Pipeline Flow Control System And Method

Abstract

A piping system and method having a plurality of power operated valves located substantial distance apart. The method continuously monitors pressure conditions at each valve and senses abnormal pressure conditions indicative of a line break. When such abnormal pressure conditions occur, valves on opposite sides of the break automatically close. Pressure sensing continues and if after closing certain predetermined pressure requirements are met, the valves are automatically opened. Where the system includes looped or parallel branch lines connected at their ends to upstream and downstream portions of the main lines, valves in both branch lines and also adjacent valves in the main line may close, after which all of the valves will be automatically opened, except the valves that isolate the break. Also apparatus for carrying out the method, including means for monitoring pressure conditions and means for effecting automatic closing and opening of the valve responsive to predetermined pressure conditions.

Description

BACKGROUND OF THE INVENTION

This application pertains generally to pipelines and more particularly to a system and method for controlling the flow of gas in a pipeline in the event a line breakage occurs with loss of gas.

Pipeline systems such as are used to convey natural gas and other compressible gasses commonly include a plurality of spaced apart valves, two or more of which can be closed in the event of a break in the line, thereby isolating that portion of the line in which the break occurs. U.S. Pat. No. 3,665,945, issued May 30, 1972 to the assignee herein, described an electronic control system and method for monitoring pressure conditions at a valve and effecting automatic closing of the valve if the pressure drops rapidly as it would in the event of a serious line break. Once closed, the valve remains closed until it is reopened manually. This approach works well in relatively simple systems, such as systems having only one flow line connecting two remote points.

Many pipeline systems today have one or more portions that are looped by a parallel line. In effect this provides two or more parallel branch lines connected at their ends to upstream and downstream portions of the main line. For example, such parallel lines are provided at river crossings where damage is likely to occur, to assure continued flow in the event that one of the lines is carried away or otherwise damaged. Valves are generally provided in both branch lines on the sides of the river, and also valves are located in the upstream and downstream portions of the main line near the junctions with the branch lines. The valves in the branch lines can be selectively operated to direct flow through one branch if the other branch is damaged. Other systems have two or more lines connected in parallel, together with crossover valves which permit the flow to be directed through one or more undamaged portions of the system in the event that one of the lines is broken or damaged. In systems as described above, it is necessary to have means for detecting a line break whereby valves can be operated to isolate the broken section.

The prior systems and methods described above have had a number of disadvantages. If a line break is detected, it is customary to shut down all of the valves in that part of the system affected, either by manual operation of the power operator at each valve, or by signals from a remote control station. The system then remains shut down until the break has been located and certain of the valves opened to bypass the break. This is time consuming and expensive.

SUMMARY AND OBJECTS OF THE INVENTION

In the system and method of the present invention, pressure conditions are monitored at each valve in a pipeline system, and certain valves are automatically closed in the event of a rapid drop in pressure. Thereafter, the pressure is monitored on the lower pressure side of each closed valve, and a valve is reopened if the pressure conditions on the lower pressure side meets certain predetermined requirements. Initially, when a break occurs, a number of valves may close on both sides of the break and in parallel lines. With the valves closed in this manner, the only place where the pressure will continue to drop is that section of the line where the break has occurred and the two valves adjacent to the break will remain closed. The remaining valves reopen automatically, and flow continues through the portion of the system that is free of the break.

It is in general an object of the present invention to Provide a new and improved system and method for controlling flow of gas in a pipeline system.

Another object of the invention is to provide a systeM and method of the above character which can be employed to detect a break in the line, to automatically isolate the portion of the line in which the break has occurred, and to maintain or reestablish flow in the remainder of the system.

Another object of the invention is to provide a system and method of the above character in which the operation of each valve is controlled independently and no connection other than the pipeline is required between the valves or with a remote station.

Another object is to provide a system and method particularly applicable to pipeline river crossings where looped or parallel branch lines are employed. The invention makes possible automatic isolation of a break in one branch and prompt automatic reestablished flow through the other branch or branches.

Another object is to provide means and a method for sensing pressure conditions near a line valve, and to effect automatic closing and subsequent opening under predetermined pressure conditions.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment of valve operating and control means incorporating certain features of the present invention.

FIG. 2 is a sectional view of a shuttle valve which is particularly suitable for sensing the pressure on the low pressure side of the line valve in the system shown in FIG. 1.

FIG. 3 is a block diagram showing a preferred embodiment of the rate comparitor circuit of the apparatus shown in FIG. 1.

FIG. 4 is a schematic diagram showing hydraulic means suitable for power operation of the line valve in the system shown in FIG. 1.

FIGS. 5a and 5b are schematic diagrams of a pipeline system having looped or parallel lines suitable for use at a river crossing, the valves being shown in different operating conditions.

FIGS. 6a- 6d are schematic diagrams of a pipeline having a plurality of lines and crossover stations, the valves being shown in different operating conditions.

FIG. 7 is a block diagram, illustrating a modification of a portion of the apparatus shown in FIG. 1.

