US1807903A - Preserving underground piping - Google Patents

Description

June 2, 1931. DI F|NLEY 1,807,903

PRESERVING UNDERGROUND PIFING Filed May 17, 1925 H/s ATTORNEY.

Patented June 2, 1931 UNITED STATES PATENT OFFICE DOZIER FINLEY, OF BERKELEY, CALIFORNIA, ASSIGNOR T THE PARAFFINE COM- PANIES, INC., 0F SAN FRANCISCO, CALIFORNIA, A CORPORATION 0F DELAWARE PRESERVING UNDERGROUND PIPING Application 1aedl may 17, 192s.. sria1 No. 109,539.

My invention relates to a method for preventing chemical disintegration, and especially to the prevention of corrosion and/or s electrolysis of underground piping. 5 It is an object of my invention to prevent tion of current egress at other than predeter mined and calculated portions of a corrodible body; and the provision of means by which these object-s may be accomplished.

Another object of my invention is to teach a met-hod, and one combination of means, for protecting pipe lines from the destructive effects of stray currents, and /or currents generatedl locally by chemical reactions. l

It is a further purpose of my invention to teach a means for accomplishing the above desired objects at a commercially feasible cost.

My invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of my invention, which is illustrated in the drawings accompanyingand forming part of the specification. It is to be understood that I do not limit myself to the showing made'by the said description, as I may adopt variant forms of my invention within the scop'e of the claims.

Referring to the drawings:

Figure 1 is an elevation of asportion of a pipe line, illustrating the connection of the bleeder in accord with my method, to an underground pipe line. Part of the pipe and insulation is broken away to disclose the bleeder connection.

Figures 2 and 3 are diagrammatic plans of applications of my method in protecting piping from stray currents from electric street railway systems. l

The art' of preventing chemical disintegration of piping and the like has in the past centered upon attempts to apply protective coatings to the metal, which were calculated to exclude air and moisture.

.In an exhaustive series of tests on underground steel and wrought iron-piping= it was found that a difference of electrical potential invariably accompanied chemical disintegration of the piping; and the following conclusions were reached (l) That in every case, such chemical action either produced, or was caused by, an electric Y current. (2) That either flow of current alone, or presence of moisture alone, is insufficient for such disintegration, but in the presence of an electrolyte such as common soil water, the rapidity of action is roughly proportioned to the quantity of current which is allowed, or caused, to flow. (3) That disintegration of the metal is substantially absent where curf rent flows from the soil to the metal and is most evident where the current Hows from the metal to the soil. (4) That the most durable protective coatings are, in general, those which are the best electrical insulators; (5) That failure of protective coatings may be caused by a phenomenon identical to that of break-down of electrical insulation.

In the change of iron from the metallic form to the materia-l known as rust it is known that the iron must undergo removal from the .parent mass of metal and that it departs therefrom in ionized form, carrying a positive electrical charge. The ferrous ion displaces hydrogen ions of the corresponding electrical equivalency which theretofore formed a port-ion of the hydrogen ion content of the electrolyte, and these displaced hydrogen ions, under normal conditions, will give up their charges to some adjacent area of the same parent mass of the ferrous metal, which charge will pass, by the ordinary laws of electrical conductivity in metallic conductors, to the point from .sheath may stop the discharge of the fer! rous ion' into the electrolyte by preventing the electrolyte from coming in contact with the metal.

In the .electrolysis due to currents from street railways4 a similar action may occur, but in this instance the charges departing from the iron by way of the ferrous ions are not returned to the same parent mass of metal but go elsewhere, usually on their route back to the power house or substation. Incoming quantities of electricity come to the corrodingmass of metal from a source other than an area of the same piece of metal, or other pieces connected therewith, asin ordinary corrosion. vBut the reception of that current thru the mass of metal and its iinal departure by outgoing ferrous ions is an identical procedure, so far as the metal is concerned, in both instances. Tt will be a preciated that the metal need not be wholly ferrous, but much of this action will take place if a portion only is'ferrous; or it may e enhanced by the presence of foreign metals; or it may occur in systems entirely comprised of metals other than iron or steel. My method involves the control of the currents set up and therefore as a preventive of corrosion it is also a preventive of electrolysis and vice versa. The fundamental purpose of my invention is to prevent disintegration no matter what its incidence may be.

This invention was prompted, and its chief fruits are realized, in the case of underground piping, where a certain amount of soil water is usually present, and where the moist ground itselfI is a conductor. Thus the conditions for continued action are complete, and the resulting problem of disintegration of underground piping is one to which no wholly satisfactory solution has yet been applied. It is estimated that in the United States alone the loss of pipe by corrosion is twenty million dollars annually.

