GB2185581A - Apparatus for and method of pressure testing gas cylinders - Google Patents

Abstract

Apparatus for hydraulic volumetric expansion testing of a gas cylinder 1 by the water jacket or non-water jacket techniques comprises two constant cross-section upright tubes 20, 21, the cross-sectional area of tube 20 being a predetermined fraction of that of the tube 21. The tubes are interconnected by a duct 22 with a shut-off valve 23 and an adjustable overflow device 27,28 is connected to the bottoms of the tubes through a duct 24 having a second shut-off valve 25. A sensor 29 indicates whether water in the larger tube 21 is at or above, or below a predetermined level. For the water jacket technique the larger tube 21 is connected to the water jacket 2 by a duct 30, the apparatus is filled with water to the predetermined level set by the overflow device 27; the shut-off valve 25 is closed and the hydraulic test pressure is applied by a pump 3 to the inside of the cylinder 1, expansion of which expels water from the jacket and raises the water level in both the tubes 20 and 21; the valve 23 is then closed and the test pressure is released from the cylinder which contracts and draws water back into the jacket 2 from the larger tube 21 only, thus lowering the water level in this tube; finally the indication of the sensing device 29 is noted to check whether the water level in the tube 21 is above, or at or below the predetermined level. Since the water volume trapped in the narrow tube 20 represents the permitted permanent volumetric expansion of the cylinder 1, should the water in tube 21 fall to or below the sensor a pass indication will be given for cylinder 1 whereas if the water level fails to fall to the sensor a reject indication is given. <IMAGE>

Description

SPECIFICATION Apparatus for and methods of pressure testing gas cylinders One ofthe recognised tests used during the manufacture and in the periodic inspection and testing of cyl inders that are used for the conveya nce or storage of compressed, liquefied or dissolved gases is known as a hydraulic volumetric expansion test.

In this test, a predetermined hydraulic test pressure is applied internally to the cylindersothatthe cylinder expands volumetrically. The internal test pressure is then released so that the cylinder contracts volumetrically again. The test pressure is such that after its release, some permanent volumetric ex- pansion ofthe cylinder remains. The cylinder only passes the test if the permanent volumetric expan- sion ofthe cylinder is less than a predetermined small percentage of its total volumetric expansion underthe test pressure. At present, it is general, in order for the test to be passed, for the permanentvolumetric expansion ofthe cylinder not to exceed 5% ofthe total volumetric expansion.

There are two techniques which are used for checkingthetotal and residual permanentvolumetric expansion of the cylinders after the internal hydraulictest pressure has been applied to them.

In thefirsttechnique, which is subsequently referred to as the waterjackettechnique,the cylinder is completely enclosed within a closed jacket and the space between the outside of the cylinder and the jacket is filled with water. Liquids other than water, for example oil, may be used, and the subsequent references in this specification to water are intended also to includethe use of other suitable liquids. The jacket is connected to a calibrated container such as a burette and when the hydraulic test pressure is applied to the inside of the cylinder, the water in the jacket is expelled into the burette so that the volume of expelled water can be accurately measured.After the test pressure has been released, a further meas- urementofthewaterwhich has flowed back into the jacket is taken by means of the burette and from these two volume readings, the permanentvolumetric expansion ofthe cylinder is measured. This per manentvolumetricexpansion can then be calculated as a percentage of the intitial total volumetric expansion underthetest pressure.

This technique is very accurate because the water in thejacket is at all times under onlyambientpressure and accordingly it is not necessary to make any corrections for possible expansion ofthe jacket or of the pipe leading from the jacket to the calibrated container.

In the othertechnique, which is subsequently referred to as the non-jacketed technique, the cylinder is filled with water, or other hydraulicfluid, which is subsequently referred to as water, by means of a pressure testing pump which has its inlet connected through shut-offvalves both to a water reservoir and to an accurately calibrated water container, which may again be a burette.