FIG. 8 is a schematic diagram of a pipeline system in which the invention is utilized in connection with a compressor station.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, the valve operating and control apparatus illustrated serves to operate a gate valve 11 which controls the flow of fluid (e.g., natural gas) in a pipeline 12. This valve includes a valve body 13, aligned flow passage 14, and a valve gate connected to an operating rod movable between open and closed positions. The valve is equipped with a power operator 16 which in this instance is of the hydraulic type, such as a double-acting piston and cylinder assembly, with the piston being connected to the operating rod of the valve. The ends of the cylinder are connected to a hydraulic system 17 through hydraulic lines 18 and 19. As is discussed more fully hereinafter, system 17 serves to supply liquid under pressure to one or the other of lines 18 and 19 for operating the valve.

Means is provided for sensing the pressure conditions in pipeline 12 adjacent the valve. This preferably includes a reverse acting shuttle valve 21 which is connected to pipeline 12 through pipes 22 and 23 which connect to the line at opposite sides of the valve 11. A suitable construction for the shuttle valve is shown in FIG. 2. In that instance, it consists of a body 24 provided with end fittings 26 and 27 through which the pipes 22 and 23 are connected. The body is bored to provide a duct 28 which is in communication with pipe 42 and which also extends between the valve seats 29 and 30. Valve members 31 and 32 are secured to the ends of a rod 33 and are adapted to move between open and closed positions with respect to the seats 29 and 30. The valve members are carried by cylindrical guide members 34 and 35 which are loosely fitted within the cylindrical bores 36 and 37 of the fittings 26 and 27. These guides are shown provided with ports 38 and 39. The valve members 31 and 32 close upon either the seat 29 or 30 depending upon the difference in pressure between the gas supplied through pipes 22 and 23. Thus if pressure applied through pipe 22 is substantially higher than that in pipe 23, the valve member 31 closes upon the seat 29 and valve member 32 is moved to open position with respect to seat 30. This in effect serves to establish communication between the pipe 23 which has the lower pressure and pipe 42. Conversely, if the pressure in pipe 23 is greater than that in pipe 22, then the valve members move to the left as shown in FIG. 2 whereby member 31 is opened with respect to seat 29 and valve member 32 closed upon seat 30. This serves to establish communication between pipes 22 and 42.

The reverse acting shuttle valve 21 is connected to a pressure transducer 41 through pipe 42. In the preferred embodiment, the pressure transducer includes a pressure sensitive resistive element and a current source which passes a current of constant magnitude through a resistive element to provide a voltage having a magnitude corresponding to the static pressure in the line pressure on the low-pressure side of valve 11, as sensed by shuttle valve 21.

The output of transducer 41 is connected through a circuit 43 to a rate comparator 44 which produces an alarm signal in the event that the pressure drops at a rate corresponding to a break in the line. One particularly suitable apparatus for use as rate comparator 44 is described in detail in U.S. Pat. No. 3,666,945, issued May 30, 1972 to the assignee herein, and is shown in block form in FIG. 3. It includes an input terminal 46 to which the pressure signal is connected through circuit 43. Terminal 46 is connected to one input of difference amplifier 47 through a circuit 48. The difference amplifier receives a second input from a capacitor memory 49 through a circuit 51. The capacitor memory includes a capacitor which is charged through a circuit 52 by the difference amplifier to provide a reference signal having a level corresponding to the normal or average pressure sensed in the pipeline. In the difference amplifier, the pressure signal is compared with the reference signal, and if the level of the pressure signal drops below that of the reference signal, the amplifier delivers a signal through a circuit 53 for turning on a timing circuit 54 and a ramp generator 56. The timing circuit delivers a signal to an output terminal 57 a predetermined time (e.g., 10 to 90 seconds) after it is turned on. Ramp generator 56 produces a voltage ramp which increases in magnitude at a rate corresponding to the maximum rate of pressure drop which would ordinarily be expected to occur in the pipeline in the absence of a break. The rate at which the ramp increases can be made adjustable to accommodate different pipeline conditions and it might, for example, cover a range on the order of 10 to 20 p.s.i. per minute. The output of the ramp generator is applied to difference amplifier 47 through a circuit 58. The ramp signal is added to the pressure signal from input terminal 46, and the level of the combined signal is compared with the level of the reference signal in the difference amplifier. The relative levels of the combined and reference signals are monitored by a memory reset circuit 59 through a circuit 61. If the level of the combined signal exceeds that of the preference signal, reset circuit 59 delivers reset signals to the memory capacitor, ramp generator and timer through circuits 62 and 63.

Operation of the rate comparator shown in FIG. 3 can be described briefly as follows: Under normal conditions, that is, when there is no break in the line, difference amplifier 47 charges the memory capacitor to a level corresponding to the average static pressure in the line. Timer 54 and ramp generator 56 remain in their off conditions. If the pressure signal at input terminal 46 begins to decrease, as it would in the event of a break in the line, timer 54 and ramp generator 56 would both be turned on. The output of the ramp generator is then added to the pressure signal, and if the pressure signal is decreasing at a rate less than the maximum safe rate set by the ramp generator, the level of the combined signal will be greater than the level of the reference signal. In this event, memory reset circuit 59 Will turn off the ramp generator and timer, reset the ramp generator to its initial level, and reduce the level of the charge on memory capacitor 49. Thereafter, the capacitor will be recharged by the difference amplifier to a level corresponding to the average pressure in the line. If the pressure signal at input terminal 46 is decreasing at a rate greater than the maximum safe rate set by the ramp generator, timer 54 will continue to operate, and at the end of tis period (e.g., 10 90 seconds), it will deliver an alarm signal to output terminal 57 indicating a break in the line.