There are also added losses due to leakage, disruption. of service and the like, as a direct result. It is proposed to show wherein the past efforts, involving the use of protective coatings, failed in an important respect to solve the problem; and to teach a practicable method for cutting down this enormous waste.

corrosive influences of soils which will bring about a destructive action on protected iron or steel. The electrical insulating quality of the former type of protective coating was an vincidental feature to which scant attention Ymethod'takes account of this. Chemical action may be prevented as well by preventing How of current as by preventing access of the electrolyte tothe metal of the pipe, and though I do not Apropose to prevent flow of current, I propose so to control its iiow that its harmful effects will'be avoided'.

Consider the corrosion of the outside surface of an uninsulated pipe buried in moist soil. the pipe at anodic areas due to the solution pressure of the, iron and these ferrous ions almost instantly meet with negatively charged 0H ions which remove them by reaction into insoluble Fe(0H) 2, thus permitting more ferrous ions to break away from the pipe.

- This Fe (OH)2 is in turn acted upon by any of the indefinite number of constituents of the ground water, to form a generally insoluble complex compound or rust. The greatest loss of ions appears to be at those points where oxygen is deficient, and so this incrustation of rust,by cutting oli' the access of oxygen to the area, enhances the previous favorableness of the situation as a seat for corrosion. This auto-acceleration of the rusting favors pitting, since the bottom of a pit is cut 0E from access to the air or oxygen carried by the electrolyte, while the oxygen around its rim acts as a depolarizer. This accounts for the continued corrosion of certain areas and the immunity of other areas, and it also acl counts for the building up of a network of currentswithin a bare buried pipe andthe observed phenomenon of a current which may travel along the pipe, possibly for miles, before it leaves it totally or only in part at an anodic area. Itis important to note that only those currents iowing from the'metal to the soil disintegrate the metal, while those currents which iiow from the soil to the meta-.l produce no e'ect upon the metal. Y

If the pipe had been coated with substantially waterproof paint, it would appear that since one of the elements necessary to any substantial rate of corrosion, namely the water or other electrolyte, has been intercepted, the problem would be solved. However, absolute waterproofing is a theoretical condition only approximated in practice. 1 ven if allv abrasion of the surface coating w l re avoided, there would be sullicient porosity to permit the seepage of a small amount of electrolyte to the piping surface. Assuming the ideal condition where all extraneous sources of potential are eliminated, this access of the electrolyte, even in minute amount, tothed surface of the pipe may give a chance for the solution pressure of the -iron to exert itself and Positively charged ferrous ions leave for the iron to go into solution in the electrolyte as ferrous ions. The repetition of this action over a period of time, granting the precipitation of the ferrous ion as a hydroxide or other insoluble iron compound at or near the point of its departure' from the parent mass, will build up a quantity of products 'of corrosion under whatever protective coating is employed and the protective coating will be mechanically disrupted, allowing the electrolyte to reach the metal in increasingly greater, quantities, and the corrosion will be'further accelerated thereby. Such an insulated pipe line then may have a higher potential than the surrounding earth and this potential will not be a mere .static condition but may be maintained in the presence of a not inconsiderable current flow. For instance, a current flow of 1000 coulombs per month may be thus maintained.. Such a current flow might produce a metal removal of 20 grams in five years which, in the case of a pipe with thin walls, would certainly bring about a puncture ofthe wall. Thus-it is seen that an ordinary paint-coated pipepeven under such a favorable condition as this, where no outside potential is imposed upon the pipe, will not be proof against disintegration. `The same is true with asphalt-dip coating. Until vrecent times, no coating which produced a highly insulating effect of durablev character was available. I have found that even such a covering as the double wrapping of specially prepared asphalt-impregnated felt, described yin my co-pending application #656,125, series of 1915 filedl August 6, 1923, will not absolutely prevent flow of current therethru,

So far, only those potentials induced by the chemical reaction itself, have been considered. There are however, other sources of potential which can cause initial failure of an insulating waterproof coating; probably the principal ones of which are stray currents and induced currents. Strays are most frequently caused by connection of electrical machinery to ground. Figures 2 and 3 illustrate examples of this source of stray cur- 'rents in street railway systems. In extreme cases potentials as high as 30 volts have been observed from this source. There are no coatings or coverings of commercially practicable price which can permanently resist such -differences of potential as this when buried in wet soil, for the traces of moisture which are gradually absorbed by any coating under such circumstances make it vulnerable. I therefore propose to insulate the pipe or other structure to be protected, by wrapping or otherwise, so far as it is practicable to do so; and in addition to this protective coating, I provide preferably metallic bleeders which are connected electrically to the pipe, and keep it drained of high electrical potential.

