EP1066494A1

EP1066494A1 - Heat exchanger tube, method for the production of a heat exchanger tube and capacitor

Info

Publication number: EP1066494A1
Application number: EP99919076A
Authority: EP
Inventors: Friedhelm Schmitz
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1998-03-27
Filing date: 1999-03-15
Publication date: 2001-01-10
Also published as: JP2002510030A; JP4276382B2; CN1139782C; KR20010034712A; WO1999050610A1; CN1295663A

Abstract

The invention relates to a heat exchanger tube (1) especially for a capacitor, comprising an inner casing area (3) which is surrounded by an outer casing area (2). The casing areas (2; 3) are firmly connected to each other. One casing area (2; 3) has a highly anti-corrosive cladding material (4) and the other casing area (3; 2) comprises a base material that is less resistant to corrosion. The invention also relates to a method for the production of a heat exchanger tube (1) and a capacitor (10).

Description

description

Heat exchanger tube, method for producing a heat exchanger tube and condenser

The invention relates to a heat exchanger tube, in particular for a condenser, with an outer jacket area and an inner jacket area which is surrounded by the outer jacket area.

Heat exchanger tubes are used in different types of heat exchangers in which the heat of one medium is transferred to another medium. In this way, for example, heating up to evaporating a medium and cooling down to a condensation can be achieved. In the information document "Rohrtechnik aktuell" from the Fischer group of companies, 7/95, the article "D1L - the new formula for an innovative pipe concept" specifies a double-wall pipe for an exhaust system, especially an exhaust manifold. This double wall pipe is made of stainless steel, which gives a smooth inner pipe surface with a good flow ratio. To produce the double-wall pipe, two slit strips are roll-formed in a continuous process and welded to the butt edges using laser welding. The double-wall pipe produced in this way, like previously known double-wall pipes, consists of two pipe walls which are connected to one another by a common weld seam. A double-wall pipe produced in this way, in which only a connection is made to the weld seam, has shown that the conduction of sound is effectively interrupted at the separation point between the inner and outer pipe, so that effective sound insulation is achieved with such a double-wall pipe.

EP 0 619 466 B1 specifies a heat exchanger described as a steam condenser, which is a surface condenser in a rectangular design for a 2 steam turbine. The condenser is connected to the steam turbine via an exhaust pipe, through which steam flows into the condenser neck. The condenser contains bundles of heat exchanger tubes, around which the steam flows over their entire length from the outside. Cooling water flows through the inside of the heat exchanger tubes. Each bundle of heat exchanger tubes is divided into compartments by support plates arranged perpendicular to the heat exchanger tubes.

The Austrian patent specification AT 350 286 specifies a heat exchanger tube for an aluminum radiator, for example for a motor vehicle. The heat exchanger tube is a composite tube made of two different aluminum alloys that are rolled together. Here, two thin strips of different aluminum alloys are rolled together. Such tightly rolled strips are transferred into a round tube by seam welding. The heat exchanger tube contains a corrosion-resistant aluminum alloy (coating, plating) on the inside and the comparatively much thicker aluminum alloy that forms the base metal on the outside. The material of the inner coating is anodic in relation to the base material in an aqueous environment, for example caused by an antifreeze solution in motor vehicle radiators. It is hereby achieved that if a local perforation of the coating (coating) occurs, the electrical current generated by the relatively large anode (coating) and the small cathode has the effect of preventing the basic material from being perforated and protecting it against white ^¬ protects cathodic destruction.

French patent application 2 389 863 describes a heat exchanger tube made of a composite, which is intended for use in cooling barriers or heating systems. The heat exchanger tube has a tubular base body made of an aluminum alloy, which inside as well 3 is also coated on the outside with a further aluminum-silicon alloy.

The object of the invention is to provide a heat exchanger tube with high corrosion resistance. Further objects of the invention consist in specifying a method for producing a heat exchanger tube and a condenser.

According to the invention, the first-mentioned object is achieved by a heat exchanger tube, in particular for a condenser, with an outer jacket area and an inner jacket area which is surrounded by the outer jacket area, the jacket areas being firmly connected to one another and the one jacket area having a highly corrosion-resistant plating material, for example a stainless steel with more than 20% by weight of chromium or a titanium, tantalum or zirconium alloy, and the other jacket area has a less corrosion-resistant base material, for example a steel with more than 10% by weight of chromium.

