above hold sulfur at 0,010 % maximum; the three nickel steels rated to − 100 °C and below halve that to 0,005 %. Phosphorus follows the same pattern, tightening from 0,025 % to 0,020 % for X12Ni5 and X10Ni9.

Product Analysis Deviations (Option 3)

Option 3 calls for a product analysis. Table 3 gives the permissible deviations from the cast analysis limits of Table 2. The nickel row is banded four ways, reflecting the wide nickel range the standard covers.

Mechanical Properties of BS EN 10216-4:2013

Mechanical properties apply irrespective of whether they are verified on the order or not. Unlike Parts 2 and 3, Part 4 does not band yield strength across many wall thickness groups: Table 4 gives a single set of values for wall thickness up to and including 40 mm, which is also the upper limit of the standard's preferred dimensions.

Room Temperature Tensile Properties

Two of the three non-alloy grades carry a thickness qualification on the yield figure: 215 MPa applies to P215NL for wall thickness up to and including 10 mm, and 265 MPa applies to P265NL for wall thickness up to and including 25 mm. Tensile strength is given as a range in every case, and the upper limit is a requirement in its own right - a tube testing above it does not conform, because excess strength compromises the toughness the standard exists to guarantee.

Impact Properties

Table 5 is the substance of Part 4. Minimum average absorbed energy KV2 is tabulated by grade, wall thickness and orientation, across ten test temperatures from + 20 °C down to − 196 °C. Clause 11.7.1 requires the impact test to be carried out at the lowest temperature specified in Table 5 for the steel grade concerned, so the table is not a menu - it fixes the mandatory test temperature grade by grade.

Longitudinal minimum average impact energy KV2 in joules:

Transverse minimum average impact energy KV2 in joules. P215NL does not appear below: it is the only grade in the standard for which Table 5 specifies longitudinal test pieces alone, with no transverse requirement.

Reading the tables by column rather than by row shows the design intent. At the lowest temperature each grade is qualified for, the requirement is the same 40 J longitudinal and 27 J transverse - the same numbers for P215NL at − 40 °C and for X10Ni9 at − 196 °C. What alloying buys is not a higher energy value, but the ability to hold that value at a lower temperature.

Wall thickness matters as much as grade. Where a grade has two wall bands, the thicker band loses one temperature step: 12Ni14 is tested at − 100 °C up to 25 mm wall but only − 90 °C above it, and X12Ni5 drops from − 120 °C to − 110 °C the same way. P255QL loses its transverse requirement at − 50 °C entirely once wall exceeds 25 mm.

Specimen and acceptance rules follow the series convention. Three standard Charpy V-notch test pieces are prepared to EN ISO 148-1; where standard 10 mm pieces cannot be produced without flattening, test pieces of width less than 10 mm but not less than 5 mm are prepared, and the largest obtainable width shall be used. Where the width W is less than 10 mm, the measured energy KVp is converted to KVc = 10 × KVp / W; where 5 mm cannot be obtained, the tubes are not impact tested. 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.

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 test pieces may be taken from the same sample at the discretion of the manufacturer; 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.

Dimensions, Masses and Tolerances

Tubes are delivered by outside diameter D and wall thickness T. Part 4 offers no option to order by inside diameter or minimum wall thickness, which is a real difference from Parts 2 and 3 and means there are no calculated Dc, dc or Tc values to work with.

Preferred dimensions are selected from EN 10220 and given in Table 6, covering outside diameters from 10,2 mm to 711 mm and wall thicknesses from 1,6 mm to 40 mm. Dimensions different from those in Table 6 may be agreed. The 40 mm wall ceiling matches Table 4, which tabulates mechanical properties for wall thickness up to and including 40 mm, and Table 5, whose thickest band also stops at 40 mm.

Table 6 sorts diameters into three series: series 1 covers diameters for which all the accessories needed to build a piping system are standardised, series 2 those for which not all accessories are standardised, and series 3 special-application diameters for which very few standardised accessories exist. Mass per unit length follows EN 10220, with no grade-specific density corrections.

Tolerances on Diameter and Wall Thickness

Out of roundness is included in the tolerances on diameter and eccentricity is included in the tolerances on wall thickness. Part 4 has only two tolerance tables, one for standard delivery and one for cold finished tube.

For outside diameters D ≥ 355,6 mm, Table 7 permits the upper wall thickness to be exceeded locally by a further 5 % of the wall thickness T, in the highest thickness-ratio band. Cold finished tube to Table 8 is roughly twice as tight on diameter and holds ± 10 % on wall regardless of T/D ratio, with no local over-run allowance.

Lengths, Straightness and End Preparation

Unless Option 8 is specified, tubes are delivered in random length, with the delivery range agreed at the time of enquiry and order. Option 8 calls for exact lengths:

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 are delivered with square cut ends, free from excessive burrs. Option 7 calls for bevelled ends: 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 alternative bevel may be specified. Unlike Part 3, Part 4 sets no minimum wall thickness for the bevel option.