GB2222032A

GB2222032A - Electric connector having underwater mateable parts

Info

Publication number: GB2222032A
Application number: GB8815254A
Authority: GB
Inventors: Den Steen Leon Van
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1988-06-27
Filing date: 1988-06-27
Publication date: 1990-02-21
Anticipated expiration: 2008-06-27
Also published as: NL8901595A; NO176635B; NO892651L; NO892651D0; GB2222032B; GB8815254D0; DE3921044A1; NO176635C; BR8903121A

Description

e;-UJ 4--- ELECTRIC CONNECTOR HAVING UNDERWATER MATEABLE PARTS T 5539 GBR

Peb The invention relates to an electric connector having underwater mateable parts.

Many underwater applications require the use of electric connectors having underwater mateable parts. This is particularly the case in equipment which is permanently installed on the seabed, such as used to produce oil and gas from offshore production installations. Electric connectors with underwater mateable parts are required if, in above systems, parts have to be retrievable for maintenance and/or repair.

The oldest type of underwater connector is the pin type (also referred to as pin-to-pin or pin and socket type) connector. This type is compact and virtually transparent with respect to its electrical characteristics. However, this type of connector has often failed, both in the field and in laboratory testing, and there is a reluctance to use it in long-life subsea systems. Detailed analysis reveals that failures can be traced back to three types of errors: (1) water ingress in the contact area, (2) water ingress in the cable/connector interface, (3) water ingress at miscellaneous locations.

Where-ever water ingress causes a (sea)water leakage path between two metals at different electric potential, electrochemical processes arise, causing electrochemical corrosion, gas development and, ultimately, the total failure of the connector. It is considered that errors (2) and (3) are related to poor engineering; various connector manufacturers master these problems and build connectors which are fully reliable at these points. However, the first source of errors, water ingress in the contact area, is considered to be a fundamental problem of pin-type underwater 2 mateable connectors, because it can arise from the slightest damage to seals during make-up. Such damage can easily be caused by small particles such as sandgrains.

Another connector type, with field-proven reliability, is the inductive coupler. However, it is bulkier, has limited efficiency and is applicable only to low power ratings (up to a few MA).

Yet another connector type is the capacitive connector. It has excellent reliability, which is due to the principle of using the presence of (sea)water, rather than attempting to avoid it. Furthermore it has a high efficiency and is simple to construct. However, it requires a high frequency of operation, which is acceptable at power ratings up to a few MA, but becomes a serious drawback at higher power ratings. It is recognised, therefore, that, for power ratings up to the MVA-range, such as required in seabed-installed pumpstations, there is a real need for reliable underwater electric connectors.

It is an object of the present invention to provide an underwater mateable electric connector for a large range of power ratings. It is also an object of the invention to combine the favourable electrical characteristics of the pin-type underwater electric connector with the reliability of the capacitive connector. It is another object of the invention to provide an underwater connector which is tolerant to some leakage across the seals between the connector parts.

The electric connector according to the invention comprises two separable parts. Each connector part comprises at least one electrical contact which is embedded in a body of an electric insulation material, said contact being mateable with an electrical contact of the other connector part in such a manner that surfaces of the surrounding bodies of electric insulation material face each other.

Furthermore, at least one of the connector parts comprises a cavity, formed in said surface at a selected distance from said contact, a curved metal shield, covering at least part of the wall of the cavity in the neighbourhood of the electrical contact and f! A 1; means for matching the electric potential of said shield to the electric potential of the adjacent electrical contact of the same connector part.

