Variable speed pipeline pig with internal flow cavity
A pipeline pig includes a plurality of relief channels and a bypass channel extending therethrough. To regulate a speed of the pipeline pig, relief valves within the relief channels open when a differential pressure between upstream and downstream ends of the pipeline pig reaches a pre-selected minimum relief pressure. If the differential pressure reaches a pre-selected maximum relief pressure, such as when the pipeline pig encounters an obstruction, the relief valves close to allow the differential pressure to further increase to clear the obstruction. If the further increase in differential pressure is insufficient to clear the obstruction and the differential pressure reaches a pre-selected minimum bypass pressure, a bypass valve opens to permit fluid flow through the bypass channel while the relief valves are closed. Flow through the bypass channel operates to reduce turbulence and permit production through the pipeline if the pipeline pig becomes stuck and obstructs the pipeline.
1. A pipeline pig, comprising:
a housing defining a trailing end, a leading end and longitudinal axis extending therebetween;
a bypass channel extending longitudinally through the housing between the trailing end and the leading end thereof;
a bypass valve disposed within the bypass channel, wherein the bypass valve is operable to maintain a restrictive configuration in which a pipeline fluid is prohibited from flowing through the bypass channel when a differential pressure established in the pipeline fluid between the trailing end and the leading end of the housing is below a pre-selected minimum bypass pressure, and wherein the bypass valve is operable to move to a bypass configuration in which the pipeline fluid is permitted to flow through the bypass channel in response to the differential pressure reaching the pre-selected minimum bypass pressure;
at least one relief channel extending longitudinally through the housing between the trailing end and the leading end thereof; and
at least one relief valve disposed within the at least one relief channel, the at least one relief valve operable to move from a first closed configuration to an open configuration in response to the differential pressure reaching a pre-selected minimum relief pressure and operable to move from the open configuration to a second closed configuration in response to the differential pressure reaching a pre-selected maximum relief pressure, wherein the at least one relief valve prohibits flow of the pipeline fluid through the at least one relief channel when in the first and second closed configurations and permits flow of the pipeline fluid through the at least one relief channel when in the open configuration, and wherein the pre-selected minimum bypass pressure is greater than the pre-selected maximum relief pressure, and the pre-selected maximum relief pressure is greater than the pre-selected minimum relief pressure.
2. The pipeline pig according to claim 1 , wherein the at least one relief valve includes a closure member that is respectively movable between first and second seats to move the at least one relief valve between the first and second closed configurations.
3. The pipeline pig according to claim 2 , wherein the closure member is biased toward the first seat and away from the second seat by a biasing member, such that the biasing member defines the pre-selected minimum relief pressure and the pre-selected maximum relief pressure.
4. The pipeline pig according to claim 3 , wherein the pre-selected minimum relief pressure is in the range of 1 psi to 3 psi and the pre-selected maximum relief pressure is in the range of 4 psi to 6 psi.
5. The pipeline pig according to claim 1 , wherein the pre-selected minimum bypass pressure is greater than 90 psi.
6. The pipeline pig according to claim 1 , wherein the bypass channel is centrally disposed within the housing, and wherein the at least one relief channel includes a plurality of relief channels radially disposed about the bypass channel.
7. The pipeline pig according to claim 1 , wherein the bypass channel includes a tapering constriction therein such that the bypass channel defines a venturi.
8. The pipeline pig according to claim 7 , wherein the tapering constriction is defined between an outer wall of the bypass channel and a closure member of the bypass valve disposed within the bypass channel, wherein the closure member is operable to move the bypass valve between the restrictive configuration and the bypass configuration.
9. The pipeline pig according to claim 8 , wherein the bypass valve further includes a biasing member operable to maintain the closure member in contact with a bypass seat to maintain the bypass valve in the restrictive configuration.
10. The pipeline pig according to claim 9 , wherein biasing member is responsive to the differential pressure to adjust the size of the tapering constriction.
11. The pipeline pig according to claim 7 , wherein the bypass valve includes an inner wall extending through at least a portion of the bypass channel, and wherein the closure member is arranged to form a tapered profile with the inner wall when the bypass valve is in the bypass configuration.
12. A pipeline pig, comprising:
a housing defining a trailing end, a leading end and longitudinal axis extending therebetween;
at least one relief channel extending longitudinally through the housing between the trailing end and the leading end thereof, the at least one relief channel defining an annular wall;
a closure member disposed within the annular wall, the closure member operable to engage a first seat to prohibit fluid flow through the relief channel and operable to disengage the first seat to permit fluid flow through the relief channel; and
an annular space defined between the closure member and the annular wall, the annular space exhibiting a smaller cross-section than regions of relief channel upstream and downstream of the closure member such that the annular space represents a constriction for fluid flow and the relief channel defines a venture,
wherein the closure member is further operable to engage a second seat to prohibit fluid flow through the relief channel while the closure member is disengaged from the first seat, and
wherein the closure member is biased toward the first seat and away from the second seat by a biasing member, such that the biasing member is operable to passively maintain the closure member in engagement with the first seat if a differential pressure established between a trailing end and a leading end of the housing is less than a pre-selected minimum relief pressure, and operable to permit the closure member to engage the second seat if the differential pressure is greater than a pre-selected maximum relief pressure.
13. The pipeline pig according to claim 12 , further comprising a bypass channel and a bypass valve, wherein the bypass channel extends longitudinally through the housing between the trailing end and the leading end thereof, and wherein the bypass valve is operable to selectively move between restrictive and bypass configurations to respectively prohibit and permit fluid flow through the bypass channel.
14. The pipeline pig according to claim 13 , wherein the bypass valve is operable to move from the restrictive configuration to the bypass configuration in response to the differential pressure reaching a pre-selected minimum bypass pressure, and wherein the pre-selected minimum bypass pressure is greater than the pre-selected maximum relief pressure such that the bypass valve moves to the bypass configuration while the closure member is engaged with the second seat and fluid flow through the at least one relief channel is restricted.
15. The pipeline pig according to claim 12 , wherein the closure member is operably coupled to an actuator, and wherein the actuator is operable to move the closure member into engagement with the first seat when a differential pressure established between a trailing end and a leading end of the housing is less than a pre-selected minimum relief pressure, and operable to move the closure member into engagement with the second seat when the differential pressure is greater than a pre-selected maximum relief pressure.