CN1207443C - Cathodic protection methods and apparatus - Google Patents

Abstract

Apparatus, compositions and methods provide cathodic protection to a structure by placing an anode layer directly between the structure and its underlying foundation. Structures contemplated to be protected in this manner include especially very large structures such as above ground storage tanks. In one aspect of preferred embodiments, the anode layer comprises sheets of at least 85 % aluminum with other alloying elements such as magnesium (0.05 to 6 %), zinc (0.1 to 8 %), indium (0.005 to 0.03 %) and tin (0.05 to 0.2 %) added for the purposes of optimizing current yield, polarization and ease of manufacturing the sheet. In another aspect of preferred embodiments, the anode layer comprises at least two overlapping sheets.

Description

Cathode protecting process and equipment

Invention field

The present invention relates generally to corrosion phenomenon, more specifically, the present invention relates to place metal construction and surperficial protection under the etching condition.Making us interested especially is galvanic protection at the bottom of the surface storage tank jar.

Background

Know, all be easy to take place corrosion phenomenon with contacted all metal constructions of the medium with electrolyte property.Such corrosion often causes damaging metal construction, and the breaking-up of this metal construction can take place in the long time or in the short time, and this depends on existing specific etching condition.In many cases, the remarkable damage of metal construction can take place within a short period of time, even the breaking-up of this metal construction does not take place as yet.

Many structures are arranged, comprise the stiffening web of bridge, transfer lime, storage tank, concrete structure, corrosion damage easily takes place in structural steel and stake.In most of the cases, this ionogen comprises water and the wet soil that contains dissolved salt concerning said structure.

Work out many energy corrosion and reduced to the technology of minimum level.Making the corrosion of steel reduce to the most general minimum method probably is exactly painting., paint is not highly effective for the condition with immersion of burying ground, and reason may be to cause the resistance of paint to reduce event gradually because pinhole porosity and moisture are penetrated into matrix metal from corrosive medium.So the protection by paints and lacquers of steel or steel sealed construction often will replenish with the other measure that is commonly referred to galvanic protection.Those surfaces that galvanic protection also can be used for not painting.

When term " galvanic protection " was used for herein, it comprised all kinds of prevent or what reduce that the corrosion of structure in the ionogen such as water, soil or chemical solution adopt is charged method at least in part.

Put it briefly, the How It Works of cathodic protection system is to utilize a kind of electric current to tackle at structure just to be protected and the corrosion current between the ionogen.The system that two kinds of electric currents of knowing that can create antagonism are arranged basically, i.e. " sacrificial system " and " impressed current system ".In sacrificial system, this electric current is by providing at another kind of metal bigger than the metal of this structure aspect the galvanic reactivity.For example, some metals such as aluminium, magnesium and zinc all are than the more active metal of steel on galvanic reactivity, so be used as " sacrificial anode " of protection steel construction.In impressed current system, the direct current that the consumable metal is used for being provided by external power source flows in the ionogen that will transfer to structure to be protected.Be called " anode " from its those parts that flow out electric current, the protection structure then is called " negative electrode ".In the sacrificial system and impressed current system of galvanic protection, anode of the two and the atoms metal path between the negative electrode are to be used to make the electric current of this structure of protection to flow basically.

The design of cathodic protection system is subjected to the influence of many factors, these factors comprise the type of metal to be protected, electrolytical character (chemistry, physics with electricity), the existence of temperature, bacterium whether, the shape of structure, life, can be structural and maintainable.Galvanic protection realizes that method is that various metals and polymer former, band, wire rod, tape and bar are used for metal construction just to be protected.For example, the US 4,992,337 (1991) that belongs to people such as Kai Ze has told about a kind of arc spraying that is used to spray the metal or alloy that comprises magnesium, zinc, lithium and aluminium and so on that has improved.This patent is also with reference to the paper of being delivered by H.D. Si Tefansi that is entitled as " electrochemical research that utilizes the galvanic protection of spraying method "; this article publication is on the 123rd page in the proceedings of the 7th international metal spraying meeting (1974), and the application of electric arc spraying and zinc, aluminium, and the corrosion test of zinc aluminium artificial alloy coating told about in this literary composition.Further; US 4; 992; 337 with reference to the paper that is entitled as " being in the galvanic protection of the Alumetized Steel in the seawater " on the 29th page of the material property that is published in June, 1987 by P.O. Jia Telan; this article has been commented on the arc spraying coating with the aluminium coated steel that contains 5wt% magnesium, and has summed up the performance of this coating in seawater.

