DE102017100378A1 - Method for producing a connection between two stainless steel tubes, tube adapters for use of the method and connection arrangement of the stainless steel tubes - Google Patents

Abstract

A method for producing a connection of two stainless steel tubes (1, 2) is presented, which is characterized by the following method steps: welding a first part (3) of a total two-piece tube adapter (4) to a free end (5) of a first stainless steel tube Welding the second part (6) of the tubular adapter (4) to the free end (7) of the second stainless steel tube (2) to be connected to the first stainless steel tube (1), sliding on a sleeve (8) Part of the separate Rohradapterteile (3, 6), - producing a screw (9) between the Rohradapterteilen (3, 6), - axial displacement of the sleeve (8) along the outer circumferential surface (10) of the Rohradapters (4), to the the Rohradapterteilen (3, 6) existing by the screw (9) forming a composite contact surfaces (11) are completely covered by the sleeve (8), -Verschweißen the sleeve (8) with the Rohradapterteilen (3, 6) along the circumference d In addition, a tube adapter (4) for connecting two stainless steel tubes (1, 2) and a connection arrangement of two stainless steel tubes is described.

Description

The invention relates to a method for producing a connection of two stainless steel tubes, a tube adapter for use of the method and a connection arrangement of the stainless steel tubes.

High-alloyed steels, such as CrNi (Mo) steels, have a high corrosion resistance against aggressive media, for the transport therefore only such stainless steel tubes are used. This chemical stability of high-alloyed steels is due to the formation of passive layers, which consist of dense, homogeneous and hardly soluble chromium oxides and protect the steel from external attack. During welding, this passive layer is destroyed in the vicinity of the weld and replaced by oxide layers, which differ significantly in elemental composition and layer structure from the previous passive layer. The thickness of this oxide layer is determined by the depth to which the oxygen atoms can diffuse. This depth is again strongly dependent on the temperature. At high temperatures, for example, thermal tarnish forms in the range of blue discoloration. The emergence of a tarnish means a visible sign of the surface oxidation of the weld with the atmospheric oxygen or when using shielding gases with the adhering to the workpiece surface residual oxygen, carbon dioxide or water.

The areas of the tarnish in contrast to the above-mentioned passive layer have no protective effect. In addition to classic pitting, a large-scale dissolution of the oxide layers occurs here, and the stainless steel thus loses its non-rusting properties.

In pipeline construction, due to the corrosion risks mentioned, clean and metallically bright surfaces are required when welding stainless steel, ie surfaces that are free of tarnish. Therefore, the previously mentioned protective gases are used during welding, which are also referred to as "forming gases". As an example of such a protective gas argon is mentioned at this point. The protective gases prevent the penetration of oxygen into the weld and thus the formation of tarnish. However, the supply of these protective gases to the welding area is relatively complicated and therefore disadvantageous.

A solution for welding long stainless steel tubes, using a protective gas, for example, from the DE 2 701 325 A1 which, in addition to the applied TIG welding process, uses a supply hose for supplying the protective gas with a tensile cable.

In many cases, despite the protective gas, a post-processing of the welding area is required to remove tarnish, scaling and slag residues. The extent and nature of the cleaning processes have a great influence on the corrosion resistance, so that, if possible, post-processing should be dispensed with. (mutatis mutandis from: Research Report of the TU Braunschweig, Institute of Welding, Prof. Dr. Ing H. Wohlfahrt, Dr. Ing H. Köstermann (AiF 11.381 N / 1, DVS 1.017): "Welding temper colors - basically bare seams must be required "Estimation of the corrosive influence of yellow tarnish on welded CrNi (Mo) steels").

Having said that, it can be stated that the reworking of tarnishing colors forming weld seams on the outer circumferential surface of a stainless steel pipe is possible without difficulty since these welds are very easily accessible. For very long stainless steel tubes, however, the accessibility of the internal welds is hardly or not at all given. Here, therefore, so far, the control and the reworking of the weld with respect to the tarnish extremely expensive or impossible.