The invention is based on the knowledge that heat exchanger tubes not only need good thermal conductivity but also good corrosion resistance, especially if they come into contact with aggressive water such as seawater, brackish water or contaminated river water, in particular due to the salinity, organic ingredients or chemical Conditioning of water or other media. A high thermal conductivity and the associated high heat transfer is achieved in particular by a small wall thickness (wall thickness) of a heat exchanger tube. In the case of a material for a heat exchanger tube, for example made of stainless steel or titanium, it is possible to achieve a high level of corrosion resistance and, thanks to a thin-walled design, also to achieve a high level of heat transfer, which, in contrast to heat exchanger tubes made of copper alloys, essentially over a long operating time no 4 wall thickness reduction takes place. In particular, in the case of particularly corrosion-resistant materials (materials), for example molybdenum-containing, stainless CrNi steel, titanium, zirconium and tantalum alloys, a reduction in wall thickness leads to considerable cost savings due to the high material and manufacturing costs. However, there are limits with regard to manufacturability, processing and stress, so that, for example, if the thickness of the base material for the manufacture of tubes falls below a certain level, the manufacturing process becomes significantly more expensive, the installation of such heat exchanger tubes becomes more difficult, in particular with regard to the increase in the risk of damage. Furthermore, such materials lead to problems in the attachment of heat exchanger tubes, for example in a tube sheet of a condenser or a heat exchanger, since a low adhesive strength and tightness can be achieved by expanding the tubes in the tube sheet. This results, among other things, from the fact that stainless steels, which are highly corrosion-resistant, such as superaustenite, superduplex or superferrite, have a high strength due to their alloy composition, so that they can be found in tubular floors made of low-alloy and low-strength steels, especially with a low tube wall thickness and low web spacing the holes are not fastened sufficiently well and have them sealed. In the case of heat exchanger tubes made of highly corrosion-resistant materials or titanium, it could therefore be necessary to weld them into the clad tube plate, which is extremely time-consuming. In addition, the fatigue strength of such tubes made of highly corrosion-resistant materials is low, so that the number of supporting walls used to dampen the vibrations of such thin-walled heat exchanger tubes would have to be large, which increases the structural outlay in the production of heat exchangers, in particular condensers. The inventive heat exchanger tube with a composite material consisting of a highly corrosion-resistant material and a material with less corrosion 5 durability is a heat exchanger tube with a high-strength and highly corrosion-resistant support material and a low-alloy and low-strength base material, which allows easy attachment to a tube sheet and has good vibration resistance with a small wall thickness. Depending on the requirements of the heat exchanger tube, either the outer jacket area or the inner jacket area can have the highly corrosion-resistant plating material. If, for example, a corrosive medium, for example saline water, flows through the heat exchanger tube from the inside, the inner jacket area has the highly corrosion-resistant plating material. If, on the other hand, a corrosive medium flows around the heat exchanger tubes, the outer jacket area has the highly corrosion-resistant plating material.

The heat exchanger tube is preferably thin-walled, so that there is good heat transfer between a medium flowing inside and a medium flowing around the heat exchanger tube. The wall thickness is preferably between 0.3 mm and 2 mm and, in particular when used as a heat exchanger tube for a condenser of a steam turbine, is in the range of approximately 0.5 mm.

The partial wall thickness of the cladding area which has the plating material is preferably less than the partial wall thickness of the cladding area which has the base material. The partial wall thickness of the base material is preferably 1.5 times the partial wall thickness of the plating material. This provides effective protection against corrosion on the surface of the heat exchanger tube, which is attacked by the corrosive medium, and at the same time the properties of the base material contribute to the stability to vibration and to the simplified fastening of the heat exchanger tube, due to the lower strength and thus 6 better deformability of the base material, in a tube sheet.

The partial wall thickness of the cladding area with the plating material is preferably between 0.1 mm and 0.5 mm, in particular approximately 0.2 mm. The partial wall thickness of the casing area with the base material is preferably between 0.2 mm and 1.5 mm, in particular about 0.3 mm.

