GB2335916A

GB2335916A - Method of flushing a fluid from a vessel

Info

Publication number: GB2335916A
Application number: GB9806816A
Authority: GB
Inventors: Ahmed Kaddani; Rebei Bel Fdhila; Said Zahari; P J Nilsen
Original assignee: Asea Brown Boveri AB
Current assignee: ABB AB
Priority date: 1998-03-30
Filing date: 1998-03-30
Publication date: 1999-10-06
Also published as: GB9806816D0

Abstract

A method of flushing a first fluid from a vessel C comprises flushing a second fluid into the vessel through a plurality of circumferentially spaced first inlets 1 to cause a first swirl in one sense, then injecting a further amount of the second fluid into the vessel through a plurality of second inlets 7 to create a second swirl that is different from the first swirl, whereby the fluids are caused to flow towards and are extracted from one end of the vessel. The method is designed for replacing sea water with a dialectric fluid in underwater electrical connectors and may involve flushing with intermediate fluids, such as distilled water and alcohol. A vessel with flushing means is also claimed.

Description

j, 1 METHOD OF FLUSHING-A FLUID FROM A VESSEL AND VESSEL WITH FLUID

FLUSHING MEANS 2335916 This invention relates to a method of flushing a fluid from a vessel and to a vessel with fluid flushing means. The invention is particularly suitable for use in connection with marine electrical connectors for flushina seawater from the connector and replacing the W seawater with a dielectric fluid, but it can be used for many other purposes.

Developments within the offshore oil and gas exploration industry have involved more and more sub-sea installations for the processing and transport of oil and gas. The sub sea installations are increasingly replacing the traditional exploration platforms in which oil and gas was transported to the platform for further processing and transport, or ftom which drilling could take place. The development of sub-sea production, processing and transport systems has resulted in an increasing need for the supply of large quantities of electrical power. However, making electrical connections beneath the sea is extremely difficult and risky, especially for three phase supplies, especially since the connections often have to be made at considerable depth using remote machines/robots.

Typically, underwater coupling devices comprise a male part and a female part or 1 perhaps two substantially identical parts with a central part located between the two identical parts and moveable between a first disconnected position and a second connected position. During. connection of these two (or three) parts under water, it is ible, without building a special enclosure, to pre.,ent ingress of x.ater into the impossi 1 coupling and accordingly, the present invention has been concel- ,..ed so that it is possible to effect the coupling while the parts of the coupling are exposed to the water and subsequently to replace the water with a dielectric medium such as ether or other insulating fluid.

1 Traditionally, marine electrical connectors are flushed out by, First replacing the original water,.Itliln the connector (nornially seawater) with distilled water. It is important to remove all the salt associated with seawater from the connector as soon as possible, since the presence of salt in an electrical connector has deleterious effect. Once the sea water has been flushed out with distilled,,,ater, the sea.,,ater is flushed out with alcohol such as ethanol, alcohol 1)Clll' Used I)Ccaiisc of its afflinity w'th,, ater so that the atcr ' 1 is 2 attracted to the flushing alcohol to remove all traces thereof. Subsequent to this second flushing operation, the alcohol is then flushed from the coupling using an insulating fluid. The preferred insulating fluid is an ester because the ester has good dielectric properties and an affinity to alcohol.

It is already known to flush out marine electrical connectors, generally along, the lines mentioned above, and for this purpose, the housing of the connector is provided w th inlet and outlet ports so located the maximum flushing is effected effect within the connector.

Because the whole flushing operation will take place usually on the seabed, perhaps at considerable depth, the whole operation is often undertaken using a remote device such as a robot. It is important that the flushing time is kept to a minimum because time is expensive and thus, flushing operations should be as efficient as possible. Furthermore, all the flushing fluids, especially alcohols and esters are expensive and hence, it is desirable that minimum quantities of flushing fluid are used. This is less important in the case of distilled water, since distilled water, after the flushing process, can be ejected into the surrounding, environment, e.g. the sea, but this is not the case with alcohols and esters, since they are pollutants.

