GB2314421A

GB2314421A - Leak detection in heat exchangers

Info

Publication number: GB2314421A
Application number: GB9712740A
Authority: GB
Inventors: Thomas Werner
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-06-18
Filing date: 1997-06-17
Publication date: 1997-12-24
Anticipated expiration: 2017-06-17
Also published as: GB2314421B; GB9712740D0; GB9612677D0

Abstract

For detecting leaks between first (12) and second (14) flow paths of a heat exchanger (particularly a plate pack exchanger) (10), a gas circulation system (24) including a helium probe or detector (26) is connected across one path (14). The other path is emptied of liquid closed off at one end (19), and helium is introduced from a supply (20) into the other end (22). The probe (26) is monitored.

Description

LEAK DETECTION IN HEAT EXCHANGERS The present invention relates to a method and apparatus for the use in detecting leaks in heat exchangers. It particularly relates to systems employing helium as a tracer for finding leaks.

There are already been various proposals for using helium as a tracer for testing heat exchangers and similar apparatus for leaks. They tend to be rather elaborate. GB-A-1,518,476 is specifically concerned with detection of leaks in a heat exchanger of a nuclear reactor, in which the heat exchanger tubes at the reactor side contain a liquid metal (particularly sodium), while the tubes at the other side contain water. Helium is added to the water, and passes through any leaks into the molten sodium. Gas is recovered from the molten sodium and analysed for helium by mass spectrography or gas chromatography.

US-A-4,688,627 describes leak detection in heat exchangers during operation, particularly heat exchangers which produce super heated steam. Helium is injected at the high pressure side of the exchanger, and leaked helium is recovered from the low pressure side. This may contain superheated steam, in which case a fraction of the steam is condensed, and the uncondensed gas is analysed by mass spectrography, to determine the helium content.

Clearly these are rather elaborate and specialised systems, involving large and expensive equipment such as mass spectrographs). The present invention arises from the realisation that simple helium detectors are commercially available, and such devices can be used for simple and economical testing of heat exchangers.

Thus in one aspect the invention provides a method of testing a heat exchanger for leaks, the exchanger having a first flow path and a second flow path which is in thermal contact with the first flow path but intended to be isolated from it as regards mass transfer. The method comprises connecting a gas circulation system including a helium detector probe across the first flow path; emptying the second flow path of. any liquid, and introducing helium into it; and using the helium detection probe to detect any helium in the first flow path. The probe may work on the basis of thermal conductivity. The gas circulation system may be a low volume air circulation system. Helium may be introduced to the second flow path through one end thereof after the other end has been closed off. It is preferably introduced at a pressure not exceeding 20 p.s.i.g. (2.4 X lO5Nm~2). The invention is primarily for use with plate pack heat exchangers.

In a second aspect the invention provides a kit of parts for testing a heat exchanger by the above method, including a gas circulation system including a helium detection probe adapted for coupling to a first flow path, and a helium gas introduction system adapted for connecting to the second flow path, of a heat exchanger.

An embodiment of the invention will now be described with reference to the accompanying drawing, which is a schematic representation of a heat exchanger undergoing leak testing by means of an embodiment of the present invention The illustrated heat exchanger 10 has a primary flow path 12 in thermal communication with a secondary flow path 14. The diagram shows schematically a heat exchanger of plate pack type, having an array of plates 15 between side chambers 16,17. For testing the exchanger for leaks, the outlet 18 of the primary path is blanked off, e.g. by means of a plug or a tap 19. A helium gas introduction system 20 is connected to the inlet 22 of the primary path. It may consist of a cylinder of helium and a pipe and bung for coupling it to the inlet 22. A low-volume air circulation system 24 and a helium detector 26 are connected across the inlet 28 and outlet 30 of the secondary path 14. Typically the circulation system employs a fan which drives 15-30 cu.ft/min (.014 .007 m3s1) . Various designs of helium detector are commercially available, e.g. working on thermal conductivity.

For running a test, the normal fluids passed through the heat exchanger may be discharged, particularly if they are liquids. The circulation system 24 is operated, and allowed to run until stabilised. Then helium is introduced into the primary path by means of the introduction system 20. Initially air is bled out via the outlet tap 18. This is then closed, and the primary flow path is pressurised with He, e.g. to 1.7 X 105cm2.

The circulation system 24 continues to run, and the detector 26 is monitored for a suitable period, e.g. 20 minutes. Of course the detection of any helium by the detector 26 is indicative of leakage.

Claims

1. A method of testing a heat exchanger for leaks, the exchanger having a first flow path and a second flow path which is in thermal contact with the first flow path but intended to be isolated from it as regards mass transfer, the method comprising connecting a gas circulation system including a helium detector probe across the first flow path; emptying the second flow path of any liquid, and introducing helium into it; and using the helium detection probe to detect any helium in the first flow path.

2. A method according to claim 1 wherein the probe works on the basis of thermal conductivity.

3. A method according to claim 1 or claim 2 wherein the gas circulation system is a low volume air circulation system.

4. A method according to any preceding claim wherein helium is introduced to the second flow path through one end thereof after the other end has been closed off.

5. A method according to any preceding claim wherein helium is introduced at a pressure not exceeding 20 p.s.i.g. (2.4 X lOsNm~2).

6. A method according to any preceding claim wherein the heat exchanger is a plate pack heat exchanger.

7. A method of testing a heat exchanger for leaks substantially as herein described with reference to and as illustrated in the drawing.

8. A kit of parts for testing a heat exchanger by the method of any preceding claim, said kit including a gas circulation system including a helium detection probe adapted for coupling to a first flow path, and a helium gas introduction system adapted for connecting to the second flow path, of a heat exchanger.