Bauge, Johannes Andreas (Øvre Kråkenes 89B, Fjøsanger, N-5042, NO)
Johnsen, Kurt J. (Tverrelvdalen, Alta, N-9500, NO)
Bauge, Johannes Andreas (Øvre Kråkenes 89B, Fjøsanger, N-5042, NO)
| 1. | Method related to checking and calibrating of level gauges and switches for tanks under pressure, in which the level gauge or switch (4) is fluid isolated from the tank (3) by the closing of valves (11,12) and the tank other wise is in a normal operational mode, c h a r a c t e r i z e d i n that it uses a device that comprises a test container (1), at least two pipes (6), the pipes being provided with at least one valve (9,9') each and the pipes being mounted on the upper portion (7) and lower portion (8), respectivly, of the test container, which is provided with a level indicator (2). |
| 2. | Method according to claim 1, c h a r a c t e r i z e d i n that it further comprises the steps of: a. closing the valves (11,12) between the tank (3) and the level gauge or switch (4) in order to pressure and fluid isolate the tank, b. connecting the pipes (6) of the test container to the connection points (10,10') of the level gauge or switch (4), in which the pipe from the upper portion (7) of test container (1) is connected to the upper portion of the level gauge or switch, and in which the pipe from the lower portion (8) of the test container is connected to the lower portion of the level gauge or switch, and opening the valves (13,13') by the connection points (10,10'), in order to provide free pressure and fluid exchange between the test container and gauge or switch, c. opening the upper valve (11) between the tank (3) and the level gauge or switch (4), in order to keep all three systems, that is, the tank, the gauge or switch, and the test container (1), respectively, pressure equalized at all times, d. opening the lower valve (12) between the tank (3) and gauge or switch (4) somewhat, in order to allow a suitable amount of the fluid through the gauge or switch and down into the test container by lowering the test container, e. closing the lower valve (12) between the tank (3) and gauge or switch (4) in order to fluid isolate the level gauge or switch and test container (1) from the tank, f. raising the test container (1) in order to let the fluid (14) flow out of the test container and into the level gauge or switch (4), whereupon the test container is held still when the level shown on the level indicator (2) is at the same exact hight as an absolute upper level, e. g. indicated by a grove on the tank, gauge og switch, and marking this level on the level indicator, as a reference maximum level (15), whereupon the maximum level (15') of the gauge or switch is checked and, if necessary, cali brated against the reference maximum level, g. lowering the test container (1) in order for the fluid (14) to flow out of the level gauge or switch (4) and into the test container, whereupon the test container is held still when the level shown on the level indicator (2) is at the same exact hight as an absolute low level, e. g. in dicated by a grove on the tank, gauge og switch, and mark ing this level on the level indicator, as a reference minimum level (5), whereupon the minimum level (5') of the gauge or switch is checked and, if necessary, calibrated against the reference minimum level. |
| 3. | Method according to claim 1 or 2, c h a r a c t e r i z e d i n that it further comprises the step of: h. raising the test container (1) to one or more inter mediate level (s) of the level indicator (2), and checking and, if necessary, calibrating the level gauge or switch (4) against these intermediate levels. |
| 4. | Method according to claim 3, c h a r a c t e r i z e d i n that the one or more inter mediate level (s) are e. g. 25%, 50%, and 75%. |
| 5. | Method according to any of the claims 2 to 4, c h a r a c t e r i z e d i n that step f and g are exchanged. |
| 6. | Method according to any of the claims 3 to 5, c h a r a c t e r i z e d i n that the test container (1) is lowered, instead of raised, to the the known inter mediate level (s) referred to in step h. |
| 7. | Method according to any of the previous claims, c h a r a c t e r i z e d i n that the pipes (6) from the test container (1) are connected to the connectionpoints (10,10') before the valves (11,12) between the tank (3) and the level gauge or switch (4) is closed in step a, and/or that one or both valves (13,13') by the connection points (10,10') are closed before the valves between the tank and the level gauge og switch are closed. |
| 8. | Method according to claim 1 or 2, c h a r a c t e r i z e d i n that the upper valve (11) between the tank (3) and the level gauge or switch (4) is closed during the excecution of step (s) f and/or g. |
| 9. | Method according to any of the claims 3 to 8, c h a r a c t e r i z e d i n that the upper valve (11) between the tank (3) and the level gauge or switch (4) is closed during the excecution of steps f and/or g and/or h, or step h alone. |
| 10. | Method according to any of the claims 1 to 7, c h a r a c t e r i z e d i n that the upper valve (11) between the tank (3) and level gauge or switch (4) is not closed during the excecution of the method. |
| 11. | Method according to any of the claims 1 to 7, c h a r a c t e r i z e d i n that the upper valve (11) between the tank (3) and level gauge or switch (4) is open during the excectution of the method. |