The plating material to be exposed to the corrosive medium is preferably a high-alloy steel, in particular a super ferrite, a super duplex or a super austenite. These steel alloys preferably have the following alloy components (details in percent by weight):

Superferrite: 27% to 31% chromium, 1% to 5% nickel and 2% to 4% molybdenum, especially about 29% chromium.

Super duplex: 23% to 27% chromium, 4% to 8% nickel, 2% to 5% molybdenum as well as over 0.1% nitrogen, in particular about 25% chromium, 5% to 8% nickel and 3% to 5% molybdenum.

Super austenite: 20 to 25% chromium, 20% to 25% nickel, 3% to 7% molybdenum and over 0.2% nitrogen.

The base material is preferably a ferritic chromium steel with between 10% and 17% chromium. Alternatively, the base material can also be an austenitic steel with 16% to 20% chromium and 6% to 10% nickel, in particular approximately 18% chromium and approximately 8% nickel.

The composite material preferably has a combination of cladding material and base material of the type super ferrite / ferrite, super duplex / ferrite, super duplex / austenite or super austenite / austenite. Other pairings can also be provided depending on the area of application of the heat exchanger tube, 7 such as super duplex / duplex or super austenite / duplex.

The heat exchanger tube is preferably bent from a band of the composite material into a tube and along one

Long seam welded, with no mixing of the base material with the plating material and vice versa taking place on an outer surface and an inner surface in the region of the longitudinal seam. This ensures that the highly corrosion-resistant plating material is present in the corresponding purity and wall thickness on the surface on which the corrosive medium is attacking, so that the longitudinal seam has the same good corrosion properties as over the entire surface to be exposed to the corrosive medium. An inadmissible impairment of the corrosion resistance by the welded longitudinal seam is thus avoided.

According to the invention, in a method for producing a heat exchanger tube with an outer jacket region and an inner jacket region which is surrounded by the outer jacket region, a low-alloy base material, a chromium steel with more than 10% by weight chromium, is plated with a highly corrosion-resistant plating material. Here, a highly corrosion-resistant plating material made of a rust-free chrome steel with over 20% by weight of chrome or a titanium, tantalum or zirconium alloy can be applied to a suitable low-alloy base material. A thin-walled sheet metal strip is produced from the base material plated in this way and the heat exchanger tube is bent from the sheet metal strip and welded along a longitudinal seam with low heat output. The use of welding processes with minimal heat input and high cooling speed, such as laser beam or electron beam welding, means that there is no disruptive mixing of the base material with the plating material in the area of the surface up to which the corrosive medium attacks Weld. The plating can be carried out using known plating methods, such as roll, weld and explosive plating. A sufficient ductility of the cladding material and the base material is required for roll and weld cladding, while hard, wear-resistant cladding materials can also be processed for explosive cladding. Large sheet metal sheets of the base material can be clad by means of cold or hot rolling. Explosive plating can also be used to plate steel with a titanium alloy.

When using the roll cladding process, a broad band is first produced, whereby different shape change resistances caused by the different alloy contents are taken into account in hot strip and cold rolling. A narrow band is then produced from the broadband, which is formed into the tube and welded in the area of a longitudinal seam with little heat input. Compared to a welding process, in particular an inert gas welding process in which a strong mixing of the base material with the plating material would occur, a weld seam of the highest purity and precision can be achieved with laser beam welding or electron beam welding without a mixing of the base material and the plating material. Electron beam welding makes it possible to produce deep, narrow weld seams with an extremely narrow goods influence zone, that is to say minimal thermal influences on the composite material. Due to the low heat input, there is also little warpage and tension build-up, so that precision welding can be carried out. It is also not necessary to take up hydrogen, oxygen or nitrogen, so that pure and unprotected weld seams are possible, particularly on reactive metals. The high energy density also allows both high welding speeds and micro-welding to be carried out on very thin parts. High-melting metals and due to the low heat absorption 9 differently melting materials can also be welded. The same advantages can also be produced with laser beam welding, laser beam welding preferably being suitable for wall thicknesses of less than 1 mm, so that laser beam welding can be used well with thin-walled tubes of approximately 0.5 mm wall thickness. Compared to the conventional inert gas welding process such as tungsten inert gas (TIG) welding with a non-consumable tungsten electrode and in an inert gas atmosphere, which is preferably used for welding high-alloy steels, fusion welding with beams with high energy density is therefore better for producing a Heat exchanger tube with a composite material suitable.