The invention will now be explained in more detail with reference to the accompanying drawings, in which Fig. 1 shows a conventional underwater mateable connector, Fig. 2 shows in detail the electrical contacts of the connector of Fig. 1, Fig. 3 shows a detail of a connector according to the invention, in which the contacts of both connector parts are provided with curved metal shields of approximately equal size, Fig. 4 s'-iows a detail of a variant, in which the contacts of both connector parts are provided with curved metal shields of different size, Fig. 5 shows a detail of a variant, in which the contacts of only one of both connector parts are provided with curved metal s' l_elds, Fig. 6 shows in detail a pair of curved metal shields of a connector according to the invention, Fig. 7 shows a connector according to the invention comprisin three electrical contacts, and Fig. 8 shows a connector according to the invention comprising male and a female electrical contact.

Fig. 1 shows a conventional two-contact pin-type connector of cylindrical design. The surfaces 10, 11 and 12 between both connector parts are accurately matched to sufficiently insulate contact pairs 2,6 and 3,7 from each other and from the (sea)water.

Usually, this is achieved by resilient insulating elements, i.e.

seals. In practice, however, minor damage to the seals can cause leakage of electric current between the contacts. Fig. 1 will now be discussed in detail. The male part 1 is provided with contact rings 2 and 3. The female part 5 has two contact rings 6 and 7 too which, when the male connector part 1 is inserted in the female part 5, are in contact with the contact rings 2 and 3 of the male connector part 1. Via cable/connector termination assemblies (not shown) the contact rings 2,3 and 6,7 are internally connected to, respectively, power cores 13,14 and 15,16 of electric cables 4 and 8. To ensure proper contact, one contact ring per pair is provided with a resilient element. This is known technology and will not be detailed. The female connector part 5 is provided with a channel 9 to allow water to be expelled from the female part during make-up. In order to sufficiently insulate the contact pairs 2,6 and 3,7 from one another and from the environment, adequate sealing must be present. This must be obtained from surfaces 10, 11 and 12, which are provided with seals (not separately shown). In practice, however, minor damage to the seals can cause leakage of electric current between the contacts. The imperfectness of the seal between the male and the female connector parts is symbolically indicated in Fig. 1 by an annular gap between both parts.

Detail of Fig. 1, showing part of the contact rings and the surrounding seals, is shown in Fig. 2. The sealing 11 between the two contact pairs 2, 6 and 3,7 is imperfect and any (sea)water in between the two surfaces allows electric current to leak between the contact pairs. The electric current, following the lowest impedance path, concentrates in the areas 15 and 16, causing high local field strengths at the metal/(sea)water boundary layer. This will ultimately cause failure of the connector through electrochemical corrosion.

It was explained already that minor damage to a seal may cause leakage of electric currents. The present invention, therefore, relates to a method of providing the connector with means to survive such leakage. The principle is illustrated in Fig. 3. The figure shows, just like Fig. 2, a cross-section of the boundary between the male 18 and the female 19 connector parts. Furthermore, the figure shows contact pairs 20,21 and 22, 23 and the seal in between 28. In addition, however, both connector parts are provided with curved metal shields 24, 25, 26, 27 which are, either directly or via a DC voltage source, connected to the contact rings 20 through 23 in the following way: 25 is connected to 21, 24 to 20, 27 to 23 and 26 to 22. If current leakage occurs across the seal J 28, it will no longer concentrate on small areas of the contact pairs 20,21 and 22,23, but it will run between the metal shields 2 through 27. The curvature of these shields is chosen such that a substantially constant current density is obtained over the metal surfaces. By proper material choice, frequency of operation and surface area of the shields 24 through 27, a design can be achieved that survives leakage of an alternating current across the seal 28 for prolonged periods, virtually without the occurrence of electrochemical degradation. Because the allowable current density at a metal/electrolyte interface increases with the frequency, the minimum shield size decreases with the frequency.

The contact rings and the corresponding shields as shown in Fig. 3 can be coupled directly, galvanically, or via a DC source, The direct coupling is the simplest, but requires attention with respect to electrochemical corrosion. Such corrosion can be avoided by:

(1) choosing compatible metals with respect to their potential in (sea)water. Constraints are that gold may be preferred as a contact material and another as a material for the shields. However, it is considered that gold can be alloyed with silver to become compatible with some other metals. Alternatively the shields can be constructed from the same material as the contact rings, for instance gold (or some other material with a gold coating). In that case it is possible to construct the contact rings and the electrodes as one integral part. (2) Providing an extra seal between the contact rings and the shields. The location of these seals is indicated by 30 and 31.