It is also important that the flushing operation is complete. In this respect, if only a minor portion of the original fluid to be flushed remains within the coupling, then this 11 W considerably reduces the life of the coupling. Furthermore, it could e.,, en cause, especially in the case of seawater or alcohol, totally, unacceptable couplillg conditions, since neither seawater nor alcohol is dielectric and in the case of seawater, salt is corrosive. If the coupling is for three-phase electricity, then the preserice of even minute quantities of sea,,ater or alcohol is extremely harmful. Accordirigly, it is an object of the present invention to pro.,;ide a rnethod of flushing and a vessel with fluid flushing means whereby at least 99% and preferably 99.9% of the fluid to be flushed is removed from the interior of the coupling C>, According to the broadest aspect of the presci-it inventi ide a rrictliod of 1,7 ion, we provi a I-irst 11Lild from a vesscl of circular cross-sectiori. coiiil)i-isiii, zn,' the 3 steps of injecting flushing fluid into the vessel through a plurality of first inlets spaced around the central longitudinal axis of the vessel so that the flushing fluid enters the vessel and causes a swirl or swirls of fluid around the central axis in a first sense, injecting further flushing fluid into the vessel through a plurality of further inlets spaced around the said axis of the vessel so that the further fluid enters the vessel moving in a sense opposite to that from the first inlets to create a further swirl or swirls around the central axis different from the swirl or swirls from the first inlets, said injecting steps also causing a flow of fluid within the vessel towards one end thereof, and extracting fluid from said one end of the vessel.

Preferably, the injection of flushing fluid through the plurality of first inlets is through 0 four inlets equally spaced around the circumference of the vessel and the injection of fluid through the further inlets is through a pair of inlets equally, spaced around the 0 W periphery of the vessel, each of said further inlets being, located between two of the first inlets.

Preferably, the injection steps occur towards that end of the vessel opposite said one end and the injection throuGh all the inlets occurs in a direction inclined awav from said one end of the vessel.

Preferably, injection of flushing fluid through each of the inlets occurs at approximately the same distance from one end of the vessel.

According to a further aspect of the present invention, -,,ve provide a vessel with means for flushing a first fluid within the vessel from the vessel, the vessel being of generally circular cross-section and having a plurality of first inlets for flushing fluid spaced around a central longitudinal axis of the vessel and so inclined that the flushing fluid enters the vessel and causes a swirl or swirls of fluid around the central axis in a first sense, a plurality of further inlets for further flushing fluid spaced around the said axis of the vessel and so inclined that the further fluid enters the vessel movincy in a sense opposite to that from the First Inlets to create a further or s,,vIrls around the central axis different From the sv,,Ifl or swirls of the First inlets, said flushing fluid flo,,-in(y 4 through all of said inlets also causing, a flow of fluid within the vessel towards one end thereof and means for extracting fluid from said one end of the vessel.

1 Preferably, there are four first inlets equally spaced around the periphery of the vessel and substantially equally spaced from one end thereof and two further inlets equally spaced around the periphery of the vessel and preferably located between pairs of first inlets and at the same distance as the first inlets from said one end of the vessel.

Preferably also, each of the first inlets extends at approximately the same acute angle to a radial plane drawn through the vessel at the inlet, whereas each of the second inlets extends at a different acute anale to a radial plane drawn through the inlet, the further acute angle being smaller than the first mentioned angle.

c) is Preferably, the four first inlets are spaced 90' apart around the central longitudinal axis of the vessel and are thus in the form of first and second diaGonalIy opposed pairs, whereas the two second inlets comprise a third pair which are diagonally opposed to one another, on a diagonal located equi-angularly between the diagonals on which the first and second pairs are located; and the first and second pairs of inlets form an angle with the diameter on which they are located of between 30' and 90', preferably 45"-75', more preferably about 60' and ideally of 61.82', whereas the third pair form an angle with the diameter on which they are located of 0- 15', preferably W-5', more preferably of between 1' and 2' and ideally, of 1.14', but of course, so as to cause a swirl about the central longitudinal axis of the vessel in an opposite sense to that caused by the first and second pairs of inlets.

