GB2075202A - Testing containers for leaks - Google Patents

Abstract

The invention discloses a method of testing for leaks in containers, suit- ably drums 34 which are sealed apart from a top bung hole. A nozzle 33 seals to the bung hole and air under pressure is introduced. The rate of increase of internal pressure during the testing operation is sensed by supporting members 23, 31 and compared to a pre-programmed rate of pressure increase, and if the rate of increase does not come up to a pre-set level, within a pre-set time, a leak is indicated, and the container can be rejected. <IMAGE>

Description

SPECIFICATION Improvements relating to the detection of leaks in containers This invention relates to the detection of leaks in containers, and has particular although not exclusive reference to the detection of leaks in metal drums used for the transportation of liquid chemical substances. Typically, chemical substances are transported in 45 gallon drums, and as these chemical substances frequency have toxic and/or corrosive characteristics, it is most important that the drums in which they are contained should be leak-free.

In fact, in the field of handling dangerous chemicals using metal drums, a surprisingly large number of the drums do have leaks, and furthermore a surprising number of these drums get into service before their leaks are discovered. The result is that dangerous situations can be created by the leaking of expensive chemicals, expense can be incurred through the loss of chemicals leaking from the drums, and frequently the leaking drums are discarded if they are found to be leaky in service.

It is to be noted furthermore that metallic drums are frequently reconditioned. To recondition a metallic drum, the top is removed for the effective cleaning of the drum interior, and then a new drum top is welded to the cleaned drum casing. The weld which is used to connect the new top and drum casing is a source of pin-hole leaks, which frequently are not discovered until the drum is placed in service by having been filled with chemical liquid. It often happens that these pin-holes are not discovered because after the drum has been reconditioned as described above, it is painted, and the paint will fill the pin-holes sufficiently so that the pin-holes will not be revealed by the conventional leak detection methods which currently are practiced.

The known method to test for leaks in reconditioned and new metal drums for the handling of dangerous chemicals, is simply to fill the drum with air and then to seal the "bung" hole at the top of the drum thereby sealing the air inside the drum. The container is then submerged in a water tank, and visual observations are made for escaping air. Apart from the fact that this method is only partially effective in that many leaking drums are not discovered by the method it is also very slow and requires a large transparent tank which takes up a considerable amount of space.

The present invention in one aspect, seeks to provide a leak detecting system which will be simpler, quicker, and we believe more effective than the known methods used heretofore.

Additionally, the embodiment of the present invention as set forth herein contains a number of novel and advantageous features, among which is a novel filling method for the effective and fast filling of containers with liquid, especially the filling of metallic drums with dangerous chemicals.

In a particular advantageous feature, the filling and leak testing arrangements are combined in a single machine, and furthermore the machine operation is preferably controlled by a micro-processor, whereby its size may be reduced and its response time and accuracy may be increased.

According to the invention there is provided a method of detecting a leak in a container comprising charging the container, when sealed, with air under pressure and sensing the rate of pressure increase inside the container during the testing. It is to be mentioned that other fluid instead of air can be used for pressurizing the container, but reference is made herein only to air because air will probably be used in by far the majority of cases. The container may be held between thrust members, the thrust members being set so as to sense any delay in reaching a predetermined thrust, resulting from a fall in pressure occasioned by a leak of air from the container through an undesired hole in the container.

In one embodiment of the invention the air under pressure is introduced into the container through a sealing nozzle which seals a bung hole in the container in the top at the side thereof, and one thrust member engages the centre of the top of the container, and the other th rust member is a plafform on which the container stands, the thrust members being coupled to a thrust sensing mechanism.

As can be appreciated, the present invention is based on the fact that when air under pressure is introduced into a sealed container, the air pressure in that container will increase at a predetermined rate. If the pressure does not increase at a predetermined rate, then this signifies a leak, if all other perameters are at a predetermined condition. In the particular embodiment of the invention, there is utilised the deflection of the container due to the increase of pressure, and that deflection, or more particularly the thrust of the thrust members which restrain that deflection, is detected by suitable thrust sensing mechanism. In the case of a 45 gallon drum, the thrust members engage the ends of the drum and restrain deflection thereof, and the rate of increase in thrust exerted by these members is detected electronically.It is of advantage to have the thrust members in the form of pads engaging the central regions of the drum ends.