Of course the grounding7 of structures is necessary for protection against li htning and short circuits, but such practice oes not suggest the use of bleeders in accordance with my invention. v

Until the invention of Wrapped coverings of the type described in my said co-pending application, no satisfactory insulation was available for controlling the path of current thru a pipe; and current might leave the pipe at a large number of points other than a specially prepared avenue of escape. 'Ihus my method .realizes its fullest possibilities with the use of such an insulating covering on the pipe.

Figurel illustrates a portion of pipe line formed of metal pipe 2. The surface of the pipe is insulated and waterproofed by a resistant covering 3, preferably of spirallywrapped bitumen-impregnated felt, as described in my said co-pending application. A metallic stem or bleeder 4 is welded to the metal pipe 2 by any well-known means, and this stem is thoroughly insulated electrically by a bituminous wrapping 6. The stem is Welded or otherwise electrically well connected at its terminus, to a bare groundingv plate 7 of metal, carbon, or other substance which will form a suitable anodic ground. The grounding plate should be buried in moist, or otherwise ood conducting earth, and for convenience o? inspection and replacement, it is placed in an easily accessible position. Experiment will indicate that different areas of the ground may vary appreciably in potential, and it is desirable to position the grounding plates in a relatively low potential area.

The bleeder 4 prevents rise of potential of the pipe to values above the safe limit of the insulation 3, and provides a harmless exit for any currents which may occur in the pipe. Thus the insulation tends to protect the pipe from' outside sources of current and in turn is protected from currents within the pipe which cannot be wholly prevented.

Since disintegration of the metal takes place only when electric current flows from the metal to the soil, it is obvious that the pipe itself will be protected from chemical action by thus carrying the current away thru the bleeders. Moreover, it is immaterial to the operation of my method whether the currentis induced by chemical action as in corrosion, or whether the current is the cause of the action, as in electrolysis. The cure in either case is to control the current.

It is obvious of course, that in this case chemical action will be transferred to the grounding plates 7, and these must be constructed to withstand it. They maybe of any convenient form and of a variety of materials. It is generally contemplated that scrap iron will be used for this purpose, and will be made accessible for inspection and replacement.

It is known that good results may also be obtained with the-use of a noncorrosive conductor such as carbon, nichrome, or the like. Specially protected, or especially massive conductor, or even such a portion of the pipe itself, may be used as the grounding connection.

So far, that typegofdisintegration which is actually caused by out-side electrical iniuences has not been considered in detail. These extraneous sources of current not only tend to break down insulation of the pipe, butlso cause serious electrolysis of the pipe itse i I Take the case illustrated by Figure 2, of' an, electric railway line 8, 9, 11, which uses a railreturn in the electric circuit to the generator station 12. A pipe line 13 in the ground, lies in close proximity to the generato; and toa remote portion 11 of the railway line, so that the pipe line forms the shortestground return between this portion of the Y -electric railway line and itsgenerator station. Injsuch a case, and especially where the rails arepoorly cqnnected, the quantity ofthe straycurrents picked up and carried by the pipemay be considerable. In general, the current will flow thru the ground and enter the pipe near the section 11, and

' will leave it near the generator 12; at which latter point rapid electrolysisof the metal will take place; assuming of course, the use of unprotected pipe. In this case a painted coating or an asphalt tar dip would be almost useless and even a double covering of the material described in my co-pending application No. 656,125 above referred to, would probably undergo an electrical and physical breakdown if the difference of potential between pipe and rail were of an order of magnitude of 12 volts andthe soil were more than distinctly da1np,'though not of necessity even Figure `2 then, illustrates the application of o my method to an important case of protectj ing objects from stray currents. A bleeder 4 should be connected to the pipe line 13, near the generator station 12, for this would normally be alow potential area of the ground, where the current tends to lirow from the pipe. A grounding plate 7 is used for the bleeder terminal, and the `manner of connecting and placing the bleeder is thesame as that illus- In fact, any readily replaceable, A

8, such as might occur-at night when the street cars stop running. The use of a plate such as 7a, which is normally cathodic, but which may become anodic at times is to be undertaken with due regard to the conditions to be met. Generally I would prefer to install an insulated coupling 14 in the line 13 if a normally cathodic plate is to be employed. Such an electrically insulated coupling may be of any well known type obtain- Aable on the market or may be made with a steel orcast iron shell with concrete used as" a j ointing material. A coupling of this character will limit the amount of current flowing in the pipe and therefore prevent excessive and needless wasting of the anodic plates. But the use of insulated couplings is attended with certain dangers since a dangerously high potential may build up on the positive side of such a coupling as compared to that on the other side Aand there may be a tendency for currentto leave the pipe, lgo around the coupling and return to the pipe again, traveling past the coupling via the surrounding moist earth. Where such a current leaves the pipe there will be metal loss.