Use aluminium, zinc, magnesium or the band of its alloy or the galvanic protection of web,, be described in 444 (1985) at the US 4,496 that authorizes Ba Niuluo.Similarly; authorize the US5 of Ge Saite; 411; 646 (1995) have told about the galvanic protection of using the meshed anode that scribbles mixed metal oxide coating; rein in the US 5 that occupies subera with authorizing; 547,560 (1996) have told about the steel that is in the seawater and the galvanic protection of alloy, and it has used the saturated calomel electrode that contains aluminium base gallium and/or cadmium alloy.

Also known in the galvanic protection field, under limited situation, use paper tinsel, but in existing many uses of paper tinsel, it is feasible especially not having a kind of.For instance, authorize the US5 of Luo Binsi, 167,352 have told about this double wall basin structure, and outer wall aluminium foil shell wherein is installed on the ready-formed basin.The aluminium foil that Luo Binsi uses is not a self-support type, and the physical strength of this paper tinsel must be strengthened, and its way is to be coated with cold coating after it installs.After installing, need to be coated with coat this The Application of Technology scope is limited to relatively little basin (diameter is less than 100 feet) strictly because this basin is finished and through the water test using must make before the aluminium foil shell.The order of desired these items is: (1) injects basin to check seepage with water; (2) emptying basin; (3) make basin inner dry, in case inboard corrosion; (4) aluminium foil is covered jar at the bottom of on to form shell; (5) in shell formation and basin lifting process, provide interim physical support for this paper tinsel; (6) coating aluminium foil; The sealing lap, promote basin and be placed on basin on the pedestal and last (7) under the very careful situation of not damaging this paper tinsel and coating, remove the interim physical support of this paper tinsel.

Also owing to other reason, the value of technology of Luo Binsi is limited, and comprising when aluminium foil intention during as auxiliaring shell, all laps of aluminium foil must seal fully.This has greatly increased manufacture difficulty.In addition, the technology of Luo Binsi can not be used for the existing surface storage tank that the corrosion base plate is changed in requirement.

Other cathodic protection system utilizes wire rod and wire cloth to replace band, web and paper tinsel.For example; authorize people's such as cron US 5; 340; 455 (1994); with the diaphragm of a horizontally disposed cathodic protection anode placement with at jar the end; this anode is be electric interconnection rectangular, the netted or latticed copper wire that is coated with titanium metal silk or titanium cladding in labyrinth, suchlike wire and titanium bar or titanium tape.These wires all have mixed metal oxide coating or noble coatings.Bar or tape also can be applied.Preferred titanium can for example aluminium, tantalum, zirconium or niobium and alloy thereof replace with other suitable metal.

Also have, other system has changed the composition of pedestal.For example, belong to your US5 of Ruse, 174,871 (1992) have told about the protection of burying ground structure of adopting high pH backfill, and the backfill of use comprises Calucium Silicate powder, nitrocalcite and the oxyhydroxide such as calcium hydroxide or aluminium hydroxide.

In a word, although doing a large amount of work aspect the research of cathodic protection system for many years,, utilize known system can not obtain uniform protection usually.One of reason wherein is that this type systematic still has uncertain factor, because:

1. design calculation is to carry out under the resistivity conditions that ionogen " is supposed ", because actual resistor rate is along with time and jar end pressure and changing in use, this design phase at cathodic protection system is unknown;

2. the spacing between the anode is subjected to the influence of " hypothesis " resistivity; With

3. there is not a kind of method of design to be proved the distribution that can be exactly comes predicted current according to the tape on the basin steel plate and wire system.The accuracy of calculating the method for distribution of current according to the distributed anodes on the basin steel plate also is problematic.If " suppose " that resistivity is incorrect, then the correction of this system is perhaps just impossible.

