DIN 2391-2 Seamless Precision steel tubes

2021-12-07
DIN 2391-81 Part 2 Seamless Precision steel tubes
 
Field of application
This Standard defines the technical delivery conditions for seamless precision steel tubes according to DIN 2391 Part 1 which are made from the steel grades listed in section 5.
 
Tubes according to this Standard are mainly used where accuracy to dimension and, possibly, small wall thicknesses and good surface condition are required.
 
 
 
Quality grade
The tubes are supplied in the following quality grades:

A
 precision steel tubes intended primarily for mechanical stressing, without any particular quality requirement and without acceptance test certificate
B
 precision steel tubes intended primarily for mechanical stressing, with special quirement and exclusively with acceptance test certificate
C
 precision steel tubes with special requirement according to section 12. Theses requirements and corresponding tests must be agreed, with the customer having to specify his requirements at the time of enquiry and on ordering



Steel grades

Table 1. Steel grades

Quality grade
Steel grade
Code number
Material number
A and B
St 30 Si
St 30 Al
St 35
St 45
St 52
1.0211
1.0212
1.0308
1.0408
1.0580
C
All steel grades according to quality grade A and B, as well as other steels, e.g. according to
DIN 1651
DIN 17 100
DIN 17 200
DIN 17 210
DIN 17 211



Chemical composition
Table 2 contains data on the chemical composition of the steels. Small departures from these data which apply to the ladle analysis, are permissible if they do not impair the properties of the steel when in use.
 
In carrying out subsequent testing on the finished tube, the maximum permissible contents in terms of carbon, phosphorus and sulfur as defined by the ladle analysis of table 2 may be increased:
 
- in the case of deviations due to sampling and method of analysis by + 5 %

- in the case of deviations due to segregation:
for rimming steels by + 20%
 
for killed steels by + 5 %

 
 
of the particular maximum content.
 
Table 2. Steel grades and chemical composition of the steels (ladle analysis)
 

Steel grade Chemical composition, %
 
Symbol		  
Material number		 C
max		 Si
max		 Mn P
max		 S
max
St 30 Si 1.0211 0.10 0.30 ≤ 0.55 0.040 0.040
St 30 Al 9) 1.0212 0.20 0.05 ≤ 0.55 0.040 0.040
St 35 1.0308 0.17 0.35 ≥ 0.40 0.050 0.050
St 45 1.0408 0.21 2) 0.35 ≥ 0.40 0.050 0.050
St 52 1.0580 0.22 0.55 ≤ 1.60 0.050 0.050
1) This steel is deoxidized using aluminum.
2) In subsequent testing on the individual tube, the C-content must not exceed 0.25%.




 
Condition on delivery
The tubes are supplied in one of the conditions listed in table 3. Other conditions on delivery are specified in table 9 (quality grade C).
 
 
Table 3. Conditions on delivery
 
Term Symbol Explanation
Cold-finished/hard
(cold-finished as-drawn)		  
BK		  No heat treatment after the last cold-forming process. The tubes therefore have only low deformability.
Cold-finished/soft
(lightly cold-worked)		  
BKW		 After the last heat treatment there is a light finishing pass (cold drawing) With proper subsequent processing,
the tube can be cold-formed (e.g. bent, expanded) within certain limits.
Annealed GBK After the final cold-forming process the tubes are annealed in a controlled atmosphere or under vacuum.
Normalized NBK The tubes are annealed above the upper transformation point in a controlled atmosphere or under vacuum.


Delivery status of each steel grade:

Grade Cold-finished/hard Cold-finished/soft Annealed Normalized
St 30 Si √ √ √ √
St 30 Al 9) √ √ √ √
St 35 √ √ √ √
St 45 √ √ √ √
St 52 √ √ √ √



 
Mechanical and technological properties
The mechanical properties depend on the condition on delivery as defined in table 3.
 
In the case of other steel grades and/or other conditions on delivery then those specified in tables 2, 3 and 8, the mechanical and technological properties must be mutually agreed. In these cases, the tubes are supplied according to quality grade C.


