Petroleum product transfer arm adapted emergency disconnection

Abstract: Emergency disconnection method for a petroleum product loading/unloading arm (1) comprising a fixed tubular portion (2) connected to a fixed pipeline (3) and a deformable tubular portion (4) equipped with a when-­ empty balancing system (6) provided with a coupling device (23) adapted to be connected to a mobile pipeline subject to fluctuations in position relative to the fixed piepeline, characterised in that, for a given direction of flow of a fluid in the arm, the flow is shut off (30) in an upstream area of the arm and, from this shut-off area, at least virtually all of the fluid contained in the deformable tubular portion (4) is propelled into a downstream area (5) of the arm by means of a scraper.

Description: The invention concerns loading/unloading arms used to transfer petroleum products between two pipelines that are mobile relative to each other and respectively carried, in practice, by a ship and a quay. It is more particularly concerned with emergency disconnection of such arms. These arms essentially comprise a fixed tubular portion adapted to be connected to the fixed pipeline and, connected to this fixed tubular portion by a rotary joint, a deformable mobile tubular portion formed in practice by three consecutive tubes articulated to each other by a rotary joint and ending with a coupling device adapted for selective connection of the arm to the mobile pipeline. Associated with the mobile deformable tubular portion is a static balancing system (usually employing a counterweight) adapted to enable the arm, when empty, to remain stable in any configuration. This is necessary for proper execution of the operations to couple up or uncouple the arm from the mobile pipeline (so that no significant force needs to be applied to hold the arm in position). During loading/unloading operations the ship carrying the mobile pipeline is of course moored to the quay to which the pipeline leads and the deformable nature of the mobile portion serves to compensate for low amplitude movements between the ship and the quay that are inevitable because of swell. The deformable tubular portion usually comprises two straight sections (approximately 10 metres long in the case of an arm with an inside diameter of 16 inches) forming a shape resembling a circumflex accent, the angle between which is variable to authorise movements with an amplitude of a few metres. Given the risk of moorings breaking, especially in bad weather, there have already been developed, for obvious safety reasons, emergency disconnection procedures directed to uncoupling the loading arm from the mobile pipeline before the arm breaks, so that the arm is protected to the greatest possible degree. Any such emergency disconnection requires purging of the arm beforehand to return it, empty, to an equilibrium configuration, the precise nature of this configuration being immaterial. Disconnecting the arm when full would inevitably result in uncontrolled movement of the mobile tubular portion totally incompatible with safety requirements in respect of personnel and equipment. It has therefore been proposed to provide a drain valve at the base of the fixed tubular portion and a "vacuum-break" valve at the top of the circumflex accent shape as defined above for venting it to atmosphere. As soon as it is realised that the moorings have broken, the pumping sets are stopped, an arm base valve is shut to isolate the loading arm from the fixed pipeline, the drain valve is opened, the vacuum-break valve is opened and the liquid contained in the arm is allowed to flow out under its own weight, partly into the mobile pipeline and partly through the drain valve into an emergency storage tank. It is only after such gravity draining that disconnection is effected. However, the operation of these valves and the subsequent gravity draining of the arm can sometimes take too long for disconnection to be effected before the arm is damaged. These operations routinely take several minutes, for example, which even if the ship drifts to only a very limited degree results in an overall drift that is outside the permissible range of relative movement. Thus in many cases this procedure is too slow to protect the loading arm until disconnection takes place, all the more so in that there is a non-negligible time lapse between the moorings breaking and the time this is detected. An object of the invention is to allow an emergency disconnection method for petroleum product loading/unloading arms comprising a fixed tubular portion connected to a fixed pipeline and an articulated tubular portion equipped with a when-empty balancing system, provided with a coupling device adapted to be connected to a mobile pipeline subject to fluctuations in position relative to the fixed pipeline. For a given direction of flow of a fluid in the arm, the flow is shut off in an upstream area of the arm and, from this shut-off area, all or virtually all of the fluid contained in the deformable tubular portion is propelled into a downstream area of the arm by means of a scraper. The use of an expulsion member disposed between the fluid to be expelled and the gas used to expel it has the advantage of avoiding any mixing of the latter and the turbulence that would inevitably result; in this way draining off is fast