The output of rate comparator 44 is shown connected to a relay 66 through a circuit 67. This relay is adapted for actuation in response to an alarm signal from the rate comparator.

Means is also provided for actuating relay 66 in the event that the pressure in the line drops below a predetermined minimum level. This means includes a low pressure detector 68 which is connected to the output of pressure transducer 41 through a circuit 69 for monitoring the level of the pressure signal. Detector 68 is adapted for providing an output signal in the event that the level of the pressure signal drops below a predetermined minimum. In the preferred embodiment, this minimum is made adjustable over a range on the order of 50 to 200 p.s.i. to accommodate different pipeline conditions. The output of low pressure detector 68 is applied one input of an AND gate 71 through a circuit 72. The output of this gate is connected to alarm relay 66 through a circuit 73.

The output of relay 66 is connected to one input of an AND gate 76 through a circuit 77 and to one input of an AND gate 78 through a circuit 79. The oFtput of AND gate 76 is connected through a circuit 81 to one input of hydraulic system 17 for initiating closing of valve 11. The output of AND gate 78 is connected by a circuit 82 to an inhibit input on a time delay relay 83. This relay is adapted for delivering a signal to an output circuit 86 a predetermined time after receipt of a signal from an input circuit 84. Circuit 86 is connected to a second input of hydraulic system 17 for initiating reopening of valve 11.

Means is provided for detecting the position of gate valve 11. This means includes limit switches 87 and 88 which are mounted on the valve operator and adapted for actuation when the valve is in its fully open and fully closed positions, respectively. The limit switches are connected to the inputs of a valve position detecting relay 91 through circuits 92 and 93. This relay has one output connected to the input of time delay relay 83 through circuit 84, and it is adapted for delivering a signal to the time delay relay upon actuation of limit switch 88. Relay 91 has additional outputs connected respectively to a reset circuit 94 and to inputs of AND gates 71, 76 and 78 through circuits 96-99. The relay is adapted for delivering an enabling signal to the circuit connected to gate 76 when the valve is in its open position and for delivering enabling signal to the circuits connected to gates 71 and 78 when the valve is in its closed position. Additionally, relay 91 is adapted for delivering a signal to the circuit connected to reset circuit 94 when the valve reaches its closed position. This reset circuit has outputs connected to rate comparator 44 and alarm relay 66 through circuits 101 and 102, respectively. With specific reference to the rate comparator shown in FIG. 3, the reset signal from circuit 101 is preferably applied to an input of memory reset circuit 59. The reset signal from circuit 102 is applied to alarm relay 66 in such manner that the relay is deactivated thereby.

Operation of the apparatus shown in FIGS. 1-3 and the method involved therein can now be described as follows: Initially, it is assumed that gate valve 11 is open and that a gas, such as natural gas, is flowing normally through pipeline 12 within a normal range of static pressure (e.g., 400 - 1,100 p.s.i.). With the valve oPen, relay 91 inhibits the operation of AND gates 71 and 78, but delivers an enabling signal to AND gate 76, thereby completing the circuit between alarm relay 66 and hydraulic system 17. Shuttle valve 21 connects pressure transducer 41 in communication with the pipeline on the side of valve 11 where the pressure is lower, and the transducer provides an electrical signal corresponding to this pressure. This signal is monitored by rate comparator 44, and as long as the pressure does not drop at a rate comparator 44, and as long as the pressure does not drop at a rate indicative of a break in the line, the rate comparator produces no signal, the relay 66 remains deactivated, and line valve 11 remains open.

In the event of a pressure drop corresponding to a break in the line, rate comparator 44 delivers a signal to relay 66 which then delivers a command signal through AND gate 76 and circuit 81 to hydraulic system 17 for closing line valve 11. When the valve closes, relay 91 delivers a signal to the delay relay 83 for initiating its operation. Once its operation is initiated, relay 83 will deliver a command signal to hydraulic system 17 for reopening valve 11 a predetermined time (e.g., 90 seconds) after it closes, unless relay 83 receives an inhibiting signal from AND gate 78 during the predetermined time.

When valve 11 closes, relay 91 delivers a signal to reset circuit 94 which resets rate comparator 44 and relay 66 to their normal condition. With the valve closed, relay 91 inhibits the operation of AND gate 76, but delivers enabling signals to AND gates 71 and 78. The signal produced by transducer 41 corresponds to the pressure conditions in the pipeline on the lower pressure side of the closed valve. This signal is monitored by both rate comparator 44 and low pressure detector 68. If the pressure continues to drop faster than a predetermined maximum safe rate (e.g., 10 p.s.i. per minute) while the valve is closed, the rate comparator delivers a signal to relay 66, and this relay produces a signal which AND gate 78 applies to the inhibit input of time delay relay 83 to prevent valve 11 from reopening. In the event that the pressure on the low pressure side of the closed valve drops below a predetermined minimum (e.g., 100 p.s.i.), low pressure detector 68 delivers an alarm signal to AND gate 71. This signal actuates relay 66 which prevents the valve from reopening in the manner described above.