The invention has for its object to ensure a connection of two stainless steel tubes by a welding process such that controllable, free of tarnishing welds can be realized. In addition, a pipe adapter and a connection arrangement of two stainless steel pipes are to be specified.

The invention solves this problem with the features of the independent claims 1, 8 and 12th

Further embodiments of the invention are the subject of the dependent claims.

• -Anschweißen eines ersten Teils eines insgesamt zweiteiligen Rohradapters an ein freies Ende eines ersten Edelstahlrohres,
• -Anschweißen des zweiten Teils des Rohradapters an das freie Ende des mit dem ersten Edelstahlrohr zu verbindenden, zweiten Edelstahlrohres,
• -Aufschieben einer Manschette auf einen Teil der voneinander getrennten Rohradapterteile,
• -Herstellung einer Schraubverbindung zwischen den Rohradapterteilen,
• -axiale Verschiebung der Manschette entlang der Außenmantelfläche des Rohradapters, bis die an den Rohradapterteilen vorhandenen, durch die Schraubverbindung einen Verbund bildenden Kontaktflächen vollständig von der Manschette überdeckt sind,
• -Verschweißen der Manschette mit den Rohradapterteilen entlang des Umfanges der Außenmantelfläche des Rohradapters.

The method according to the invention for producing a connection of two stainless steel tubes is characterized by the following method steps:

• Welding a first part of a generally two-piece pipe adapter to a free end of a first stainless steel pipe,
• Welding the second part of the tubular adapter to the free end of the second stainless steel tube to be connected to the first stainless steel tube,
• Pushing a cuff on to a part of the separated tubes,
• - Production of a screw connection between the tube transport parts,
• axial displacement of the sleeve along the outer circumferential surface of the tube adapter until the contact surfaces forming a composite on the tubesheet parts are completely covered by the sleeve,
• -Verschweißen the cuff with the Rohradapterteilen along the circumference of the outer circumferential surface of the tube adapter.

The inventive method is mainly used for stainless steel tubes, which have a considerable length and / or a large diameter, which diameter is usually more than 200 mm. These stainless steel pipes may be, for example, pipelines for the transportation of oil or natural gas. By using the tube adapter used, it is possible with the invention for the first time to control the inside of the weld seam of a stainless steel tube, to check it again after the welding process and to remove any tarnish that may be present without this requiring considerable expenditure. In other words, the tube adapter ensures easy accessibility of the internal weld seams. For the feasibility of the present solution, it goes without saying that at least one of the stainless steel pipes to be joined must be shortened by the length of the pipe adapter. Advantageously, both stainless steel tubes are shortened by half the length of the tube adapter, so that the tube adapter can be inserted between the ends of the stainless steel tubes.

The procedure for integrating the tube adapter in the stainless steel tube can be such that first of the screw through the unit forming a tube adapter is welded to the end of one of the stainless steel tubes, the Rohradapterteile are then separated by loosening the screw to then the exact position of the weld determine and mark the end of the second stainless steel pipe. After cutting or cutting to length the second stainless steel tube, the second part of the separate tube adapter is welded to the end of this stainless steel tube. After checking the welds produced, the pipe adapter can be reassembled by means of the screw connections and the sleeve can be displaced in the manner described above and then welded.

However, a sequence of steps is to be regarded as considerably simpler, according to which each part of the separate tubes is welded to one end of the previously cut to size stainless steel tubes, wherein subsequently the screw connection is made between the tubes and the sleeve, viewed in the axial direction of the tube adapter, pushed over the contact surfaces of the tube adapter and finally welded.

In a manner known per se, it is also useful for the method according to the invention to carry out the welding of the stainless steel tubes using a protective gas, in particular a forming gas. The protective gas has the task of keeping oxygen and its reactive compounds from the weld.

Before the Rohradapterteile be coupled by the screw together, it is advantageous if after welding the Rohradapterteile to be joined together ends of the stainless steel tubes at least a control of the welds produced between the stainless steel tubes and Rohradapterteilen is performed, as previously indicated , In this way, an optionally formed tarnish of the welds can be eliminated easily, including, for example, use chemical solutions such as pickling.

