GB2296560A

GB2296560A - Method of lining condenser tubes

Info

Publication number: GB2296560A
Application number: GB9426411A
Authority: GB
Inventors: Frank Banner
Original assignee: Ensign Plastics Ltd
Current assignee: Ensign Plastics Ltd
Priority date: 1994-12-30
Filing date: 1994-12-30
Publication date: 1996-07-03
Anticipated expiration: 2014-12-30
Also published as: GB2296560B; GB9426411D0

Abstract

A method of protecting condenser tubes in a heat-exchanger from corrosion is disclosed. The method comprises introducing into the condenser tube 2 a tubular liner 1 having a flange 9 at one end for seating against one end of the condenser tube or a tube plate 3 in which it is fixed, and squeezing a sealing composition 7 between the interior of the condenser tube 2 and the exterior of the liner 1. A tubular liner is also disclosed for protecting a condenser tube 2 in the region of a tube plate 3, said liner 1 having a flange 9 at one end, a ferrule 10 which is a sliding fit over the flange 9 so as to provide an annular space between the exterior of the liner 1 and the interior of the ferrule 9 and a sealing composition 7 disposed in said annular space prior to being squeezed into gap 8. <IMAGE>

Description

METHOD OF LINING CONDENSER TUBES This invention relates to a method of protecting condenser tubes in a heat-exchanger from erosion.

Condensers and heat-exchangers are used in a variety of industries, especially power generation, in which steam is condensed by passing it around a series of tubes having heat-conductive walls, the tubes being cooled by passage of another fluid, such as water. The condenser tubes are conventionally mounted in tube plates at the inlet and outlet ends of the heat-exchanger and the space between the tube plates forms a jacket through which the steam is passed. The condenser tubes, which are commonly copper or manufactured from a copper alloy such as brass, are typically swaged into the tube plates. Because of erosion or corrosion (or a combination of the two), the interior surfaces of the condenser tubes become pitted during a period of use.Such damage is generally confined to a short distance at the inlet end of the condenser tubes, and eventually necessitates closing down the heat-exchanger and associated plant to effect a repair. Emergency shut-down of heat-exchange equipment can cause serious disruptions, particularly in power generation equipment.

It has been the practice to protect one or both of the inlet or outlet ends of the condenser tubes by inserting plastics liners which extend from the tube plate over a distance of up to about 30 cms. While this system of protecting condenser tubes has been generally satisfactory, problems can arise in securely fitting and sealing the liners within the condenser tubes if the condenser tubes are already worn when the liners are fitted.

The present invention is therefore concerned with providing a solution to the problem of fitting liners to condenser tubes which for one reason or another have surfaces which are not entirely uniform at the time when the liners are fitted.

According to one aspect of the present invention there is provided a method for protecting a condenser tube from a heat-exchanger which comprises introducing into the condenser tube a tubular liner having a flange at one end for seating against one end of the condenser tube (or against a tube plate in which the condenser tube is fixed), and squeezing a sealing composition between the interior of the condenser tube and the exterior of the tubular liner.

Preferably, the sealing composition is applied to the exterior of the plastics liner prior to introducing the liner into the condenser tube. The sealing composition will generally be applied to the area of the liner in the region of its flange.

Preferably, the liner is manufactured from a plastics material. However, metal liners having an erosion resistant surface can be used.

A preferred technique for introducing the sealing composition into the gap between the condenser tube and the plastics liner is by shrouding the free end of the plastics liner with a ferrule, while forcing the plastics liner into the condenser tube. As a result of this arrangement, the flange on the plastics liner acts as a piston moving within the plastics ferrule. In this embodiment, the plastics ferrule is preferably made from a flexible plastics material which is a tight but sliding fit over the flange of the plastics liner, and has a flange which abuts against the flange of the plastics liner.

The invention also includes a plastics tubular liner for protecting a condenser tube in the region of a tube plate, said plastics liner having a flange at one end, a ferrule which is a sliding fit over the flange so as to provide an annular space between the exterior of the plastics tube and the interior of the ferrule, and a sealing composition disposed on the external surface of the liner.

The plastics liner is preferably formed from a material which expands on absorption of water, so that after installation it locks itself into the condenser tube. Suitable materials are polyamide plastics, particularly nylons.

One embodiment of the present invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a sectional view through a tube and tube plate showing a plastics liner in the course of installation, and Figure 2 is a part section on an enlarged scale, showing the plastics liner in place in the condenser tube.

Referring to the accompanying drawings, a plastics liner (1) is shown partially inserted into a condenser tube (2), which is swaged into a hole in the face of a tube plate (3). Typically, this will be the inlet end of the heat-exchanger through which cooling liquid is passed, the steam circulated in the space (4) between the condenser tubes.

