GB2323421A

GB2323421A - A method and plant for internal cleaning of a fluid piping system

Info

Publication number: GB2323421A
Application number: GB9805804A
Authority: GB
Inventors: Jens Peder Hog Thomsen
Original assignee: Ocean Team Scandinavia A S
Current assignee: Ocean Team Scandinavia A S
Priority date: 1997-03-18
Filing date: 1998-03-18
Publication date: 1998-09-23
Anticipated expiration: 2018-03-18
Also published as: NO981081D0; NO981081L; GB9805804D0; DK172595B1; DK29997A; NO312883B1; GB2323421B

Abstract

The invention relates to a method and a plant for internal cleaning of piping systems. The method is utilised in piping systems comprising a primary fluid circuit 12 in which a first technical process takes place, and a secondary fluid circuit 10 in which a second technical process takes place. The secondary circuit is in connection with the primary circuit so that irregularities in the fluid in the primary circuit may be controlled in the fluid in the secondary circuit. The method comprises cleaning of the secondary circuit by creating pulsations in the fluid in the secondary circuit at the same time as the first technical process in a primary circuit is still taking place. Hereby, it is possible to maintain the process in the primary circuit even when the secondary circuit is cleaned. This means reduction in the loss of resources as the technical process in the primary circuit does not have to be interrupted. The method and the plant according to the invention primarily find their utilisation within oil extraction and oil refining, but can be utilised in all other systems with a primary circuit and a secondary circuit as described above.

Description

The present invention relates to a method for internal cleaning of a fluid piping system said fluid being intended to take part in a technical process, and which method com- prises generating a turbulent flow of the fluid in the piping system, where the turbulent flow comprises several series of pulsations, each series running over a certain period of time and with predetermined intervals between successive series of pulsations.

The present invention also relates to a plant for internal cleaning of a fluid piping system by means of the method according to the invention.

Methods and systems for internal cleaning of piping systems for fluid media are known. The cleaning may take place in many ways, but one way is to expose the fluid to pulsations so that a strong turbulent flow is created in the piping system. The strong turbulent flow implies that impurities adhering to the inside of the piping system are torn loose and flushed away by the fluid in the piping system. Afterwards, the fluid has to be filtered to remove the impurities.

Known methods utilise plants that are successively coupled to different places in the piping system so that all of the piping system is cleaned successively. This implies that the fluid in the parts of the piping system being cleaned cannot take part in any technical processes apart from the cleaning process. This is a drawback as it is necessary to interrupt the technical process like oil extraction or refining on production platforms and on onshore drilling rigs, or in refineries. This implies considerable costs due to missing production in the period of time where the cleaning takes place.

WO 88/07633 describes a device which not directly concerns the cleaning of piping systems, but concerns exchange of oil in a hydraulic cylinder. The exchange of the oil in the hydraulic cylinder takes place in order to supply fresh, cool oil in order to increase the efficiency of the hydraulic cylinder. The oil exhange takes place via a bypass valve through which an amount of fresh oil is supplied from a reservoir while at the same time an amount of used oil is discharged from the hydraulic cylinder.

As compared with the present invention, this device only has the similar feature that a flow of oil takes place in a piping system, in the known device a hydraulic cylinder with a piping system belonging to it. The technical process of which the oil forms a part consists in establishing a sur-pressure in the hydraulic cylinder and thereby a hydraulic force on a piston. However, this is not possible when the oil in the hydraulic cylinder is exchanged as the by-pass valve is open in the period of time in question, and the building-up of pressure cannot take place to a sufficient degree when the bypass valve is open. For the device this is also only of minor importance, as the device is intended as hydraulic piston in digging machines, pile driving machines, and other apparatuses which may be started quickly after the oil in the hydraulic cylinder has been changed.

It is the object of the present invention to provide a method and a plant for use with the method, which is capable of performing an internal cleaning of a fluid piping system, and where it is not necessary to stop a technical process in which the fluid is taking part.

This object is achieved with a method peculiar in that the pulsations are generated at the same time as the fluid is taking part in the technical process.

A preferred method is characterised in that the technical process takes place in a primary circuit of e.g. an oil extraction plant, the primary piping system comprising pumping of e.g. oil from an oil field, and that the turbulent flow is established in a secondary piping system of the oil extraction plant.

The use of the method according to the invention may e.g. take place in an oil extraction plant where the function of the primary piping system will be pumping of oil as the technical process. The secondary piping system will be a hydraulic security circuit comprising a first branch which is a pressurised conduit, and the second branch, which is a pressure-less return conduit. The first and the second branches are in connection with, but not necessarily connected with, the primary piping system through actuators.

