GB2221997A

GB2221997A - Leak detection

Info

Publication number: GB2221997A
Application number: GB8917776A
Authority: GB
Inventors: John William Child
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1988-08-16
Filing date: 1989-08-03
Publication date: 1990-02-21
Anticipated expiration: 2009-08-03
Also published as: GB2221997B; GB8917776D0; GB8819440D0

Abstract

In a method to detect and locate a leak from a duct or tube enclosed by a casing e.g. a tube in shell heat exchanger, the casing is viewed by an infra red camera, while a pressurised liquid just above its normal boiling point is caused to flow along the tube. The liquid might be liquid nitrogen at about 77 K. The portion of the casing facing any leak will be hit by a jet of liquid, and so will be of significantly lower temperature than the remainder of the casing. The duct or tube is throttled at one end by a nozzle and initially, the duct or tube being at a higher temperature than the liquid, only nitrogen gas flows along the duct or tube to emerge from the nozzle. Within a few minutes liquid nitrogen emerges from the nozzle whereupon the liquid jet emanating from a leak in the tube or duct will impinge on the casing and rapidly cool it locally.

Description

Leak Detection This invention relates to a method and to an apparatus for detecting and locating a leak, in particular a leak from a tube or pipe enclosed within an outer casing.

Many pieces of equipment incorporate tubes, pipes or other ducts enclosed within an outer casing, for example a tube-in-shell heat exchanqer. If a small leak occurs in one of the tubes it can be very difficult to detect and still more difficult to locate because the tubes are hidden by the casinq.

According to the present invention there is therefore provided a method for detecting and locating a leak from a duct enclosed within an outer casing, the method comprising the operations of passing a liquid under pressure along the duct, the liquid being at a temperature above its normal boiling point, viewing the casing with an infra-red camera, and observing the occurrence and location of any portion of the casing differing significantly in temperature from the rest of the casing.

By normal boiling point is meant the boiling point temperature when the liquid is at atmospheric pressure.

Where there is a leak, pressurized liquid will jet out of the leak and impact onto the inside of the casing, changing the temperature of the casing in that location. The heat transfer due to such a liquid jet is greater than that caused by a gas jet at the same temperature because the greater density of the liquid more than compensates for its increased viscosity. The preferred liquid is a liquified gas such as liquid nitrogen; in this case the temperature change observed will be a decrease, this decrease being due not only to the heat capacity of the cold liquid jet but also to the latent heat absorbed from the casing as the liquid vaporizes. The method may also require the partial blocking of one end of the duct to enable an adequate pressure difference to be attained.

The invention will now be further and more particularly described by way of example only. The method was used to detect and locate a small leak in a component of a gas turbine engine consisting of five parallel tubes within an empty jacket (which in normal use of the component would have contained a coolant liquid). One end of each tube was partially closed by a nozzle, and nitrogen from a supply of liquid nitrogen was passed along the tubes at a pressure above atmospheric of 80 kPa (12 psi) to emerge through nozzles. The jacket was viewed with an Agema Thermovision 680 infra-red camera sensitive to radiation between 2 and 5.6 micrometres wavelength, and which provides a temperature resolution of 0.1 K around ambient temperatures, connected to a display screen.

Initially the tubes were much hotter than the liquid nitrogen (which was at about 77 K) so only nitrogen gas flowed along the tubes, but after several minutes the tubes themselves cooled sufficiently that liquid nitrogen flowed along them, to emerge through the nozzles. Within a minute a cold patch on the surface of the jacket was clearly visible on the screen display of the camera image. This indicated the presence of a tube leak, and the location of the leak was more precisely determined by marking isothermal contours on the screen display, these being centred on the point of impact of the jet of nitrogen from the leak.

It will be appreciated that the invention might be performed in a different manner to that described above, for example using a different liquid such as liquid hydrogen or oxygen, or even a liquid boiling at above ambient temperature, such as water.

Claims

1. A method for detecting and locating a leak from a duct enclosed within an outer casing, the method comprising the operations of passing a liquid under pressure along the duct, the liquid being at a temperature above its normal boiling point, viewing the casing with an infra-red camera, and observing the occurrence and location of any portion of the casing differing significantly in temperature from the rest of the casing.

2. A method as claimed in Claim 1 wherein the liquid is liquified nitrogen.

3. A method as claimed in Claim 1 or Claim 2 also including partially blocking that end of the duct remote from the source of the liquid.

4. A method for detecting and locating a leak from a duct enclosed within an outer casing substantially as hereinbefore described.