Corrosion Preventing Apparatus And Method

Abstract

The present invention pertains to a splash zone coating system for the protection of metallic surfaces subject to active corrosion. More specifically, the present invention pertains to novel means for covering and coating metallic structures, e.g., pipe leg supports of an offshore oil well structure, from seawater corrosion in the splash zone of the structure which is that area subjected to intermittent contact by seawater.

Description

BACKGROUND OF THE INVENTION

The present invention pertains to that field of the art concerned with means for protecting a metallic surface subject to active corrosion by the intermittent wetting and/or splashing of water. More particularly, the present invention is concerned with the combination of novel means for covering a metallic surface subject to the corrosive action of seawater whereby the surface is constantly treated with a rust inhibiter.

A metallic structure erected in water is subject to considerable corrosion especially in those instances where the water has any degree of salinity. That part of such a structure subjected to the intermittent or frequent contact of water, either due to splashing or by tidal changes, experiences the most severe corrosion. This zone which is normally referred to as the splash zone, is defined as that existing between the highest point reached by the water due to either wave action or splashing, to the lowest point reached by air. Corrosion in this splash zone is usually most severe and difficult to protect. As is well known, for surfaces located above the splash zone, various well known corrosion systems can be employed, e.g., conventional paints, plastic coatings, and the like. Below the splash zone, corrosion can be effectively combated by cathodic protection.

There are various well known techniques and/or means for protecting a metallic structure, such as an oil well rig, from the effects of active corrosion caused by seawater which mainly attacks the supports of the structure that are located in the splash zone. For example, in the case of offshore oil rigs, their steel pilings, pipe legs, or conductor pipes can be coated with a sacrificial metal layer over its length defined within the splash zone. Or, such a surface can be covered over with a rust resistant metal coating. In either case, it can be appreciated that the initial expense of the rust resistant coating or the subsequent maintenance of the sacrificial coating is costly. The present invention provides a relatively inexpensive manner of covering such surfaces as above described whereby they can be constantly subjected to corrosion proofing by well known rust inhibitors. Further advantages and features of the present invention will become apparent as the discussion proceeds.

SUMMARY

The present Splash Zone Coating System basically comprises a flexible membrane adapted to operably fit over and around the surface of a metallic structure over its area that is subjected to intermittent contact of water. The flexible membrance defines a cavity between its inner surface and the surface of the metallic structure. Closure means are provided which is attached to the flexible membrane whereby the membrane can be conveniently attached to, over, or around the metallic structure. Sealing means operably connected to the flexible membrane are provided for sealing the flexible membrane to the metallic structure. A suitable rust inhibitor is injected into the cavity defined by the flexible membrane whereby the surface of the metallic structure is kept constantly coated with the inhibitor.

Preferred embodiments include means for filling and venting the flexible membrane, as well as means for attaching the membrane to a cylindrical surface to be protected.

DESCRIPTION OF THE DRAWING

FIG. 1 in the drawing represents an elevation view of a preferred form of the present invention as adapted for protecting a cylindrical structure.

FIG. 2 represents a sectional view taken along the line A--A of FIG. 1 showing the cavity created between the flexible membrane and the surface to be protected from corrosion by a surrounding aqueous environment.

FIG. 3 depicts a partial sectional view taken along the line B--B of FIG. 1 showing a preferred manner of sealing and protecting the end portion of the flexible membrane as it is adapted to fit around and protect a cylindrical structure.

PREFERRED EMBODIMENT

The present Splash Zone Corrosion proofing means 10 comprises the flexible membrane 11 which as shown in FIG. 1 is adapted to fit over and around the external surface of a specific metallic structure to be protected. The wrapper or jacket 11 is made of a flexible material that is capable of withstanding the elements. Additionally, the wrapper 10 is preferably a tenacious material capable of withstanding battering by vessels or objects floating in the water. A fabric reinforced synthetic rubber, such as neoprene, or a chlorosulfonated polyethylene, are preferred materials of construction. However, many other types of flexible materials can be employed as long as they are compatible with the elements and the rust inhibitor employed in the cavity between the wrapper and the metallic structure.

