BS EN 10216-3:2013 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". Four of the five parts are organised by service temperature; Part 3 is the exception, organised by steel type.

The parallel series for welded product is EN 10217, Welded steel tubes for pressure purposes - Technical delivery conditions. Because Part 3 is defined by steel type rather than temperature, its low-temperature qualities overlap in application with EN 10216-4; the distinction is that Part 3 grades are alloy fine-grain steels reaching up to 690 MPa minimum yield, whereas Part 4 covers the non-alloy and alloy grades characterised specifically for low-temperature duty.

The Four Steel Qualities

Clause 5.1.1 divides the grades into four qualities, and the suffix on the steel name identifies which one applies. This is the first decision to make under Part 3, because it determines the impact test temperature, sulfur limit and whether elevated temperature data is available at all.

Under the classification system of EN 10020, the grades P275NL1, P355N, P355NH and P355NL1 are classified as alloy quality steels. Every other grade in the standard is classified as an alloy special steel.

The N and Q letters carry a second meaning that is easy to miss. N-grades are supplied normalized; Q-grades are supplied quenched and tempered. So the suffix simultaneously tells you the quality level and the heat treatment condition: P460NL1 is a normalized low-temperature quality tube, while P690QL1 is a quenched and tempered one.

Test Category 1 vs Test Category 2

The test category is a classification indicating the extent and level of inspection and testing. It is mandatory order information, except for P620 and P690, and it forms part of the tube marking on the grades where it applies.

Tubes are inspected and tested to test category 1 or test category 2 as specified in the order, except that P620 and P690 grades are always tested to test category 2. There is no test category 1 route for the two highest strength levels.

The practical difference is non-destructive testing and sampling depth. Test category 2 puts every tube through NDT for longitudinal imperfections and draws two sample tubes per test unit instead of one, which is why it is the only route permitted for the quenched and tempered high-strength grades.

BS EN 10216-3:2013 Steel Grades

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

The steel name is built from the capital letter P for pressure purposes, the specified minimum yield strength for the lowest applicable wall thickness group expressed in megapascals, and one of the additional symbols N, NH, NL1, NL2, Q, QH, QL, QL1 or QL2. P460NL1 therefore reads as a pressure-purpose steel with 460 MPa minimum yield in the thinnest wall group, supplied normalized, in low-temperature quality.

Not every strength level is available in every quality. P275 exists only in the two low-temperature qualities, and P620 has no special low-temperature version.

Manufacturing, Heat Treatment and Delivery 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.

Two grade-specific provisions modify that table. For P355N and P355NH, normalizing may be replaced by normalizing forming. For P460, it may be necessary to apply delayed cooling or additional tempering after normalizing, and for the N-grades generally, accelerated cooling after austenitising may be necessary to achieve the intended structure and material properties where wall thickness exceeds 25 mm or the T/D ratio exceeds 0,15.

In both cases, the decision rests with the manufacturer, but it has to be stated to the customer at the time of enquiry and order. Steel tubes treated with accelerated cooling are designated by the steel name supplemented by the symbol "+QT". A purchaser receiving P460NL1+QT rather than P460NL1+N is not receiving a substitution error; it is the standard's own mechanism for heavy wall.

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 authorized 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, and NDT operations are authorized by a level 3 individual approved by the employer.

Chemical Composition of BS EN 10216-3:2013

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 added to finish the cast.

Five footnotes govern how the table is applied. Total aluminium is a minimum, not a maximum, and the requirement Al/N ≥ 2 applies; where nitrogen is fixed by niobium, titanium or vanadium, the requirements for total aluminium and for Al/N do not apply. For the P275 and P355 grades, the sum of chromium, copper and molybdenum shall not exceed 0,45 %. For P460, where copper exceeds 0,30 %, nickel shall be at least half the copper content. And Option 2 allows an agreed maximum copper content lower than tabulated, together with an agreed maximum tin content, to facilitate subsequent forming operations.

The combined Nb + Ti + V cap is what makes these fine-grain steels work. Those three micro-alloying elements form the carbonitride precipitates that pin grain boundaries and hold the ferritic grain size at 6 or finer, and the cap rises with strength level - 0,05 % for P275, 0,12 % for P355, 0,22 % for P460 and P620 - because higher strength requires more precipitation strengthening. P690 controls the same elements individually rather than through a combined limit.

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. Most deviations are single-sided, in the direction that would otherwise take the product out of specification.

Mechanical Properties of BS EN 10216-3:2013

Yield Strength by Wall Thickness

Table 4 bands upper yield strength ReH, or the 0,2 % proof strength Rp0,2 where no yield phenomenon is present, across seven wall thickness groups. The drop from thin to heavy wall is steepest in the quenched and tempered grades, where P690Q falls from 690 MPa to 500 MPa across the range.