A plant for use by the method is connected to a first branch and to a second branch of a secondary piping system, said first first and second branch having first ends connected to a power unit, where a fluid in the first branch of the secondary piping system has a pressure P1, and where a fluid in the second branch has a pressure level, which is less than the pressure P1, which first branch and second branch of the secondary piping system are connected to a primary piping system by a number of actuators, where the peculiar features are that the first branch and the second branch at second ends are mutually connected by a conduit extending between the second ends of the first branch and the second branch, that the pipe conduit comprises a valve which is intended for opening and closing for the passage of the fluid through the conduit from the first branch to the second branch in the secondary piping system.

In connection with large plants e.g. for oil extraction, it is possible with the method according to the invention to maintain the technical process in which the fluid in a primary piping sytem takes part, e.g. pumping of crude oil at the same time as the cleaning of the secondary piping system. This means that interruption of operations because of the need for cleaning of the secondary piping sytem is avoided.

The plant according to the invention also has the advantage that it is not necessary to do much installation work in order to perform the method according to the invention.

The valve between the first and the second branches implies that it is possible to control when the fluid has to be directed from the second end of the first branch to the second end of the second branch.

In a further preferred embodiment the plant comprises a first power unit for pumping of the fluid, the first power unit comprising an outlet that is connected to the first branch and an inlet that is connected to the second branch, which power unit is intended for establishing the pressure P1 in the first branch, and is peculiar in that the plant comprises a second power unit for pumping the fluid, and that the second power unit comprises an outlet connected to the first branch and an inlet connected to the inlet of the first power unit.

By providing a further power unit it is possible to establish sufficient turbulent flow in the piping system for building up a sufficiently large Reynolds number in order to make the cleaning of the piping system satisfactory. A further power unit implies that the first power unit of the existing plant is not overloaded at the cleaning while at the same time the magnitude of the combined force acting on the hydraulic liquid may be increased.

The invention will now be explained in detail with reference to the accompanying drawing, in which Fig. 1 is a schematic diagram of a possible embodiment of a plant according to the invention, Fig. 2 is a diagram of a first embodiment of a control unit for use in a plant ac cording to the invention, Fig. 3 is a diagram of a second embodiment of a control unit for use in a plant according to the invention, Fig. 4 is a diagram of a third embodiment of a control unit for use in a plant ac cording to the invention, and Fig. 5 is a graph with a curve for a theoretical progress of a pressure in a piping system with a plant according to the invention.

Fig. 1 is a diagram of the principle of a basic embodiment of a plant according to the invention. In a preferred embodiment, the plant is intended for internal cleaning of piping system on e.g. an oil extraction plant, which internal cleaning is called oil flushing implying flows with a Reynolds number R over 2300 in a fluid in the piping system. In the following an example of a plant according to the invention will be a cleaning plant on an oil extraction plant, and the process will be called oil flushing.

Fig. 1 shows a plant comprising a stationary power unit 1 provided with an outlet 2 and an inlet 3. The outlet has a connection to a first end 4 of a first branch 5 of a secondary piping system. In a preliminary situation, the first branch 5 of the secondary piping system is blocked at a flange 6. The inlet 3 has a connection to a first end 7 of a second branch 8 of the piping system. In a preliminary situation, the second branch 8 of the piping system is also blocked at a flange 9. The first branch 5 and the second branch 8 of the piping system constitute a secondary piping system 10 of the oil extraction plant. The first branch 5 and the second branch 8 of the piping system are provided with branches 11 having connections through actuators 13 to a primary piping system 12 of the oil extraction plant.

The stationary power unit 1 comprises a pump 14 powered by a motor 15. The pump 14 has an inlet 16 connected with a storage tank 17 for the fluid in a secondary pipe system and an outlet 18 connected with the outlet 2 for the stationary power unit 1.

Between the outlet 18 for the pump 14 and the outlet 2 for the stationary power unit 1, there is mounted a check valve 19 and a filter 38. Between the outlet 18 of the pump 14 and the check valve 19 there is mounted an overflow valve 21 in a side branch 20 between the outlet 18 and the storage tank 17. A pressure accumulator 22 which in the shown embodiment is a bladder accumulator or a piston accumulator is connected between the check valve 19 and the outlet 2 for the stationary power unit 1. A pressure switch 23 is also connected between the check valve 19 and the outlet 2 of the stationary power unit 1. The pressure switch 23 is intended to control the pressure in a first branch 5 of a secondary piping system 10 between operating pressure P(max.) and a minimum operating pressure P(min.). The inlet 7 of the power unit 1 has a connection to the storage tank 17. Between the inlet 7 of the power unit 1 and the storage tank 17, there is mounted a filter 24. The stationary power unit 1 is intended to maintain a certain operating pressure in a first branch 5 of a secondary piping system 10. The second branch 8 of the secondary piping system 10 is pressure-less.