The jacket 11 is preferably provided with the slide fastener means 12 which extends along its edges parallel to the longitudinal axis of the oil rig pipe support 13. The slide fastener means 12 can be any suitable heavy duty slide fastener closure means which is essentially water-tight. Such means are well known and available in the art. The slide fastener means 12 can be either glued to the membrane 11 or sewn thereto with nylon thread or the like.

As shown in FIG. 2, the flexible member 11 and the metallic structure 13 form the cavity or annulus 14 therebetween. In the installation of the assembly 10, a suitable rust inhibitor is injected into the cavity 14 in the manner described hereinafter. The rust inhibitor can be any suitable material that is capable of floating on water and which has a higher affinity for metal than water. In such manner, the material will coat the metallic surface of the membrane 13 forcing the water away. The inhibitor is preferably a petroleum base hydrophobic cationic material which is readily available in the art. These materials are generally black liquids which combine mineral oils with wetting agents and rust inhibitors. Such materials will generally penetrate existing rust and displace water; adhere to and give full protection to either wet or dry surfaces; will not dry out, harden, or crack; they float as a liquid layer on top of water; and resist water washing once applied.

The present corrosion proofing means 10 also preferably comprises the inlet valve assembly 15 which is operably connected to the member 11 in any conventional or well known manner. For example, the wrapper 11 can be provided with a rubber jacketed conduit connector that is glued or sewn to the wrapper 11. Thereafter, a suitable hand operated valve is attached for achieving the mode of operations brought out below. The valve outlet assembly 16 is also preferably provided and which functions in a similar manner as the assembly 15. Likewise, it can be operably connected to the jacket 11 in a similar manner. The valve portion of the assembly 16 preferably comprises a flow check valve whereby any material in the cavity 14 can flow outwards at any time to avoid rupturing of the wrapper 11 due to over pressurization, yet avoid the re-entry of seawater, as well as acheive the mode of operation described below.

As shown in FIG. 1, the jacket 11 is also preferably provided with the inlet slit or opening 17 which in turn preferably further comprises a zipper construction 18 similar to the slide fastener means 12. The inlet 17 is provided for injecting or pouring the liquid rust inhibitor into the cavity 14. However, the inlet 17 can be dispensed with and the rust inhibitor injected in the cavity 14 via the valve assembly 15. Such an operation would naturally require more expensive equipment, consequently, the separate filling opening 17 is preferred.

Referring to FIG. 3, the flexible membrane 11 is preferably provided with the additional section 18 which is generally made up of the same material of construction as the membrane 11. The resilient member 19, preferably a sponge rubber, is provided so as to foem a seal between the membrane 11 and the external surface of the metallic structure 13. The resilient member 19 in combination with the portion 18 define the radial width of the cavity defined between the members 11 and 13. The member 18 also serves to reinforce the end portion, generally over a width of about 4 inches, from the mechanical forces induced by the strap means 20. The strap means 20 is preferably a corrosion resistant material, e.g., monel, stainless steel, or the like, which is banded around the end portion of the membrane 11 and operably clinched in position by use of various well known banding devices. Of course suitable screw operated clamping devices could be employed in lieu thereof. Moreover, the assembly could actually be glued into position with a suitable adhesive, such as an epoxy resin, or the like.

In operation, the flexible membrane 11 is first wrapped around the surface to be protected which is that area generally known as the splash zone. The slide fastener 12 is then brought together and the wrapper 11 fastened tight, for further protection the end portions are wrapped with a heavy tape, e.g., polyethylene, or the like. The band or strap means 20 is then applied. In such manner, the assembly 10 forms the enclosed cavity 14 between the external surface of the member 13 and the inner surface of the membrane 11. Since a part of the jacket 11 will extend beneath the surface of the water, it is necessary to employ a diver to secure and clamp the lower portion.

