TUBE AND A METHOD OF MANUFACTURING A TUBE

Abstract

A high temperature iron-chromium-aluminium (FeCrAl) alloy tube extending along a longitudinal axis, wherein the tube is formed from a continuous strip of a high temperature FeCrAl alloy and comprises a helical welded seam. The high temperature FeCrAl alloy tube is manufactured by feeding a continuous strip of the high temperature FeCrAl alloy toward a tube shaping station, helically winding the strip such that long edges of the strip abut each other and a rotating tube moving forward in a direction parallel to its longitudinal axis is formed, and continuously joining said abutting long edges together in a welding process directly when the tube is formed, whereby a welded tube comprising a helical welded seam is obtained.

Claims

1. A high temperature iron-chromium-aluminium alloy tube, comprising: a tube wall extending extending along a longitudinal axis; and a helical seam wherein the tube is formed from a continuous strip of iron-chromium-aluminium alloy, and wherein the iron-chromium-aluminium alloy comprises: 5-25 wt.% Cr, 2.5-8 wt.% Al, 0-5 wt.% Mo, the balance being Fe and normally occurring impurities, and optionally other intentionally added alloying elements.

2. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein the tube has almost a constant inner diameter or a constant inner diameter along a longitudinal axis.

3. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein the tube has a wall thickness of 0.5-7.5% of an inner diameter of the tube.

4. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein the helical welded seam extends at a helix angle of 1 to 89° with respect to the longitudinal axis of the tube.

5. The high temperature iron-chromium-aluminium alloy tube according to claim 4, wherein the helical welded seam extends at a helix angle of 40-70° with respect to the longitudinal axis of the tube.

6. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein the high temperature iron-chromium-aluminium alloy comprises: 9-25 wt.% Cr; 2.5-8 wt.% AI; 0-5 wt.% Mo; the balance being Fe and normally occurring impurities, and optionally other intentionally added alloying elements.

7. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein a content of Cr is from 11 to 17 wt.%.

8. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein a content of Cr is from 5 to 15 wt.%.

9. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein a content of Cr is from 20.5 to 25 wt.%.

10. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein a content of Al is 3 to 7 wt.%.

11. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein a content of Mo is from 1 to 4 wt.%.

12. The high temperature iron-chromium-aluminium alloy tube according to claim 1, wherein the high temperature iron-chromium-aluminium alloy comprises 0.1 to 3 wt.% Si.

13. The high temperature iron-chromium-aluminium alloy tube according to claim 6, wherein the high temperature iron-chromium-aluminium alloy comprises one or more elements selected from: 0.05-0.60 wt.% Y; 0.01-0.40 wt.% Zr; 0.05-0.50 wt.% Hf; 0.05-0.50 wt.% Ta; 0-0.10 wt.% Ti; 0.01-0.05 wt.% C; 0.01-0.06 wt. % N; 0.02-0.10 wt.% O; 0.05-0.50 wt.% Mn; 0-0.08 wt.% P; 0-0.005 wt.% S.

14. The high temperature iron-chromium-aluminium alloy tube according to claim 6, wherein the high temperature iron-chromium-aluminium alloy comprises one or more elements selected from : 0.01-0.1 wt.% C; 0.001-0.1 wt.% N; 0.02-0.10 wt.% O; 0-0.01 wt.% B; 0-0.5 wt.% Mn; 0-2.2 wt.% Y; 0-0.2 wt.% Sc+Ce+La; 0-1.7 wt.% Ti; 0-0.4 wt.% Zr: 0-0.4 wt.% Nb: 0-0.1 wt.% V: 0-0.3 wt.% Hf+Ta+Th.

15. A method of manufacturing a tube having almost a constant or almost constant inner diameter extending along a longitudinal axis, comprising the steps of: feeding a continuous strip of a high temperature iron-chromium-aluminium alloy toward a tube shaping station; helically winding the strip in the tube shaping station such that long edges of the strip abut each other and a rotating tube moving forward in a direction parallel to the longitudinal axis is formed ; and continuously joining said abutting long edges together in a welding process directly from the high temperature iron-chromium-aluminium alloy tube to form a welded high temperature iron-chromium-aluminium alloy tube, wherein the welded high temperature iron-chromium-aluminium alloy tube includes: a tube wall extending extending along the longitudinal axis, and a helical seam wherein the high temperature iron-chromium-aluminium alloy has a composition including: 5-25 wt.% Cr, 2.5-8 wt.% Al, 0-5 wt.% Mo, the balance being Fe and normally occurring impurities, and optionally other intentionally added alloying elements.

16. The method according to claim 15, wherein the welding process is selected from a fusion welding process or a solid state joining process.

17. The method according to claim 15, wherein the welding process is selected from one of a tungsten inert gas welding process, a metal inert gas welding process, a laser welding process, and a plasma arc welding process.

18. The method according to claim 15, wherein a shielding gas is used during the welding process, which shielding gas is an inert gas.

19. The method according to claim 15, further comprising the step of preheating the strip prior to forming the high temperature iron-chromium-aluminium alloy tube.

20. The method according to claim 19, further comprising the step of annealing the high temperature iron-chromium-aluminium alloy tube subsequently to the welding process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Embodiments of the proposed high temperature FeCrAl alloy tube and method of manufacturing will in the following be described with reference to the appended drawings, in which

[0091] FIG. 1 schematically shows a perspective view of a tube according to an embodiment.