In such a case several insulated couplings may be employed at or near the place of the single coupling 14. The drop of ,potential around any one of the several may thus be kept below a dangerous figure.

' My method also permits the use of various means supplemental or alternative tothe insulated coupling for controlling current. In

Figure 2 I have illustrated a shunt 16 across the coupling, and a resistance 17, of 'determinedly adjusted value in this shunt. The value of this resistance must be adj usted with due regard to existing conditions such as o' pipe and soil potential, which are not the same/in diiferent installations. This shunt permits a limited current ilow to bleed away vthe dangerous peak voltages. f y

A polarized or Aother current-directioncontrolled switch 18, or a time controlled switch, or even a manually operated switch, may also be provided either in parallel or in series with the resistance, or it may entirely displace the resistance in the-shunt 16. These connections are illustrated in the several couplings 14, 14a, and 146 respectively in Figures 2 and 3.

It is apparent that, due to the presence of trated in Figure l. When the pOteIlal 0fl the insulating'coupling 14, a certain potential the ground in the vicinity of section 11- is higher than atsection 8, current which leaks into the pipe thru the insulation at section 11 will flow harmlessly out thru the bleeder near section 8. Y

A bleeder 4a leading to a grounding plate 7a, may be provided near section 11. Its purpose is first, to prevent breakdown of insulation where the current enters the pipe, and second, to take care of a freak condition of inversion of potential at sections 11 and will build up on the positive side of said coupling. When this potential reaches a su'licient value, the current will energize the switch and cause a momentary closing of the circuit. The value of the current necessary to do this is dependentupon the value of resistance 17. As this occurs, the accumulated charge is dissipated, and the switch magnet is de-energized, thus allowing the spring arm of the switch to open and re-establish initial conditions, except that there is no longer an aci12 near section 19 of the railway.

cumulated charge on the positive side of thel coupling. The switch will remain open until the charge again accumulates to a value sufficient to energize the switch, when the same conditions will re-occur.

A similarchoice of set-up is possible in connection with each bleeder, and in Figure 3 I have diagrammed a hypothetical set-up illustrating such combinations. An insulated pipe line 13 is in proximity to a railway line 19, 21, 22, 23, 24 having its generator station Bleeders 4b, 4c and 4d with their grounding plates 7 b, 7c and 7d, provide points of egress for currents from the pipe line. Resistances 17 b and 170 of values adjusted in accord with the other factors previously mentioned, are interposed in the bleeders 7b and 7 c to distribute the load Between bleeders. A current-direction-controlled switch 180 is provided in bleeder 4c in series with its resistance, to prevent influx of current to the pipe at this point which is subject to inversion of potential. The bleeder 7 CZ is provided with a resistance 17d and current-direction-controlled switch 18d in parallel, allowing free egress of current and limiting its possible ingress to the pipe. Insulated couplings 14a and 14]) between each bleeder, separate the pipe into controllable sections, and have shunts 16e and 167 around them. The shunt 16e has a resistance 17 e and current-direction-controlled switch 18e in series, and the shunt 16; has its resistance reduced to a negligible value and is provided with a current-direction-controlled switch 187. As a rule, it will not be necessary or even advisable to combine all these safeguards in any single limited area of a?,

system such as this. It is to be understood that my method contemplates a proper determination of the conditions encountered in any case, and teaches the meansiwith which to meet these conditions.

In all of this it is understood that the ob ject of the various devices used is to reduce the accumulation of a high positive potential on or at any point or area of the nominally insulated pipe in conjunction with a potentially large current whereby a considerable volume of metal removal might be brought about Of course I have illustrated simple ideal systems in the drawings and specifications. In practice vthere may be many branches of one or more street car systems which pass over or near or which parallel buried` pipe lines and there may be many .points on a single line which are normally anodic instead of just one or two points, as hereinabove discussed. But voltage measurements, and where possible ammeter measure-- ments, will reveal thaty the pipe surface is either anodic or cathodic', or suii'ers periodic alternation between these two states, and it is believed the above methods of treatment provide for any and all of these three conditions.

erning these potentials are manifold, and it f is advisable to determine the relative potentials in each case by experiment.