FIG. 4 illustrates a hydraulic system incorporated with the control apparatus for the power operation of the gate valve 11. It includes the four-way control valve 111 which controls the direction in which liquid is supplied to the hydraulic cylinder 16 through lines 18 and 19. These lines connect with the ends of the hydraulic cylinder through a check valve assembly of the type disclosed in U.S. Pat. No. 3,523,675, issued Aug. 11, 1970 to the assignee herein. The operating member of the four-way valve 111 is schematically shown operatively connected to a pneumatic operator 111a of the piston-cylinder type. Also a hand operating lever 111b is schematically indicated. Liquid under pressure is applied to the four-way valve 111 from the discharge side of a hydraulic pump 112 which connects through a check valve 113 and takes liquid from a reservoir 114. Device 115 represents a pressure relief valve which bypasses liquid back into the reservoir in the event the pump pressure becomes excessive. In addition to pump 112 there is an emergency pump 116 which when operated applies liquid through check valve 117. This pump takes liquid from the reservoir 114 and is shown provided with a crank for manual operation. The pump 112 is operatively connected to a gas motor 118.

The pneumatic operator 111a of the four-way valve is connected to normally closed solenoid operated valves 119 and 121. These valves are adapted to be opened in response to control signals received through circuits 81 and 86, respectively, which in turn are energized by the circuitry 122, which represents the circuitry of FIG. 1. The two sides of the pneumatic operator 111a connect with the discharge sides of solenoid valves 119 and 121 through lines 123 and 124. Gas under pressure is supplied to the solenoid valves 119 and 121 from the shuttle valve 126, the ends of which are connected to the lines 22 and 23 to take gas under pressure from either side of the gate valve 11, whichever side has the higher pressure. The reverse acting shuttle valve 21, which also connects to lines 22 and 23, is shown connected to the circuitry 122 by line 127.

The line 128 which connects with shuttle valve 126 is connected with a pressure storage tank 129 through the check valve 131. Tank 129 serves to store gas under pressure, and this gas is available for operating the gas motor 118 and the various pneumatic operators even though the pressure on both sides of the gate valve 11 should drop to a relatively low value. Storage tank 129 is connected by line 132 to the solenoid valves 119 and 121 through the air filter 133 and pressure reducing regulator 134. The tank 129 is also connected by line 136 with the gas motor 118 through the valve 137 and filter lubricator 138. Valve 137 may be bypassed by manually operated valve 139. The pneumatic operator 141 for the valve 137 connects with another shuttle valve 142, the ends of which are connected to the lines 123 and 124. The valve 137 is normally urged toward and in closed position, and is opened by application of pressure to the pneumatic operator 141 from shuttle valve 142.

Operation of the complete apparatus shown in FIG. 4 is as follows. Under normal conditions no control signals are being applied by circuits 81 and 86, and valves 119, 121, 137 and 139 are normally closed. It may be explained that these valves are constructed whereby when closed the lines 123 and 124 are vented to the atmosphere. Application of a control signal to circut 81 causes valve 119 to be opened whereby gas under pressure is delivered through line 123 to the pneumatic operator 111a, thus positioning the four-way control valve 111 for delivering liquid from pump 112 to the hydraulic cylinder 16 to effect closing of the valve 11. Application of pneumatic pressure to line 123 also positions the shuttle valve 142 whereby pressure is applied to the operator 141 of valve 137, thus opening this valve whereby gas under pressure is supplied to the gas motor 118 for operating pump 112. Normally such gas is supplied from the shuttle valve 126. However, if the conditions re such that there is insufficient pressure in the line near the valve 12 to operate the pump, then sufficient gas is stored in the tank 129 to effect the desired operations. When valve 11 reaches the closed position, circuitry 122 removes the signal from solenoid 119, which closes, bleeding pressure from line 123. The bleeding of line 123 allows valve 137 to close, shutting off gas to the gas motor, even though the four-way valve remains in the same position. Valve 11 remains closed until the four-way valve 111 is moved to its other position, either manually or in response to a control signal from circuitry 122, Assuming that such a signal is received, solenoid valve 121 is opened to apply gas under pressure to line 124 and operator 111a. Thus, the four-way valve 111 is positioned whereby hydraulic liquid applied to the valve from pump 112 causes the operator 116 to open the valve. During this opening operation pressure applied from line 124 to the shuttle valve 142 permits such pressure to be applied to the operator 141 of the valve 137, and therefor this is opened to permit continuous supply of gas to the motor 118.

In FIG. 5a, the invention is shown in connection with a gas pipeline system having a main line connected by parallel branch lines 147 and 148 at a river crossing 149. Lines 147 and 148 can be suspended above the river or extended along the river bottom, as dssired. Gas such as natural gas flows through the system in the direction indicated by arrow 150, and line valve 151 and 152 are provided in main line 146 on the upstream and downstream sides of the river crossing. Line valves 153 and 154 are provided in branch line 147, and line valves 156 and 157 are provided in branch 148, the valves in each branch line being located on opposite sides of the river. Valves 151-157 are preferably gate valves similar to valve 11, and each of these valves is provided with a control system of the type illustrated in FIGS. 1-4 and described above.