and total. Such method dispenses with the current practice of draining the loading arm by gravity partly in the downstream direction and partly in the upstream direction, from a high point. It will be understood that this disconnection procedure entails a small number of operations and forced expulsion of the fluid, which results in a significant timesaving. Scrapers of this kind are already known in themselves, for example from French patent FR-2.222.587, for the purpose of cleaning the inside surface of a transfer pipeline of primarily fixed configuration intended to convey selectively one or other of various liquids, oils in practice, on changing from one kind of fluid to another. However, the method recognizes the benefit of a scraper of this kind for solving the specific problem of emergency disconnection of articulated configuration loading arms despite the large number of right-angle elbow-bends that such loading arms comprise and which could seem at first sight incompatible with rapid movement of the scraper. Such a method may be derived from FR-A-2.283.857 which discloses a device which may be used for shutting off an upstream portion of the arm and for propelling a scraper. Such device is located in a T-shaped member and includes a piston the rod of which is tubular and extends forward till a cup shaped to bear on a rear portion of the scraper. Pressurized air or fluid may be injected through the tubular rod and through an opening provided in the cup at the end of the tubular rod. An object of the invention is to provide a loading/unloading arm in which the structure and location of the injection and shut off device are improved so that: there is no significant head loss in service, it allows an emergency disconnection procedure that is much faster than the known solutions, taking in practice between 30 and 60 seconds depending on the inside diameter of the arm (in practice between 6 and 24 inches, that is between 0.16 and 0.65 metres), or even less; it allows an efficient shutting off when needed, it allows a liable return of the scraper after a draining phase. The invention proposes an articulated fluid loading/unloading arm comprising a fixed tubular portion connected to a fixed pipeline and a movable tubular portion provided with a when-empty balancing system a coupling device carried by an outer swingable end of this tubular portion for coupling same to a movable pipeline having a fluctuating position with respect to the fixed pipeline, a scraper sphere and a scraper injector and fluid shut-off device connected to a fluid receiving end of the arm for shutting off fluid flow and launching the scraper in case of emergency disconnection, a scraper trapping stop member near a fluid discharge end of the arm and an injection means for returning the scraper towards the scraper injection and shut-off device, said device comprising a cylindrical casing mounted adjacent the fluid receiving end, a scraper pushing end fluid shut-off element mounted in the casing for movement between a non-blocking position at one end of the casing and a blocking position at the other end of the casing, a double acting hydraulic piston and cylinder unit mounted to a closed external end of the casing and having a piston rod connected to the scraper pushing and fluid shut-off element for use in moving said element between the two positions, and means for injecting compressed gas for propelling the scraper sphere from the element in the blocking position down to the scraper trapping stop member, said articulated fluid loading/unloading arm being characterized in that: the cylindrical casing is mounted in an elbow adjacent the fluid receiving end and having a linear pasageway axis tangentially intersecting with a curved passageway axis of the elbow, the scraper pushing and fluid shut-off element comprises a cylindrical sliding bush forming a spool valve and an ejector nozzle, and a perforated circular plate mounted between opposite ends of the cylindrical sliding bush and connected to the rod of the double acting hydraulic piston and cylinder unit, forming one chamber for holding the sphere therein and a second chamber for receiving an injection of said compressed gas. According to preferred features of the invention, which may be combined or implemented separately: the injection and shut-off device is situated in the fixed tubular portion whereas the stop member is situated near the coupling device; the injection and shut-off device is situated at the upstream end of the fixed tubular portion of the arm; the injection and shut-off device is situated near the junction between the fixed and deformable tubular portions; the injection and shut-off device is situated near the coupling device whereas the stop member is situated in the fixed tubular part; the stop member is situated near the upstream end of a valve connecting the arm to the fixed pipeline; it comprises sensors responsive to passage of the sphere near the injection and shut-off device. Objects, characteristics and advantages of the invention will emerge from the following description given by way of non-limiting example with reference to the appended drawings, in which: figure 1 is a schematic view in elevation of a loading arm in accordance with the invention particularly intended for loading petroleum products; figure 2 is a detail view of it on the