| 12. | Method according to any of the previous claims, c h a r a c t e r i z e d i n that the test container (1) is raised after step h in order to drain out as much fluid as possible from the test container and into the tank (3) and level gauge or switch (4) before the test container is disconnected. |
| 13. | Method according to one of the claims 3 to 10, c h a r a c t e r i z e d i n that the test container (1) is not raised after step h, in order to keep the fluid (14) in the test container, the test container is isolated by closing the valves (9,9') on the pipes (6), which pipes are reconnected to another tank with a level gauge or switch to be checked and calibrated, and the check and calibration of the other level gauge or switch is executed without having to execute steps d and e. |
| 14. | Device related to checking and calibrating level gauges and switches for tanks under pressure, in which the level gauge or switch (4) is fluid isolated from the tank (3) by the closing of valves (11,12) and the tank other wise is in normal operational mode, c h a r a c t e r i z e d i n that it comprises a test container (1) and at least two pipes (6), which pipes have at least one valve (9,9') each and are mounted on the upper portion (7) and lower portion (8) of the test contai ner, which is provided with a level indicator (2). |
Background of the invention Pressurized tanks in the process industry may contain e. g. oil products, chemicals or cooling water. These tanks will usually include level gauges and/or level switches in add- ition to pressure gauges. Level gauges and level switches may be of a number of kinds, e. g. the float, displacement, or sight glass kind. In addition, the gauges and switches may be remotely situated, e. g. a control room.
Level gauges and switches must, as understood by those of ordinary skill in the art, regularly be checked and, if necessary, i. e. in case of errors, be calibrated. Of economic reasons the downtime of the prosess should be as short as possible or, preferably, eliminated. In both cases it is disirable to excecute such checks and calibra- tions with the least possible degree of process interfer- ence.
The main problem in the checking and calibrating of gauges and switches often relates to the high operational pres- sure, explosive hazard, toxic hazard, or high temperatures.
A prior known method of checking and calibrating gauges is set forth in WO 87/01446 and comprises a standpipe of flexible tubing and various temperature sensors that are arranged to be connected to the tank gauge system. The tank is isolated from the tank gauge system by closing two
valves. After the system is isolated from the tank, it is depressurized, drained, and flushed, and a calibration fluid such as distilled water traceable to a standards organisation is introduced under gravity by way of a dis- connectable column through the bottom of the stand pipe.
By using the precise knowledge of the fluid properties and readings from the gauges and temperature sensors various aspects of the system can be cheched and calibrated. The tank is fully operational during the checking and calibra- tion.
There are several disadvantages with this method. Parti- cularly the depressurization, the draining and collection of fluid, and the following flushing and introduction of calibration fluid results in a number of complcated opera- tions which have to excecuted with great care and precision in order to avoid contamination of the area surrounding the tank and errors in cheching and calibration. In addition, several more operations are necessary in order to refill the tank fluid, repressurization and calculations. In the case of high fluid temperatures, the temperature difference and cooling time will also complicate and prolong the operation. Also, this method does not apply to level switches.
Scope of the invention One aspect of the present invention is to introduce a method and a device that can reduce the number of opera- tions that are necessary to excecute the checking and calibration and at the samme time simplify these opera- tions. An other aspect of the present invention is to cut down on the time necessary to excecute the checking and calibration. A futher aspect of the present invention is to utilize the process fluid as the calibration fluid, in order to avoid problems arising with transportation, con- tainment and disposal of an external calibrating fluid, depressurization, flushing and so forth.
Short description of the invention By the present invention the various mentioned problems are resolved by a method and device, of the mentioned kind, by the features claimed in the characterizing clause of the disclosed claims 1 and 7, respectively. Further features and advantages of the present invention are presented in the following description of an embodiment of the inven- tion, considered in relation with the disclosed drawings.
Short description of the drawings Fig. 1 presents a schematic sectional side view of a test container, which is connected to the level gauge or switch, in a lowered position.
Fig. 2 presents a schematic sectional side view of the samme test container, which is connected to the level gauge or switch, in a elevated position.