Preferably, also, each of the six inlets makes an angle with the plane defined by the three diameters on,Iiich they are located of between 45', (i.e. directed away from said one end at an angle of 45' to said plane) and -30', (i.e. directed towards said one end at an an-le of 30' to said plane), more preferably an anglc of belk.ecn 10' and 2T, and W idealIv an angle of 14.27.

1 - Preferablv, the nicans for extracting fluid from said one crid of the vessel comprises a plurality of outlet opciiiii(,s in the wall of the vessel adjacent said one crid of the vessel, the outlet openings each being connected to conduits located externally of the vessel. Preferably, each of the inlet openings also has a conduit connected thereto.

The conduits connected to the outlet openings preferably communicate with one or more annular spaces extending around the vessel from which further conduits lead to a resen,,olr for flushed fluid, whereas the conduits leading to the inlets are connected to a suitable pumping device for flushing fluid. Preferably, the pumping means and the reservoir are carried by a remote device such as a robot.

According to a preferred feature of the method of the present invention, the first fluid is not flushed continuously in a single operation from the vessel but intermittently. This means that flushing fluid is pumped to the first and second inlets continuously for a predetermined period of time, c... for 10 seconds, whereupon pumping and hence flushing is discontinued for a further period of time, e.g. for 5 seconds, whereupon is pumping, and flushing is started up again for a further period of time, e.g. for 10 seconds. It has been found that the provision of at least one time delay duning the flushing, operation provides the most efficient flushing of the vessel. More than one time delay may be provided duning the flushing operation.

It has also been found that the shape of the inlet openings to the interior of the vessel has a distinct influence on the efficiency of the flushing operation. Accordingly, it is preferred that the cross-sectional shape of each of the inlet openings, instead of being 0 p circular is rectangular so as to provide a maximum surface area of flushing fluid entering the vessel. Preferably the rectangular flushing inlets are arranged with their Ion. axis extending generally parallel to the longitudinal axis of the vessel.

c) It) _) Preferably, the vessel is a marine electrical connector for three-phase high voltage electrical supplies, for example, in the ran.e of 1 to 36 kV or hi-lier. Accordin-1v, W within the vessel there is a plurality of tenninals for caming the three phases of the 1 electrical supply. Because these terminals are easily,' corroded with seawater and the presence of salt is extremely harmful to the teniiiiials, the seawater must First be flushed frorn within tile vesscl and this is best achleved using a supply of distilled water. It has been found that distilled water 'Is the niost sultable 1Li)d l^or flushing sniall aniounts of 6 salt from the vessel. Once the vessel has been flushed through with distilled water, that must be removed in a separate flushing operation from within the vessel, since distilled water is conductive. It has been found that the best fluid for flushing out the distilled water is an alcohol. Once the vessel has been flushed through with alcohol, this must be flushed from within the vessel, since alcohol is conductive and accordingly, a dielectric material such as an ester is used in a third flushing operation.

The present invention is now described by way of example with reference to the accompanying somewhat schematic drawings, in which:- Figure 1 is a perspective view of a part of a coupling for a three-phase electricity supply, the coupling part being shown schematically only with all the electrical conducting components of the coupling being omitted for the sake of clarity; Figure 2 is a schematic perspective view illustrating the swirls achieved within the vessel; Figure 3 is a section taken on the line III-III in Figure 2, and Figure 4 is a section on the line IV-IV of Figure 2, showing the direction of the swirls.

Referring to the drawings, Figure 1 discloses a part C of a casing for a three-phase electrical supply, all of the components within the casing parts being omitted for the sake of clarity. The casing part C is generally cylindrical with a longitudinal central axis B, but is of enlarged diameter as shown at 4 at a lower or second end L, to accommodate a hollow annulus or ring (not shown) for the supply of flushing fluid. The casino, part C is arranged to cooperate with upper and lower parts (not shown) and 0 ty when assembled therewith, to form a liquid-tight vessel for use under water. Located within each of the casing parts are connector components to enable a connection in a three-phase electrical power line to be established, under water, using remote control means, such as a robot, to effect the connection. Because the connection is effected under water, the casing will become full of water, e.g. sea water and before the power line can be used, it is necessary to remove the water ftom within the casing. This is 7 achieved by injecting flushing fluid through the previously mentioned ring into the interior of the casing and extracting flushed fluid from the casing at a first end, opposite the lower end L, where the injection occurs.