The electrical resistivity range of the pedestal of system can be 10,000 ohm-cms～300,000 ohm-cms, even and in same pedestal, to another location, resistivity normally changes from a location.When electric anode is imbedded in the pedestal according to existing technology, because high volts lost is arranged between this anode and structure, so anode can not be worked satisfactorily.Power impressed anode can be used in this class high resistivity medium, but in chemical reaction process, they can produce oxygen and chlorine, and these gas accumulations are in this structure.Unless with rare gas element for example nitrogen oxygen and chlorine are thoroughly disposed, otherwise at the bottom of jar pitting can take place.Neither reality is also uneconomical for nitrogen purge and its effect of check completely.

Further; test shows; the device of impressed current cathodic protection design should not be used in the annulus of water bottom storage tank; this is because the oxygen that is produced by the power impressed anode system can remain in this sealed system, continues corrosion (reference: the paper " evaluation of guard method at the bottom of about the surface storage tank jar " that this S.R. of the riyal of Conoco Inc and Ji Fu J.H. deliver) thereby help on the material property journal of in June, 1993 whole nation corrosion engineering Shi Xiehui.

The another problem that relates to existing system is about the potential damage after anode and anode are then in being embedded in soil.Sagging in order to prevent this structure, require rammed earth on every side usually, and the compacting measure may damage anode and positive contact.The compacting measure also can influence resistivity, thereby may make it be different from the resistivity that is adopted when cathodic protection system designs.

When the protection structure is during such as this class formation of petrochemical complex storage tank, these problems are obvious especially, because the surface-area to be protected of this class formation is big, and in many difficult points relevant with the structure of this structure and pedestal.So, still have necessity of improving cathodic protection system.

Summary of the invention

The present invention relates to a kind of outer metallic surface to the structure that is subject to dielectric corrosion provides the method for galvanic protection, and comprising: a kind of anode layer is provided, and this kind anode layer is more active than this metallic surface aspect galvanic reactivity; This anode layer is placed between medium and the structure; With being arranged to, this metallic surface make the metallic surface of this anode layer and this structure have direct electric current to be connected.Wherein said structure comprises the surface storage tank that metal bottom is arranged.Below this anode layer, be provided with a pedestal, wherein comprise at least a in soil, sand, clay and the gravel.This anode layer comprises the thin plate of many overlapping placements.Wherein this anode layer comprises at least a in paper tinsel, thin plate and the sheet material.

This related structure has centre portions and the peripheral part adjacent with described medium in the method for the invention; This anode layer comprises positive plate, so that produce the cathodic protection current of x unit at adjacent centre portions; This anode layer comprises positive plate, so that produce the cathodic protection current of y unit at adjacent peripheral part, wherein x is greater than y.Wherein this anode coating has the corrosive medium face, comprises anti-corrosion coating is coated on the corrosive medium face of anode layer.Comprise anode layer is placed to directly and contact with described structure.Also comprise and utilize anode layer as dividing plate, with stop ionogen from medium flowing to this structure.Wherein said structure has load bearing component, also is included in this structure of assembling on the anode layer.

The present invention relates to come structure is provided the device of galvanic protection by between structure and its underlying foundation, directly placing anode layer, combined member and method.The expection according to said method structure of protection mainly comprises very big type structure, for example surface storage tank.

With regard to an aspect of preferred embodiment, this anode layer comprises and contains at least 85% the aluminium and the thin plate of some other alloying element, these alloying elements are magnesium (0.05～6%), zinc (0.1～8%), indium (0.005～0.03%) and tin (0.05～0.2%) for example, adding these elements is in order to obtain the best magnitude of current, polarized action and the manufacturing that is easy to thin plate.With regard to preferred embodiment on the other hand with regard to, this anode layer comprises the thin plate of at least two plies.

Many purposes of the present invention, characteristics, aspect and advantage will become more obvious owing to following detailed description and accompanying drawing to the preferred embodiments of the invention, in these accompanying drawings, and the identical identical parts of number representative.

The accompanying drawing summary

Fig. 1-A adopts SALSA ^SMThe vertical section sketch map of the storage tank of system and pedestal.