Fig. 3 presents a side view of the test container, partly in section, while it is elevated and the level is low.
Fig. 4 presents a side view of a test container, partly in section, while it is lowered and the level is high.
Detailed description of the preferred embodiment A tank 3, provided with a level gauge or switch 4, which can be isolated from the tank 3 by means of valves 11,12, is presented in fig. 1. A device comprising a test contai- ner 1 and two pipes of flexible tubing 6, each provided with at least one valve 9,9', which pipes are mounted on the upper portion 7 and lower portion 8, respectivly, of the test container. The test container is provided with A level gauge 2 (hereafter called"level indicator") and is placed in suitable proximity of the level gauge or switch 4 which is to be cheched and, if necessary, calibrated.
When the device is to be used, the level gauge or switch 4
is first isolated from the tank 3 by closing the valves 11 and 12. The gauge or switch 4 is now both fluid and pres- sure isolated from the tank 3.
The pipes 6 of the test container 1 are connected to con- nectionpoints 10 and 10'on the gauge or switch 4 in such a manner that the pipe from the upper portion of the test container 1 is connected to the upper portion of the gauge or switch 4, and the pipe from the lower portion of the test container 1 is connected to the lower portion of the gauge or switch 4, as suggested in figs. 1 and 2. The valves 13 and 13'by the connection points 10 and 10'are opened in order to provide free pressure and fluid exchange between the test container 1 and gauge or switch 4.
Thereafter the valve 11 between the tank 3 and the gauge or switch 4 is opened in order to keep all three systems, that is, the tank 3, the gauge or switch 4, and the test contai- ner 1, respectively, pressure equalized at all times.
Now, the test container 1 and gauge or switch 4 has to be filled with a suitable amount of fluid 14 from the tank 3.
This is preferably done by lowering the test container somewhat, as suggested in fig. 1, and by thereafter opening the lower valve 12 between the tank 3 and gauge or switch 4 somewhat, in order to, in a controlled manner, allow a suitable amount of fluid 14 through the gauge or switch and down into the test container.
When the amount of fluid in the test container 1 or the gauge or switch 4 is satisfactory, the lower valve 12 between the tank 3 and the gauge or switch 4 is closed.
The test container and the gauge or switch is now a fluid isolated system that at all times has the same pressure as the tank.
Then, the test container 1 is raised, as suggested in fig.
2, in order for the fluid to flow out of the test container and down into the gauge or switch 4. When the level of the test container is at the same hight as an absolute upper level, often indicated by a grove on the tank, gauge og switch, it is held still at this point and the level is marked on a level indicator 2, mounted on the test contai- ner, as a reference maximum level 15. The maximum level 15'of the gauge or switch 4 is checked and, if necessary, calibrated against the reference maximum level 15.
Thereafter, the test container 1 is again lowered down until the level in the test container, indicated by the level indicator, is at the samme level as a absolute low level, likewise indicated as the absolute upper level by e. g. a grove on the tank, gauge or switch. The minimum level of the gauge or switch 5'is checked and, if neces- sary, calibrated against the reference minimum level 5.
Lastly, the test container 1 is raised until the level indicator shows a known intermediate level of the test container, in order to check and, if necessary, calibrate the gauge or switch 4 at this level. This can be done for as many intermediate levels as desirable, e. g. 25%, 50% and 75%.
Both gauges and switches 4 that are situated near the tank 3, and gauges and switches that are situated remotely from the tank, e. g. in a control room, may be checked and cali- brated by using this method and device.
After the check and control has taken place, the test container 1 may be raised in order for the fluid 14 to flow back into the gauge or switch, whereupon the the valves 13 and 13'are closed and the valve 12 between the tank 3 and gauge or switch 4 is opened, which leaves the system in full functional operation. In this case, the test contai- ner is empty and no problems with containment or disposal
of calibration fluid are encountered.
Alternately, the fluid 14 may be kept in the test container 1 by lowering the test container somewhat, in order for the fluid to flow from the gauge or switch 4 and into the test container, whereupon the valves 13,13', 9 and 9'are closed and the pipes 6 are disconnected from the connection points 10 and 10'. Thereafter, the test container may be moved and connected to an other tank with a gauge or swi- tch, in order to check and calibrate it in the samme manner described above, but without having to go through the fluid filling stages. This is of course only possible if the process fluid in the process tanks are identical.