JPH0535357B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a shell-and-tube heat exchanger.

Shell-and-tube heat exchangers include a shell with at least one tubesheet to which the open-ended tubes are welded. In use, a first fluid flows through the tube and a second fluid flows through the shell to effect heat transfer between the fluids. When a pipe leaks, it is common practice to plug it and make it redundant, but if you have a large number of redundant pipes, the heat exchanger loses efficiency. Therefore, it is clearly advantageous to repair defective tubes in a heat exchanger instead of plugging the tubes.

British Patent No. 2032559A discloses a shell-and-tube heat exchanger comprising inserting a tubular sleeve into the defective tube of the shell-and-tube heat exchanger and sealingly joining the end region of the sleeve to the tube and tubesheet to bridge the defect. Discloses a method for repairing a defective tube in a vessel. Although such repairs are acceptable under normal operating conditions, they are questionable under extreme temperature conditions due to the stiffness of the sleeve which causes more than a safe amount of loading on the end joints.

According to the present invention, a method for repairing a defective tube of a shell-and-tube heat exchanger includes inserting a tubular sleeve into the defective tube and sealingly coupling the end region of the sleeve to the tube to bridge the defect. In the method, the tubular sleeve has one or both of the following characteristics: axial deflection and being mechanically keyed to the tube at a location adjacent said joint in the end region of the sleeve. It is characterized by having a combination.

Axial deflection is imparted by corrugating the sleeve circumferentially at multiple locations along its length.

Mechanical keying may be accomplished by pressing or expanding the material of the sleeve into tight engagement with the tube or tubesheet, with or without grooves.

The connection between the sleeve and the tube may be an explosion weld at both ends, or an explosion weld at one end and a brazed connection at the other end.

Typically, if below-excessive temperatures occur,
The rigid sleeve contracts, causing the end joint to become severely distorted. However, when subjected to axial deflection, the sleeve can contract axially to sufficiently relieve the load on the end joint, and the joint retains its integrity.

If circumferential corrugations are employed, the corrugations flex and act like a bellows to provide the required axial movement. The sleeve design avoids concentrating shrinkage strains at temperatures below excessive temperatures (or expansion strains at temperatures above excessive temperatures) into specific thin areas where this could weaken or create failure points. You have to be careful. A constant wall thickness should be maintained throughout the sleeve.

If a mechanical keying without axial deflection of the sleeve is employed, the keying should absorb axial contraction/expansion loads to reduce the load on the end joints. There is.

The combination of axial deflection and mechanical keying increases reliability of repair integrity in the face of temperature extremes.

The present invention relates to a shell-and-tube exchanger when repaired by the method described above.

A method of repairing tubes of a shell-and-tube heat exchanger according to the invention will be explained by way of example with reference to the accompanying drawings, which are fragmentary cross-sectional views.

The drawing shows tube sheet 1 and tubes 2 of a shell-and-tube heat exchanger.
is shown, the heat exchanger providing heat transfer between the liquid metal flowing through the shell and the water flowing through the tubes. There are a number of tubes 2, each sealed to the tubesheet by welding. During use, some of the welds between the tubes and the tubesheet become bad, and in order to avoid plugging the tubes and making them redundant, each tube with defective welds 4 is fitted with a tube. A sleeve 3 is inserted, which is hermetically connected to the tube at one end region and to the tube sheet at the other end region, thereby bridging the defective weld.

The sleeve 3 has a number of circumferential corrugations, which act like bellows and can expand axially in the event of excessive temperatures.

The lower end region of the sleeve 3 shown in the drawings is connected to the tube by high-temperature brazing, and the upper end region to the tube sheet by explosive welding. Two lands 5 are formed in the lower end region of the sleeve, the outer diameter of which is such that there is adequate clearance for the lands to slide freely into the tube. In the middle of the land are two grooves 6 for accommodating brazing material, generally toroidal in shape, which engage the grooves like a circular clip prior to inserting the sleeve into the tube. is formed. Also, before inserting the sleeve into the pipe, both the inner wall of the pipe and the tube hole in the tube plate are cleaned, and after inserting the sleeve, the lower end is expanded radially outward by roll swaging to form a land. It is almost in contact with the tube wall, thereby creating a capillary gap for the molten brazing material between the sleeve and the tube. Of course, the swaging tool is inserted from above the tubesheet.