In accordance with the present invention, flushing fluid is supplied to the flushing annulus through a plurality of supply pipes 2, and within the inner wall of the annulus, special inlet ports 1 and 7 are provided. Each of these inlet ports is located towards the lower end of the casing part C, there being a first pair of inlets 1 located on a first diameter 3, and a second pair of inlets 1 located on a second diameter 5,. with the diameters 3 and 5 being arranged at right-angles to each other. Hence, each of the four inlets 1 is equally spaced around the circumference of the casing part and spaced 90' from each of its two adjacent inlets 1. As is apparent from Figure 3, the preferred angle P that each inlet 1 makes with its respective diameter 3 is 61.82', but it should be appreciated that reasonably satisfactory results can be obtained, provided the angle P is within the range of 30' to 9T. Each of the inlets 1 is fed by flushing fluid through its supply pipe or conduit 2 and each of the four inlets 1 is so inclined that flushing fluid which exits through the four inlets will cause a swirl in an anti-clockwise direction relative to the longitudinal axis B of the casing portion within the casing. A third pair of second inlets 7 is also formed in the casing part C at the same level as the inlets 1, the two inlets 7 being diametrically opposed to one another on a third diameter 9 of the casing part C which diameter 9 forms an angle of 45' with each of the diameters 3 and 5. Flushino, fluid is fed to each of the inlets 7 through inlet pipes or conduits 6 and the flushing fluid enters the casing part in such a manner as to cause a counter-swirl within the casing in a clockwise sense, i.e. opposite to the sense of the swirl produced from the inlet ports 1. Each of the inlets 7 forms an angle cc of 1. 14' with the diameter on which the inlets are located, although it should be appreciated that reasonably satisfactory results can be achieved if the angle cc is anywhere within the range of 0 to 15'. It is important, however, that the swirl produced by the flushing fluid entering the casing portion from the second inlets 7 is in the opposite sense relative to i.e. around the longitudinal axis B of the casing portion, to the swirl produced by the inlets 1.

As is apparent from Figure 1, each of the three diameters on which the inlets 1 and 7 is located is arranged in the same horizontal plane adjacent the lower end L of the casing 8 portion. Furthermore, each of the inlets is slightly inclined towards the base of the casing portion (i.e. away from the end of the casing not shown) at an angle of 14.27'. Reasonable results, however, can be obtained so long as this angle is somewhere within the range of 45' to - 30', i.e. even when the angle of inclination is not towards the base of the casing portion, but is at an inclination of up to 30' to the diametrical plane, but directed away from the base towards the nonillustrated end of the casing.

While satisfactory results are obtainable by providing the apertures at the inlets 1 and 7 of a circular construction, it is preferred that the inlets are rectangular with the rectangles being upright, i.e. with their longer dimension extending parallel to the longitudinal axis D of the casing part C. Preferably, the longer dimension of the rectangle can be of the order of 10 times the length of the shorter dimension. In this way, each of the inlets 1 and 7 can extend over a major portion of the length (as measured in the direction of the longitudinal axis B of the casing part Q of the annulus in which the six inlets 1 and 7 are located.