With the internal pressure in the drum in the order of 5 p.s.i., it is possible to detect holes which are in the range 0.004 to 0.006 of an inch within two to three seconds, after an initial charge up time of approximately 3 seconds, and the whole cycle time can be made as short as of the order of 6 to 7 seconds. At 5 p.s.i., and in testing 45 gallon drums, a hole in the range size mentioned above causes a loss in the thrust rate increase, and hence a loss in rate of the pressure increase inside the container, of 1 kg per second.

It is preferred that the air be supplied to the interior of the container from two reservoirs which are charged up after each cycle. One reservoir supplies the air during an initial charge up period, until the thrust sensed by the sensors reaches a predetermined level. Automatically at this point, the second receiver opens and the first receiver is closed and the second receiver admits air through a restriction, so that there is controlled pressurizing of the container, and the rate of change of thrust is constantly sampled, to ensure that it is accordance with a predetermined rate of increase. If it is less, then there is an indication that there is a leak in the container.

In a sophisticated arrangement, there is provision for an analog signal from a barometerto compensate for atmospheric pressure changes which can effect air flow rate through small diameter holes.

This sophisticiation is in the majority of cases not necessary, since the machine operates on a dynamic system in that air is airways entering the drum during the testing, and the results are not substantially effected by minute pressure drops.

If there are large holes in the drum, then these will be detected during the intial charge up period, because the predetermined thrust will not be detected in the predetermined time.

In this embodiment, the said sealing nozzle also houses a filling needle which is adapted to extend into the container through the said aperture used for pressurization of the container, and the filling needle is arranged to fill the container in a cycle commencing with charging of the liquid into the container at the bottom region thereof, from the bottom of the needle, when it is close to the base of the container, followed by a retraction of the needle, whilst the charging of the liquid into the container continues as an initial fast charging rate period, followed by a small charging rate period to complete the filling of the container, for the avoidance of splashing, and for the accurate metering of the liquid into the container.

For example, the said cycle may comprise a 27 second fast filling period, followed by a 3 second slow filling period. During the fast filling period, the needle retracts more quickly from the container base than it does during the slow filling period.

The filling and leak testing equipmentwill preferably be controlled by a suitable micro-processor which is also connected for justification sensing to ensure: a) that there is a container in position before leak testing commences, and b) the upper th rust member is in correct register with the filling and leak testing aperture before leak testing commences.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows a diagrammatic perspective representation of an automatic drum filling machine in accordance with the embodiment of the invention; Figure 2 shows a side elevation of the filling nozzle of the apparatus shown in Figure 1; Figures 3 and 4 show respectively a plan and side elevation of a nozzle fitting; Figure 5 is a side elevation of the machine shown in Figure 1; Figure 6 is a side view showing how the top end of a metal drum deflects under internal pressure; Figure 7 is a circuit diagram showing the arrangement for supplying air under pressure to the interior of the drum; and Figure 8 is a graph of thrust -v- time to explain the operation of the machine described.

Referring to the drawings, the machine shown in Figure 1 is provided with frame 10 and to the front of the frame 10 is roller decking 12, whilst the rear portion of the frame which extends above the decking 12 is provided with a slide pedestal 14, which slidably receives a collar 16. Extending radial liy from the collar 16 is a support arm 18, and attached to the support arm 18 is a valve spindle 20, and a thrust leg 21. The spindle 20 has an air ram 33 whereby the lower end of the spindle 20 can be jacked downwards relative to the remainder, as will be explained. A collar 22 connects the arm 18 and the spindle 20, and a stirrup arm 24 slidably carried on a second pedastal shaft 26 supports the lower end of spindle 20 through the stirrup bracket 28. To the lower end of leg 21 is a thrust pad 23.

A control unit 30 is supported by a crank arm 32 which extends vertically from the top of the rear portion of the frame 10, and then forwardly into a location supporting the control unit 30 at a convenient position for operator observation.

A second thrust member comprising pad 31 rests on decking 12.

Essentially, the apparatus described operates in that a drum 34 (see Figure 5) is placed on the pad 31 on the decking 12 either automatically or manually, and is brought into register with the spindle 20 and leg 21 so that the filling and leak testing aperture 36 is in register with the lower end of the spindle 20, as shown in Figure 5, and pad 21 is in register with the centre of the drum. The spindle 20 carries at the top end a liquid flow valve 38, and at the lower end a nozzle head 40.

