JPH0440637B2 - - Google Patents

Description

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

This type of heat exchanger includes a shell with at least one tubesheet, to which tubes with open ends are secured by joints, such as by welding. In use, 1st
heat transfer between the fluids occurs by passing a second fluid through the shell and a second fluid through the shell. One example of an application for such a heat exchanger is for power-generating fast nuclear reactors,
In this reactor, liquid sodium metal, heated (sometimes indirectly in most practical designs) by heat generated in the reactor core, flows through a heat exchanger shell, water flows through tubes, and the shell The heat transferred from the liquid sodium in the water vaporizes the water and subsequently superheats the steam to generate electricity using a turbine. In such a heat exchanger, which serves as an evaporator in this example, the junction between the tube and the upper tubesheet is protected by confining an inert protective gas above the liquid level of the sodium in the shell. It is common to avoid direct contact between the sodium and the joint. Despite this, experience shows that if the joint is welded, tearing will occur at the joint;
It was found that high pressure water leaked through this slit and reacted with the sodium vapor in the protective gas, increasing the impurities and contaminating the sodium to an unacceptable degree.
If an unprotected weld leaks,
It is common practice to make steam pipes redundant by plugging the associated steam pipes, but if a large number of pipes have to be made redundant, heat exchangers loses efficiency. It is therefore clearly advantageous to be able to repair defective joints should they occur, instead of having to rely on cooling with a stopper.

British Patent No. 2032559A discloses a method for repairing a shell-and-tube heat exchanger when one or more defective joints between tubes and tubesheets occur, the method comprising:
It consists of inserting a tubular sleeve into the tube with the defective joint and sealingly joining the end regions of the sleeve to the tube and the tube sheet to bridge the defective joint.
Examples of methods for achieving such a bond disclosed in this British patent are explosion welding and brazing.
In the particular construction disclosed in the British patent, the upper end of the sleeve is hermetically joined to the upper tubesheet by explosion welding, and the lower end of the sleeve is hermetically joined to the associated tube by high temperature brazing. For brazing,
At the lower end of the sleeve, for example, two lands are formed with sufficient clearance to allow the lands to slide freely into the tube. For example, there are two grooves for placing brazing material between the lands. The inner wall of the tube is cleaned prior to inserting the sleeve into the tube, and after insertion, the lower end of the sleeve is expanded radially by roll swaging to deposit molten wax between the land of the sleeve and the tube. The land is brought to a position where a capillary gap is formed to accommodate the attached material. This gap is critical and is difficult to reproduce with absolute certainty by roll swaging each time a repair is performed.

It is an object of the invention to successfully facilitate brazing joints in connection with the protection of tube-to-tubesheet joints or in connection with the repair of heat exchangers with defective tube-to-tubesheet joints. The goal is to achieve the conditions that make it possible.

Another countermeasure to the problem of poor tube-to-tubesheet joints is to protect these joints from the outset, which can be achieved by designing the heat exchanger with such protection. Ru. Thus,
After a defect occurs, there is an additional cost to draining and cleaning the normal tube-to-tubesheet joint, with downtime and the need to drain and clean before repairs begin. Instead of having to incorporate a sleeve with the need to make additional joints, it is advantageous to adopt the above-mentioned sleeve provision in the design of the heat exchanger.

According to the present invention, a shell-and-tube heat exchanger having a joint between each tube and each tube sheet includes a joint between each tube and at least one tube sheet in each tube. bridging tubular sleeves, the end regions of each sleeve being sealingly affixed to the tube at one end of the sleeve and to the tubesheet at the other end of the sleeve, each tube having a taper on its inner surface; has a matching taper on its outer surface at or near the end of the sleeve mating with each tube, and each sleeve has at least one land on its tapered surface.
Two grooves are formed to attach each sleeve to its respective tube by engaging the tapered surfaces, and to create a solder between each sleeve and each tube with brazing material contained in the gap between the desired surfaces created by the grooves. A joint is created, which individually protects the joint between the tube and the tubesheet.

According to another aspect of the invention, a method of repairing a defective joint between a tube and a tubesheet of a shell-and-tube heat exchanger comprises:
It consists of making a brazed joint between the tube with the defective joint and one end of the sleeve used to bridge the defective joint into the tube, providing a taper on the inner surface of the tube, the taper being aligned with a taper in the outer surface of the sleeve at or near the end of the sleeve, the tapered surface of the sleeve having at least one
mounting the sleeve within the tube with two lands and at least one groove, engaging the tapered surfaces, and brazing material in the groove between the tube and the sleeve at or near the end of the sleeve; It is characterized by performing bonding.

By providing a tapered surface, the sleeve and tube can be assembled with a fairly wide tolerance between the sleeve diameter and the tube diameter. The only modification is the amount by which the tubesheet end of the sleeve is moved away from the outside surface of the tubesheet. However, the technique of explosion welding is flexible enough to accommodate such variables, provided that such variables are not too large.

Representative repair embodiments will now be described by way of example with reference to the accompanying drawings.

