Classification of steel grades for the production of steel pipes

Designation of steel for the production of pipes

The designations for the grade of the steel, used during the production of the pipes, are specified in the following EN standards:

• EN 10027-1 – basic symbols and abbreviated markings;

• EN 10027-2 – numerical designations; and

• EN ECISS IC10 – supplementary symbols.

The EN 10027-1 standard categorizes steel grades into two groups, which include smaller subgroups. The first group includes steel with different mechanical properties. The following types of steel are in this group:

• S – steel intended for the construction of general use structures. These are, for example, grades S355J2H, S235JRH, and S420NLH. The numerical value given in the designations is the value of the minimum yield strength, measured in N/mm2. The letter “J” indicates the undercut ductility value and the default is 27J. The letter “R” indicates ambient temperature, the letter “H” indicates a hollow profile, the letter “N” indicates a standardized structure, and the letter “L” indicates a low temperature series;

• P – steel used in pressure equipment, for example P235TR1 or P265GH. The number also represents the value of the minimum yield strength. The letter “T” indicates steel intended for pipes, the letter “R” indicates ambient temperature (where “L” is low temperature, and “H” is high temperature), the letter “G” indicates general characteristics which represent the meaning of the second character. The TR1 character string indicates steel for pipes intended for the transport of media, and TR2  indicates steel for pipes used in piping systems and pressure equipment;

• L – steel used to create pipeline installations, for example L245NB or L210GA. In this case, the number also represents the value of the minimum yield strength, and the individual letters indicate: “N” for normalizing or annealing, “A” or “B” for the class of requirements for installation pipes, “M” for thermo-mechanically rolled steel, “Q” for refined steel, “G” for general characteristics which represent the meaning of the second character;

• E – steel used for machine parts. We distinguish steels in this subgroup for machined pipes (for example E355+N or E355+AR, where “N” indicates normalizing and “AR” indicates that no heat treatment is necessary), a fixed marking in connection with their chemical composition (for example 20MnV6), steels to be machined without heat treatment, steels with specific properties (for example E355K2, where “K” is the value of the undercut ductility 40J at ‒20°C), and steels for thermochemical treatment and heat treatment after machining (38Mn6 steel or C22E steels, where “C” indicates steel with a 0.22 percent carbon content, and “E” indicates the maximum controlled content of P and S).

Check out our other article on: Steel pipes and their application in the construction industry.

The second group of steels, defined in the EN 10027-1 standard, consist of steels that differ in terms of their chemical composition. There are four subgroups:

• unalloyed steels – no free-cutting steels. They are designated, for example, with C22, where “C” stands for carbon and the number is 100 times the value of the average predicted content of this element in the steel;

• unalloyed steels with a Manganese (Mn) content greater than 1 percent and alloy steels with no alloying element greater than 5%;

• alloy steels – these are steels in which the content of at least one alloying element exceeds 5 percent. They are marked, for example, X11CrMo9-1, where the number 11 means 100 times the average carbon content, the numbers 9-1 refer to the content of the Cr and Mo alloying elements, and “X” is an identification letter; and

• high-speed steels – for example HS 6-5-2, where “HS” are identification letters and the numbers provide information on the content of individual alloying elements.

The numbers in the EN 10027-2 standard are built on the basis of one schema. The first digit is always one, the next two indicate the steel group, and then the consecutive number indicates the steel. On the other hand, the EN ECISS IC10 standard defines supplementary symbols, which are placed at the very end in the steel designation (for example S 275 J0). Sometimes, symbols related to steel products are also given. They appear after a separating plus sign (for example S 275 J0+A).