METHOD FOR CONNECTING COATED STEEL PIPE ENDS
The invention relates to a method for connecting the ends of internally coated steel pipes according to Claim 1. Developments are specified in dependent claims.
The inner coatings of the steel pipes can be metallic, for example, a zinc coating, or be non-metal, for example, made of plastic or ceramic.
Only steel pipes with a non-metal inner coating are considered below.
Pipelines composed of welded-together pipes are used, for example, for drinking water and wastewater as well as for transporting aggressive media.
On the outside, the pipes are usually protected from corrosion by a non-metal, three- layer plastic coating.
Pipelines with non-metal inner coatings made of plastic or ceramic are used, for example, in the transportation of aggressive media in the oil and gas production industry in the onshore and offshore sectors.
Known coatings made of plastic consist, for example, of polyurethane, polyethylene, epoxy resin,
or polyamide.
In industrial manufacturing, in order to ensure perfect welding, the pipes provided with a non-metal inner coating are either kept free of the coating where the pipes are later butt-welded together end-to-end on the construction site to form a pipeline, or the pipes are provided throughout with an inner coating which is removed again in the weld seam region by a cutback before welding on the construction site, or which is thermally damaged during the welding process.
As a result, in addition to a perfect welding of the pipe ends, damage to the coating by heat input during welding is also to be prevented.
After the pipes have been welded together, the connection regions kept free from the coating must be re-coated with a corresponding coating in order to meet the requirements of corrosion protection, something which requires considerable effort and is often not possible inside a pipeline.
In order to solve this problem, a method for connecting the ends of internally coated steel pipes is known, for example, from published patent application DD 291 495 A5, in which a pipe section of corrosion-inert steel at least 10 cm long is first welded onto prepared uncoated pipes.
The pipes are then coated on the inside, the coating being applied from 2 to 3 cm over the weld seam between pipe and welded-on pipe section.
When assembling or installing the pipes, the non-coated pipe ends of corrosion-inert steel are then welded together without the coating being damaged by the influence of heat.
A disadvantage here is that, depending on the diameter of the pipe, corresponding pipe sections made of corrosion-inert material must be kept available and the welding-on of such a flange is very complicated and thus cost-intensive.
In addition, the pipe ends of corrosion-inert material must be designed such that they withstand the loads during operation of the line (generally internal pressure). In this way, more material is used than is necessary for corrosion protection alone.
Another method for connecting the ends of steel pipes is known from US 3 453 004 A.
It is an object of the invention to provide an alternative method that is more cost-effective and simpler to implement for connecting the ends of steel pipes with a non-metal inner coating.
Furthermore, a steel pipeline made of the pipes welded in this way is to be specified.
According to the invention, a method according to Claim 1 offers a more economical and simpler possibility for connecting internally coated pipes to one another to form a pipeline.
Compared to the prior art, the effort for producing a pipe connection on internally coated steel pipes is considerably reduced since no pipe section made of corrosion-inert steel that fits the respective pipe dimension is required for welding onto the pipe ends, but the corrosion protection in the weld seam region of the inner coating is realized by a simple lining of the inner wall at the pipe ends.
Irrespective of the pipe diameter, corrosion protection can thus be ensured in a simple manner in the weld seam region of the pipe ends in the case of internally coated pipes.
According to the invention, the pipe ends themselves can be lined, for example, by means of thermal, chemical, electrochemical, physical-chemical or mechanical plating.
It has proven to be favorable for a compromise between corrosion protection in the weld seam region and economic viability if the lining extends over a length of at least 5 mm in the longitudinal direction of the pipe, starting from the pipe end.
The length of the lining depends on the size of the weld seam region,
which is in turn dependent on the welding method used and the energy input introduced per unit length into the pipe ends to be welded.
The length of the lining at the pipe end can thus also be, for example, 10 mm, 20 mm, 30 mm or more.
In a first advantageous embodiment of the invention, the lining is carried out by means of thermal plating.
The plating itself can advantageously include deposit welding, soldering or a thermal spraying.
According to the invention, deposit welding can be carried out, for example, by means of electroslag welding, sub-arc welding, laser beam welding, plasma welding or metal inert-gas welding.
However, other methods, such as hybrid welding methods, with which planar deposit welding is achieved may also be used.
Both strip and wire electrodes may be used.
In one embodiment of the invention, the deposit welding is advantageously carried out in a partially or fully mechanized/automated manner, but manual deposit welding is also possible.
Deposit welding may be carried out by means of a rod electrode, TIG welding, gas welding, plasma welding (with powder, hot wire) as well as friction welding and resistance pressure welding.