The inspection of the welds is carried out according to a development of the invention non-destructive, wherein in each case an optical control is performed and additionally an ultrasonic test method and / or an X-ray method is used to determine the inner structure of the weld exactly.

For safety reasons, it is also useful to chemically treat each weld, if they should have formed a tarnish during the welding process. For this purpose, the previously mentioned pickling are used, which is known to cause a neutralization of the resulting oxide layers.

Although the screw connection of Rohradapterteile by sliding over the cuff and its welding with the tube adapter forms a reliable and tight connection of stainless steel tubes. Nevertheless, it may be useful to provide at least one separate seal, which is arranged between the Rohradapterteilen. Such a seal can compensate for tolerances to a small extent and also optionally facilitate the assembly of Rohradapterteile.

A special embodiment of this proposed solution is that the screw connection of Rohradapterteile with the interposition of at least one flat gasket and at least one O-ring. Of course you can Also, multiple flat gaskets and / or O-rings are used.

The tube adapter according to the invention for connecting two stainless steel tubes is used for the application of the method described above and is characterized in that the inner diameter of the total two-piece tube adapter corresponds to the inner diameter of the stainless steel tubes to be connected and the tube adapter on the outside a reinforced in its cross section wall portion, at least in the region of his screwed state has abutting contact surfaces.

The fact that the tube adapter has an inner diameter that corresponds to the inner diameter of the stainless steel tubes, which means in practice that the inner diameters are identical, leads to a turbulence-free fluid flow and thus optimal flow conditions within the stainless steel tubes, whereby the flow is also free of velocity. and pressure fluctuations is.

Of considerable importance beyond that is the fact that the tube adapter has on the outside a reinforced in its cross section wall portion. Due to this reinforced wall section, the weld seam for fixing the sleeve on the pipe adapter does not influence the geometry of the flow cross section and does not lead to the formation of a tarnish paint on the inside of the pipe adapter. The reinforced wall section thus has several advantages for the special connection according to the invention of the stainless steel tubes.

In order to improve the connection of Rohradapterteile with each other and to facilitate a further proposal of the invention is that the interconnectable contact surfaces of the tube adapter at least partially have a mutually complementary and in the assembled state positive or non-positively interlocking contour. In simpler terms this means that the Rohradapterteile can be pushed into each other or each other, while at the same time develop the existing seals their effect. After assembling the Rohradapterteile these are fixed by the aforementioned screw to each other.

For this purpose, a plurality of engagement recesses are provided along the circumference of the reinforced wall portion of the one part of the tube adapter, which have a sufficient size to insert a screw and tighten or loosen this with a tool can. In the part of the tube adapter having the engagement recesses, a through hole is also provided in the area of the engagement recesses for each screw in the contact surface side wall through which the screw is passed in order to produce the screw connection. In the corresponding, second part of the tube adapter, a matching thread is further provided in each case into which the screw can be screwed in order to thereby connect the tubes to the tubes. This is initially still a detachable connection. By sliding over the sleeve and the welding of the same with the outer circumferential surface of the tube adapter, however, a cohesive connection is then created.

A special embodiment of the aforementioned screw is moreover that the through hole in the first part of the tube adapter and the thread in the second part of the tube adapter are aligned coaxially to the center axis of the tube adapter. It has also proven to be sufficient if along the circumference of the tube adapter a total of three, each offset by 120 ° to each other arranged engagement troughs for the preparation of the screw connections are available.

The inventive connection arrangement of two stainless steel tubes, which is produced by the method described above and uses a tube adapter according to the invention, is characterized in that the abutting contact surfaces of the tube adapter and the engagement recesses with the screw through the sleeve in its welded to the Rohradapterteilen position completely are covered. By this measure, an additional seal and, as described above, a cohesive connection of Rohradapterteile and thus the stainless steel tubes created. Overall, all welds are easily accessible with this solution and can therefore be easily controlled, which also creates the opportunity to intervene corrective in the formation of a tarnish.