Fig. 1-B is the enlarged view of two layers of positive plate shown in Fig. 1-A.

Fig. 1-C is the sketch map of weathering resistance sealing ply that is placed on the joint of basin steel plate edge and positive plate.

Fig. 1-D is a sketch map of describing the dock positive plate of anode layer.

Fig. 1-E is the sealing ply sketch map in the overlapping interface region of two layers of positive plate.

Fig. 1-F is the sketch map of screw that is positioned at the overlapping of two layers of positive plate.

Fig. 2-A adopts SALSA relatively ^SMThe vertical section sketch map of the storage tank of system and pedestal.

Fig. 2-B is the enlarged view of three layers of positive plate shown in Fig. 2 A.

Fig. 3 is a storage tank, the corrosion in a Geju City the jar end and one use SALSA ^SMThe sketch map at the new jar end of system protection.

Detailed Description Of The Invention

According to theme of the present invention hereinafter described, comprise the system of device, combined member and method, say on the dependency, can be counted as SALSA ^SM(sacrificing the aluminium sheet anode) system.In a preferred embodiment of the said system shown in Figure 1A and the 1B, two layers or more multi-layered aluminium sheet anode layer 10 be placed in basin 20 the jar end 22 below.Aluminium sheet 10 is shelved on the sand bed 30, and this sand bed includes plastic gasket or other fluid-tight relatively moisture-proof barrier 35.

When term " corrosive medium " is used for herein, means and contain the metal parts corrosive of a kind of meeting, or quicken the electrolytical any medium of its corrosive structure.Corrosive medium comprises hosqt media, such as any medium of the fully loaded basin weight of river sand, quartz sand, natural soils, clay, crushed rocks, gravel and working supporting.Sand is prevailing a kind of pedestal medium, so all represent corrosive medium with it on various figure.

When term " structure " is used for herein, has meant one and be in for a long time with ionogen and contact, thereby any structure of corrosive metallic surface or other parts has easily taken place.The structure of expection comprises petrochemical complex storage tank, water tank, commerce, industry and residential building and bridge.To comprise especially be the surface storage tank at the bottom of the individual layer jar and corrosion base plate and/or multi decker cage are arranged at the bottom of existing surface storage tank.

When term " anode layer " was used for herein, meaning any was active thin slice on electric current, and this thin slice both can separate with structure just to be protected on structure basically, can separate with corrosive medium again.This definition is very extensive, and for example, the thin slice that it comprises has paper tinsel, thin plate or sheet material or its assembly, though above-mentioned thin slice be screwed in or the welding structurally.Embodiment can have one deck or more multi-layered above-mentioned anode layer, and such anode layer can be adjacent to place in the following manner, and is overlapping or not overlapping, is staggered or is not staggered, in lap, be with or without sealing ply and be with or without machanical fastener at overlapping.The other example of the anode layer of expection is plastic plate or other dividing plate that is deposited with metal or metal composites on it; The aluminising plastic plate; And steel plate galvanized.In above-mentioned anode layer, this deposit can adopt any suitable method to form, comprising japanning, vapor deposition, thermospray, hot dipping plating, electrodeposit, mechanical plating, plasma coated.Can expect that in these preferred embodiments, having one deck anode layer at least is to be made by a kind of the ratio at the more active metal of the structure of protecting on electric current.Aluminium is preferably used as anode layer, and this is to be made of steel because of the most jar of end basically, and aluminium is more active than steel on electric current.Though other metal (term used time comprise alloy) herein, when contacting with the iron phase that contains metal with iron, may be more active on electric current than aluminium, aluminium has other advantages, and for example cost is low, in light weight and flexible.

It is important pointing out more following, promptly is used for term " anode layer " herein, do not comprise from structure both can not separate basically with structure to be protected, also can not with the isolating thin slice of corrosive medium.So for example desired herein anode layer should not comprise the aluminium powder layer of jar at the end that it is painted on structure to be protected.Above-mentioned coating is estimated and may be adhered to structurally securely, so on structure, can not separate with structure basically.On the other hand, this term " anode layer " should comprise and tamp the sandy soil pedestal upper surface aluminium powder coating of fusion mutually, because this anode layer still can separate with remainder with sandy soil basically.