The above-described marine electrical connector is designed for sub-sea use and hence, after the connector has been used to effect the necessary electrical connection of component parts located therein, it will be full of sea water. Before the power line in which the connector is located can be used, it is necessary to flush out the sea water and replace it with a dielectric material. Satisfactory flushing is best achieved by first replacing the sea water with distilled water, then replacing the distilled water with alcohol and then replacing the alcohol with a dielectric material. Optimum flushing is achieved by arranging for the flushing liquid to be pumped through the inlets at a rate of between 2 and 4 m/s and preferably at 2.60 m/s and arranging for the diameter of the inlets, if they are circular, to be between 4 and 7 mm or of an equivalent cross-sectional area if rectangular flattened inlets as described above are used. The most satisfactory results are achieved not by continuous flushing, but by first pumping the flushing fluid into the casing for approximately 10 seconds to achieve the swirls described above, then pausing for a period of about 5 seconds and then repeating the pumping operation for another 10 seconds. Subsequent pauses and pumping sequences may be carried out. Once the sea water has been replaced by distilled water, substantially all traces of salt will have been removed, but it is then necessary to replace the distilled water with ! 1 9 alcohol which has a good affinity to water. However, alcohol is conductive and this is then replaced by a dielectric material such as an ester. Similar flushing sequences for each liquid are preferably used.

It will, of course, be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

For example, the precise number of inlets 1 and 7 for flushing fluid, and their spacing relative to each other and around the longitudinal central axis B of the casing could be altered from the construction(s) described and illustrated.

Claims

I 1 A method of flushing a first fluid from a vessel of generally circular cross- Z section, comprising the steps of injecting flushing fluid into the vessel through a 1 W --> plurality of first inlets spaced 'around the central longitudinal axis of the vessel so that the flushing, fluid enters the vessel and causes a swirl or swirls of fluid around the central axis in a first sense, injecting further flushing fluid into the vessel through a 1 W plurality of further inlets spaced around the said axis of the vessel so that the further fluid enters the vessel moving in a sense opposite to that from the first inlets to create a lo further swirl or swirls around the central axis different from the swirl or swirls from the first inlets, said injecting steps also causing a flow of fluid within the vessel towards one end thereof, and extracting fluid from said one end of the vessel.

2. A method as claimed in claim 1 wherein, the injection of flushing fluid through 1 tl the plurality of first inlets is through four inlets equally spaced around the circumference of the vessel and the injection of fluid through the further inlets is 1 through a pair of inlets equally spaced around the periphery of the vessel, each of said further inlets bein. located between two of the first inlets.

0 -)o 1 1 1 1 1 A method as claimed 'n claim 1 or 2 wherein, the injection steps occur towards that end of the vessel opposite said one end and the injection through all the inlets occurs in a direction inclined away from said one end of the vessel.

4. A rnethod as claimed in claini 1. 2 or ') whercin, Injection of flushing fluid through each of the Inlets occurs at approximately the same distance from one end of 1 - the -essel.

5. A vessel provided \,,.ltii mcans f'oi- lliislilii,(, a First fluid \. ltlilii the vessei fron---i the vessel, the vessel being of generally circular cross-section and a plurality of First inlets for flushing fluid spaced around a central longitudinal axis of the vessel and so W inclined that the niislilii,-., fluld enters the -vessel and causes a s,,. irl or s,,,,-lrls of fluld around the central axis in a Frst sense, a or further Mlets ror further f1LISIliliki fluld spaced around the sald axis of the \.cssel.ind so Inclined tlial Ilic flirtlier lluld 11 enters the vessel moving in a sense opposite to that from the first inlets to create a further swirl or swirls around the central axis different from the swirl or swirls of the first inlets, said flushing fluid flowing through all of said inlets also causing a flow of 1 - fluid within the vessel towards one end thereof and means for extractincy fluid from said 5 one end of the vessel.

6. A vessel as claimed in claim 5, wherein four first inlets are equally spaced around the periphery of the vessel and substantially equally spaced frorn one end thereof and two further inlets are equally spaced around the periphery of the vessel.

7. A vessel as claimed in claim 6 wherein the further inlets are located between pairs of first inlets and are at the same distance as the first from said one end of the vessel.

8. A vessel as claimed in claim 6, 7 or 8 wherein each of the first inlets extends at approximately the same acute angle to a radial plane drawn through the vessel at the 1 W inlet, whereas each of the second inlets extends at a different acute angle to a radial plane drawn throu-h the inlet, the further acute angle being smaller than the first mentioned angle.