The object directed to a condenser is achieved according to the invention by a condenser, in particular for a steam turbine, which has a multiplicity of heat exchanger tubes made of a composite material with an outer jacket region and an inner jacket region, the composite material being a highly corrosion-resistant plating material and a less corrosion-resistant base material having. The cladding material forms an outer jacket area when the outer surface of the heat exchanger tubes comes into contact with a corrosive medium. If the inner surface of the heat exchanger tubes comes into contact with a corrosive medium, the plating material forms an inner jacket area. In the case of heat exchanger tubes of a condenser, through which cooling water flows, which are taken, for example, from a river, a lake or from a sea, the inner jacket region is correspondingly formed from the plating material. This increases the corrosion resistance of the heat exchanger tubes and, on the other hand, the outer jacket area made of the base material provides high vibration stability and good fastening in a tube plate of the condenser. 10 The heat exchanger tube and the condenser are explained in more detail in the exemplary embodiments shown in the drawing. Some of them do not show to scale and schematically

1 shows a sheet metal strip made of a composite material,

2 shows a heat exchanger tube made of a composite material and FIG. 3 shows a section of a condenser in a longitudinal section.

The reference symbols used in FIG. 1 to FIG. 3 have the same meaning throughout.

In Figure 1, a sheet metal strip 7 is shown in an oblique view. This sheet metal strip 7 has a base material 5 made of a low-alloy and low-strength steel, on which a highly corrosion-resistant, high-alloy steel is plated by means of a plating process, in particular a roll plating process. The sheet metal strip 7 has a wall thickness 15 in the range of 0.5 mm. The base material 5 has a partial wall thickness 17 which is larger than a partial wall thickness 16 of the plating material 4. In the case of a heat exchanger tube 1 (see FIG. 2) with a wall thickness 15 of approximately 0.5 mm, the partial wall thickness of the base material is approximately 0.3 mm and the partial wall thickness 16 of the plating material 4 is approximately 0.2 mm.

2 shows a heat exchanger tube 1 in an oblique view, which is formed from a sheet metal strip 7 (see FIG. 1). The heat exchanger tube 1 is welded along a longitudinal seam 6 by means of electron beam welding or laser beam welding. The heat exchanger tube 1 has the plating material 4 in an inner jacket region 3 and the base material 5 in an outer jacket region 2. By welding the heat exchanger tube 1 along the longitudinal seam 6 by means of electron beam welding or laser beam welding it is achieved that there is no mixing either on an outer surface 8 or on an inner surface 9 11 between base material 5 and plating material 4. This ensures the required material properties along the longitudinal seam 6, namely high corrosion resistance on the surface which is exposed to a corrosive medium and low strength for fastening, in particular in a tube sheet of a condenser. The corrosive medium, for example cooling water, flows through the heat exchanger tube 1 from the inside.

3 shows a section through a longitudinal section of a capacitor 10. The condenser 10 has a large number of heat exchanger tubes 1, of which only four are shown for the sake of clarity. The heat exchanger tubes 1 are fastened in a tube plate 11 of the condenser 10. They are also supported between the two ends of the heat exchanger, not shown, by a plurality of support plates 12. Due to the high vibration stability of the heat exchanger tubes 1 by using the composite material made of the base material 5 and the plating material 4, the number of support plates 12 can be kept low. A coolant 13, in particular water, flows through the heat exchanger tubes 1. Steam 14 from a steam turbine (not shown) flows around its outer surface 8 (see FIG. 2), which steam 14 condenses on the heat exchanger tubes 1 (condenser tubes) and is discharged from the condenser 10. If the coolant 13 is supplied, for example, from a river, a lake or from the sea, the coolant 13 could lead to increased corrosion of the heat exchanger tube 1. This is significantly reduced if not prevented by the plating material 4, which is highly corrosion-resistant. By rolling the tubes 1 inside in the area of the tube sheet 11, the tubes 1 are widened with a corresponding deformation of the base material 5, as a result of which the tubes 1 are securely fastened (braced) in the tube sheet 11.