If, according to the invention, thermal spraying is used for producing the lining, this can be, for example, flame spraying, plasma spraying, laser spraying or arc spraying, but other spraying methods not mentioned here are conceivable for the intended use.
However, lining the pipe ends can also be carried out by means of chemical, electrochemical or physical-chemical plating.
Examples which may be mentioned here are electroless metal deposition, cathodic deposition or PVD coating.
Alternatively, lining can also be carried out according to the invention by mechanical plating, for example by inserting a pipe ring into the pipe end, the pipe ring being connected to the pipe in a force-fitting or integral manner.
The force-fitting connection of the pipe ring to the pipe end can advantageously take place by shrinking, snap-fitting, press-fitting, impressing or rolling.
The integral connection of the pipe ring to the pipe end is advantageously carried out by means of welding.
Depending on strength reguirements, the tubular steel can consist of an unalloyed or low-alloy structural steel, such as a grade B, X42, X52, X60, X65, X70, X80, X100, and depending on the corrosion properties reguirements, the plating can, for example, be a high-alloy Cr, CrNi, CrNiMo steel or an Ni base material.
In the case of high wear resistance reguirements, a carbon steel may also be used, for example.
In accordance with the corrosion and/or wear resistance reguirements, the non-metal inner coating of the pipes can consist, for example, of polyurethane, polyethylene, epoxy resin, polyamide or a ceramic coating.
Furthermore, in terms of flow technology, the invention advantageously provides that the lining be applied at least with a thickness corresponding to the thickness of the subsequently applied inner coating and is then processed mechanically again to an exact prespecified thickness corresponding to the thickness of the coating.
This ensures a uniform, flow-favorable transition to the inner coating.
The inner coating in the overlap region with the lining is likewise mechanically processed again to the thickness of the inner coating.
In this way,
the thickness in the overlap region can likewise be ideally adapted to the intended thickness of the plastic inner coating without there being an excess elevation in the overlap region, which would interfere with the flow of material of the transported medium during operation of the pipeline.
According to the invention, the overlap region of plating and inner coating is dimensioned generously in order to rule out any corrosive medium to be transported penetrating under the coating and into the steel pipe.
Overlap lengths of at least 3 mm have been found to be advantageous.
Depending on the length of 5 the lining, the overlap length can also advantageously be 5 mm, 10 mm, 20 mm or more in order to achieve optimal protection against penetration under the coating.
In a further advantageous embodiment of the invention, it is provided that the surface of the plating that is in contact with the inner coating is provided in the overlap region with a surface structure that improves mechanical interlocking with the inner coating.
In addition to the desired material bonding of the plating and the covering inner coating, a mechanical connection of the layers is thereby additionally realized, which offers advantages in particular during the transport of abrasive media.
According to the invention, roughness is therefore increased, for example, by a mechanical surface treatment in order to improve mechanical interlocking.
According to the invention, a pipeline made of steel with a non-metal inner coating is also provided, consisting of individual pipes welded to one another, whose end regions to be welded are free of the coating in the weld seam region, and the pipe end is connected to a corrosion-inert metal in the region of the weld seam of the pipe connection, and the coating covers the corrosion-inert metal with the exception of the weld seam region of the pipe ends, which is characterized in that the corrosion-inert metal is applied as lining to the inner sides at least in the weld seam region of the pipe ends.
In particular, it is advantageously provided here that the inner sides of the pipe ends at least in the weld seam region of the pipe connection have a thermally applied plating of corrosion-inert and wear-resistant metal as lining.
A pipeline is also provided, wherein the pipe ends have been prepared and subsequently welded according to the method steps described above.
The invention is explained in more detail below with reference to Fig. 1. The ends of two pipes A, B, which are to be welded together, are shown.
The pipes A, B, each consisting of a steel pipe 1, 1', are provided with a non-metal inner coating 2, 2' and a corrosion-inert plating 3, 3' applied to the inner surface of the pipe ends.
The inner coating 2, 2' has an overlap region 4, 4! with the plating 3, 3', wherein the weld seam region 5, 5! of the pipe connection remains uninvolved in order to prevent an impairment of the coating by the heat introduced during welding.
Inthe overlap region 4, 4', the plating 3, 3' is mechanically processed to such a dimension that the coating applied thereto does not have any excessive elevation in relation to the plating 3, 3' in the weld seam region 5, 5'. For welding the ends of the pipes A, B, they are provided with a welding chamfer 6 as a seam preparation.
It is not shown here that the surface of the plating 3, 3' in contact with the inner coating 2, 2' is provided in the overlap region 4, 4' with a surface structure which improves the mechanical interlocking with the inner coating and in which roughness was increased.
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