9. A vessel as claimed in claim 8 k,,.lierein the four first Inlets are spaced 90' apart around the central lon-itudinal axis of the vessel and are thus In the form of first and second diagonally opposed pairs,,. licreas the two second inlets comprise a third pair which are diagonally opposed to one another, on a diagonal located equi-angularly between the diagonals on which the first and second pairs are located.

10. A vessel as clainied in ail, one of claims 5-9 wherein the First arid second pairs o1 1 lailletcl, 011 Whicli tlicv are located oi'bet,;ccii 30' and Finlets Fol-111 ail anw-lc with the di 900 1 1 1 Irs A vcssel as clainied in anly one ol'clx'iiis 5-10 whercin the first and second pai of Inlets 1,01-111 an anole with the dianicter on which tlic are locatcd ol'l)ct-%,ccii 45'-'5.

12 12. A vessel as claimed in any one of claims 5-10 wherein the first-and second pairs of inlets form an angIewith the diameter on which they are located of about 60.

13. A vessel as claimed in any one of claims 5-12 wherein the first and second pairs of inlets form an anale with the diameter on which they are located of 61.821.

14. A vessel as claimed ill any one of claims 5-13 wherein the third pair of inlets form an angle with the diameter on which they are located of W15', is A vessel as claimed in any one of claims 5-14 wherein the third pair of inlets form an angle with the diameter on which they are located of W-5'.

16. A vessel as claimed in any one of claims 5-15 wherein the third pair of inlets form an angle with the diameter on which they are located of between 1' and 2'.

17. A vessel as claimed in any one of claims 5-16 wherein the third pair of inlets fonii an angle of 1. 14' vith the diameter on which they are located.

Z 1 18. A vessel as claimed in any,' one of the preceding claims 5-17 wherein each of the six inlets makes an angle with the plane defined by, the three diameters oil which they 0 are located of between 45', (i.e. directed away from said one end at an angle of 45' to 1 - sid plane) and -30', (i.e. directed tov,.ards said one end at all angle of 30' to said al plane).

19. A vessel as claimed ill aiillr olle of claims 5-18 wlierein each of the six inlets 1 makes all angle the plane defined by the tlirce diarneters oil %.Iiicli tlicy are located of between 10' and 20'.

20. A vessel as clain-led Ill anyone of- the preceding clalnis 5-19 xllerciii eacil of the 30 six inlets makes all angle \vith the plane defined by the three diameters on wIlich they are located of' 14.27- A vessel as claimed in any one of claims 5-20 wherein the means for extracting fluid from said one end of the vessel comprises a plurality of outlet openings in the wall of the vessel adjacent said one end of the vessel, the outlet openings each being, connected to conduits located externally of the vessel.

A vessel as claimed in any one of claims 5-21 wherein the cross-sectional shape of each of the inlet openings is circular.

23. A vessel as claimed in any one of claims 5-21 wherein the crosssectional shape of each of the inlet openings is rectangular so as to provide a maximum surface area of flushing fluid entering the vessel.

24, A vessel as claimed in claim 23 wherein the rectangular flushing inlets are arranged with their Ion. axis extending generally parallel to the longitudinal axis of the vessel.

25.

A method as claimed ill an,.,,, one of claims 1 -5,.hercin the flusliiii, (,,, fluid is not flushed continuously in a single operation from the vessel but inter- rnittently.

26. A method as claimed 'Ill claim 25 wherein the flushing fluld is pumped to the First and second inlets continuously for a peniod of 10 seconds, whereupon pumpiner 0 and hence flushin- is discontinued for a further period of 5 seconds,,- liercupoii W pumping and flushing started up again for a further period of 10 seconds.

27. 1 1 1 1 A vessel, substant ally as hercinbefore described with reference to the accompanying draw' 2S. A rriethod accordlll,,, to allY olle ol'cla'iiis 1 -S or 25 or 26 and siibstaiit'ail\. as hercinbefore described \vith i-el'ci-ciice to the accoiiipaii%,lii,, dra%-iii(IS.