Operation of the system shown in FIG. 5a and the method involved therein can be understood with reference to FIG. 5b. In the absence of a break, gas flows through the upstream section 146a and 146b of the main line, through both branch lines 147 and 148, and then through the downstream sections 146c and 146d of the main line. Now let it be assumed that a break occurs in section 147b of branch line 147 at a location 159 between valves 153 and 154. When the break occurs, the pressure will drop rapidly throughout the system, and valves 151-157 will all close, assuming that the rate of pressure drop is greater than a predetermined value. With the valves closed, pressure can continue to drop only in the section of the line where the break has occurred. The break in section 147b is illustrated as occurring close to valve 153, leaving only a short section of line between the valve and the break. Gas will escape rapidly from the short section, and the static pressure on this side of valve 153 will drop to a low value below a predetermined level. This low pressure will be detected by the control system associated with the valve 153 and prevent this valve from reopening. There is a longer section of line between valve 154 and the break, and the pressure will drop in this section as long as gas continues to escape. This continued drop in pressure is detected by the control system associated with valve 154 and, assuming that it is greater than a predetermined rate, it prevents valve 154 from reopening. With the valves closed, the pressure at the lower pressure side of valves 151, 152, 156 and 157 remains above the predetermined static pressure level and at a rate of pressure drop not indicating a break. Therefore, these valves automatically reopen a predetermined time after they are closed. Thus, valves 153 and 154 continue to isolate the section 147b of line 147 in which the break occurs, and flow is restored through the path line sections 146a, 146b, 148a, 148b, 148c, 146c and 146d.

In FIG. 6a, the invention is illustrated in connection with a pipeline system having a plurality of parallel lines together with crossover valves. Gas from a line 161 flows to a compressor station 162 from which it is delivered to parallel lines 163, 164 and 166. Crossover stations, as illustrated at 167 and 168, are provided at spaced apart locations on the downstream side of the compressor station. Such stations are preferably provided at intervals on the order of 10 to 100 miles throughout the system. At crossover station 167, line valves 171-173 are connected in series with the main lines, and valves 176-179 are connected between the lines. Similarly, at crossover station 168, valves 181-183 are connected in series with the main lines, and valves 186-189 are connected between the lines. Valves 171-180 are preferably gate valves, and they are all provided with control systems of the type illustrated in FIG. 1. If desired, the crossover valves, namely, valves 176-179 and 186-189, can be of smaller diameter than the main line valves 171-173 and 183-183.

Operation of the system shown in FIG. 6a and the method involved therein can be understood with reference to FIGS. 6b-6d. Compressor station 162 delivers gas from line 161 to the upstream sections 163a, 164a and 166a of the three main lines. During normal conditions, that is in the absence of a line break, valves 171-189 are all open, and gas flows through the entire system.

Now let it be assumed that a break occurs in section 163b, as indicated at 191 in FIG. 6b. When the break occurs, pressure drops rapidly throughout the system, and valves 171-189 all close in response to the drop. Valves 171, 178, 181 and 186 remain closed because of the low level of pressure and/or high rate of pressure drop on their low pressure sides. Valves 172-177, 179, 182, 183 and 187-189 all reopen automatically, restoring flow in all line sections except section 163b where the break occurs.

FIG. 6c illustrates a break 192 occurring in line section 164b close to crossover station 168. When the break occurs, valves 171-180 will all close as before. Valves 172, 178 and 179 will remain closed because the pressure on their low pressure side continuous to drop faster than the alarm rate, and valves 182, 186 and 187 will remain closed because of low static pressure on their low pressure side. Valves 171, 173-177, 181, 183 and 188-189 reopen, restoring flow in all line sections other than section 164b.

In FIG. 6d, a break 199 is illustrated as occurring between compressor station 162 and crossover station 167. In this figure, additional line valves 196-198 are shown connected to the main lines at the compressor station. Valves 196-198 are preferably of the gate type, and they all have control systems of the type illustrated in FIG. 1. If desired, these valves can be connected to the safety controls of the compressor for shutting the compressor down in the event of a serious line break. When break 199 occurs, valves 171-179 and 196-198 all close. Valves 181-180 may also close, depending upon the magnitude of the pressure drop at crossover station 168. Valves 173 and 177 will remain closed because of the low static pressure on their upstream side, and valve 198 will remain closed because of the rapid drop in pressure on its downstream side. Valves 171-172, 176, 178-179 and 196-197 will all reopen automatically, as will the valves at crossover station 168. Thus, flow is restored in all sections of the system except section 166a.

In the system described above, both the pressure level and the rate of pressure drop are monitored on the low pressure side of a closed valve, and the valve is prevented from reopening if either the pressure level or rate of drop indicates a break in the line. In some instances, however, it may not be necessary to sense both pressure level and rate of drop when the valve is closed, and the control system can be modified accordingly. If, for example, reopening is to be dependent only upon the rate of drop, low pressure detector 68, AND gate 71 and the circuitry associated therewith can be omitted from the apparatus shown in FIG. 1. FIG. 7 illustrates a modification of the apparatus which permits selection of the parameters to be monitored when the valve is closed. In this modification an AND gate 201 is inserted between the output of rate comparator 44 and the input of alarm relay 66, the output of the rate comparator being connected to one input of the AND gate, and the output of this gate being connected to the input of the alarm relay. Another input of AND gate 201 is connected to a circuit 202 for receiving an enabling signal from valve position detector relay 91 when valve 11 is open. A manually operable switch 203 having open and closed positions is connected between the output of the rate comparator and the input of the alarm relay. A similar switch 204 is inserted in the circuit between the output of AND gate 71 and the other input of the alarm relay.

