Types of steel:
By the standards:
Stainless steel tubes – are long products (round, oval, square / rectangular). By the way of manufacturing, stainless steel pipes are divided into two classes: welded and seamless.
Welded tubes imply a welding process for at least one step of the manufacturing process, typically, in forming a closed pipe profile.
About the Methods of Tube Welding, Operational Characteristics
About the main advantages of tube produced by each of the above methods.
Until recently, the attitude to high-alloy steel welds was wary, but over time, with the development of new methods of welding, it has gradually improved. This sceptical attitude to welded tubes since the dawn of their production has led to the prohibition of the use of welded stainless steel tubes at important, and even more so, dangerous objects.
However, time does not stand still, and with the development of new welding processes, technologies and the quality control of welded joints, the consumer properties of welded stainless steel tubes constantly improved until, at its extreme, it reached the level of the consumer properties of seamless tubes and has even surpassed them in some parameters. Over time, welded tubes took over a very large market share from seamless tubes and currently, the share of seamless tubes in the global consumption of tubular stainless steel products is vanishingly small. Welded tubes have been successfully applied in all industries, including dangerous sites classified as having a hazard class no higher than the class 2, i.e. almost everywhere, except for very specific and super-critical applications such as the manufacture of the fuel assemblies of nuclear reactors. To be fair, it should be noted that not every seamless tube, but only those manufactured and tested according to very strict standards, can be used in super-critical industries. I.e. it can be argued that in its consumer properties and performance, welded tube is at least not inferior to the ordinary assortment of seamless tubes (manufactured according to DIN 17458; ASTM A312, A213; GOST 9940 and 9941).
Main applications of stainless steel tubes:
Diam. mm |
0,80 (*) kg/m |
1,00 kg/m |
1,20 kg/m |
1,50 kg/m |
2,00 kg/m |
2,50 kg/m |
3,00 kg/m |
8 |
0,144 |
0,175 |
0,204 |
||||
10 |
0,184 |
0,255 |
0,264 |
||||
12 |
0,224 |
0,275 |
0,325 |
0,394 |
|||
16 |
0,304 |
0,376 |
0,445 |
0,545 |
0,701 |
||
18 |
0,345 |
0,426 |
0,505 |
0,620 |
0,801 |
||
19 |
0,365 |
0,451 |
0,535 |
0,657 |
0,581 |
||
20 |
0,385 |
0,476 |
0,565 |
0,695 |
0,901 |
||
21,3 |
0,411 |
0,508 |
0,604 |
0,744 |
0,967 |
1,184 |
|
22 |
0,425 |
0,526 |
0,625 |
0,770 |
1,002 |
1,228 |
|
25 |
0,485 |
0,601 |
0,715 |
0,883 |
1,152 |
1,409 |
|
26,9 |
0,523 |
0,649 |
0,772 |
0,954 |
1,247 |
1,527 |
|
28 |
0,676 |
0,805 |
0,995 |
1,302 |
1,596 |
||
30 |
0,726 |
0,865 |
1,070 |
1,402 |
1,722 |
||
32 |
0,776 |
0,925 |
1,146 |
1,502 |
1,847 |
2,178 |
|
38,1 |
0,929 |
1,109 |
1,375 |
1,808 |
2,229 |
2,637 |
|
40 |
0,977 |
1,166 |
1,446 |
1,903 |
2,348 |
2,779 |
|
42,4 |
1,037 |
1,238 |
1,536 |
2,023 |
2,498 |
2,960 |
|
48,3 |
|
1,415 |
1,758 |
2,319 |
2,867 |
3,403 |
|
50 |
1,227 |
1,466 |
1,822 |
2,404 |
2,974 |
3,531 |
|
50,8 |
1,247 |
1,490 |
1,852 |
2,444 |
3,024 |
3,591 |
|
51 |
1,252 |
1,496 |
1,859 |
2,454 |
3,036 |
3,606 |
|
52 |
1,277 |
1,526 |
1,897 |
2,504 |
3,099 |
3,681 |
|
53 |
1,302 |
1,556 |
1,934 |
2,554 |
3,161 |
3,756 |
|
60,3 |
1,776 |
2,209 |
2,920 |
3,618 |
4,304 |
||
63,5 |
1,872 |
2,329 |
3,080 |
3,819 |
4,545 |
||
76,1 |
2,251 |
2,802 |
3,711 |
4,607 |
5,491 |
||
88,9 |
3,283 |
4,352 |
5,409 |
6,453 |
Diam. mm |
1,00 kg/m |
1,20 kg/m |
1,50 kg/m |
2,00 kg/m |
3,00 kg/m |
15х15 |
0,453 |
0,538 |
0,661 |
||
20х20 |
0,613 |
0,729 |
0,900 |
||
25х25 |
0,772 |
0,951 |
1,140 |
1,494 |
|
30х15 |
0,693 |
0,825 |
1,020 |
1,335 |
|
30х30 |
0,932 |
1,112 |
1,379 |
1,813 |
|
40х20 |
0,932 |
1,112 |
1,379 |
1,813 |
|
40х40 |
1,251 |
1,495 |
1,857 |
2,451 |
|
50x25 |
1,399 |
1,738 |
2,292 |
|
|
50х50 |
1,878 |
2,336 |
3,089 |
4,559 |
|
60х40 |
1,878 |
2,336 |
3,089 |
4,559 |
|
60х60 |
2,814 |
3,727 |
5,516 |
||
80х40 |
2,814 |
3,727 |
5,281 |
Tolerance on dimension EN ISO 1127
Outside diameter D mm |
Tolerance on O.D. D |
Thickness tolerance Т |
||
Tolerance class |
Allowed deviation |
Tolerance class |
Allowed deviation |
|
D ≤ 168.3 |
D3 |
± 0,75 % min ± 0,3 mm |
Т3 |
± 10 % min ± 0,2 mm |
D4a |
± 0,5 % min ± 0,1 mm |
|||
D > 168.3 |
D2 |
± 1,0 % Min ± 0,5 mm |
The welding line consists of the following technical and functional components:
1. A container where rolls of steel tape are placed; the tape goes from the container to an accumulator.
2. An accumulator designed for the accumulation of the necessary amount of tape to ensure the continuity of tape rolling in the rolling mill during the docking tape rolls (when one roll of tape ends, it is joined to another). The amount of tape placed to the accumulator is determined by the speed of tape rolling and the time necessary for joining the tape.