cross-section line II-II; figure 3 is a detail view of another loading arm distinguished from the arm of figure 1 by the location at III of the scraper injection and shut-off device; figure 4 is a view in axial cross-section of the injection and shut-off device from figure 3, in a passive configuration; figure 5 is a similar view of it in an active configuration; figure 6 is a detail view of the free end of the loading arm from figure 1; figure 7 is a schematic view in elevation of an unloading arm in accordance with the invention particularly intended for unloading petroleum products; figure 8 is a detail view of it showing its free end; and figure 9 is another detail view of it, showing its fixed end. Figures 1 and 7 show two loading arms 1 and 1′ in accordance with the invention, differing in terms of the liquid flow direction under normal conditions of use: the arm 1 is designed for loading liquid onto a ship provided with an appropriate pipeline from a fixed storage tank to which the arm is permanently connected, whereas the arm 1′ is intended for unloading from a ship of this kind to a storage tank of this kind. In practice, loading arms are primarily dedicated to one or other only of these two opposite types of transfer. These loading arms primarily comprise a fixed tubular portion 2 or 2′ adapted to be connected to a fixed pipeline 3 or 3′ leading to a storage tank (not shown) and a deformable tubular portion 4 or 4′ ending in a coupling device 5 or 5′ designed to be connected to a second pipeline (not shown); the latter, subject to fluctuations in its position relative to the fixed pipeline 3 or 3′, is in practice carried by a ship. Associated with this deformable tubular portion is a balancing system 6 or 6′ adapted to hold this deformable position in equilibrium, irrespective of its configuration, provided that the deformable tubular portion is empty. The remainder of the description refers more particularly to figures 1 through 6, although component parts in these figures which also feature in figures 7 through 9 have the same reference numbers distinguished by a prime. The fixed tubular portion comprises, fixed to a base 7 carrying a vertical mast 8, a horizontal tubular section 9 connected to the fixed pipeline 3 by a communication valve 10, often referred to as the arm base valve, and fitted with a branch pipe equipped with a drain valve 11, and a vertical tubular section 12 inside the vertical mast 8. As seen in figure 2, these sections 9 and 12 communicate with each other through a short transverse section 13 which is connected to them by right-angle elbow-bends 14 and 15. As seen in figure 3, the vertical section 12 ends at a rotary joint 16 with a vertical axis in turn connected by elbow-bends 16A and 18A to the deformable tubular portion via a rotary joint 17 with a horizontal axis, these joints being carried by a support 8A attached to the mast 8. The deformable tubular portion 4 essentially comprises two tubes 18 and 19 connected by a horizontal axis rotary joint 20, so forming a circumflex accent shape of variable angle. One of these tubes, the so-called inside tube 18, is connected to the fixed tubular portion 2 while the other tube, the so-called outside tube 19, is connected by a horizontal axis rotary joint 21 and a vertical axis rotary joint 21A to a curved tube 22 fitted with a coupling device 23 driven by a hydraulic motor 24, or any other known type of connection/disconnection (coupling) unit. The balancing device 6 comprises a beam 25 attached to the inside tube 18 and extending beyond the rotary joint 17 together with two horizontal axis wheels 26 and 27 free to rotate relative to this beam, over which passes a cable 28 and which are respectively attached to a cantilever-type counterweight 29 and the outside tube 19. The loading arm 1 comprises a high-speed purging device 30 disposed at an upstream position and adapted in this upstream position to shut off the fluid flow which circulates in the arm and to propel the fluid contained in the deformable tubular portion 4 into a downstream area of the arm. In figures 1 and 2 this high-speed purging device is situated at the base of the arm, in the elbow-bend 14 and in an upstream extension of the transverse section 13, so as to expel the fluid contained in all of the arm to the downstream end of the bent tube 22. In the embodiment of figures 3 through 5 a comparable device 30′ is provided in an upstream extension of the elbow-bend 16A joining the two rotary joints 16 and 17. The expulsion of the fluid is therefore limited to purging the deformable tubular portion, which is sufficient to re-establish the when-empty equilibrium condition of the latter. It would in fact be equally permissible for this device 30′ to be carried by the elbow-bend 18A of the deformable tubular portion. The device 30 essentially comprises a cylindrical casing 31 attached to the elbow-bend 14 in which a sliding bush 33 with the same inside diameter as the transverse tube 13 (and the remainder of the arm) can move as a result of the operation of a double-acting actuator 32. This sliding bush 33 has a retracted position (see figure 2) in which it is completely removed from the fluid flow circulating in the arm and an advanced position in which it shuts off this fluid flow. Its sliding is facilitated by the presence of two linings 34 and 35 