Water is pumped from the reservoir into the cylinder until the cylinder is completely full, but is still at ambient pressure. The intake from the reservoir is then closed and the intake from the calibrated con tainer is opened. Furtherwateristhen pumped into the cylinder until the required test pressure is reached and the volume of water drawn from the calibrated container necessary to raisethe pressure is measured. This volume gives an indication ofthe total volumetric expansion ofthe cylinder, but corrections must be made for any volumetric expansion there may be under pressure ofthe piping connecting the pump to the cylinder. It is also essential to ensurethatthewater pumped into the cylinder is completely free of air so that the water itself is not compressible.

Afterthetest pressure has been reached, the cylinder is vented through the pump back into the calibr ted container and the volume of watervented is again measured. From these two measurements taken from the calibrated container, the permanent volumetric expansion of the cylinder as a percentage of the total volumetric expansion can be calculated.

Although both these techniques are quite ac curate, the waterjackettechnique being more so, they are both slow to carryoutand are dependent on the precision ofthe readings taken by the operator of the water levels in the burette or other calibrated container. They also, of course, depend upon the accm racy of the calculations that are subsequently carried out from these readings.

The object of the present invention is to provide an apparatus for use in hydraulic volumetric expansion testing of gas cylinders by both the water jacket and the non-jacketed techniques in an improved and more efficient manner. The apparatus enables the tests to becairred out very much more quickly than is possiblewhen they are carried out in the mannerdescribed above and it also enables them to be carried out without the necessity for an operator to take any volume readingsorto make anycalculations. The apparatus therefore enables the tests to be carried out more accurately as well as more speedily.

The apparatus also gives rise to new methods of hydraulicvolumetric expansion testing of gas cylinders by both the water jacket and non-jacketed techniques.

Thus, according to one aspect of the present invention, such apparatus comprises two tubes of con stant cross-sectional area along their lengths, the tubes being held upright side by side in a holderand a first one of the tubes having a cross-sectional area which is a predetermined fraction of that ofthe other, second tube, a first duct or other passage having a first shut-off valve interconnecting the bottoms of the tubes, an overflow device connected through a second duct or other passage having a second shut offvalve connected to the first, smallertube, the overflow device enabling both tubes to befilledwith liquid to a predetermined level, which may be adjustable, when thefirst and second shutoffvalves are open, a liquid level sensing device which provides an indication of whether water in the second, larger tube is at or above, orbelowthe predetermined level, and a water inlet and outlet pipe or other passage connected to the second, largertube below the predetermined level and arranged to be connected to the waterjacketof a gas cylinder during testing by the waterjackettechnique, or to the inletof the pressure testing pump during testing of a cylinder by the non jacketed technique.

The use ofthis apparatus gives rise, in accordance with another aspect of the invention,to a method of hydraulic volumetric expansion testing of a gas cylinder by the waterjackettechnique wherein:- (a) The waterinlet and outlet pipe or other passage ofthe apparatus is connected to the jacket; (b) The apparatus is filled with water to the predetermined level, which is determined by the overflow device, with the shut-off valves open; (c) The second shut-off valve is closed and the hydraulic test pressure is applied to the inside of the cylinder which is thus caused to expand to expel water from the jacket and raise the water level in both the tubes;; (d) The first shut-offvalve is closed and the test pressure is released from the cylinder, which contracts and drawswater back into the jacket from the second, largertube only, thus lowering the water level inthistube; and, (e) The indication of the sensing device is noted to check whether the water level in the second tube is above, or at or below the predetermined level.

The "predetermined fraction" which represents the ratio of the cross-sectional area ofthefirstsmal- lertube to the total cross-sectional area of the two tubes is made equal to the percentage ratio ofthe permanent expansion of the cylinderto the total ex pansion which must not be exceeded if the test isto be passed. Thus, when as at present the permanent expansion must not exceed 5% of the total expansion,the cross-sectional area of the first smallertube is made exactly 5% of the sum of the cross-sectional areas ofthe two tubes.