An alternative may be to compensate for the potential difference between the metals of the contact rings and the shields by the addition of an external DC source. DC sources may be kept at the other ends of the cables 4 and 8 in Fig. 1 if these cables are provided with extra conductors for the shields. However, this makes the connector more complex and it creates the problem of possible small voltage differentials across opposing shields (e.g. 24 and 25) because of difference in the DC sources at the cable ends. Hence direct coupling is recommended.

In Fig. 3 the shields 24, 26 are shown to have approximately the same size as the shields 25, 27. In practice, different sizes may be chosen, as shown in Fig. 4. Shield 37 is considerably smaller than shield 38.

It may even be preferred that only one of the connector parts be equipped with shields. Such a variant is shown in Fig. 5. In this particular case only the male part 39 has cavities 40 and 41 with shields 42 and 43. The female connector part 44 has a cylindrical sealing surface 45. Such a construction facilitates cleaning of the female part, for instance by a water jet. Moreover. the male part is often the retrievable part in a subsea installation. Hence, the only protective curved metal shields are in the retrievable part and they can be inspected and, if necessary, renewed.

As has been indicated hereinbefore, the curvature of the shields is chosen such that a substantially constant current density is obtained over the metal surfaces. To avoid boundary effects, the edges of the shields 34 (in Fig. 3) may be rounded of4 (not shown). If the seal 28 would be a flat plane, the ideal cross-sections of the shields 24,25 and 26,27 would form circle sectors with the boundaries 32 and 33 of the seal 28 with the cavities 35,36 coinciding with the centres of the circles.

In practice the plane of the seal 28 has a cylindrical shape and is curved downwards. This causes the optimum cross-section to be somewhat different from a true circle. Fig. 6 shows the actual cross-section 50 of the shields compared to the pure circle sector 51.

The material from which the shields are constructed should be capable of withstanding, preferably, highest possible current densities at the metal/(sea)water interface. Various metals and alloys are suitable, such as titanium, gold, platinum, Hastelloy-G and Monel. To obtain maximum allowable current densities it is recommended to sand-blast the metal surfaces of the shields thus maximising the effective surface area.

J 1 Allowable current densities for sand-blasted titanium may be 8, 80 and 800 mA/cm 2 at, respectively, 50, 1000 and 10,000 Hz.

From Fig. 3 it is clear that, upon unmating of the connector, cavities 36 and 35 become visible in, respectively, the male and the female part. One may consider to fill these cavities by some porous material, allowing the (sea)water to penetrate, so as to avoid the cavities being filled up with debris. A porous material between two metal electrodes in an electrolyte slows down the ion transfer and consequently electrochemical corrosion, which is known from electro-chemistry. However, the use of this porous material has two disadvantages; (1) the material can foul. It will be difficult to clean, as dirt and grease penetrate into the porous material and clog the pores, thus rendering the shields in-effective. (2) The condition of the shields cannot be examined anymore. Consequently it is generally preferred to leave the cavities open and clean them prior to installation.

Fig. 7 shows a three-phase implementation of the connector according to the present invention where three electrical contact pairs 71, 72, 73 are each surrounded by two pairs of metal shields 75.

Fig. 8 shows an alteyjiative implementation. This connector is a single contact pair design. The male part 80 has a contact pin 81, protected by a surrounding shield 82. The contact 83 of the female part 84 is protected by a surrounding shield 85. The sealing is achieved by O-ring 86.

From these examples it will become apparent to those skilled in the art that there are numerous possible implementations of the present invention. Accordingly it should be clearly understood that the embodiments of the invention depicted in the accompanying drawings are illustrative only.