3. The joining of the tape ends is made by argon-arc welding in the tape joining device.
4. After passing through the guide rollers, the belt goes into the molding and finishing group of stands of the drive (motorized) and non-drive (idle) of the "Duo" type rolling stands – where each stand is provided with two rolling rolls. After passing through the aforementioned stands, the automatic welding of the edges of a formed tubular profile is performed.
5. Welding is performed by the AAW method, allowing it to achieve the same mechanical strength as of the pipe itself in the welding area and in the solid metal area of as well.
6. After welding, the unrolling of the internally welded seam is carried out (optional) by means of cold drawing.
7. At the same time, a continuous monitoring of the integrity of a welded seam is carried out in a non-destructive way by using the eddy current method.
8. Weld seams or marks outside the pipe are polished by means of a device for the removal of external burrs.
9. The pipe profile that has been prepared through this method goes to a group of gauge stands that are driven (motorized) or non-driven (idle) to rolling stands of the "Duo" type - each stand is provided with two rolling rolls. In each gauge group, cold deformation of the welded profile occurs - reducing the pipe diameter and wall thickness to the desired values - the process is generally similar to the rolling of seamless pipes on a rolling mill with two-roll stands.
10. After the gauge stands, the pipe passes through a set of four non-driven roller stands - round - heads designed to make the pipe straight.
11. Further on, the pipe surface is polished with an orbital grinding machine (optional).
12. Then the pipe is cut into pieces of the desired lengths in a pipe cutting device.
13. And finally enters the discharge roller table for the discharge of the pipes.
14. Sampling for the testing of mechanical properties and the tool control of the pipe geometry is performed.
15. Quality certificates are issued
16. The ready pipe is packed in bundles and stored in the warehouse – it is ready for shipment to the consumer.
Welded tubes - manufacturing methods and operational characteristics.
When exposed to high frequency currents on the strips (raw material for tube welding), the edges of the strips are heated, melted and then squeezed together by means of welding rolls, and then seam water quenching occurs, after which the excess metal is removed from the weld zone mechanically (cut off).
This welding method is actively used in the manufacture of welded tubes made from carbon and low alloyed steel. However, the welding of chromium stainless steel is limitedly to its suitability, and it is not recommended for the welding of chromium-nickel stainless steel. Only ornamental stainless steel tubes can be produced using this method of welding, i.e. for those tubes which are not directly involved in the transport of fluids. The reasons for this are as follows: the low corrosion resistance of stainless steel tube welded seams, tube seams that are welded with high frequency (HF) are not strong as those made by other methods of tube welding, or where the welding method does not guarantee the strength of the welded tube seam.
Advantages: Very high welding speed - lower production costs - a small contribution to the cost of production.
Disadvantages: Reduced strength and corrosion resistance of the welded seam as compared with other methods of stainless steel pipe production.
In this welding process, the edge strips are melted by a laser beam in a protective gas atmosphere, whereupon they are connected by a clamp in a system of supporting welding rollers, the welding assembly. Tubes welded by this method are used widely, except for very important applications - heat exchangers, boilers and evaporators.
Advantages: High welding speed and a very narrow zone of heating the welded seam involving a small amount of metal in the seam formation – a very thin, threadlike seam.
Disadvantages: High cost of equipment - large depreciation - large cost of the production process. Accordingly, the price is higher than that of tubes produced by other methods. The fact that the process involves the formation of a metal weld in a very small area of space has a positive impact on the complexity of the tube surface processing, but affects the strength of the welded seam adversely: the strength of the welded seam is less as compared to the strength of a tube joint welded by arc welding. Limitations of the thickness of the welded tube walls - from 0.5 to 3.0 mm, where the use of laser welding for walls of only 1- 2.5 mm is economically justified.
It is performed in a protective atmosphere by means of a heat source, melting the stainless steel - an electric arc.
Usually, argon arc welding (AAW) is used in the production of welded stainless steel tubes, as a non-expendable tungsten electrode (TIG), where an electric arc formed between the electrode and edges of the stainless steel strip leads to melting the edges of strips and the formation of welding trays, followed by the crystallization of the welded seam there under the inert, protective atmosphere of argon, which prevents the molten metal from oxidizing or from contamination with the gases normally present in atmospheric air; or a consumable electrode (MIG), where the electrode material consumed during the welding process is involved in the completion of a welding bath; as for the rest, the MIG process is similar to the TIG welding process. The MIG option of argon-arc welding is used for the production of thick wall thickness welded stainless steel tubes.
Advantages of the method:
Versatility – it is suitable for welded tubes of any kind of stainless steel or welded tubes of any final destination; it has the highest welded seam strength.
Disadvantages: relatively low welding speed – the cost of the manufacturing process is higher than that for manufacturing tubes welded by high frequency currents.