It will thus be seen that using the method in accor dance with the invention described above, since the watervolume which represents the total expansion is discharged into both tubes, but the water which is drawn back into the jacket is drawn only from the second largertube, which represents 95% of the total cross-sectional area of the two tubes, if the perma nent expansion is less than 5% of the total expansion, the water level in the second tube will fall below the predetermined level when the test pressure is re leased.

Accordingly ifthe sensing device indicates thatthe water level is at or below the predetermined level, then the cylinder has passed the test, but if the water level is above the predetermined level, then the test isfailed.

The method using the apparatus in accordance with the invention accordingly involves no volumet ric readings or calculations by the operator but merely an observance of the indication ofthe liquid level sensing device as to whether this level is above, or at or below the predetermined level.

To make this observance particularly simple, the level sensing device preferably has an electrical output and lights different coloured indicator lamps, forexample red and green lamps, one or otherof which is illuminatedto providetherequiredindica- tion.

The apparatus in accordance with the invention can also be used in a method of hydraulic volumetric expansion testing of a gas cylinder by the nonjacketed technique and in this case, in accordance with yet another aspect of the present invention,this method comprises the following steps:: (a) The water inlet and outlet pipe ofthe apparatus is connected through a further shut-off va Ive to the intake ofthe hydraulic pressure testing pump; (b) The cylinder isfilled with waterfrom the re- servoir by the pump to ambient pressure; (c) The apparatus is filled with water to the predetermined level, which is determined by the overflow device, with the first, second, and furthershut- offvalves open; (d) The second shut-off valve is closed,the reservoir is shut-off and the hydraulictest pressure is applied to the cylinder drawing water from within both the tubes of the apparatus;; (e) The first shut-off valve is closed, the test pressure is released and water in the cylinder is discharged back into the second tube only of the apparatus thus raisingthewaterlevel inthistube; and, (f) The indication of the sensing device is noted to checkwhetherthe level in the second tube is at or above, or below the predetermined level.

When as described above in connection with the waterjackettechnique, the fi rst, sma I ler tu be has a cross-sectional area equal to 5% of the sum of the cross-sectional areas of the two tubes, it will be seen that with this method if the sensing device indicates thatthefinal level in the second tube is atorabove the predetermined level, the test is passed, but ifthe level is belowthe predetermined level, then the per- manentvolumetric expansion of the cylinder is more than 5% ofthe total volumetric expansion and the test has been failed.For the purpose ofthistest, therefore, a level sensing device with an electrical output is used to illuminate a green lamp ifthe level is at or above the predetermined level, and to illuminate a red lamp ifthe level is below the predetermined level.

The overflow device readily enables the two tubes to befilled to the predetermined level without any accurate observations being necessary, because any filling above this level causeswaterto overflow through the device until the predetermined level is reached, after which the second shut-offvalve is closed.

It is essential for the level sensing device to provide an accurate reading, butforthis purpose,the device may operate, for example, photo-electrically, with a float or with capacitance or conductivity probes. An optical sensor is preferred and this may be of the kind in which an infra-red beam is directed from a light emitting diode into a glass prism within the second tube. When no liquid is present atthe surface of the prism onto which the beam is shone, total internal reflection of the beam takes place and the beam is reflected onto a phototransistorwhich provides a signal indicating that the liquid level is below the prism, which is set at the predetermined level.

When liquid is at or above the predetermined level, the beam passes into the liquid without any total internal reflection so that it does not impinge upon the phototransistorand accordingly a different signal is produced to indicatethatthe liquid is at orabovethe predetermined level.

Examples of the apparatus and of the methods in accordancewith the invention will now be described with reference to the accompanying drawings in which Figure lisa diagrammatic representation ofthe apparatus in accordance with the invention connected to testapparatus for hydraulicvolumetric expansion testing of a gas cylinder by the waterjackettech- nique; and, Figure2 is a diagrammatic representation ofthe apparatus in accordance with the invention connected to test apparatus for the hydraulic volumetric expansion testing of a gas cylinder by the non-jacketed technique.