On Figure 1A and 1B, each piece preferred sizes of aluminium sheet 10 is widely to be about 36 or 48 inches, thick about 0.020 inch, and comprise minimum 85% aluminium alloy 3003,3004,3005,3105,5005,5010,7006,7011,7075 and 7178 (ASTMB-209) of being about of aluminum content.But should admit, the metal sheet of other sequence number, the size of thin plate and thin plate combined member also can adopt.

In other embodiment, this thin plate can contain different percentile aluminium.Further again, though should be straight and slick at this thin plate of many occasions,, can expect that above-mentioned thin plate may comprise ripple, embossing or other surface detail to a certain degree, increase friction so that cause in earthquake on the area of inclination.About the width and the length of thin plate, they can depart from the existing standard that aluminium supplier is provided significantly.

The aluminium sheet 10 of Figure 1A and 1B is preferably in the staggered modes that engage, horizontal bottom sheets 22 times pedestal on.Aluminium sheet among the anode layer 10A of lowermost layer directly is flat on the pedestal, and the moisture-proof barrier 10P that can have one deck factory to use, for example polymeric coating layer (epoxy or polypropylene) or plastic lamination goods (Tedlar for example ^TM) be added on one side of ground.The upper side of this anode layer 10A should be preferably without any the coating of type.For the performance of native system, moisture-proof barrier 10P is optional, but comprises that it is because it is that the low-down product of cost is but estimated to prolong the anodic life-span.Can expect that all this class moisture-proof barrier 10P choose wantonly.

Preferred two sides of aluminium sheet in the anode layer 10B of upper strata all are light, without any electrically insulating material.The aluminium sheet of anode layer 10B should directly be placed on the aluminium sheet of anode layer 10A, and should be to contact with aluminium sheet and the two direct metal to metal of basin steel plate of anode layer 10A.

Fig. 1-D, 1-E and 1-F show the various possible spread pattern of the aluminium sheet 10 of every layer of anode layer.

On Fig. 1-D, aluminium sheet 10 is that phase ground connection is placed each other, does not have overlapping.

On Fig. 1-E, aluminium sheet 10 is that pattern is placed in an overlapping, and optional moisture sealed layer 10S arranged in lap.

On Fig. 1-F, aluminium sheet 10 is that pattern is placed in an overlapping, and lap tightens up with screw 10F machinery.

It is important pointing out more following, i.e. the placement of arbitrary layer aluminium sheet 10 can not be subjected to the restriction of the arrangement mode of other layer.For example, the aluminium sheet 10 of anode layer 10A can be placed by shown in Fig. 1-E, and the aluminium sheet 10 of anode layer 10B then can be placed by shown in Fig. 1-D.

In a preferred embodiment of the invention, anode layer is placed with the end face of preparing the corrosive medium of displacement structure on it that covers of energy 100%.But if the local galvanic protection of this structure is an acceptable, then anode layer can be placed to the corrosive medium end face that covers and is less than 100%.

On Fig. 2 A and 2B, many bottoms aluminium sheet 10 is placed on the pedestal that contains sandy soil 30 (corrosive medium) and moisture-proof barrier 35.Just as discussed above, every block of aluminium sheet in the anode layer 10A of lowermost layer preferably all is about 0.020 inch thickness, and preferably it has been mounted to and is coated with down laminatedly, and exposed/uncoated one faces up.Two layers or the anode layer 10B of more multi-layered interpolation, the aluminium sheet of 10C, its thickness also is about 0.020 inch, but two people sides all are light (all not having electrical insulating coating on arbitrary side), then these aluminium sheets are installed on the end face of lowermost layer anode layer 10A with staggered pattern, the part that is overlapping preferably is about 24 inches.The aluminium sheet 10C of the most last one deck anode layer be with jar at the bottom of 22 contacted.In this manner, great majority or all substrates are entirely aluminium sheet and cover, and great majority or all jar ends 22 are contacted with aluminium sheet.