Claims

12 claims

1. Heat exchanger tube (1), in particular for a condenser (10), with an outer jacket region (2) and an inner jacket region (3) which is surrounded by the outer jacket region (2), the jacket regions (2, 3) being fixed are connected to one another and the one jacket area (2; 3) is a highly corrosion-resistant plating material (4) and the other jacket area (3; 2) is a less corrosion-resistant base material (5), the less corrosion-resistant base material (5) being a chrome steel with more than 10 % By weight of chromium and / or the cladding material has a stainless steel with more than 20% by weight of chromium or a titanium, tantalum or zirconium alloy.

2. Heat exchanger tube (1) according to claim 1, which is thin-walled, with a wall thickness (15) of between 0.3 mm and 2 mm.

3. Heat exchanger tube (1) according to claim 1, or 2, wherein the partial wall thickness (16) of the jacket region (2; 3) with the plating material (4) is less than the partial wall thickness (17) of the jacket region (3; 2) with the Base material (5), in particular around 50% less.

4. Heat exchanger tube (1) according to claim 3, wherein the partial wall thickness (16) of the jacket region (2; 3) with the plating material (4) is between 0.1 mm and 0.5 mm, in particular approximately 0.2 mm.

5. Heat exchanger tube (1) according to claim 3 or 4, in which the partial wall thickness (17) of the jacket region (3; 2) with the base material (4) is between 0.2 mm and 1.5 mm, in particular approximately 0.3 mm .

6. heat exchanger tube (1) according to any one of the preceding claims, wherein the plating material (4) is a Superfer- 13 rit is, in particular with 27% - 31% Cr, 1% - 5% Ni and 2% - 4% Mo (data in percent by weight).

7. Heat exchanger tube (1) according to one of the preceding claims, in which the plating material (4) is a super duplex, in particular with 23% - 27% Cr, 4% - 8% Ni and 2% - 5% Mo as well as over 0 , 1% N (figures in percent by weight).

8. Heat exchanger tube (1) according to one of the preceding claims, in which the plating material (4) is a super austenite, in particular with 20% - 25% Cr, 20% - 25% Ni, 3% - 7% Mo, as well as over 0.2% N (data in percent by weight).

9. heat exchanger tube (1) according to claim 5 or 6, wherein the base material (5) is a ferritic chromium steel with between

10% - 17% Cr is (data in percent by weight).

10. heat exchanger tube (1) according to claim 6 or 7, wherein the base material (5) is an austenitic chromium steel with between 16% - 20% Cr and 6% - 10% Ni, in particular 18% Cr and 8% Ni (details in weight percent).

11. heat exchanger tube (1) according to any one of the preceding claims, which has an outer surface (12) and an inner surface (13) and is welded along a longitudinal seam (6), wherein along the longitudinal seam (6) in a respective environment of the outer surface (12) and the inner surface (13) each only the plating material (4) or the base material (5) is present.

12. A method for producing a heat exchanger tube (1) with an outer jacket area (2) and an inner jacket area (3) which is surrounded by the outer jacket area (2), wherein a) a low-alloy base material (5) with a highly corrosion-resistant plating material (4) is plated, with a low-alloy base material (5) 14 Chrome steel with over 10% by weight of chromium and / or as a highly corrosion-resistant plating material (4) a rustproof chrome steel with over 20% by weight of chromium, a titanium, tantalum or zirconium alloy is used, b) a thin-walled one Sheet metal strip (7) is produced and c) the heat exchanger tube (1) is bent from the sheet metal strip (7) and welded along a longitudinal seam (6) with low heat input, in particular by means of laser welding.

13. condenser (10), in particular for a steam turbine, with a plurality of heat exchanger tubes (1), each with an outer jacket region (2) and an inner jacket region (3) which is surrounded by the outer jacket region (2), the jacket regions (2, 3) are firmly connected to one another and one jacket area (2; 3) has a highly corrosion-resistant plating material (4) and the other jacket area (3; 2) has a less corrosion-resistant base material (5).

RECTΪF1ED SHEET (RULE 91) ISA / EP