Referring to Figure 1, a gas cylinder 1 which is to be tested is enclosed within a water jacket 2 and the inside ofthe cylinder is connected to the inlet and outlet of a single-acting positive displacement hydraulic testing pump 3 by piping 4 provided with a shut-off valve 5. The pump 3 is also connected to a water re servoir6through piping 7 and a shut-offvalve 8. The piping 4 has a drain connection 9 and a pressure gauge 10. The piping 7 leading from the reservoir6 also has a connection 11 leading to the jacket 2 through a valve 12 to enable the jacket 2 to be filled with water.

The apparatus in accordance with the invention comprises a first precision bore 91 ass tube 20 and a second precision bore glasstube 21.Thetubes 20 and 21 are held vertically side by side in a holder which is not shown. The tube 20 is of much smaller diameter than thetube 21 and its diameter is such that its cross-sectional area is equal to 5% ofthe sum of the cross-sectional areas ofthe two tubes 20 and 21. Thetubes 20 and 21 are connected at their bottoms by a pipe 22 provided with a shut-off valve 23 and the bottom ofthetube 20 is connected bya further pipe 24 having a shut-offvalve 25 to an overflow device 26.The overflow device 26 comprises an overflow nozzle 27 within a funnel 28 the bottom of which is connected to a drain.

The tube 21 is provided with a water level sensing device 29, which may be set at a fixed datum level which is the same level as that ofthe nozzle 27, or it may be adjustable upwards and downwards along the length ofthe tube 1. Ifthe level sensing device 29 is adjustable to adjust the datum level, the overflow device 26 is arranged to move upwards and downwards with it.

In this example, the level sensing device comprises a prism, a source emitting an infra-red beam and a phototransistor arranged in the manner already generally described.

Awaterinletand outlet pipe 30 leads from the pipe 22 to a filter31 and beyond the filter31 is connected to jacket 2. The water inlet and outlet pipe 30 has a drain connection 32 provided with a shut-off valve 33 and between the filter 31 and jacket2, it isfit- ted with a non-return valve 34 which permits flow in a direction only from jacket 2 towards the pipe 22.

A by-pass pipe 35 by-passes the filter 31 and is providedwith a shut-offvalve36.

To pressure test the cylinder 1, the jacket 2 together with the whole of the apparatus in accordance with the invention is filled with water from the reservoir 6through the pipes 7,11 and 30. Asfilling takes place, the valves 23 and 25 are open, butthe valve 36 is closed so that any dirt on the outside of the cylinder 1 is prevented by the filter 31 from entering the apparatus in accordance with the invention. A vent 37 on the jacket 2 is opened to ensure thatthe jacket 2 is completely filled with water and when overflow starts to take place from the device 26, the vent 37 and the valve 12 are closed. The valve 25 is also closed.Water is then pumped by the pump3 from the reservoir6 into the inside of the cylinder 1 until the cylinder reaches the required test pressure as indicated by the pressure gauge 10.

Asthecylinderl expandsvolumetricallyunderthe test pressure, water is forced from the jacket 2 through the filter 31 into the tubes 20, 21 so thatthe water level in these tubes rises equally. The valve 23 is then closed, the by-pass valve 36 is opened and the valve 9 is opened to release the hydraulic test pressure in the cylinder 1. As the cylinder 1 contracts, water is drawn from thetube 21 alone so thatthe water level in this tube fal Is. Provided that the volumetric contraction ofthe cylinder 1 is equal to at least 95% of its volumetric expansion under the test pressure, the level inthetube 21 will fall to the datum level at which the sensor 29 and the overflow device 26 are situated, or below this level.If the sensor 29 indicates thatthe water level has fallen to or below the datum level, it illuminates a green lamp to show that the cylinder 1 has passed the pressure test. If the level does notfall as far as the datum level,thenthe sensor 29 illuminates a red lampto showthatthetest has been failed.