Operation and use of the modified system shown in FIG. 7 is generally similar to that described above, except that switches 203 and 204 provide means for selectively determining whether a low pressure and/or a rapid drop in pressure will prevent the valve from reopening. The signal applied to AND gate 201 by circuit 202 enables the gate to pass the signal from the rate comparator to the alarm relay only when the valve is open. When the valve is closed, AND gate 201 is disabled, and the signal from the rate comparator can pass to the alarm relay only if switch 203 is closed. The signal from flow pressure detector 68 and AND gate 71 can pass to the alarm relay only if switch 204 is closed. Thus, if both switches are closed, either a low pressure or a rapid drop in pressure will prevent the valve from reopening. If switch 203 is closed and switch 204 is open, only a rapid drop in pressure will prevent the valve from reopening, and if switch 203 is open and switch 204 is closed, only a low pressure condition will prevent reopening.

Valves provided with automatic cycling control means may be provided upstream and downstream of a compressor station. FIG. 8 illustrates a portion of a pipeline system 206, including a compressor station 207 and valves 208 and 209 on the upstream and downstream sides of the compressor station. These valves are preferably gate valves similar to valve 11, and each of them is provided with operating and control apparatus of the type illustrated in FIGS. 1-4. In this system, if the pressure change produced by the compressor turning on or off is sufficient to cause one or both of the valves to close, the valve or valves that close will reopen automatically unless there is a break in the line.

The invention has a number of important features and advantages. Abnormal pressure conditions are sensed at each individual valve, and the valves are automatically closed to isolate a line break. The system automatically seeks out a portion of the pipeline which is free of breaks, and flow is resumed in this portion of the line. The operation of the system is fully automatic, and no connection other than the pipeline itself is required between the valves. The control apparatus for each valve can be enclosed in a cabinet mounted on the valve, and power for the electrical portion of the system can be provided by a battery in the cabinet.

Although the main and crossover valves referred to above are of the gate type, it may be desirable in some instances to employ other types of valves provided with power operators, such as ball valves having hydraulic operators of the rotary type for turning the valve ball through 90.degree.. Also, in some instances it may be desirable to employ operators energized pneumatically or electrically instead of hydraulically.

It is apparent from the foregoing that a new and improved pipeline flow control system and method have been provided. While only the presently preferred embodiments have been described herein, as will be apparent to those familiar with the art, certain changes and modifications can be made without departing from the scope of the invention as defined by the following claims.

Claims

We claim:

1. In a method for controlling the flow of fluid in a pipeline having a normally open flow control valve provided with power operating means to close and open the same, the steps of energizing the power operating means to close the valve when the static pressure in the line near the valve decreases more rapidly than a predetermined rate, sensing the pressure conditions in the line at that side of the valve of lower static pressure, and reopening the valve a predetermined time interval after it is closed when predetermined pressure requirements at said lower pressure side are met.

2. A method as in claim 1 in which the predetermined pressure requirements include the presence of static static pressure at said lower pressure side that is greater than a predetermined minimum.

3. A method as in claim 1 in which the predetermined pressure requirements include the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

4. A method as in claim 1 in which the predetermined pressure requirements includes the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum and the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

5. In a pipeline system comprising piping for conveying fluid flow under pressure, at least one valve connected in the line, power operated means for operating the valve between open and closed conditions and means for energizing said power operated means responsive to line pressure conditions, said last means including means responsive to a drop in static pressure in the line near the valve at a rate greater than a predetermined rate to energize the operating means to close the valve and means responsive to a predetermined pressure condition in the line at that side of the valve where the pressure is lower for energizing said operating means to open the valve.

6. A system as in claim 5 in which the predetermined pressure condition includes the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum.

7. A system as in claim 5 in which the predetermined pressure condition includes the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

8. A system as in claim 5 in which the predetermined pressure condition includes the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum and the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

9. A system as in claim 5 together with a fluid pressure sensing line and a fluid pressure operated device connected to said line and having fluid connections with the pipeline on opposite sides of the valve, said device serving to stablish fluid pressure communication between said sensing line and that side of the valve that is at a lower static pressure, and means for controlling the actuation of the power operating means to close and open the valve, said controlling means being pressure conditions in said sensing line.

10. A system as in claim 5 together with timing means for ensuring maintenance of the valve in closed condition for a predetermined time interval before opening of the same.

11. A system as in claim 5 wherein the means for energizing the power operated means includes means for producing an electrical signal corresponding to the static pressure in the line on that side of the valve where the pressure is lower, electronic circuit means responsive to the electrical signal for producing an alarm signal when said static pressure is either below the predetermined level or decreasing more rapidly than the predetermined rate, means for sensing the conditions of the valve, timing means responsive to the last named means for delivering a control signal to the power operated means for opening the valve a predetermined time after the valve is closed, and logic gate means connected for receiving inputs from the circuit means and the means for sensing the condition of the valve, said gate means being adapted for delivering a control signal to the power operated means for closing the valve in response to an alarm signal occurring when said valve is open and for delivering a signal to the timing means to inhibit the delivery of the control signal for opening the valve in response to an alarm signal occurring when the valve is closed.