In particularly preferred embodiments, these metal sheets should extend beyond basin steel plate edge and are few 1/4 inch and are used for new basin.If desired, the gap-filling glue 36 that can apply optional anti-rainwater in an open-air side and the corner regions on the aluminium sheet at basin steel plate edge enters in the interface of anode layer and basin base plate, shown in Fig. 1 C to prevent any rainwater.

In Fig. 3, SALSA ^SMSystem is together with having the situation that basin and pedestal are used now.Basin 130 has housing 131 and installs in advance and normally corrodes base plate 132 among the figure.Dielectric layer (being generally the polyethylene board or the Bulk coat of 40～80 mil thick) 134 is lain on the end face of corrosion base plate 132, more preferred about 4～about 6 inches thick sand beds 136 is placed on the end face of dielectric layer 134.Then with one deck or more the aluminium sheet 140 of multianode layer be placed on the end face of sand bed 136, at last a new jar end 150, be placed on the end face of aluminium sheet 140.The arrangement mode of these aluminium sheets 140 basically can be identical with the arrangement mode of the aluminium sheet 10 shown in the 1-F with Fig. 1-D, 1-E.Native system has substituted previously known system, in the system known to former, dielectric layer withstand on the sand bed of placing be about 1 inch thick.A kind of conventional cathodic protection system of being made up of mixed type metal oxide anode (tape formula, grid type or coil form) is placed on the sandy soil, then the about 5 inches thick sand beds of one deck is placed on this anodic end face then.

When storage tank bottom is placed on the corrosive medium, had intrinsic electromotive force at the bottom of this jar, promptly there is higher corrosion potential at the middle part at the bottom of jar, and the outer rim direction at the bottom of jar then has low relatively corrosion potential.In order to compensate this variation of corrosion potential; the cathodic protection current at middle part was bigger than the cathodic protection current at jar end at the bottom of cathodic protection system should be designed to jar, and this can by the anode mass ratio placed at the middle part around the anode quality of placing want big way realize.In order to form the anode parameter of above-mentioned variation, be used for being at least the SALSA of those large-scale petroleum chemical storage tanks of 100 feet such as the diameter that contact area is arranged ^SMSystem, favourable scheme can include 3 layers of the anode layers that the radial spacing that records from the basin center does not surpass 25 feet, are no more than 25～40 feet anode layer 2 and are no more than anode layer one deck of 40～50 feet.In embodiment relatively, the thickness rather than the number of plies of the metal sheet that can change.Some parameters that influence the above-mentioned variation design of anode quality are basin sizes, the thickness of positive plate, and the soil property of pedestal, rainfall amount and rainwater are from the situation of basin, and the The Design of Storage Tank life-span.

SALSA described herein ^SMThere is significant advantage in system than system known in the past.Comprising, aluminium sheet is saturating moisture not basically, so, probably except the aluminium sheet overlapping, can prevent that ground moisture is seeped on the structure.At the overlapping of aluminium sheet, also can use organic sealing ply 10S, to prevent ground moisture infiltrate overlapping layer.But even without above-mentioned sealing ply 10S, the pressure that acts on the aluminium sheet overlapping part by base plate can prevent that also moisture from moving at the aluminium sheet overlapping.

SALSA ^SMAnother advantage of system be aluminium sheet can be placed to directly and the basin steel plate be up to 100% contact the uniform protection that this just can provide and pedestal resistivity has nothing to do.The main method that improves the exposure level between aluminium sheet and the basin steel plate is, at the bottom of the basin full load has caused sizable weight to be applied to jar on, improved the degree of integration of the aluminium sheet of basin base plate lap-joint.

SALSA ^SMThe another advantage of system is that before anode was installed, basin need not finished and make and pressure test.Thereby the basin base plate can be directly installed on the end face of positive plate, and perhaps, anodic is installed and the manufacturing of basin base plate will one afterwards be finished earlier with one.