As a modification of the operation just described, instead of keeping the valve 23 closed as the test pressure in the cylinder 1 is released and the cylinder contracts, priorto release ofthe test pressure, the valve23 may be closed andthevalve 25 openedto reduce the water level in the tube 20 to the datum level. After this the valve 25 is closed and the valve 23 is opened again and after this the operations proceed as before. When the valve 23 is opened, the water levels in the pipes 20 and 21 will be equalised, but still the volume ofwaterwithdrawn from the apparatus as the cylinder 1 contracts is still only 95% ofthe water expelled into the apparatus, in order to reduce the water level in both the tubes 20 and 21 to the datum level. The sensor 29 accordingly provides an indication of whetherthe test is passed or failed by illuminating a green or red lamp in the samewayas when the apparatus is operated as first described.

Referring to Figure 2,the apparatus in accordance with the invention is the same as already described, except that the overflow device 26 and the sensor 29 are adjusted to set the datum level closerto the tops of the tubes 20 and 21.

In this example, the pipe 30 is connected through a furthershut-offvalve38toan inlet pipe 39 leading to a hydraulictesting pump 40. The inlet pipe 39 is also connected through a shut-offvalve 41 and further pipe 42 to a reservoir43.

The outlet ofthe pump 40 is connected through a pipe 44 and an air bleed valve 45 to a cylinder 1'.

At the start of the pressure testing operation, the valves 38 and 41 amd the valves 23 and 25 ofthe apparatus in accordance with the invention are all open so that water flows from the reservoir 43 into the apparatus in accordance with the invention until it overflows from the device 26. When this happens, the valve 25 is closed. The pump 40 is then operated with the air bleed valve 45 open until the cylinder 1' and the pipe 44 leading to it are completelyfilled with water at ambient pressure and so also is a pipe 46 whichleadstoa pressure gauge 47. The air bleed valve 45 is then closed and so is the valve 41 so that the inlet of the pump 40 remains only connectedto the apparatus in accordance with the invention through the pipe30.

Operation ofthe pump 40 is then continued until the pressure gauge 47 indicates that the required test pressurewithinthecylinder1' has been reached. In reaching this pressure, water is drawn from the apparatus in accordance with the invention through the by-pass 35, the valve 36 being open and the water levels in both the tubes 20 and 21 fall belowthe datum level. The volume represented bythefalling water level in the tubes 20 and 21 is equal to thetotal volumetric expansion ofthe cylinder 1', butcalcula- ted allowances must be made forthe elasticity and accordingly the expansion of the connecting pipework.

The valve 23 is then closed and a valve in the pump 40 is opened to release the pressure in the cylinder 1' slowly and allow reverse flow to take place through the pump 40 and the pipes 39 and 30 so that the water discharged from the cylinder 1 ' raises the water level in the pipe 21 alone, since the valve 23 is closed.

If volume ofwater expelled from the cylinder 1' as the pressure is released is equal to at least 95% of the total volumetric expansion ofthe cylinder, that is to say if the permanent volumetric expansion of the cylinder1' is less than 5% ofthetotal volumetricex pansion, the water level in thetube2l will rise above the datum level. This is indicated by the sensor 29, which in this example is arranged to illuminate a green lamp if the water level rises upto or above the datum level indicating that the pressure test has been passed, orto illuminate a red lamp if the water level does not reach the datum level.If the water does not reach the datum level, this indicates that there is morethan 5%ofthetotal volumetricexpan- sion ofthecylinder 1 remaining as permanentex pansion.

It will thus be ssen that when used for pressure testing by the non-jacketed technique, the passing or failure ofthetest is indicated solelyby indication of the level sensor29 and nothingotherthantheobser- vance of this indication is required from the operator to enable the operator to decide whether or notthe test is passed.