Values are minimum ReH or Rp0,2 in MPa. P690QL2 is the outlier worth noting: it holds 690 MPa in a full-thickness band further than the other P690 grades and stays above them at every band thereafter.

For P275NL1 and P275NL2, the T ≤ 12 and > 12 to 20 bands share the same value of 275 MPa, reflecting a combined ≤ 20 mm entry in Table 4 of the standard. For P355 grades, the ≤ 12 mm column entry reflects the same value as > 12 to 20 mm (355 MPa); Table 4 of the standard presents these as a combined ≤ 20 mm band. The ≤ 12 mm column is a distinct entry only for P460 grades and above.

Tensile Strength and Elongation

Tensile strength is banded across four thickness groups rather than seven, and elongation is a single pair of values per strength level.

Tensile strength in this standard is a range, not a floor. The upper limit matters as much as the lower one because it caps hardness for weldability and forming. A tube testing above the range fails the standard just as one testing below it does.

Impact Properties

Table 7 is the heart of Part 3 and the reason the low-temperature qualities exist. Minimum average impact energy KV2 is tabulated by grade group, wall thickness and test temperature, in both longitudinal and transverse directions, from + 20 °C down to − 50 °C.

Longitudinal minimum average impact energy in joules:

Transverse minimum average impact energy in joules:

The test temperature is set by quality, not by choice. Clause 11.7.1 requires the impact test to be carried out at − 20 °C for the basic and elevated temperature quality, and at the relevant lowest temperature in Table 7 for the low and special low temperature quality. So an NL2 grade in wall up to 40 mm is tested at − 50 °C and must return 40 J longitudinal, while the same strength level in NL1 quality is tested at − 40 °C for the same 40 J. Option 13 adds testing at a further temperature selected from those given in Table 7 for the grade, on top of the standard test temperature.

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, 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. 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. The average value of the six tests shall equal or exceed the specified minimum average value; not more than two of the six individual values may be lower than the specified minimum average value; and not more than one of the six individual values may be lower than 70 % of the specified minimum average value.

Elevated Temperature Properties

Elevated temperature data is tabulated only for the NH and QH grades, plus P275NL1 and P275NL2 in Annex A. Verification is mandatory for P620QH and P690QH at 300 °C; for everything else, it is optional.

Minimum 0,2 % proof strength Rp0,2 in MPa, from Table 5 and Annex A Table A.1:

Minimum tensile strength Rm in MPa, from Table 6 and Annex A Table A.2:

The tables above are a subset; Tables 5 and 6 and Annex A give every wall thickness band for each grade. Two features are worth noting. The QH grades carry no data above 300 °C at all, which caps their design temperature under this standard. And unlike Part 2, Part 3 gives no creep rupture data in any form, so these grades are not characterised for service in the creep range.

Dimensions, Masses and Tolerances

Unless Option 10 is specified, tubes are delivered by outside diameter D and wall thickness T. Preferred dimensions are selected from EN 10220 and given in Table 8, covering outside diameters from 10,2 mm to 711 mm and wall thicknesses from 1,6 mm to 100 mm. Dimensions different from those in Table 8 may be agreed upon. Mass per unit length follows EN 10220 with no grade-specific density corrections.

Table 8 sorts diameters into three series: series 1 covers diameters for which all the accessories needed to build a piping system are standardized, series 2 those for which not all accessories are standardized, and series 3 special-application diameters for which very few standardized accessories exist.

Alternative Dimension Sets (Option 10)

Where tubes are ordered by d, dmin or Tmin, calculated values Dc, dc and Tc are used in place of D, d and T for the requirements that depend on them - including the accelerated cooling trigger in 7.2.5, the flattening test, the hydrostatic test pressure, dimensional inspection, NDT acceptance levels and marking. Where the order is by inside diameter d, Dc is simply d + 2T; where it is by dmin or Tmin, half the applicable tolerance is added to the ordered dimension first.

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. Which of the five tolerance tables applies depends on how the tube was ordered.

In Tables 9 to 12, for outside diameters D ≥ 355,6 mm, it is permitted to exceed the upper wall thickness locally by a further 5 % of the wall thickness T, in the highest thickness-ratio band of each table. Table 13, for tube ordered cold finished, carries no such allowance and is roughly twice as tight on diameter as the hot finished tables.

Lengths, Straightness and End Preparation

Unless Option 11 is specified, tubes are delivered in random lengths, with the delivery range agreed at the time of enquiry and order. Option 11 calls for exact lengths:

The exact length table starts at 2 000 mm. Below that length, the standard gives no tolerance, so shorter exact lengths have to be agreed separately rather than assumed to fall under the + 10 mm / 0 band.

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 9: The tubes with wall thickness ≥ [threshold shown in Figure 1 context] shall be delivered with 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.