coming into contact with the inside wall of the cylindrical casing via annular sealing gaskets 36. In the advanced configuration the forward edge of the sliding bush (possibly together with a contracted portion of the lining 34) is inserted into a cylindrical bearing surface 37 the diameter of which is between the inside diameters of the casing 31 and the transverse section 13. This bearing surface is preferably also provided with a sealing gasket 38. The sliding bush 33 comprises a perforated bottom 39 attached to the piston rod 40 of the actuator 32. Pipes 41 and 42 are connected to a pressure source (not shown), in practice a supply of oil under pressure. Inside this bush is a sphere 43 forming a scraper which for preference is usually held in position by a ring 44 adapted to retain the sphere in the bush under normal operating conditions of the arm. The cylindrical casing 31 has a bottom wall 45 provided with a bore 46 adapted to enable injection of compressed gas, nitrogen, for example, or venting to atmosphere via pipes 47. Analogous elements 31′ through 47′ are included in the device 30′ of figures 3 through 5, the reference numbers for which are primed. Figures 4 and 5 show the presence of detectors 48 and 49 respectively adapted to respond to the presence of the sliding bush 33′ in the advanced configuration and the passage of the sphere 43′. In these figures the actuator 32′ penetrates part way into the cylindrical casing 31′. Figures 4 and 5 differ from each other in that in one the bush is in the retracted configuration and in the other in the advanced configuration. Initiation of the emergency disconnection procedure entails two immediately consecutive or even virtually simultaneous operations while the arm base valve 10 is being shut off. On the one hand, the actuator 32 is operated so as to move the sliding bush into the advanced position, so shutting off the fluid flow (this constitutes a tubular or slide valve). On the other hand, compressed gas (at a pressure of 2 to 3 bars, for example) is injected into the casing through the orifice 46, so causing downstream propulsion of this fluid with a negligible quantity of residue in the shut-off area. This expulsion, effected by the sphere itself propelled by the compressed gas, does not entail any mixing of gas and fluid, and therefore no formation of bubbles in the fluid, and is therefore of good quality. The expulsion continues up to a stop member 50 advantageously provided at the downstream end of the deformable tubular portion, situated in figure 6 in the immediate vicinity of the coupling device. This stop member, the presence of which enables re-use of the sphere, is here formed by a cross-shaped member shaped so as to arrest the sphere along two crossed semi-circles, without introducing any significant head loss under normal fluid transfer conditions. A sphere detector 51 is advantageously provided just upstream of the stop member 50 to indicate the end of the purge phase. Decoupling of the coupling device 23 can then be commanded. This completes the emergency disconnection procedure. It has been possible to verify that all of these operations, for a total length of approximately 25 m, can be completed in approximately 15 seconds (speed of movement of the sphere approximately 1.5 to 2 metres/s) which makes it possible to meet the overall target of a total of 30 seconds. To return the sphere to its initial position, where required, a flange plate 52 is fitted into the coupling device and the sphere is then propelled back by injecting compressed gas 53 between this flange plate and the sphere. When the detector 49 again senses the sphere passing it and its return into the bush, retraction of the actuator 32 or 32′ is commanded. The arm 1 is then ready for further service. The construction of the unloading arm 1′ is readily deduced from that of the loading arm 1, with the reference numbers primed. This arm comprises near the coupling device 23′, that is to say in the upstream area of the arm given the direction of flow of the fluid, an injection and shut-off device 130 of the same type as the device 30 or 30′ in the previous figures, with reference numbers increased by 100. A stop member 150 similar to the stop member 50 is provided at the base of the arm, that is to say in a downstream area thereof. In an alternative arrangement (not shown) this stop member is situated near the rotary joint 16′. A compressed gas pipe 147 runs along the arm to the device 130 while a compressed gas pipe 153 is connected to the horizontal section 9′ between the stop member 150 and the valve 10′ for return propulsion of the sphere after an emergency disconnection operation. The emergency disconnection procedure is similarly effected by shutting down the pump (not shown) downstream of the coupling device, operating the actuator 132 and injecting the sphere 143 as far as the stop member 150, while the valve 10′ is shut off and the drain valve 11′ is opened. It is obvious that the preceding description has been given by way of non-limiting example only and that numerous variations may be put forward by the man skilled in the art without departing from the scope of the invention as claimed. In particular, the coupling (connection/disconnection) unit may be replaced by a so-called "emergency disconnector" device of any type known in the loading arm art.