All ofthe shut-off valves are preferably solenoid opeated and are controlled from a console. In this way the apparatus in accordance with the invention enables hydraulicvolumetric expansion testing of gas cylinders to be carried outvery much more quickly than has previously been possible. The accuracy is also increased because opeator error is to all intents and purposes eliminated.

Claims (9)

1. Apparatus for use in hydraulic volumetric expansion testing of gas cylinders by the water jacket and the non-jacketed techniques, the apparatus comprising two tubes of constant cross-sectional area along their lengths,thetubes being held upright side by side in a holder and a first one ofthe tubes having a cross-sectional area which is a predetermined frac tion ofthat ofthe other, secondtube, a firstductor other passage having a first shut-off valve interconnecting the bottoms of the tubes, an overflow device connected through a second duct or other passage having a second shut-offvalve connected to the first, smallertube, the overflow device enabling both tubes to be filled with liquid to a predetermined level whenthefirstand second shut-offvalves are open,a liquid level sensing device which provides an indication of whether water in the second, larger tube is at or above, or below the predetermined level, and a water inlet and outlet pipe or other passage connected to the second, largertube, below the predetermined level and arranged to be connected to the water jacket of a gas cylinder during testing by the waterjackettechnique, orto the inletof a pressure testing pump during testing of a cylinder by the non jacketed technique.

2. Apparatus according to Claim 1,furthercomprising means for adjusting the overflow device to adjust the predetermined level.

3. Apparatus according to Claim 1 or Claim 2, in which the level sensing device has an electrical output and lights different coloured indicator lamps, one or other of which is illuminated to provide the indication.

4. Apparatus according to Claim 3, in which the level sensing device is an optical sensor ofthe kind in which an infra-red beam is directed from a lightemitting diode into a glass prism within the second tube.

5. Apparatus according to any one of the preceding Claims, in which the shut-offvalvesare solenoidoperated and are controlled from a console.

6. Amethodofhydraulicvolumetricexpansion testing of a gas cylinder by the water jackettechnique using apparatus in accordance with anyone of the preceding Claims, wherein: (a) The water inlet and outlet pipe or other passage of the apparatus is connected to the jacket; (b) The apparatus is filled with water to the predetermined level, which is determined by the overflow device, with the shut-offvalvesopen; (c) The second shut-offvalve is closed and the hydraulic test pressure is applied to the inside ofthe cylinder which is thus caused to expand to expel water from the jacket and raise the water level in both the tubes; (d) The first shut-off valve is closed and the test pressure is released from the cylinder, which contracts and draws water back into the jacket from the second, largertubeonly,thusloweringthewater level inthistube;; and, (e) The indication ofthe sensing device is noted to check whether the water level in the second tube is above, or at or below the predetermined level.

7. A method of hydrau I ic volumetric expansion testing of a gas cylinder by the non-jacketed technique using apparatus in accordance with any one of Claims 1 to 5, wherein: (a) The water inlet and outlet pipe ofthe apparatus is connected through a further shut-offvalve to the intake ofthe hydraulic pressure testing pump; (b) The cylinder is filled with water from the reservoirbythe pump to ambient pressure; (c) The apparatus is filled with water to the predetermined level, which is determined by the overflow device, with the first, second, and further shutoff valves open; (d) The second shut-offvalve is closed, the reservoir is shut-off and the hydraulictest pressure is applied to the cylinder drawing water from within both the tubes of the apparatus; ; (e) The first shut-off valve is closed, the test pressure is released and water in the cylinder is discharged back into the second tube only of the apparatus thus raising the water level in this tube; and, (f) The indication of the sensing device is noted to check whether the level in the second tube is ator above, or below the predetermined level.

8. Apparatus according to Claim 1, substantially as described with reference to the accompanying drawing.

9. A method according to Claim 6, substantially as described with reference to Figure 1 of the accompanying drawings.