When the drum is in the correct position, a hydraulic power unit 42 housed in the frame 10 is operated to cause a hydraulic ram (not shown) to move the collar 16 downwards and also to move the spindle 20 and leg 21 downwards. The pad 31 initially engages the centre of the top of the drum, and then the ram 23 is extended to move the nozzle head 40 to engage in the said aperture 36 and provided the aperture is in the correct position of registration, the machine will continue to operate. If the aperture 36 is not in correct registration, the correct travel of the nozzle will be prevented, and this is sensed by the control unit 30. An appropriate signal would be emitted by the control unit to warn the operature that the drum is not properly positioned.

Alternatively, if for any reason no drum is present, then the downward motion of the spindle 20 and leg 21 will continue and this also will be detected by the control unit 30, which is also set up to detect the presence of an obstruction in the path of movement of the spindle 20.

Figure 6 shows in dotted lines by reference numeral 48, how the top of the drum 34 deflects upwardly as it is pressurized with air. The thrust members 23 and 31 restrain this deflection, and therefore the thrust thereon increases as the drum is pressurized.

The air circuit for the supply of pressure air to the interior of the drum is indicated in Figure 7, and it will be seen that a source line 50 passes through a cut-off valve 52, and then the supply is split to two reservoirs 54 and 56. The outlets from the reservoirs lead through control valves 58 and 60 respectively, and the outlet from valve 60 passes through a control restrictor 62. The respective outlets from the reservoirs lead to a common charging inlet 64, which is in nozzle 40, for charging the drum 34.

When the control unit 30 senses the drum is in the correct position, and the spindle 20 registers properly with the drum so that the nozzle head 40 is in sealing engagement therewith, there will be a prede termined thrust on the thrust pads 23,31, as set by the control unit 30. The decking 12 is arranged as a thrust sensing unit, an is appropriately coupled to the unit 30. The unit 30 is also programmed so that the decking 12 will act as a thrust sensor only at the correct instant in the cycle of operations i.e. at a predetermined time after the drum 34 is clamped between the pads 23,31. The control 30 senses the existence or absence of a container, and if a container is present the control unit 30 senses whether or not the container is correctly positioned.

If a container is present and is correctly engaged by nozzle 40, then the machine can proceed to the next stage in the cycle of operations. This stage is to test for leaks, and air under a high pressure is supplied from reservoirs 54, 56 through the nozzle head 40 into the drum 34 in a manner now to be described in detail with reference to Figure 8.

Referring now to Figure 8, which is a graph of thrust-v-time, when the thrust pads are brought into engagement with the ends of the drum, there is a predetermined thrust LT SET, which is achieved in time T SET. After time T SET, the valve 58 (Figure 7), opens, valve 60 and 52 being closed, and air under pressure is charged from reservoir 54 into the drum 34, until, if there are no large leaks, a loading thrust LT3 is achieved in a time Ta from the starting time.

The increase in thrust arises due to the expansion of the drum which is constrained by the thrust members. If there is a large leak, it will be detected during this period, because thrust LT3 will not be achieved in time Ta. If there are no large leaks, at the end of time Ta, valve 58 closes, whilst valve 60 opens, valve 52 remaining closed, and air is charged from the reservoir 56 through the restriction 62, keeping the control flow of air to the interior of drum 34, and this causes the thrust to increase from LT3 to LT2 over time Tb, assuming there are no leaks in the drum. It is best if the thrust LT3 and LT2 are chosen so that the drum will be within its elastic limit when it is subjected to the internal pressures which give rise to LT3 and LT2.If there is a leak, then thrust LT2 will not be achieved in time Tb, and the sensing system will sense this, indicating that the drum has a leak. The thrust is constantly sampled during the time Tb in order that the results can be averaged. When the thrust LT2 is achieved, the valve 60 is closed, and there is no further supply of air under pressure to the drum. It is interesting to note from Figure 8 that in fact the thrust continues to increase up to a turning value LT1. This is due to the resiliency or springyness of the drum which undergoes a contraction after the supply of air is cut off, in effect causing a still further but transient increase in the internal pressure in the drum.

If a "no leaks" condition is determined in the testing process, the drum can be filled as described herein.

If there are no leaks, in the next stage of operation, the collar 16 is moved even further in a downwards direction, causing a filling needle 44 (Figure 2) to move into the interior of the drum, so that the end of the nozzle from which liquid is discharged lies close to the bottom of the drum. The control unit will also be arranged to sense this condition. At this instant, the valve 38 is caused to open permitting flow of the liquid to be charged into the drum through the nozzle 40. In the first stage of the filling cycle, the discharge rate of the liquid from the end of the nozzle is relatively high, and as the drum progressively fills, so the needle is continuously retracted.