Claims: An articulated fluid loading/unloading arm (1, 1') comprising a fixed tubular portion (2, 2') connected to a fixed pipeline (3, 3') and a movable tubular portion (4, 4') provided with a when-empty balancing system (6, 6'), a coupling device carried by an outer swingable end of this tubular portion for coupling same to a movable pipeline having a fluctuating position with respect to the fixed pipeline, a scraper sphere and a scraper injector and fluid shut-off device connected to a fluid receiving end of the arm for shutting off fluid flow and launching the scraper in case of emergency disconnection, a scraper trapping stop member (50, 150) near a fluid discharge end of the arm and an injection means (53, 153) for returning the scraper towards the scraper injection and shut-off device, said device comprising a cylindrical casing (31, 31', 131) mounted adjacent the fluid receiving end, a scraper pushing and fluid shut-off element mounted in the casing for movement between a non-blocking position at one end of the casing and a blocking position at the other end of the casing, a double acting hydraulic piston and cylinder unit (32, 132) mounted to a closed external end of the casing and having a piston rod (40, 40', 140) connected to the scraper pushing and fluid shut-off element for use in moving said element between the two positions, and means for injecting compressed gas for propelling the scraper sphere from the element in the blocking position down to the scraper trapping stop member, said articulated fluid loading/unloading arm being characterized in that: the cylindrical casing (31, 31', 131) is mounted in an elbow adjacent the fluid receiving end and having a linear passageway axis tangentially intersecting with a curved passageway axis of the elbow, the scraper pushing and fluid shut-off element comprises a cylindrical sliding bush forming a spool valve and an ejector nozzle, and a perforated circular plate (39, 39', 139) mounted between opposite ends of the cylindrical sliding bush and connected to the rod of the double acting hydraulic piston and cylinder unit, forming one chamber for holding the sphere therein and a second chamber for receiving an injection of said compressed gas. A fluid loading arm according to claim 1, characterized by the closed end of the casing having a means (46) for communicating a source of the compressed gas to the second chamber of the spool valve. A fluid loading arm according to claim 1 or claim 2, characterized by the scraper trapping stop member comprising a pair of crossed semi-circular members (50', 150) mounted in the fluid receiving end. The fluid loading arm according to claim 3, characterized by the fluid discharge end having means (52', 153) for injecting compressed gas downstream of the semi-circular members for returning the scraper to the one chamber of the spool valve. The fluid loading arm according to claim 4, characterized in that the fluid receiving end is adjacent a stationary fluid line and that the fluid discharge end is connected to the coupling. The fluid loading arm according to claim 4, characterized in that the fluid receiving end is connected to the coupling and that the fluid discharge end is connected to a stationary fluid line. The fluid loading arm according to claim 6, characterized by the gas injecting means comprising a flange plate (52) having a gas injection port which is connectable to the coupling. Loading/unloading arm according to any one of claims 1 to 7 characterized in that the bush comprises internally, near its forward edge, a ring (44, 44', 144') for retaining the scraper in the bush adapted to retain the scraper in a stowage position during normal operation of the arm. Loading/unloading arm according to any one of claims 1 to 8 characterized in that the bush slides inside the casing by means of linings (33, 34, 33', 34', 133, 134) provided with sealing gaskets (36, 36', 136) whereas the casing comprises a sealing gasket (44, 44', 144) with which the sliding bush comes into contact in the advanced position. Loading/unloading arm according to any one of claims 1 to 9, characterized in that it comprises a detector (48, 148) responsive to when the sliding bush comes into the advanced position. Loading/unloading arm according to any one of claims 1 to 10, characterized in that it comprises in the vicinity of the injection and shut-off device and the stop member detectors (49, 149) responsive to passage of the scraper.

Inventors: LE DEVEHAT EUGENE, LE DEVEHAT, EUGENE, Le Devehat, Eugène
Applicants: FMC EUROPE, FMC EUROPE S.A.
Application year: 1988
Main classification: B67D5
IPC codes: B67D9