In order not to create weak points in the connection arrangement according to the invention that are susceptible to oxidation, that is to say, more easily, that can rust, the pipe adapter and the sleeve are also made of stainless steel. It goes without saying that in this case, the screws for the screw connections are designed as stainless steel screws.

The invention will be explained in more detail with reference to the accompanying drawings. The exemplary embodiment shown here represents no restriction to the illustrated variant, but merely serves to explain a principle of the invention.

Identical or similar components are always denoted by the same reference numerals. In order to be able to illustrate the mode of operation according to the invention, only greatly simplified schematic representations are shown in the figures, in which the components which are not essential to the invention have been dispensed with. However, this does not mean that such components are not present in a solution according to the invention.

• 1: eine Explosivdarstellung der freien Enden zweier Edelstahlrohre mit einem dazwischen dargestellten Rohradapter,
• 2: ausschnittsweise und vergrößert eine Schraubverbindung zur Kupplung der Rohradapterteile

und

• 3: die Darstellung aus 2 in einer räumlichen Ansicht und im Teilschnitt.

It shows:

• 1 : an exploded view of the free ends of two stainless steel tubes with a tube adapter shown therebetween,
• 2 : partial and enlarged a screw connection for coupling the Rohradapterteile

and

• 3 : the presentation 2 in a spatial view and in partial section.

From the 1 goes an exploded view of the free ends 5 and 7 two stainless steel tubes 1 and 2 with a pipe adapter shown in between 4 out. With the help of the tube adapter 4 become the stainless steel pipes 1 . 2 in the axial direction of the center axis 18 connected with each other. The tube adapter 4 consists of a first part 3 and a second part connected thereto 6 , their contact surfaces 11 in the area of a reinforced wall section 14 of the tube adapter 4 have geometrically complementary to each other, so that the Rohradapterteile 3 . 6 can be positively connected with each other. To improve the fixation of Rohradapterteile 3 and 6 In addition, screw connections serve each other 9 , which are described below in connection with the description of 2 and 3 will be explained in more detail. The entire contact surface 11 , including the screw 9 is by a in the axial direction along the outer circumferential surface 10 of the reinforced wall section 14 of the tube adapter 4 slidable cuff 8 covered, with the cuff 8th with the tube adapter 4 welded, so that thereby a cohesive and tight connection of the stainless steel tubes 1 , 2 is created.

The figures the 2 and 3 show each different views of a screw 9 between the Rohradapterteilen 3 and 6 , From the illustrations it can be seen that in the first Rohradapterteil 3 several, over the circumference of the tube adapter 4 distributed engagement recesses 15 are present, of which in the 2 and 3 only one engagement recess 15 is shown. The size of the engaging troughs 15 is sufficient to a screw 19 in a through hole 16 in the reinforced edge area 14 of the first part 3 of the tube adapter 4 insert and this screw 19 tighten or loosen with a suitable tool. The screw 19 is through the through hole 16 in a corresponding thread 17 screwed in, which is coaxial with the through hole 16 in the second part 6 of the tube adapter 4 located. In this way, the screw is 9 between the Rohradapterteilen 3 . 6 of the tube adapter 4 produced. As previously stated, the parts to be joined together 3 and 6 of the tube adapter 4 in the area of their contact surfaces 11 designed complementary to each other so that they interlock positively. Between the first part 3 of the tube adapter 4 and the second part 6 are also a flat gasket 12 and a seal in the form of an O-ring 13, the sealing of the tube adapter 4 opposite to inside the tube adapter 4 or in the stainless steel pipes 1 and 2 Serve flowing medium. As in particular from the illustration in 2 clearly shows, here is the cuff 8th in the axial direction over the contact surfaces 11 of the tube adapter 4 been pushed and with the outer surface 10 of the tube adapter 4 welded. The welded connection between the cuff 8th and the tube adapter 4 goes out of the 2 and 3 but not apparent.

In the 3 was on the appearance of the cuff 8th waived the contact area 11 between the Rohradapterteilen 3 . 6 to make visible.