12. In a method for controlling the flow of fluid under pressure in a pipeline having at least two flow control valves located at remote points along the line, the steps of monitoring the pressure conditions in the pipeline near each of the valves, closing both of the valves when the monitored pressure in the line decreases more rapidly than a predetermined rate, sensing the pressure at the lower pressure side of each of the closed valves, and reopening a closed valve a predetermined time interval after closing of the same when predetermined pressure requirements are met at the lower pressure side of said valve.

13. A method as in claim 12 in which the predetermined pressure requirements include the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum.

14. A method as in claim 12 in which the predetermined pressure requirements include the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

15. A method as in claim 12 in which the predetermined pressure requirements includes the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum and the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

16. In a method for controlling the operation of a plurality of valves located at spaced points along two parallel flow lines of a pipeline system, the corresponding ends of the parallel lines being connected to upstream and downstream portions of a main flow line conveying fluid under pressure, each parallel line having at least two valves located at remote points along the same and each main line portion having a main line valve, the flow of fluid being through both the parallel flow lines or through one of said lines, depending upon the condition of the valves controlling flow through the same, each valve being provided with a power operator serving to close or open the same when energized; the method starting with the valves in open position with fluid flow occurring through both parallel lines, comprising closing all of the valves in the system when the static pressure in the system decreases more rapidly than a predetermined rate, sensing the static pressure at that side of each valve of lower static pressure and reopening each valve a predetermined time interval after closing of the same when the sensed pressure meets predetermined requirements whereby in the event a line break occurs between two valves in one of the parallel lines of the system, said two valves remain closed and the other valves are reopened to continue flow through the other parallel line.

17. A method as in claim 16 in which the predetermined pressure requirements include the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum.

18. A method as in claim 16 in which the predetermined pressure requirements include the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

19. A method as in claim 16 in which the predetermined pressure requirements include the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum and the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

20. In a pipeline system having piping for conveying fluid under pressure, at least two valves connected in the line for controlling the flow of the fluid, power operated means for operating each valve between open and closed conditions, and means for energizing said power operated means in response to line pressure conditions, said last means including means responsive to a drop in static pressure in the line at a rate greater than a predetermined rate to energize the operating means to close the valve and means responsive to a predetermined pressure condition in the line on that side of the valve where the pressure is lower for energizing said operating means to open the valve.

21. A system as in claim 20 in which the predetermined pressure condition includes the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum.

22. A system as in claim 21 in which the predetermined pressure condition includes the absence of a rate of pressure drop at said lower pressure side that is greater than the predetermined maximum value.

23. A system as in claim 20 in which the predetermined pressure condition includes the presence of a static pressure at said lower pressure side that is greater than the predetermined minimum and the absence of a rate of pressure drop at said lower pressure side that is greater than the predetermined maximum value.

24. A system as in claim 20 together with a fluid pressure sensing line and a fluid pressure operated device connected to said line and having fluid connections with the pipeline on opposite sides of the valve, said device serving to establish fluid pressure communication between said sensing line and that side of the valve that is at a lower static pressure, and means for controlling the actuation of the power operating means to close and open the valve, said controlling means being pressure conditions in said sensing line.

25. A system as in claim 20 together with timing means for ensuring maintenance of the valve in closed condition for a predetermined time interval before opening of the same.

26. A system as in claim 20 wherein the means for energizing the power operated means includes means for producing an electrical signal corresponding to the static pressure in the line on that side of the valve where the pressure is lower, electronic circuit means responsive to the electrical signal for producing an alarm signal when said static pressure is either below the predetermined level or decreasing more rapidly than the predetermined rate, means for sensing the condition of the valve, timing means responsive to the last named means for delivering a control signal to the power operated means for opening the valve a predetermined time after the valve is closed, and logic gate means connected for receiving inputs from the circuit means and the means for sensing the condition of the valve, said gate means being adapted for delivering a control signal to the power operated means for closing the valve in response to an alarm signal occurring when said valve is open and for delivering a signal to the timing means to inhibit the delivery of the control signal for opening the valve in response to an alarm signal occurring when the valve is closed.

27. In a pipeline system, a main flow line for conveying fluid under pressure, said line having upstream and downstream portions, a plurality of parallel lines connected at their ends to the upstream and downstream portions of the main flow line, a main line valve connected in each main line portion for controlling the flow therein, at least two valves located at remote points along each of the parallel lines for controlling the flow of fluid therein, power operator means at each valve for closing or opening the valve when energized, and means for energizing the power operated means in response to line pressure conditions, said last means including means responsive to a drop in static pressure near the valve at a rate greater than a predetermined rate to energize the power operated means to close the valve and means response to a predetermined pressure condition in the line at that side of the valve where the pressure is lower for energizing said operator means to open the valve.

28. A system as in claim 27 in which the predetermined pressure condition includes the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum.