The tubesheet 1 has its tubes 2 (a portion of one of the tubes is shown), the tubes 2 being secured to the tubesheet 1 by welds 3 so as to coincide with the bores 4 of the tubesheet 1. ing. When the weld 3 becomes bad, the sleeve 5, only the lower end of which is shown (its upper end is explosive welded (not shown)
(fixed to the tubesheet 1 at the upper end of the bore 4 by means such as Avoid the need to chill. Machine the pipe 2 to create a tapered surface 6,
Material is removed from the inside of tube 2 by suitable machining techniques. The outer surface of the sleeve 5 is also machined to create a matching tapered surface 7. The degree of consistency is carefully adjusted to be high. The machining of the sleeve leaves a land 8 at the lower end of the sleeve 5 and a tapered surface 7.
This is done so as to leave a groove 9 of brazing material. The height of the land 8 determines a parallel capillary gap 10 between the tapered surface 6 and the upper tapered portion of the land 8, which capillary gap is filled with molten brazing material when brazing is performed. Make the required hermetic joint. Since the height of the land 8 can be precisely adjusted by ordinary machining methods, the capillary gap 10 can be made uniform, and when the tapered surfaces 6 and 7 are engaged, roll swaging is not required after assembly. It is possible to predict characteristics for each joint that were not available with previous technologies.

Yet another advantage is that according to the invention, the weakest part of the tube after machining is located at a level where it is protected by a sleeve after the joint has been made, as opposed to previous techniques involving roll swaging. In this case, the weakest part of the tube is at a level below the lower end of the sleeve after joining and is therefore unprotected. Moreover, machining with previous techniques leaves notches that are not protected and can act as stress concentrators during subsequent operations. However, the taper process does not leave a notch that acts as a subsequent stress concentration as previous techniques leave.

The repair technique described with reference to the drawings involves repairing each normal tube-to-tubesheet joint by inserting a tube into each tube, bridging the joint, and sealing one end to the tube and the other end to the tubesheet. It can be easily modified so that a heat exchanger can be manufactured that is protected by a sleeve that is permanently attached, thus providing double protection against leakage.
Heat exchanger manufacturing processes allow matching tapers, sleeve lands, grooves, and capillary gaps to be created in tubes and sleeves by consistent production molding techniques that provide high accuracy and repeatability. Moreover, the brazed joints are made under carefully controlled conditions in the factory, and both joints of the sleeve can be directly inspected by well-known factory techniques.

The selected taper angle is determined by the wall thickness of the tube, since if the taper angle is too large, the tube becomes unduly weak. A narrow cone angle of about 92° (ie, 1° from the line of the tube wall) is often satisfactory. However, other taper angles may be used. The length of the tapered surface is selected to ensure leaktightness of the brazed joint.

The height of the land 8 should be between 0.013 mm and 0.051 mm to create an optimal capillary gap 10 for the brazing material.

[Brief explanation of the drawing]

The attached drawing is a fragmentary cross-sectional side view showing a joint between a tube and a tube sheet of a shell-and-tube heat exchanger. 1...tube sheet, 2...tube, 3...junction, 5...
Sleeve, 6...Tapered inner surface, 7...Tapered outer surface, 8...Land, 9...Groove, 10...Gap.

Claims (1)

[Claims] 1. Having a joint 3 between the tube 2 and the multi-tube sheet 1, in each tube 2, bridging the joint 3 between each tube 2 and at least one tube sheet 1. each sleeve 5 has at least one land 8 and at least one groove 9 formed in the surface of each sleeve at or near one end thereof, each sleeve 5 having: Inner surface 6 of tube 2 and sleeve 5
is inserted into each tube such that a gap 10 is formed between said inner surface 6 and said outer surface 7, and a brazed joint is formed between said inner surface 6 and said outer surface 7 by means of brazing material contained in a groove 9. and the other end of the sleeve 5 is joined to the tube sheet 1 by explosive welding, thereby sealingly securing the sleeve 5 to the tube 2 at one end and to the tube sheet 1 at the other end. In a shell-and-tube heat exchanger that protects the joints 3 between tube sheets 1, each tube 2 has a tapered inner surface 6 and each sleeve 5 has a land 8 on the insertion of the sleeve 5 into the tube 2.
A shell-and-tube heat exchanger, characterized in that it has a matching taper (7) on its outer surface (7) for tapering said land (8) such that an engagement takes place between said land (8) and said tapered inner surface (6). 2. A heat exchanger according to claim 1, wherein the tapered inner surface 6 of each tube 2 is a conical angle of approximately 2°. 3. The heat exchanger according to claim 1 or 2, wherein the land 8 has a height of 0.013 mm to 0.051 mm. 4. In repairing a defective joint 3 between tubes 2 and tubesheets 1 of a shell-and-tube heat exchanger, at least one land 8 formed on the outer surface 7 at or near one end; , a tubular sleeve 5 having at least one groove 9 is inserted into the tube 2, the sleeve bridging the defective joint 3 and sealingly joining one end of the sleeve 5 to the tube sheet 1 by explosive welding, the tube 2 a gap 1 provided between the inner surface 6 of the sleeve and the outer surface 7 of the sleeve;
0 and sealingly fix the sleeve 5 to the tube 2 at the other end, thereby protecting the joint 3 and brazing said inner and outer surfaces together by brazing material. In the method according to the present invention, the step of creating the brazed joint portion includes
is tapered, forming a matching taper on the outer surface 7 of the sleeve 5, thus tapering said land 8 so that an engagement takes place between said land 8 and the tapered inner surface 6 of said tube 2. A repair method comprising the step of inserting the sleeve sleeve 5 into the pipe 2 until the gap 10 is formed. 5. A method according to claim 4, characterized in that the tapered inner surface is formed with a conical taper of about 2°. 6. The method according to claim 4 or 5, characterized in that the land is made with a height of 0.013 mm to 0.051 mm.