[0092] FIG. 2 shows a side view of the tube in FIG. 1.

[0093] FIG. 3 shows an end view of the tube in FIG. 1.

[0094] FIG. 4 schematically shows a method of manufacturing the tube in FIG. 1.

[0095] FIG. 5 is a flow chart illustrating steps of a method of manufacturing a tube according to an embodiment.

DETAILED DESCRIPTION

[0096] A high temperature iron-chromium-aluminium (FeCrAl) alloy tube 1 according to an embodiment of the present disclosure is schematically shown in FIGS. 1-3. The tube 1 is in the form of a circular cylinder extending along a longitudinal axis C. The high temperature iron-chromium-aluminium alloy tube 1 is formed with a helical welded seam 2 extending around and along the tube at a helix angle α. In the shown embodiment, the helix angle α is 54°. The shown tube 1 has an outer diameter D of 108 mm, a length L and a wall thickness t of 2 mm, thus having an inner diameter d of 104 mm. The inner diameter d is constant along the longitudinal axis C.

[0097] The tube 1 is formed from a continuous strip 3 of high temperature FeCrAl alloy using spiral welding, as schematically illustrated in FIG. 4 and in the flow chart in FIG. 5. In a first step S1, a continuous strip 3 of the high temperature FeCrAl alloy, having a width w, is fed in a feeding direction X toward a tube shaping station 4, which is here in the form of three shaping rolls 5. The shaping rolls 5 are arranged with their axes of rotation at an angle with respect to the feeding direction X of the strip 3.

[0098] When the strip 3 enters between the shaping rolls 5, it is in a second step S2 helically wound into a tube 1, with long edges 6, 7 of the strip 3 abutting each other. A rotating tube is formed, moving forward in a direction parallel to its longitudinal axis C.

[0099] In a third step S3, the abutting long edges 6, 7 are continuously joined together in a welding process directly when the tube is formed, whereby the welded tube 1 comprising the helical welded seam 2 is obtained. The welding process is in the shown embodiment carried out using a welding electrode 8 positioned radially outside of the formed tube 1. Thus, the welded seam 2 is created with a welding root on an inside of the formed tube 1. The welding may be carried out using e.g. tungsten inert gas (TIG) welding, metal inert gas welding, laser welding, or plasma arc welding. As a shielding gas during the welding process, an inert gas such as Ar and/or He is used. Also a root gas consisting of Ar and/or He may be used to protect the root during welding.

[0100] In a fourth step S4, the tube 1 is cut into its final length L.

[0101] The strip 3 may be preheated up to a temperature of 100° C. or less before being wound into a tube 1. The formed tube 1 may furthermore be annealed after welding, before or after cutting the tube 1 into its final length L. During the annealing process, the tube 1 is heated to a temperature of 850-875° C. and is thereafter allowed to cool.

[0102] The present disclosure is further illustrated by the following non-limiting example:

Example

[0103] For production of test specimens, a tube 1 as described with reference to FIGS. 1-3 above was produced from a strip having a width w of 200 mm and a thickness t of 2 mm. The chemical composition of the strip is shown in table 1.

TABLE-US-00001 C Si Mn Cr Al Fe Nominal composition 5.3 Bal. Min - - - 20.5 Max 0.08 0.7 0.4 23.5

[0104] The welding process performed was a TIG process without filler material and with a gas mixture of 70% Ar and 30% He, which was used as both a root gas and a shielding gas. The welding was carried out from outside of the formed tube 1. No support was used on the inside of the tube 1 during welding. The welded high temperature FeCrAl alloy tube 1 was cut into a final length L of 3 m using an angle grinder, without annealing prior to cutting. After cutting into test specimens (tubes) of final length and cooling of the welded seam 2, one of the test specimens 1 was annealed for 1 h at 875° C.

[0105] The welded seam 2 had a good appearance directly after welding, on the inside of the tube 1 as well as on the outside. The welded seam 2 was concave on the outside and convex on the inside. Cross sections across the welded seam 2 were visually inspected using light optical microscopy after etching and polishing. No defects were found during the inspection.

[0106] The hardness HV10 was investigated across the welded seam 2 and was found to be between 220 and 265 HV across the welded seam, with the highest value in the base material next to the welded seam.

[0107] Two other test specimens were pre-oxidised at 1050° C. for 8h and were thereafter tested in a furnace, mounted vertically with 80 mm diameter cartridge heating elements (26 kW at 200 V voltage) mounted inside the tubes.

[0108] The test specimens were subjected to a continuous cycling for one week according to the following scheme: [0109] Heating from room temperature up to 950° C.; [0110] 20 min holding time at 950° C.; [0111] Cooling to 600° C.; [0112] Heating up to 950° C.; [0113] 20 min holding time; etc.

[0114] After one week, the test specimens looked very well upon visual inspection and the testing was continued for another 18 days with a tougher testing cycle. This testing cycle was carried out according to the following scheme:

[0115] Heating from room temperature up to 950°; [0116] 20 min holding time at 950° C.; [0117] Cooling to 100° C.; [0118] Heating up to 950° C.; etc.

[0119] Visual inspection showed that the test specimens looked very fine.

[0120] In addition, another test specimen was put at the bottom of the furnace to study whether the weight of the test specimen would result in any deformation during exposure, i.e. a simplified sag test. This test specimen showed no tendency to be distorted during the 18 days exposure.