SALSA ^SMSystem also has some advantages, is exactly that structure to be protected is passable, but does not require, uses inorganic or organic coating.For the cathodic protection system of great majority known to other, require structurally to be coated with organic coating, but with structure unit and in the annex of the cathodic protection system established be welded in the process of base plate the organic coating sensitive for damages.First problem can be eased by the exposed way of seamed edge that makes structure., this exposed surface requires bigger cathodic protection current, and coated surface then requires less current, so be difficult to solve this additional galvanic protection requirement with known cathodic protection system.Second problem relates to the organic coating that can damage the somewhere, and this place promptly is a weld of establishing the annex that the base plate anode uses in fixing.Occur in that above-mentioned damage below this base plate normally can't repair, the carbonization coating plays cathodic process, so if can not obtain enough cathodic protection currents, it will speed up the corrosion of the base plate of pedestal one side.

On the basin steel plate; use the desired organic coating of other cathode protection technology also to have problem; problem is to be lower than at galvanic protection voltage-situation of 1.2V (adopting copper-copper sulfate reference electrode to record) under, these organic coatings may with matrix metal generation cathodic disbonding.For the sake of security, the basin that stores inflammable liquid should make its dead ground and should be at ozzle place queuing electric insulation, to avoid that electrical spark takes place when the lightning.In these cases, ground system is drawn conventional cathodic protection system with a large amount of electric currents, and the above-mentioned electric current of small portion is only arranged as protection.A kind of possible terms of settlement is the electric current that increases from rectifier output, and still, after the electric current from rectifier output increased, wanting near anodic structure coating zone can be owing to the effect that is subjected to excessive galvanic protection voltage suffers cathodic disbonding.Release coating can shield matrix metal usually, makes its influence that is not subjected to the cathodic corrosion electric current, thereby has reduced the abundant effect of galvanic protection.Use SALSA ^SMThis class problem just can be got rid of by system, and this is both because SALSA ^SMSystem does not require and structurally is coated with organic coating, again because positive plate is directly contacted with uncoated structure.

SALSA ^SMSystem compares with the system of use such as zinc tape formula zinc negative electrode, and some special advantages are arranged.The zinc anode system is limited in use temperature and is lower than 140 °F, because under 140～250 of temperature, when moisture existed, the polarity of zinc can be oppositely.After the pole reversal of zinc, it can quicken the corrosion of steel, so can not be about the protection of basin of 250 hydrocarbon polymer (residual oil) as the storage operation temperature.Aluminium does not have this reversed polarity, and can use down until 1200 °F in all temperature.In addition, the power impressed anode system should not be used for heat structure, because desired bigger electric current is exported the oxygen that also can produce than quantity under comparatively high temps.The pitting of structure increases along with the increase of oxygen storage.In addition, when comparing with the power impressed anode system, SALSA ^SMSystem is one to be selected preferably, because SALSA ^SMThe oxygen that system produced is inappreciable.

Described as upper section ground, compare SALSA with other system ^SMSome advantages that system also has owing to this system and soil property or other pedestal conditional independence.For example, though can not preventing ground moisture, other system reaches structure, SALSA ^SMPositive plate in the system but can be waterproof fully.Similarly, to be based on the soil resistivity below the putative structure be impartial and equal current density will be accepted in all steel surfaces of supposition basin in the design of other system.At SALSA ^SMIn the system, what these need be considered always all is trouble question, because electric current and soil resistivity are irrelevant.What anode was followed burns, and current decay and electrical grounding are also and SALSA ^SMSystem is irrelevant.Similarly, reference electrode does not need, and preferred SALSA not ^SMSystem.

With respect to previously known system, SALSA ^SMSystem also has some other advantage.For example, impressed current system can produce the stray current that can damage reinforcing bar on the basin ring-type wallboard, and uses SALSA ^SMSystem does not just have the problems referred to above.Other advantage relates to engineering and structure.For example, SALSA ^SMReduce to 1 or 2 hour the servicing time of system, and this is lower than other system of use.SALSA ^SMSystem does not need the skilled worker to install yet, and said system helps to improve the progress that the basin steel plate is shipped to the construction site, because reduced the paint work of structure.In addition, the aluminium of Shi Yonging is easy to buy or orders goods short to the required time of delivering goods.Cable, testing station etc. do not require.Further again, anode is installed and board structure can carry out simultaneously and need not carry out according to the order of sequence.This can save the structure time in 2～3 weeks.