LIST OF REFERENCE NUMBERS

1

stainless steel tube

2

stainless steel tube

3

First part (of the tube adapter)

4

tube adapter

5

Free end (of the first stainless steel pipe)

6

Second part (of the tube adapter)

7

Free end (of the second stainless steel pipe)

8th

cuff

9

screw

10

Outer casing surface

11

contact area

12

Seal (flat gasket)

13

Seal (O-ring)

14

reinforced wall section

15

engagement trough

16

Through Hole

17

thread

18

mid-axis

19

screw

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 2701325 A1 [0005]

Claims (13)

Method for producing a connection between two stainless steel tubes (1, 2), characterized by the following method steps: welding a first part (3) of a total two-part tube adapter (4) to a free end (5) of a first stainless steel tube (1), welding the second part (6) of the tubular adapter (4) to the free end (7) of the second stainless steel tube (2) to be connected to the first stainless steel tube (1), pushing a sleeve (8) onto a part of the separate tubular conveyor parts (3 , 6), -Production of a screw connection (9) between the Rohradapterteilen (3, 6), -axiale displacement of the sleeve (8) along the outer circumferential surface (10) of the Rohradapters (4) until the Rohradapterteilen (3, 6) existing, by the screw (9) forming a composite contact surfaces (11) are completely covered by the sleeve (8), -Welding the sleeve (8) with the Rohradapterteilen (3, 6) along the circumference of the outer circumferential surface (10) of the tube adapter (4). Method according to Claim 1 , characterized in that the welding of the stainless steel tubes is carried out using a Formiergases. Method according to one of the preceding claims, characterized in that after welding the Rohradapterteile (3, 6) to the ends to be joined together (5, 7) of the stainless steel tubes (1, 2) at least a control of the welds produced between the stainless steel tubes ( 1, 2) and the Rohradapterteilen (3, 6) is performed. Method according to one of the preceding claims, characterized in that the inspection of the welds non-destructively, optically and by means of an ultrasonic testing method and / or by the use of an X-ray method. Method according to Claim 3 or 4 , characterized in that each weld is chemically treated when it has formed a tarnish during the welding process. Method according to one of the preceding claims, characterized in that the screw connection (9) of the Rohradapterteile (3, 6) with the interposition of at least one seal (12, 13). Method according to one of the preceding claims, characterized in that the screw connection (9) of the Rohradapterteile (3, 6) with the interposition of at least one flat gasket (12) and at least one O-ring (13). Tube adapter (4) for connecting two stainless steel tubes (1, 2) using a method according to one of the preceding claims, characterized in that the inner diameter (1, 2) of the total two-piece tube adapter (4) the inner diameter of the stainless steel tubes to connect (1 , 2) and the pipe adapter (4) on the outside has a reinforced in its cross-section wall portion (14) in the region of its abutting in the screwed state contact surfaces (11). Tube adapter after Claim 8 , characterized in that the mutually connectable contact surfaces (11) of the tubular adapter (4) at least in sections have a mutually complementary and in the assembled state positive or non-positively interlocking contour. Tube adapter after Claim 8 or 9 , characterized in that along the circumference of the reinforced wall portion (14) of the one part (3) of the tubular adapter (4) a plurality of engagement recesses (15) each having a through hole (16) for producing a screw connection (9) with the respective one corresponding thread (17), the second part (6) of the tubular adapter (4) are formed. Tube adapter after Claim 10 , characterized in that the through hole (16) in the first part (3) of the tube adapter (4) and the thread (17) in the second part (6) of the tube adapter (4) coaxial with the central axis (18) of the tube adapter (4) are aligned. Connecting arrangement of two stainless steel tubes, produced by a method according to one of Claims 1 to 7 using a tube adapter according to one of Claims 8 to 11 , characterized in that the abutting contact surfaces (11) of the tube adapter (4) and the engagement recesses (15) with the screw connections (9) are completely covered by the sleeve (8) in its welded to the Rohradapterteilen (3, 6) position , Connecting arrangement according to Claim 12 , characterized in that the tube adapter (4) and the sleeve (8) made of stainless steel.

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