When the jacket 11 is initially placed into position and fastened shut, water will natrually be trapped between the jacket 11 and the structure 13 at a level essentially equal to that of the surrounding water. A rust inhibitor is then added to the cavity 14, preferably via the opening 17 after which the slide fastener 18 is closed.

Next, compressed air or some other suitable medium is then introduced into the jacket 11 by through of the valve assembly 15. The pressurizing medium need only be of sufficient pressure to force the water out of the cavity 14 through the exit valve assembly 16. In other words, the pressure must be sufficient to overcome the head established by the depth to which the valve assembly 16 is immersed beneath the surface of the water. The pressure forces the rust inhibitor to flow down and coat the steel to the depth established by the valve assembly 16. The valve assembly 16 being a check valve, allows the water to flow out, yet prevents back-flow thereafter.

The source of pressure is then cut off and disconnected from the valve assembly 15. Where the member 11 is tightly sealed to the structure 13, the valve assembly 15 should preferably thereafter be opened to the atmosphere. This allows the rust inhibitor to rapidly return upwards depending upon the amount of leakage back into the cavity 14. It can be appreciated that if and when water does force itself back into the cavity 14, the above sequence of operations can be repeated at desired intervals which again coat the surface of the structure 13. Recoating of the metallic surface can also be effectuated by massaging the wrapper 11 with a suitable means such as a garter spring. The massaging action will also naturally occur as the water level outside of the jacket rises above the water and rust inhibitor level inside the jacket whereby the outside water pressure will squeeze the jacket against the structure 13. This action forces these fluids within the space 14 to rise.

It will be apparent to one skilled in the art that considerable changes and modifications can be made in the above described embodiment of our invention without departing from its true scope and spirit. For example, the wrapper 11 can be made in a number of separate parts, all of which can be zippered together to form the desired diameter of wrapper. Moreover, the wrapper 11 could be binded to the structure 13 in diverse manners. Additionally, where the splash zone is defined over a considerable length, a series of superposed or stacked jackets 11 could be utilized.

Claims

We claim:

1. Means for corrosion proofing a metallic structure subject to intermittent contact by seawater, said means comprising:

a. a flexible membrane covering the metallic structure over that area subjected to intermittent contact by seawater so as to define a cavity between said flexible membrane and the metallic structure; a body of a water immiscible liquid rust inhibitor, lighter than water, in but not completely filling the cavity whereby the said area of the metallic structure will be periodically completely coated by the rust inhibitor upon the rise and fall of the seawater due to wave action and/or tidal changes and the resulting flexure of said membrance;

b. closure means fixedly attached to said flexible membrane and metallic structure and sealing off the portion of the metallic structure subject to intermittent contact by seawater; and

c. sealing means for sealing the ends of said flexible membrane to the metallic structure.

2. The corrosion proofing means of claim 1 further characterized as comprising:

d. filling means attached to said flexible membrane adjacent the top thereof whereby said water immiscible liquid rust inhibitor can be injected in the cavity defined between said flexible membrane and the metallic structure.

3. The corrosion proofing means of claim 2 wherein:

e. said filing means comprises inlet valve means connected to said flexible membrane whereby the cavity defined between said flexible membrane and the metallic structure can be pressurized; and

f. outlet valve means connected to said flexible membrane adjacent the bottom thereof for venting the cavity defined between said flexible membrane and the metallic structure.

4. The method of corrosion proofing a metallic structure subjected to intermittent contact by sea water at the surface of a body of said water, comprising the steps of:

establishing a zone around said structure, by flexible confining means, at said seawater surface of a size to extend throughout the range of change of level of said surface;

confining a body of liquid, water-immiscible corrosion inhibiting material in said zone within said confining means and in contact with said metallic structure;

excluding sea water from said zone; and

maintaining said confining means in contact with said body of water at said surface whereby movement of sea water at said surface distorts said confining means and the outer boundary of said zone and thereby agitates and produces flow of said corrosion inhibiting material along the surface of said metallic structure.

5. The corrosion proofing means of claim 1 further characterized in that said flexible membrane comprises a rubber-fabric composition.