The arrangement described above constitutes a known secondary circuit 10 for an oil extraction plant. The plant according to the invention is furthermore provided with a pipe conduit 26 coupled to the flanges 6,9, and which is able to establish a passage for the fluid in the secondary piping system 10 between a second end 25 of the first branch 5 and a second end 27 of the second branch 8. In the conduit 26 and between the second end 25,27 of the first branch 5 and the second branch 8, respectively, there is mounted a filter 28 and an automatic valve 29. The automatic valve 29 is controlled by a control unit 30 (see Figs. 2-4).

In a preferred embodiment, the plant according to the invention is furthermore, as illustrated, provided with a further power unit 31 coupled to the first branch 5 in parallel with the stationary power unit 1. The further power unit 31 comprises also a pump 32 driven by a motor 33. The pump 32 has an outlet 34 which likewise is in connection with the first branch 5 of the secondary piping system 10. Between the pump 32 and the secondary piping system 10, there are likewise mounted a check valve 35 and a filter 39. An accumulator 36 is also coupled to the outlet 34 for the pump between the filter 39 and the check valve 35. The pump 32 has an inlet 37 which is likewise connected to the storage tank 17. The further power unit 31 is connected in parallel with the stationary power unit in order to establish sufficient flow speeds in the secondary power unit 10 at the cleaning of the piping system.

When the piping system is to be cleaned this takes place by a method according to the invention. Cleaning takes place by opening the automatic valve 29 at a given time and within a given period. The time of the opening of the valve and the period of the open state of the valve are determined by empiric data for the piping system in question, of the fluid in the piping system, and of the requirements to the cleaning of the piping system.

A given pressure P1 in a first branch 5 is built up before oil flushing is performed.

When the pressure has attained an empirically determined upper value P3, the pressure is maintained for a period in order to ensure that no pressure drop takes place in the secondary piping system 10 as a result of the operation of the actuators 13. When it has been ensured that the pressure P3 in the first branch 5 is maintained the automatic valve 29 is opened. The fluid in the secondary piping system 10 which in this case is oil, next flows from the other end 25 of the first branch 5 to the second end 27 of the second branch 8 through the filter 28 and through the automatic valve 29.

When the automatic valve 29 is opened there is created a strong current in the first branch S and the second branch 8. The strong current implies the creation of a turbulent flow of the fluid in the first branch S and the second branch 8 and with a Reynolds number R over 2300, preferably over 3000. The turbulent flow causes impurities in the piping system to be torn loose and taken along by the fluid. When the pressure in the first branch 5 has dropped to an empirically determined lower value P2, the automatic valve 29 is shut off. Next, a new building-up of pressure takes place in the first branch 5, whereafter the process is repeated. The building up of pressure to the upper value for the pressure P3 in the first branch 5 takes place by means of both the stationary power unit 1 and the further power unit 39.

Fig. 2 shows a first embodiment for a control unit 30 for the automatic valve 29 (see Fig. 1). The control unit 30 comprises a transformer 40 for transforming a signal 41 from a pressure gauge (not shown) in the first branch 5 to a signal 42 for a microprocessor 43. The microprocessor 43 contains empirical or recorded data for the duration of the period in which the automatic valve 29 is to be open, and for the duration of the period between the periods in which the automatic valve 29 is open. Data may be recorded by means of a control panel 44 with buttons 45 and a display 46. The control unit 30 also comprises a control unit 47 for, on the basis of a control signal 48 from the microprocessor 43, performing control of an actuator 49 by means of a control signal 50.

In the shown embodiment, the actuator comprises a first pneumatic valve 51 and a second pneumatic valve 52. The first pneumatic valve 51 and the second pneumatic valve 52 are coupled in parallel. The actuator also comprises a pneumatic cylinder 53 with piston 54 and a mechanical spring 58. An air supply 55 for the pneumatic cylinder 53 is connected to the actuator.