It is understood that there are sources of destructive currents other than that illustrated by Figures 2 and 3. In general it may be said that regardless of the source, if it is found that a pipe is at a higher potential than the surrounding earth and a suficient current flow occurs to be a potential cause for serious chemical disintegration', the situation may be brought under control by insulating the pipe by means of the covering above referred to, and installing a bleeder to take the current to a point removed from the pipe itself and there distribute it to the surrounding earth by a renewable corrodible or non-corrodible plate.

I claim:

1. A system of pipes in a medium carrying a plurality of currents, insulating covering on said pipes, non-conductive couplings electrically separating said system of pipes into sections, shunts of determinedly adjusted resistance around said couplin s, switches in combination with said shunts or controlling iiow of current around the couplings,

and a plurality of bleeders electrically connecting portions of said system of pipes to portions of said medium which are at lower' electrical potential than the said portions of said system of pipes, whereby the electrolytic corrosion of said system of pipes may be materially reduced.

2. A system of pipes in a medium carrying a plurality of currents, insulating covering on said pipes, non-conductive couplings electrically separating said system of -pipes into sections, shunts of determinedly adjusted resistanceI around said couplings, current-direction-controlled switches in combination with said shunts, and a plurality ofbleeders electrically connecting portions of said sys-J tem of pipes to portions of said medium which are at lower electrical potential than the said portions of said system of pipes, whereby the electrolytic corrosion of said system of pipes is materially reduced.

3. A system of pipes in a medium carrying a plurality of currents, insulating covering on said pipes, non-conductive couplings electrically separating said system of pipes into sections, shunts around saidcouplings, switches in series with saidshunts, and a plurality of bleeders electrically connecting portions of said system ofpipes to portions of' said medium which are at lower electrical potential than the'said portions of said sys;

tem of pipes, whereby the electrolytic. corrosion of said system of pipes is materially reduced.

4. A system of pipes in a medium carrying a plurality of currents, insulating covering on saidlpipes, non-conductive couplings electrically'separating said system o pipes into sections, shunts around said couplings, current-direction-controlledl switches in series withsaid shunts, and a .plurality ofbleeders electrically connecting portions of said system of pipes'to portions of said medium whlch are at lower electrical potential than the said portionsof said system of pipes, v'whereby the electrolytic corrosionof said system of' pipes is materially reduced.

5. A system of pipes in a medium carrying a plurality of currents, insulating covering on said pipes, non-conductive couplings electrically separating saidsyste'm of pipes into sections, shunts of determinedly adjusted' resist-ance aroundsaid couplings, switches vin combination with said `shunts for controlling 3o /ow of current around the couplings, and a plurality of' bleeders -electrically connecting portions of said system of pipes to portions of said medium which are normally at lower electrical potential than the said portions of said system ofpipes, and current-directioncontrolled switches interposed in said bleeders, whereby the electrolytic corrosion of said system of pipesmay be materially reduced.

6. A systemof pipes in a medium carrying a plurality of currents, insulating covering on said pipes, non-conductive couplings electrically separating said system of pipes into sections, shunts of determinedly adjustedl resistance around said couplings, current-direct1on-controlled switches 1n comblnatlon with said shunts, and a plurality of bleeders electrically connecting portions of said system of pipes to portions oi said medium which are normally at lower electrical potential than the said .ortions of said systemof pipes, and

currentrection-controlled switches inter-V posed in lsaid bleeders, whereby the electrolytic corrosion of said. system of pipes is materially reduced.

7. In an insulated pipe lil-Ie, an insulating coupling interposed in said, pipe line, and a determinedly adjusted resistance shuntedl across said coupling, and a switch in combination with said resistance shunt for con- I trolling current flow around the coupling.

8. In an insulated pipe line, an insulating coupling interposed'in said pipe line, and .a

determnedly adjusted resistance shuntedl across said coupling,'and a polarized switch in combination with said resistance shunt.

Leoaoa 9. ln an insulated pipe line, an insulating coupling interposed in said pipe line, and a determinedly adjusted resistance .shunted across said coupling, and a polarized switch in series with said resistance shunt.

l0. In an insulated pipe line, an insulating coupling interposed in said pipe line, a shunt my hand.

DOZIER FINLEY.

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