29. A system as in claim 27 in which the predetermined pressure condition includes the absence of a rate of pressure drop at said lower pressure side that is greater than the predetermined maximum value.

30. A system as in claim 27 in which the predetermined pressure condition includes the presence of a static pressure at said lower pressure side that is greater than the predetermined minimum and the absence of a rate of pressure drop at said lower pressure side that is greater than the predetermined maximum value.

31. A system as in claim 27 together with a fluid pressure sensing line and a fluid pressure operated device connected to said line and having fluid connections with the pipeline on opposite sides of the valve, said device serving to establish fluid pressure communication between said sensing line and that side of the valve that is at a lower static pressure, and means for controlling the actuation of the power operating means to close and open the valve, said controlling means being pressure conditions in said sensing line.

32. A system as in claim 27 together with timing means for ensuring maintenance of the valve in closed condition for a predetermined time interval before opening of the same.

33. A system as in claim 27 wherein the means for energizing the power operated means includes means for producing an electrical signal corresponding to the static pressure in the line on that side of the valve where the pressure is lower, electronic circuit means responsive to the electrical signal for producing an alarm signal when said static pressure is either below the predetermined level or decreasing more rapidly than the predetermined rate, means for sensing the condition of the valve, timing means responsive to the last named means for delivering a control signal to the power operated means for opening the valve a predetermined time after the valve is closed, and logic gate means connected for receiving inputs from the circuit means and the means for sensing the condition of the valve, said gate means being adapted for delivering a control signal to the power operated means for closing the valve in response to an alarm signal occurring when said valve is open and for delivering a signal to the timing means to inhibit the delivery of the control signal for opening the valve in response to an alarm signal occurring when the valve is closed.

34. In a method for controlling the operation of valves in a pipeline system having two parallel flow lines provided with line valves located at remote points along each line and crossover valves connected between the lines, said valves being movable between open and closed conditions for directing the flow of fluid through one or both of the lines, each valve being provided with a power operator for moving the valve between its open and closed conditions; the method, starting with the valves in their open position with fluid flow occurring through both parallel lines, comprising closing all of the valves when the static pressure in the system decreases more rapidly than a predetermined rate, sensing the static pressure at the side of each closed valve where the pressure is lower, and reopening each valve a predetermined time after the closing of the same when the sensed pressure meets predetermined requirements whereby in the event of a break in one of the lines, the valves adjacent to the break remain closed and the other valves are reopened to continue flow through the remainder of the system.

35. A system as in claim 34 in which the predetermined pressure requirements includes the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum.

36. A system as in claim 34 in which the predetermined pressure requirements includes the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

37. A system as in claim 34 in which the predetermined pressure requirements includes the presence of a tatic pressure at said lower pressure side that is greater than a predetermined minimum and the absence of a rate of pressure drop at said lower pressure side that is greater than a predetermined maximum value.

38. In a pipeline system having at least two parallel flow lines for conveying fluid under pressure, line valves located at spaced points along each of the lines and crossover valves connected between the lines for directing the flow through one or both of the parallel lines, power operated means at each valve for operating said valve between open and closed conditions, and means for energizing said powered operated means in response to line pressure conditions, said last means including means responsive to a drop in static pressure at a rate greater than a predetermined rate to energize the power operated means to close the valves, and means responsive to the predetermined pressure condition in the line at the side of the valve where the pressure is lower for energizing the power operated means to open the valve.

39. A system as in claim 38 in which the predetermined pressure condition includes the presence of a static pressure at said lower pressure side that is greater than a predetermined minimum.

40. A system as in claim 38 in which the predetermined pressure condition includes the absence of a rate of pressure drop at said lower pressure side that is greater than the predetermined maximum value.

41. A system as in claim 38 in which the predetermined pressure condition includes the pressure of a static pressure at said lower pressure side that is greater than the predetermined minimum and the absence of a rate of pressure drop at said lower pressure side that is greater than the predetermined maximum value.

42. A system as in claim 38 together with a fluid pressure sensing line and a fluid pressure operated device connected to said line and having fluid connections with the pipeline on opposite sides of the valve, said device serving to establish fluid pressure communicated between said sensing line and that side of the valve that is at a lower static pressure, and means for controlling the actuation of the power operating means to close and open the valve, said controlling means being pressure conditions in said sensing line.

43. A system as in claim 38 together with timing means for ensuring maintenance of the valve in closed condition for a predetermined time interval before opening of the same.

44. A system as in claim 38 wherein the means for energizing the power operated means includes means for producing an electrical signal corresponding to the static pressure in the line on that side of the valve where the pressure is lower, electronic circuit means responsive to the electrical signal for producing an alarm signal when said static pressure is either below the predetermined level or decreasing more rapidly than the predetermined rate, means for sensing the condition of the valve, timing means responsive to the last named means for delivering a control signal to the power operated means for opening the valve a predetermined time after the valve is closed, and logic gate means connected for receiving inputs from the circuit means and the means for sensing the condition of the valve, said gate means being adapted for delivering a control signal to the power operated means for closing the valve in response to an alarm signal occurring when said valve is open and for delivering a signal to the timing means to inhibit the delivery of the control signal for opening the valve in response to an alarm signal occurring when the valve is closed.