The pressure gauge (not shown) transmits a signal 41 to the transformer 40 concerning a current pressure P1 in the first branch 5. The transformer 40 is provided with a stabiliser 56 that registers whether the current pressure P1 is maintained for a sufficiently long period of time, and thus is stable. The transformer 40 hereafter transmits a signal 42 to the microprocessor 43 that a current pressure P 1 has been attained in the first branch and that the pressure P l is stable. The microprocessor 43 hereafter determines if the current pressure P1 corresponds to a given upper operating pressure P3. If this is the case, the microprocessor 43 transmits a signal 48 to the control unit 47 for opening the automatic valve 29. The control unit 47 hereafter transmits a signal to the pneumatic valves 51,52 for conducting air from the air supply 55 to the pneumatic cylinder 53. Thereafter, the pneumatic valves 51,52 are opened and air is conducted from the air supply 55 to the pneumatic cylinder 53. Then the pneumatic cylinder 53 activates the piston 54 in the pneumatic cylinder 53 by sliding the piston 54 forwards in the pneumatic cylinder 53, whereafter the piston 54 activates the automatic valve 29. The fluid in the secondary piping system 10 (see Fig. 1) then flows with great speed from the second end 25 of the first branch 5 to the second end 27 of a second branch 7 through the conduit 26.

The pressure gauge transmits a continuous signal 41 to the transformer 40 about the current pressure P 1. The transformer 40 transmits a continuous signal 42 onwards to the microprocessor 43 about the current pressure P 1. The microprocessor 43 determines whether the current pressure P1 corresponds to a given lower operating pressure P2. If this is the case, the microprocessor 43 then transmits the signal 48 to the control unit 47 for closing the automatic valve 29. The control unit 47 then transmits a signal to the pneumatic valves 51,52 for conducting air from the pneumatic cylinder 53 to an air outlet 57. Then the pneumatic valves 51,52 are closed, and air is conducted from the pneumatic cylinder 53 to the air outlet 57. Then the pneumatic cylinder 53 deactivates the piston 54 in the pneumatic cylinder 53, whereafter the piston 54 deactivates the automatic valve 29 by a sliding of the mechanical spring 58 of the piston 54 back in the pneumatic cylinder 53. Then the flow of the fluid in the secondary piping system 10 is stopped from the second end 25 of the first branch 5 to the second end 27 of the second branch 7 through the conduit 26. New building-up of pressure then takes place in the first branch 5 and the process is repeated.

Fig. 3 shows an alternative control unit for a plant according to the invention. The control unit in Fig. 3 differs i.a. by having the first pneumatic valve and the second pneumatic valve coupled in series instead of in parallel as in Fig. 2, and that the capacity is greater. The operation of the control unit in Fig. 3 is the same as the operation of the control unit in Fig. 2.

Fig. 4 shows a further alternative embodiment for a control unit for a plant according to the invention. The control unit in Fig. 4 differs from the control unit in Fig. 2 and the control unit in Fig. 3 in that deactivation of the piston in the pneumatic cylinder and thereby deactivation of the automatic valve take place by a pneumatic pressure from the air supply instead of by a mechanical force from a mechanical spring. The operation of the control unit in Fig. 4 is the same as the operation of the control unit according to Fig. 2 and Fig. 3, respectively, except for the deactivation of the automatic valve as mentioned above.

Fig. S is a graph with a curve of a theoretical progress for a pressure in the first branch in connection with cleaning by the method according to the invention. The curve extends between a lower operating pressure P2 and an upper operating pressure P3 in the first branch (see Fig. 1). The second branch (see Fig. 1) is pressure-less, and the progress for the pressure in the second branch is not shown. During a period tl a pressure P1 is added to the lower operating pressure P2 by means of the stationary power unit (see Fig. 1), and alternatively also by the further power unit, until the upper operating pressure P3 is attained. The building-up of pressure is thereafter maintained in a period t2 in order to establish whether the pressure P1 at the upper operating pressure P3 is stable. If this is the case, as illustrated, the automatic valve is opened and the pressure drops from the upper operating pressure P3 to the lower operating pressure P2 during a period t3. Hereafter, the automatic valve is closed, and the pressure P2 is maintained in a period of t4. Hereafter, the method is repeated.

During a period tS a pressure P1 is builded up again and added to a lower operating pressure P2 until the upper operating pressure P3 is reached. Again the pressure buildup is maintained in a period t6 in order to establish whether the pressure P1 is stable at the upper operating pressure P3. If this is not the case, as illustrated by a pressure drop in the period t6, the pressure P1 is rebuilt during a period t7 up to the upper operating pressure P3. The building-up of pressure is maintained again in the period t8 in order to establish if the pressure is stable at the upper operating pressure P3. If this is now the case, as illustrated by a constant pressure during the period t8, the automatic valve is opened, and the pressure drops from the upper operating pressure P3 to the lower operating pressure P2 during the period t9. Hereafter, the automatic valve is closed and the pressure P2 is maintained during a period tlO. Hereafter, the method is repeated.

