GB2284674A

GB2284674A - Testing vessel for leakage

Info

Publication number: GB2284674A
Application number: GB9419868A
Authority: GB
Inventors: Michael Bowling
Original assignee: Somerset Technical Laboratories Ltd
Current assignee: Somerset Technical Laboratories Ltd
Priority date: 1993-10-02
Filing date: 1994-10-03
Publication date: 1995-06-14
Anticipated expiration: 2014-10-03
Also published as: GB2284674B; GB9419868D0

Abstract

A vessel such as a dairy pasteuriser having a path B for product and a separate path A for coolant in intimate relationship is tested for leaks by circulating a donor electrolyte under pressure in path A whilst a recipient fluid such as clean tap water is circulated in path B. A probe 12 is placed in path B to measure the conductivity of the recipient fluid. A rise in conductivity over a period indicates leakage between the two paths, the rate of change indicating the size of the leak. <IMAGE>

Description

LEAKAGE TESTING TECHNICAL FIELD OF THE INVENTION This invention relates to a method of testing heat exchangers and the like for leakage.

BACKGROUND Pasteurisers used in the dairy process industry typically include a product path in which the milk is placed for treatment. A heating and/or cooling medium is passed through a separate circuit in close heat-exchange relationship with the product path. Modern pasteurisers of this kind are known as HTST (High Temperature, Short Time) pasteurisers.

From time to time, leaks between the heating/cooling medium and the product can develop. Such leaks can be very costly, not only because the contaminated product must be discarded but also due to the cost of finding and rectifying the leak. Present preventive maintenance techniques involve shut down of the plant, dismantling of the pasteuriser, detailed examination and testing of the individual components, careful cleaning of the components, re-assembly with new seals, pressure and leak testing, and recommission of the re-assembied pasteuriser. Such a procedure results in considerable lost production time whilst the equipment is out of commission, is extremely labour intensive, and involves the cost of new seals. In addition, there is a substantial risk that further leaks can inadvertently be introduced during the re-building process.

An aim of the present invention may be viewed as being to overcome these problems.

SUMMARY OF THE INVENTION The present invention proposes a method of testing for leakage between physically separate first and second fluid paths arranged in an intimate relationship, which comprises: - placing a donor fluid in the first path, - placing a recipient fluid in the second path, and - analysing the recipient fluid for presence of the donor fluid caused by leakage between the two paths.

The donor fluid is preferably an electrolyte and the recipient fluid a nonelectrolyte. The presence of the donor fluid in the recipient fluid can thus be reliably and accurately tested for by measuring the electrical conductivity of the recipient fluid. Preferably, the rate of change of concentration of the donor fluid in the recipient fluid is calculated, which may be used to indicate the size of the leak. Such rate of change is preferably repeatedly calculated at intervals to obtain a more accurate value.

A positive pressure differential is preferably applied between the first and second paths to reduce the testing time and increase the accuracy of the result.

In a dairy pasteuriser, the recipient fluid is preferably placed in the product path of the pasteuriser whilst the donor fluid is placed in a heating or cooling circuit.

BRIEF DESCRIPTION OF THE DRAWINGS The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. The drawing is a diagrammatic representation of a dairy pasteuriser undergoing a testing method in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS The dairy pasteuriser in question is outlined in the drawing by dashed lines.

The pasteuriser is a form of heat exchanger having a first path A for coolant and a second path B for the milk product. The two paths A and B are in intimate relationship to provide heat exchange between the two paths in normal use so that, should any leaks develop between paths A and B, the product in path B will become contaminated with coolant.

In the method of the invention, the pasteuriser is tested for leaks between paths A and B without any necessity to dismantle the pasteuriser. A donor fluid (see below) is circulated through path A in a closed loop by means of a circulation pump P1, while a recipient fluid (again, see below) is circulated in a closed loop through path B using a pump P2. Contacting type conductivity probes 10 and 12 of known construction are placed in the donor fluid and recipient fluid paths A and B respectively. Each probe is connected via a suitable electronic interface circuit 14, 16 (e.g. the Model 697C1 Conductivity Transmitter available from Great Lakes Instruments, Inc. of Milwaukee, Wisconsin) to a digital display 18, 20 respectively, which gives a conductivity readout in suitable units such as milli siemens/cm.The probe 12 in the recipient fluid circulation path B is also connected to an electronic circuit 22 that monitors the conductivity reading at regular intervals, stores the reading, and displays the difference between the last two readings (which will be referred to below as value X).

By way of example, clean tap water can be used as the recipient fluid with a solution of a salt and water as the donor fluid. The donor fluid is usually circulated under pressure, e.g. at 45 psi. Any suitable electrolyte may be used as the donor fluid, but ordinary common salt (sodium chloride) gives good results. The presence of common salt in water increases the conductivity of the water by an amount which depends upon the salt concentration. For example, a salt concentration of 0.05 grams/litre gives a conductivity of 100 micro siemens/cm whereas a concentration of 0.25 grams/litre gives a conductivity reading of 500 micro siemens/cm.Thus, if value X is zero (no change in conductivity in the recipient fluid) there is no leak, but a steady increase in the conductivity of the water circulating in the recipient fluid path B indicates that electrolyte has leaked from the donor fluid into the recipient fluid. For a given concentration of salt in the donor fluid and applied pressure differential, the rate of change in conductivity, X, gives a direct indication of the size of the leak, larger leaks giving rise to a greater rate of change in conductivity and hence a larger value of X.

The equipment may give spurious readings at first whilst salt concentrations, pressures and flow rates stabilise, but after a short period the value of X will stabilise. Probe 10 allows the salt concentration on the donor fluid side to be monitored. By using a standard concentration of salt in the donor fluid (or by making an appropriate adjustment for salt concentration) and a known pressure differential, the equipment can be calibrated to accurately correlate the size of the leak with the measured rate of change in concentration X in the recipient fluid.

Common salt in potable water at a concentration of 15 g/litre with a pressure differential of 45 psi (3 bar) can be detected leaking into soft water through a hole as small as 70 microns. Hence the equipment can be accurate enough to give an assurance of serviceability in applications where leakage through a defect of less than 70 microns is negligible.

Claims

1. A method of testing for leakage between physically separate first and second fluid paths arranged in an intimate relationship, which comprises: - placing a donor fluid in the first path, - placing a recipient fluid in the second path, and - analysing the recipient fluid for presence of the donor fluid caused by leakage between the two paths.

2. A method according to Claim 1, in which the donor fluid is an electrolyte and the recipient fluid a non-electrolyte.

3. A method according to Claim 2, in which the recipient fluid is analysed for presence of the donor fluid by measuring the electrical conductivity of the recipient fluid.

4. A method according to any preceding claim, which includes calculating the rate of change of concentration of the donor fluid in the recipient fluid.

5. A method according to Claim 4, in which the said rate of change is repeatedly calculated at intervals.

6. A method according to any preceding claim, in which a positive pressure differential is applied between the first and second paths.

7. A method according to any preceding claim, in which the said first and second paths are comprised in a dairy pasteuriser, and the recipient fluid is placed in the product path of the pasteuriser whilst the donor fluid is placed in a heating or cooling circuit.

8. A method of testing for leakage between physically separate first and second fluid paths arranged in an intimate relationship, substantially as described with reference to the drawings.

9. A method of testing for leakage between the product path and the heating or cooling circuit of a diary pasteuriser, substantially as described with reference to the drawings.