Quality grade C:
Special requirements(examples)
Line Special requirement Features and/or technical delivery conditions
1 Steel grades other than specified in table 1 As specified in DIN 1651,DIN EN 10025,DIN EN 10083 Parts 1 and 2,or DIN 17210
2 Tubes for pipelines As specified in DIN 1629,DIN1630,or DIN 2445 Part 2
3 Other geometry and surface Tubes with an outside diameter smaller than 4 mm and greater than 260 mm,
with a non-circular cross section,subject to other tolerances than those specified in DIN 2391 Part 1,
other tolerance positions or special requirements regarding the surface condition,stralghtness and squareness of pipe ends
4 Final supply condition other than specified in table 3 Tempered;annealed to obtain speciflc microstructure
5 Other mechanical properties Deviations regarding the mechanical properties specified in table 4

 
The steels listed in table 2 are deemed to be suitable for welding because of their chemical composition and metal lurgical treatment.
In the BK or BKW conditions on delivery, the mechanical properties are modified in the zone which has been subjected to heating. This should be taken into account (see DIN 8528 Part 1) in assessing the weldability of a component.
 
Table 4. Mechanical properties of the tubes at room temperature

Steel grade
Condition on delivery
Cold-finished/hard
(BK) 3)
Cold-finished/soft
(BKW) 3)
Annealed
(GBK) 3)
Normalized
(NBK)
Code
number
Material
number
Tensile
strength

Rm
N/㎟

min

Elonga-
tion at
repture

A5(%)

min

 Tensile
strength

Rm
N/㎟

min

Elongation at
repture

A5(%) 
min

Tensile
strength

Rm
N/㎟

min

Elongation at
repture 

A5(%) 
min

Tensile
strength

Rm
N/㎟
Upper
yield point

ReH
N/㎟

min
Elongation
at repture 

A5(%) 
min
St 30 Si
1.0211
400
8
330
12
280
30
290 to 420
215
30
St 30 Al
1.0212
400
8
330
12
280
30
290 to 420
215
30
St 35
1.0308
440
6
370
10
315
25
340 to 470
235
25
St 45
1.0408
540
5
470
8
390
21
440 to 570
255
21
St 52
1.0580
590
4
540
7
490
22
490 to 630
355
22


3) The yield point for the annealed (GBK)condition on delivery is at least 50% of the (ultimate) tensile strength. Depending upon the degree of deformation in the drawing operation, the yield point of tubes delivered in the cold-finished/hard (BK)and cold-finished/soft(BKW) conditions, may be increased to a level close to the tensile strength. In calculating the yield point, the following values are recommended : cold-finished/hard condition on delivery ≥ 80% of the tensile strength, cold-finished/soft condition on delivery ≥ 70% of the tensile strength.

4) In the case of tubes of outside diameter ≤ 30 mm, the wall thickness of which is ≤ 3mm, the minimum value of the yield point is 10 N /㎟ lower.



 
 
Testings
 
Tensile test  
Flattening test    
Moasurement of surface roughness   
Dimensional  check
Surface inspection   
Leal tightness test      
Non-destructive test




Welded Steel Tubing and Pipe-Corresponding to DIN 2391-1


Wall thicn-esss Nominal dim-ension 0.5 0.8 1 1.2 1.5 1.8 2 2.2 2.5 2.8 3 4.5 5 5.5 6 7 8 9 10 12 14 16 18 20 22 25
Permissible deviation                                                    
Outside diameter da                                                    
Nominal dimension Permissible deviation                                                    
4 ±0.1

 