This relatively fast filling rate continues for the majority of the filling cycle, but as the end of the needle approaches the top of the drum, the filling rate is slowed down for the final filling stage, in order that the quantity of liquid charged into the drum can be accurately metered, and there will be no spillage. It should be mentioned that this equipment will be used with expensive chemical materials, and spillage and loss of material represents a considerable expense. The filling cycle may be suitably, for a 45 gallon drum, 27 seconds at a high filling rate, of the order of 600 litres per minute, and then 3 seconds at a slow filling rate of the order of 120 litres per minute.

When the drum has been filled, the assembly comprising spindle 20, valve 38 and nozzle 40 is retracted and a bung cap is inserted in the filling aperture 36 in a sealing fashion, in order that the contents will be held in the drum until it is opened for use of the said liquid.

The control unit 30 can be adjusted to vary the sensitivity thereof to suit the size of container being tested so that it will respond quicker or slower when leak testing is taking place.

It can be appreciated that an extremely novel and advantageous machine has been provided by the present invention, and the invention also sets forth a novel method for the testing of leaks in drums.

The control unit 30 may suitably contain a microprocessor suitably programmed to control the functions of the machine as herein described.

Although in this specification reference is made to the use of a means for sensing the rate of pressure increase inside the container, when detecting for leaks, it is to be appreciated that the sensing means can be set for infinite time detection, which means that rather than sensing a rate of pressure increase, the sensing unit senses the rate of pressure increase over an infinite time, which of course means sensing the absolute pressure. If the absolute pressure inside the container during leak testing does not reach the pre-set level i.e. that of the pressure source, then a leak is indicated. It is not intended therefore that the present invention be limited specifically to a mathematical rate of pressure increase detection, but rate of detection is specified simply because in a practical case it would be extremely expensive in terms of testing time to allow an infinite time on the pressure sensing step.

Claims (15)

1. A method of detecting a leak in a container comprising charging the container, when sealed, with air under pressure and sensing the rate of pressure increase inside the container during the testing.

2. The method according to claim 1, wherein the method is applied to drums and the pressure sensed by restraining the expanding of the ends of the drums by thrust members, and by detecting the rate of thrust increase on said thrust members, with increase of pressure inside the drums.

3. A method according to claim 2, wherein the thrust members comprise thrust pads which engage the centres of the ends of the drum.

4. A method according to claim 2 or 3 wherein the thrust members engage the ends of the containerwith a predetermined thrust prior to charging the container with air under pressure.

5. A method according to claim 4, wherein the container is charged from a first reservoir with air under pressure with a view to reaching a first pre-set thrust during an initial charging period to test for large leaks in the container, and is charged with air under pressure through a restrictorfrom a second reservoir with a view to reaching a second pre-set thrust (higher than the first thrust), during a second charging period to test for pin-hole leaks.

6. A method according to any of claims 2 to 5, wherein the drum is disposed upright during the testing operation, and the ends are engaged by the thrust members from above and below.

7. A method according to any of claims 2 to 6, wherein the drum has a bung hole, and in the method a nozzle co-operates with the bung hole sealingly and provides the means through which air under pressur is introduced.

8. A method according to claim 7, including means sensing whether or not the nozzle has correctly engaged the bung hole before permitting the leak testing cycle to commence.

9. A method according to claim 7, wherein the nozzle is associated with the liquid filling needle, which fills the container in the event of the leak testing operation indicating that there is no leak in the container.

10. A method according to claim 9, wherein the filling needle is, after the leak detecting procedure, lowered through the nozzleto a position close to the bottom of the container, whereupon liquid is charged into the containerthrough the filling needle at a first rate, the needle retracting as filling proceeds, until a predetermined position is reached, when filling takes place at a slower rate, to complete the filling operation.

11. A method according to any preceding claim, including the step of sensing the presence or absence of a container in the leak testing position, to prevent the leak testing operation in the event of absence of such a container.

12. An apparatus for the detection of leaks in a container comprising means for charging air under pressure into the container when sealed, means for sensing the rate of internal pressure increase, as related to an anticipated rate of pressure increase, - and means for indicating, by sensing said rate of pressure increase, whether or not the container has a leak.

13. An apparatus according to claim 10, wherein the means for sensing the rate of internal pressure increase comprises a pair of thrust members which clamp the container therebetween and are located to restrain expansion of the container as the pressure therein increases.

14. A method of detecting a leak in a container, substantially as hereinbefore described with reference to the accompanying drawings.

15. An apparatus for the detection of leaks in a container, substantially as hereinbefore described with reference to the accompanying drawings.