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Claims

C L A I M S

T 5539 CBR 1. An electric connector having two underwater mateable parts, each connector part comprising at least one electrical contact which is embedded in a body of an electric insulating material, said contact being mateable with an electrical contact of the other connector part in such a manner that surfaces of the surrounding bodies of electric insulating material face each other, wherein at least one of the connector parts further comprises: - a cavity formed in said surface at a selected distance from said contact, - a curved metal shield covering at least part of the wall of the cavity in the neighbourhood of the electrical contact and - means for matching the electric potential of the shield to the electric potential of the adjacent electrical contact of the same connector part.
2. The connector of claim 1 wherein both connector parts comprise a cavity which is located such that in use adjacent cavities form a confined space, each of said adjacent cavities containing a curved metal shield which covers at least part of the wall of the cavity in the neighbourhood of the electrical contact.
3. The connector of claim 1 wherein the connector parts have a co-axial orientation, the electrical contacts consist of metal contact rings which are located at opposite sides of a cylindrical plane of separatIon between the connector parts, the cavities consist of annular grooves formed in the adjacent cylindrical surfaces of the bodies of insulation material, and the metal shields consist of dome-shaped rings.
4. The connector of claim 1 wherein each connector part comprises a plurality of electrical contacts, each contact being accompanied by at least one cavity containing a curved metal shield.
5. The connector of claim 4 wherein each contact ring of at least one connector part is accompanied by a pair of cavities containing 1 11 a curved metal shield, the cavities of each pair being located at opposite sides of the contact ring.
6. The connector of claim 1 wherein one connector part is provided with at least one male electrical contact which protrudes into a female electrical contact which is located within a recess in the body of electrical insulating material of the other connector part, the bodies of insulation material having substantially flat surfaces which face each other, and an annular shaped cavity is formed in at least one of said surfaces at a predetermined distance from said contacts.
7. The connector of claim 6 wherein both connector parts comprise a cavity, each cavity having the shape of an annular trough, and the side of each cavity in the neighbourhood of the adjacent contact being covered by a curved metal shield, the curvature of each shield being selected such that leaking currents are equally distributed over the surfaces of the shields.
8. The connector of any preceding claim wherein each shield is galvanically coupled to an adjacent electrical contact of the same connector part.
9. The connector of any preceding claim wherein the shields are made from a metal or alloy which is compatible with the material of the contacts with respect to their electric potential in an aqueous environment.
10. The connector of claim 2 wherein adjacent shields are constructed from dissimilar metals or alloys and seals are present between the contacts and the shields so as to prevent galvanic corrosion of the shields and contacts.
11. The connector of claim 2 wherein adjacent shields are constructed from the same metal and are separated from each other by an open gap of a predetermined width.
12. The connector of claim 2 wherein said shields are connected to the adjacent electrical contacts via a local DC potential source.
13. The connector of claim 2 wherein adjacent shields are constructed from dissimilar metals or alloys and the shields and contacts are connected via separate electrical conductors to remotely located DC poten tial sources of such a magnitude that the galvanic potential difference between the metals or alloys of the shields and the contacts is compensated.
14. The connector of claim 2 wherein said cavities are open and filled with water when the connector is submerged into a body of water.
15. The connector of claims 2 wherein said cavities are filled with a porous medium, said porous medium absorbing upon submersion of the connector into a body of water a sufficient amount of water to obtain constant current densities over the shields.
16. An electric connector according to claim 1 substantially as described with reference to the accompanying drawings.

1 T10/T5539M.doc Published 1990 at ThePatent Office State House. 66 71High Holborn. LondonWC1R4TP.Further copies maybe obtained from The Patent Office Sales Branch. St Ma"y Cray. Orpingtor. Ke. - FRS 3RE Pr-:j Ily TvT.;:ip:ex techniques it--- S Mary Cray. Kent. Con 187