The brazing head for making the bond has a high frequency induction heating coil positioned within the bore of the sleeve at the desired brazing area. Another heating coil of longer length is used to temper the joint after brazing. Preferably, the brazing equipment has feedback production and uses millivolt signals from the sensing device to automatically control the brazing cycle. The sensing device is a thermocouple, but other devices use fiber optics to measure temperature changes, a light guide directed downwards, a supply tube provided to guide the conductor, and a cover gas tube for the brazing operation. An appropriate sensing device may be developed.

The upper end of the sleeve is explosively welded to the tubesheet at 7 by detonating gunpowder placed in the sleeve and violently expanding the sleeve radially into abutment with the tube holes in the tubesheet. metallographically bond the sleeve to the tubesheet.

In another method, the inner walls of the tubes and the bores in the tubesheet are cleaned by galvanic or electrochemical techniques prior to bonding. Electrolytic erosion technology is a technique in which material is removed from the bonding surfaces of tubes and tubesheets by short-lived, repetitive electrical sparks between electrodes inserted into holes in the tubes and tubesheets and the bonding surfaces of the tubes and tubesheets. be.

Yet another method uses explosive welding instead of brazed joints. In this way, there is no need to provide a groove for the brazing material.

In addition to providing axial flexibility in the sleeve, the sleeve may be mechanically keyed to the tubesheet and tube just inside 8,9 of the bonded joint. In these positions, keying is effected, for example, by press-fitting the sleeve into a small groove cut in the tube plate and/or tube wall after joining the end regions, or in another example, by pressing the sleeve into a This is done by a very tight contact spreading force applied from If an expansion method is used to create the required braze fit gap, this often creates the keying by a bulge in the tube and sleeve just above the braze area.

[Brief explanation of the drawing]

The accompanying drawings are fragmentary cross-sectional views showing the relationship between tubes, tube sheets, and sleeves of a multi-tubular heat exchanger according to the present invention. 1...tube plate, 2...tube, 3...sleeve.

Claims (1)

Claims: 1. A tubular sleeve is inserted into the defective tube, forming a sealing connection between one end region of the sleeve and the tubesheet, and a sealing connection between the other end region of the sleeve and the tube. In a method of repairing defective tubes retained in the tubesheet of a shell-and-tube heat exchanger, the sleeve is bonded to provide axial flexibility to the sleeve. A method of repairing a defective tube, comprising: a non-bonded portion having a plurality of circumferential corrugations between the disposed end regions. 2. A method according to claim 1, characterized in that the corrugations are positioned such that they are located within the tube. 3. The method of claim 2, including mechanically keying the sleeve to the tubesheet and tube adjacent the end region joint. 4. Mechanical keying is achieved by expanding the material of the sleeve into tight engagement with the tube and tubesheet after joining the end regions. the method of. 5. The connection between the sleeve and the tube and the connection between the sleeve and the tubesheet are characterized in that both are performed by explosion welding, or one by explosion welding and the other by brazing. Claim 1
4. The method according to any one of items 4 to 4. 6. The area of the tube and tubesheet opposite to the area where the end area of the sleeve is located is cleaned by galvanic erosion techniques, and a relatively small circumferential groove is cut inside and adjacent to the area of the tube and tubesheet where the end area of the sleeve is located. A metal sleeve having a plurality of circumferential corrugations around the end region is machined into the adjacent section and inserted through the tubesheet and the tube such that the corrugations are located within the tube between the tubesheet and the tube groove. the sleeve has a brazing material thereon, and the end region of the sleeve remote from the tubesheet is expanded to define a capillary gap between the tube and the brazing material. heating said distal end region of the sleeve by induction heating to effect the bonding, forming an explosion weld joint between the tubesheet and the adjacent end region of the sleeve, and inserting the sleeve into the groove of the tubesheet and tube. 2. The method of claim 1, further comprising mechanically keying the sleeve to the tubesheet and tube by expanding the sleeve.