SALSA ^SMSystem also has some to use advantage.For example, SALSA ^SMSystem can automatic job, in case and base plate be placed into and just protected base plate on the aluminium sheet immediately.Do not need the start-up procedure of galvanic protection or temporary protection.Further again, do not required the testing station, because the whole surface of structure and pedestal soil are isolated.

So, SALSA ^SMEmbodiment that some of system are specific and application example are open.But, except those that narrated improve, have more, do not violate the improvement of inventive principle herein, this point should be conspicuous for those skilled in the art.So except the spirit that will meet appended claims, content of the present invention is with unrestricted.

Claims (25)

1. the outer metallic surface to the structure that is subject to dielectric corrosion provides the method for galvanic protection, and this method comprises:

A kind of anode layer is provided, and this kind anode layer is more active than this metallic surface aspect galvanic reactivity;

This anode layer is placed between medium and the structure; With

Be arranged to make the metallic surface of this anode layer and this structure to have direct electric current to be connected this metallic surface.

2. the process of claim 1 wherein the surface storage tank that this structure comprises metal bottom.

3. the method for claim 1 also is included in and is provided with a pedestal below this anode layer, wherein comprises at least a in soil, sand, clay and the gravel.

4. the process of claim 1 wherein that this anode layer comprises the thin plate of many overlapping placements.

5. the process of claim 1 wherein that this anode layer comprises at least a in paper tinsel, thin plate and the sheet material.

6. the process of claim 1 wherein:

This structure has centre portions and the peripheral part adjacent with described medium;

This anode layer comprises positive plate, so that produce the cathodic protection current of x unit at adjacent centre portions;

This anode layer comprises positive plate, so that produce the cathodic protection current of y unit at adjacent peripheral part, wherein x is greater than y.

7. the process of claim 1 wherein that this anode coating has the corrosive medium face, also comprise anti-corrosion coating is coated on the corrosive medium face of anode layer.

8. the method for claim 1 also comprises anode layer is placed to directly contacting with described structure.

9. the method for claim 1 also comprises and utilizes anode layer as dividing plate, with stop ionogen from medium flowing to this structure.

10. the process of claim 1 wherein that this structure has load bearing component, also be included in this structure of assembling on the anode layer.

11. the process of claim 1 wherein that this anode layer comprises the eclipsed parts.

12. the method for claim 11, wherein these overlapping parts have defined a kind of overlappingly, and this is overlapping to comprise sealing.

13. the method for claim 11, wherein these overlapping parts have defined a kind of overlappingly, and this is overlapping but also comprise mechanical fixation.

14. the method for claim 1 also comprises with electrically conducting coating being coated on the anode layer.

15. the method for claim 1 also comprises being that the many metal sheet forms of local eclipsed form anode layer at least, these metal sheets mainly comprise and are selected from least a metal in aluminium, zinc and the magnesium.

16. the method for claim 15, wherein this anode layer mainly comprises aluminium, also comprises one or more alloying elements in indium, magnesium, tin and the zinc.

17. the method for claim 15, wherein this anode layer mainly comprises zinc.

18. the method for claim 15, wherein this anode layer mainly comprises magnesium.

19. the method for claim 15 also comprises the anode layer with surfacial pattern is provided, to improve the frictional force between this anode layer and the structure.

20. the method for the claim 19 and then anode layer that provides one deck to have surfacial pattern is provided is to improve the frictional force between the positive plate.

21. the method for claim 15 also comprises providing to have adjacency and anode layer multiple eclipsed metal sheet and paper tinsel.

22. the method for each of claim 1～21, wherein this structure comprises the basin that has with the contacted base plate of canned fluid, and this method also comprises anode layer is placed on below the base plate.

23. the method for each of claim 1～21 also comprises at least a portion jar basal surface toward being lowered to pedestal.

24. the method for each of claim 1～21, wherein this structure has weight, and electrically contacts between metallic surface and anode layer, and it is that weight by this structure is kept basically that wherein this electrically contacts.

25. the method for each of claim 1～21, wherein this structure comprises the basin of Double bottom.

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