                                                  
5                                                    
6                                                    
7                                                    
8                                                    
9                                                    
10                                                    
12 ±0.08                                                    
14                                                    
15                                                    
16                                                    
18                                                    
20                                                    
22                                                    
25                                                    
26                                                    
28                                                    
30                                                    
32 ±0.15                                                    
35                                                    
38                                                    
40                                                    
42 ±0.20                                                    
45                                                    
48                                                    
50                                                    
55 ±0.25                                                    
60                                                    
65 ±0.30                                                    
70                                                    
75 ±0.35                                                    
80                                                    
85 ±0.40                                                    
90                                                    
95 ±0.45                                                    
100                                                    
110 ±0.50                                                    
120                                                    
130 ±0.70                                                    
140                                                    
150 ±0.80                                                    
160                                                    
170 ±0.90                                                    
180                                                    
190 ±1.0                                                    
200                                                    
220 ±1.20                                                    
240                                                    
260 ±1.30                                                    

1) For outside diameters of nominal dimensions 4 and 5 mm, the permissible deviation from the nominal dimension s of the wall thickness is ± 20 % For outside diameters of nominal dimensions 6 to 8 mm, the permissible deviation from the nominal dimension s of the wall thickness is ±15%.
  
  s/D
=1/60
  s/D
=1/40
  s/D
=1/20







 


Equivalent steel grade


JIS ASTM BS DIN NF ISO  
Index Number
Standard
Number		  
Grade		  
Type		 Standard
Number		  
Grade		  
Type		 Standard
Number		  
Grade		  
Type		 Standard
Number		  
Grade		  
Type		 Standard
Number		  
Grade		  
Type		 Standard
Number		  
Grade		  
Type
G3445 STKM11A C A512 MT1010 C 1717 ERWC1 C 2391 St30Si C       3304 R28 C C017
      A513 MT1010 C         St30A1 C       3305 " C  
                  2393 St28 C       3306 " C  
                    RSt28 C              
                  2394 St28 C              
                    USt28 C              
                    RSt28 C              
  STKM12A C A512 MT1015 C 1717 ERWC2 C 2391 St37-2         3304 R33 C  
      A513 MT1015 C 6323 HFS3 C   RSt37-2         3305 " "  
  STKM12B C A512 MT1015 C       2394 St37-2         3306 " "  
      A513 MT1015 C         Ust38-2                




      A519 MT1015 C         RSt-2                
  STKM12C C       1717 CEWC2 C       A49-322 TU37b C        
            " CFSC3 C       A49-327 TU37b C        
            6323 CFS3 C                    
            " CFS3A C                    
  STKM13A C A312 MT1020 C 1717 ERWC3 C 2391 St45 C A49-324 TU37b C 2937 TS4 C  
      A513 MT1020 C       2393 St44-2 C A49-330 TU37b C 3304 R37 "  
                  2394 St44-2 C A49-343 TU38b C 3305 " "  
  STKM13B C A513 MT1020 C                   3306 " "  
  STKM13C C       1717 CEWC3 C                    
            " CFSC4 C                    
            6323 CFS4 C                    
  STKM14A C A513 MT1020 C 6323 HFS4 C             2937 TS9 C  
                              3304 R42 "  
  STKM14B C       6323 HFS5 C             3305 R42 C  
  STMK14C C                         3306 " "  
  STKM15A C A513 1030 C                          
      A519 1030 C                          
  STKM15C                                  
  STKM16A C A519 1040 C             A49-311 TUXC35 C        
                        A49-312 TUXC35 C        
  STKM16C C                                
  STKM17A C A519 1050 C 6323 HFS8 C                    
  STKM17C C       6323 CFS8 C                    




  STKM18A C A519 1518 C 1717 ERWC5 C       A49-310 TU52b C        
                        A49-311 TU52b C        
                        A49-312 TU52b C        
  STKM18B C                   A49-321 TU52b C        
                        A49-323 TU52b C        
                        A49-326 TU52b C        
  STKM18C C                   A49-330 TU52b C        
                        A49-341 TS42a C        
                        " TS47a C        
                        A49-343 TS18M5 C        
  STKM19A C A519 1524 C       2391 ST52 C       2937 TS18 C  
                  2393 ST52-3 C       2938 Gr.1 C  
                  2394 ST52-3 C       3304 R50 C  
                              3305 R50 C  
                              3306 R50 C  
  STKM20A C                                

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