DIN2391 Standard specification

DIN 2391 standard specifies the Seamless steel tubes used forMechanical and Automobile.

The main products of steel / steel grade: DIN2391-1(ST35, ST45, ST52).

DIN 2391 is included in DIN Handbook 3 and 272. Gives dimensions for seamless precision steel tubes; these tube dimensions have been selected from the range of manufacturable tube dimensions which are mainly used as design elements.

What is the difference between Din 2391 and Din 3304?

DIN 2391 applies to seamless precision steel tubes and in compliance with ISO/DIN 3304, those tube dimensions have been selected from the range of manufacture dimensions which are mainly used as design elements.

DIN2391 Part 2 specifies dimensions for cold finished, seamless precision steel tubes and is to be used in conjunction with DIN2391 part2 which states the relevant technical delivery conditions. The preferred sizes listed in standard are mainly used in mechanical and automotive engineering.

Where steel tubes of dimensions specified in this standard are to comply with the technical delivery conditions listed in subclause 1.2 of DIN 2391 Part 2.

DIN 2391 seamless precision tubes applications – Used in Hydraulic & pneumatic cylinder, Mechanical and Automotive engineering.

Chemical Composition (%) of DIN2391

Standard Grade Chemical Components (%)
Symbol Material No. C Si Mn P S
DIN2391 St 30 Si 1.0211 ≤0.10 ≤0.10 ≤0.55 ≤0.025 ≤0.025
St 30 Al 1.0212 ≤0.10 ≤0.05 ≤0.55 ≤0.025 ≤0.025
St 35 1.0308 ≤0.17 ≤0.35 ≥0.40 ≤0.025 ≤0.025
St 5 1.0408 ≤0.21 ≤0.35 ≥0.40 ≤0.025 ≤0.025
St 52 1.058 ≤0.22 ≤0.55 ≤1.60 ≤0.025 ≤0.025

Delivery Conditions

The tubes shall be manufactured from cold drawn or cold rolled processes. The tubes shall be supplied in one of the delivery conditions as follows:

Designation Symbol Description
Cold finished (hard) BK Tubes do not undergo heat treatment following the final cold forming and thus, have a rather high resistance to deformation.
Cold finished (soft) BKW The final heat treatment is followed by cold drawing involving limited deformation. Appropriate further processing allows a certain degree of cold forming (e.g. bending, expanding).
Cold finished and stress-relieved BKS Heat treatment is applied following the last cold forming process. Subject to appropriate processing conditions, the increase in the residual stresses involved enables both forming and machining to a certain degree.
Annealed GBK The last cold forming process is followed by annealing in a controlled atmosphere.
Normalized NBK The last cold forming process is followed by annealing above the upper transformation point in a controlled atmosphere.

Delivery Condition Symbol in accordance with EN10305 and DIN2391.

Symbol in accordance with EN 10305 Symbol in accordance with DIN2391

Mechanical Properties

Steel Grade Minimum values for the delivery condition
Steel Name Steel Number BK BKW BKS GBK NBK
Rm A % Rm A % Rm ReH A % Rm A % Rm ReH A %
Mpa Mpa Mpa Mpa Mpa Mpa Mpa
St 30 Si 1.0211 430 8 380 12 380 280 16 280 30 290 to 420 215 30
St 30 Al 1.0212 430 8 380 12 380 280 16 280 30 290 to 420 215 30
St 35 1.0308 480 6 420 10 420 315 14 315 25 340 to 470 235 25
St 45 1.0408 580 5 520 8 520 375 12 390 21 440 to 570 255 21
St 52 1.0580 640 4 580 7 580 420 10 490 22 490 to 630 355 22

Inspection and test list for the DIN 2391 Standard

Inspection or test types Test frequency
Internal test Acceptance test
Chemical analysis M M
Tensile testing M One per tested batch
Flattening test or extension test M Two per tested batch
Dimension verification M M
Visual inspection M M
NDT in order to identify leaks Individual Individual


The following marking shall be shown on a label attached to the bundle:

Protection and Packing:


【H】 Ceramic lined pipe

Ceramic lined pipe is made through self-propagating high-temperature synthesis (SHS) technique.

【H】 Cast basalt lined steel pipe

Cast basalt lined steel pipe is composed by lined with cast basalt pipe, outside steel pipe and cement mortar filling between the two layers.

【H】 Ceramic Tile Lined Pipes

Ceramic tile lined pipes have very uniform coating of specially formulated ceramic material that is affixed to the inner of the pipe.

【H】 Rare earth alloy wear-resistant pipe

The material of the rare earth alloy wear-resistant pipe is ZG40CrMnMoNiSiRe, which is also the grade of rare earth alloy steel.

【H】 Tubes Erosion Shields

Tubes Erosion Shields are used to protect boiler tubing from the highly erosive effects of high temperatures and pressures thereby greatly extending tube life.

【H】 ASTM A213 T91 Alloy Tube

The ASTM A213 T91 seamless tubes are primarily used for boiler, superheater, and heat-exchanger.