In cases where protective plastics liners are fitted only some time after the condenser is commissioned, irregularities in the internal surface of the condenser tubes may have already arisen, due to erosion or corrosion, and this is indicated schematically in Figure 2 at (5) and (6). Because of the surface irregularities, it may be difficult to properly seal the liner (1) into the interior of the condenser tube. In order to overcome this problem, a sealing composition such as bituminous mastic (7) is introduced into the gap (8), between the interior of the condenser tube and the exterior of the plastics liner. Initially, the sealing composition (7) may be applied as an annular mass or bead to the exterior of the plastics tube, in the region of the flange (9).

Alternatively or additionally the sealing composition may be applied to other parts of the exterior, e.g. close to the end remote from the flange. Surplus sealant squeezed out during insertion of the liner will be captured in ferrule (10) and forced back into the gap (8) during the insertion of the final part of the liner.

A plastics ferrule (10) fits over the plastics tubular liner (1) so as to be a sliding but tight fit on the flange (9). The ferrule (10) has an inward flange (11) which abuts the end face of the flange (9) of the plastics liner (1). The liner may be introduced by hand or with a tool into the condenser tube (2) until the end (12) of the ferrule (10) abuts against the outer face of the tube plate (3).

It is then convenient to use a tool to continue the introduction of the liner into the condenser tube. The tool comprises a spigot (13) which is shaped to push the liner into the condenser tube, while a tubular external part of the tool (14) presses on the flange (11) of the ferrule (10), and holds the end face over the ferrule against the tube plate (3). The part (14) may be a spring or a part which is spring or hydraulically biased to press the ferrule (10) against the tube plate (3). As a result, the flange (9) forms a piston moving within a cylinder formed by the ferrule (10) and forces sealing composition into the gap (8) between the condenser tube and the tube plate.As a result, the sealing composition fills the space (15) between the cavities in the surface of the condenser tube and ensures that no water lodges between the condenser tube and the plastics liner which could cause further corrosion.

Once the condenser tube is in the position shown in Figure 2, the ferrule (10) can be removed and discarded.

As can be seen in Figure 1, the wall thickness of the plastics liner tapers to a thin web (16) so that there is no sharp discontinuity between the end of the plastics liner and the condenser tube in that area.

The plastics liner is formed from a material which is generally hard and less flexible than the plastics ferrule. Also, the plastics liner is manufactured from a plastics material which expands in contact with water, so that after a short period, it expands to lock itself firmly into the condenser tube. Suitable materials include polyamide plastics such as nylon.

As indicated above, the ferrule should be manufactured from a plastics material which is more flexible and preferred materials are polyolefins such as polyethylene or polypropylene.

Claims

The plastics liner, ferrule and sealing composition may be pre-assembled as shown in Figure 1 for insertion into the condenser tubes. Alternatively, the sealing composition may be introduced using an insertion tool which applies a shroud temporarily over the flange of the plastics liner, and applies a sealing composition to the exterior of the plastics liner at the point when it is introduced into the tube plate. CLAIMS:

1. A method of protecting a condenser tube in a heat-exchanger which comprises introducing into the condenser tube, a tubular liner having a flange at one end for seating against one end of the condenser tube or a tube plate in which it is fixed, and squeezing a sealing composition between the interior of the condenser tube and the exterior of the liner.

2. A method as claimed in claim 1 in which the sealing composition is applied to part or all of the exterior of the liner prior to introducing the liner into the condenser tube.

3. A method as claimed in claim 2 in which the sealing composition is applied to the liner in the region of the flange.

4. A method as claimed in any one of the preceding claims in which sealing composition is squeezed into a gap between the end of the condenser tube or tube plate and the liner by temporarily shrouding the free end of the liner while forcing the liner into the condenser tube, whereby the action of forcing the liner into the condenser tube causes sealing composition to be squeezed into said gap.

5. A method according to claim 4 in which the liner is shrouded with a ferrule which tightly fits over the flange of the liner so that the liner flange moves like a piston in a cylinder formed by the ferrule as the sealing composition is forced into said gap.

6. A tubular liner for protecting a condenser tube in the region of a tube plate, said liner having a flange at one end, a ferrule which is a sliding fit over the flange so as to provide an annular space between the exterior of the liner and the interior of the ferrule and a sealing composition disposed in said annular space.

7. A liner as claimed in claim 6 wherein the ferrule has an internally extending flange at one end which is engageable with the flange of the liner so as to act as an abutment.

8. A liner as claimed in claim 7 in which the ferrule is manufactured from a relatively flexible plastics material compared with the material of the tubular liner.

9. A liner as claimed in claim 8 wherein the tubular liner is manufactured from a hygroscopic polyamide and the ferrule is manufactured from a polyolefin.