The invention is described above with reference to schematic figures and to specific arrangements of embodiments for control units for plants according to the invention. It will be possible to construct control units in other ways than shown. Control units configured in other ways than described are possible. It will also be possible to omit parts of the plant according to the invention, like the further power unit or the filter in the further conduit.

Claims

1. A method for internal cleaning of a secondary fluid piping system which is connected with a primary piping system, and where a first technical process takes place in the fluid in the primary piping system at the same time as a second technical process takes place in the fluid in the secondary piping system, which method comprises generating a turbulent flow of the fluid in the second piping system, and where the turbulent flow comprises several series of pulsations, each series running over a certain period of time and with predetermined intervals between successive series of pulsations, c h a r a c t e r i s e d in that the pulsations in the fluid in the secondary piping system are generated at the same time as the fluid in the primary piping system is forming a part of the first technical process.

2. A method according to claim 1, c h ar a c t e is e d in that Reynolds number for the turbulent flow is at least 2300, preferably at least 3000.

3. A method according to any of the preceding claims, and where the secondary piping system consists of a first branch and a second branch of a circuit in the piping system, said first first and second branch having first ends connected to a power unit, where the first and and second branches via a number of actuators are connected with the primary piping system and where the first and second branches in second ends are mutually connected, c h a r a c t e r i s e d in that the first technical process takes place in the primary piping system, e.g. of an oil extraction plant, the primary piping system comprising pumping of e.g. oil from an oil field, and that the turbulent flow is established in the first branch and the second branch of the secondary piping system of the oil extraction plant.

4. A plant for internal cleaning of a piping system in a fluid plant by means of the method according to any of the preceding claims, which plant is connected to a first branch (5) and to a second branch (8) of a secondary piping system, said first first and second branch having first ends (4,7) connected to a power unit (1), where a fluid in the first branch (5) of the secondary piping system has a pressure P1, and where a fluid in the second branch (8) has a pressure level, which is less than the pressure P1, which first branch (5) and second branch (8) of the secondary piping system are connected to a primary piping system by a number ofactuators (13), c h a r a c t e r i se d in that the first branch (5) and the second branch (8) at second ends (25,27) are mutually connected by a conduit (26) extending between the second ends (25,27) of the first branch (5) and the second branch (8), that the pipe conduit comprises a valve (29) which is intended for opening and closing for passage of the fluid through the conduit (26) from the first branch (5) to the second branch (8) in the secondary piping system.

5. A plant according to claim 4, c haracte ri se d in that the valve (29) is intended for opening for passage of the fluid at a pressure P3 greater than or equal to P 1, and that the valve (29) is intended for closing for passage of the fluid at a pressure P2 which is less than or equal to the pressure P 1.

6. A plant according to claim 4 or claim 5, characteri s ed in that the conduit (26) between the first branch (5) and the second branch (8) comprises a filter (28), and that the fluid is intended for passing through the filter (28) by passing through the conduit (26) from the first branch (5) to the other branch (8).

7. A plant according to any ofthe claims 4 - 6, char ac te ri s e d in that the valve (29) consists of a shut-off valve provided with an actuator which comprises a fluid operated activation means for opening the valve, that the fluid operated activation means is intended for activation at the pressure P3, that the fluid operated activation means is intended for for deactivation at the pressure P2, and that the actuator comprises a mechanical spring element for closing the valve.

8. A plant according to any of the claims 4 - 6, c h a r a c t e r i s e d in that the valve (29) consists of a shut-off valve provided with an actuator which comprises a fluid operated activation means for opening the valve, that the fluid operated activation means is intended for activation at the pressure P3, that the actuator comprises a fluid operated activation means for closing the valve, and that the fluid operated activation means for closing the valve is intended for activation at the pressure P2.

9. A plant according to any of the claims 4 - 8, c h a r a c t e r i s e d inthatthetech- nical process in the primary piping system comprises pumping of oil, and that the technical process in the secondary piping system comprises a surveillance of the technical process in the primary piping system.

10. A plant according to any of the claims 4 - 9, which plant comprises a first power unit (1) for pumping of the fluid, the first power unit comprising an outlet (2) that is connected to the first branch (5) and an inlet (3) connected to the second branch (8), which power unit (1) is intended for establishing the pressure P1 in the first branch (5), characterised in that the plant comprises a second power unit (31) for pumping the fluid, the second power unit comprising an outlet (34) connected to the first branch (5) and an inlet (37) connected to the inlet (3) of the first power unit (1).