US1671173A - Process and device for the protection of metallic parts against corporation - Google Patents

Description

May 29, 1928. 1,671,173

' F. VON WURSTEMBERGER PROCESS AND DEVICE FOR THE PROTECTION OF METALLIC PARTS AGAINST CORROSION Filed April 30, 19.24

Patented May 29, 1928.

UNITED STATES 2 1,671,173 PATENT OFFICE.

FRANZ V ON WUBSTEMBERGEB, OF ZURICH, SWITZERLAND.

PROCESS AND DEVICE FOR THE PROTECTION OF METALLIC PARTS AGAINST CORROSION.

Application 1116a April 30, 1924, Serial No.

It is known that stray currents in pipes and machlne-partsln electric power stations may give rise to destructive corrosion.

effects. such currents originate mainly from current-distributing circuits in which the return lines (according to the nature of the purpose of the circuit) lie in or on the ground. Such circuits are for example those of traction and quay-crane installations. Stray currents are only harmful when they flow through certain easily destructible metal parts in such a direction that the said parts are anodically attacked in streams of water with which they are in contact. The cooling pipe systems of surface condensers, suctioir pipes, and strainers of pumping plants, for example, at electric power stations are particularly endangered.

As the grounding of the return pole of systems of the kind mentioned is mostly effected merely through the running rails, and at a certain distance from the power station, and as on the other hand cable coverings and gas and water mains conduct certain return currents to the power station, the potential of the entire mass of metal at the power station adjusts itself for the most part to a certain voltage above the potential of the return pole of the source of current that feeds the system. This potential difference between the metal mass of the power station, and the return pole may amount to from 5 to 10 volts or more;

If as a result of fortuitous circumstances or of protective measures of any kind at "another place in the neighbourhood of the power station a good grounding of the return pole takes place, a current of considerable strength may arise as a result of the aforesaid potential difference existing between the metal mass of the power station and the returnpole, which current flows from the said metal mass to the return pole and may utilize cooling tubes and also suction pipes as anodes, whereby their destruction is occasioned.

The simplest and most efl'ectual remedy for this, at "least in the case of continuouscurrent systems with return-flow rails situated on the ground, would be to connect in a manner known in itself all the metal parts ofthe power station with one another, with the earth and with the return pole. The said parts would thereby be prevented from becoming anodic.

By this means however the power station 710,185, and in Switzerland Kay 14, 1928.

would undergo an excessive grounding of the circuits. Its potential would be lower by about the same amount as it was pre 'vlously higher than zero, but by this fact the electric conditions controlling the distribution of the return currents in the earth would become strongly altered. Very considerable return currents from all parts of the distribution system might then be set up and would flow toward the station by way of the cable covering, the gas and the Water mains, and would then produce on their Way dangerous electrolytic destruction phenomena.

In power stations where a difi'erence of potential between the iron work andthe negative pole exists, it is on this account, as a rule, not admissible to reduce-this difference to zero in the manner mentioned. On the contrary, it is advisable to maintain the potential of the iron work of the power house somewhat above the potential of the negative pole of the source of current.

Also in the continuous-current two-wire system with grounded neutral wire a direct connection of the parts to be protected to the negative pole is not permissible.

The method of protection, also known, wherein by the introduction of an auxiliary counter-current from a special source of current the metal parts to be protected are made cathodic, has the disadvantage that it is difiicult to render an anodic attack of the stray currents, which constantly vary in strength according to the working conditions, ineffective by a constant counter-current.

The necessary protection, from the harmful influences of stray currents, of metal parts of installations of the kind indicated conductively connected to the earth by streams of water may however now be attained according to the present invention in a simpler manner by making a metal part to be protected, which may consist of an individual part or of a number of individual parts well connected metallically with one another, cathodic by controlling the stray currents themselves to such an extent that the potential of the said metal part adjusts itself to a voltage somewhat below that of the adjacent metal parts of the plant and of the water, without, however attaining the potential of the return pole of the source of them being adjusted as a partial cathode.

the anodic corrosions' to other parts ot the total metal mass of the plant is attained.

' In a device for carrying out this process the of complete insulation, preventive measures of even quite small insulating power, for example a coat'of oil colour on the connect- .ing surfaces, intermediate layers of washers painted with oil colour and the like may suffice as insulation. As only excee ingly small currents are set in motion, the total potential of the power station is not appreciably altered. The process may therefore be employed without the danger arising of disturbances on the other side being produced in the system. In one and the same power station several individual parts may even be protected in this manner independently of one another, each individual one of Under some circumstances also it may be i serviceable to-lead the anodic current out of the metal mass of the plant at arbitrarily selected places through special electrodes into the water, whereby the anodic corrosions of the plant as a whole, which in any case are unavoidable, are not merely kept away from the metal part to be protected but are limited to definite anodes serving solely for consumption.

If such anodes are put into the water and J brought into the neighbourhood of the parts to be protected they strengthen, at a given potential ofthe latter, the cathodic behaviour of the neighbourhood, the resistance of the column of water serving as electrolyte may be decreased by the diminution of the distance between the electrodes.

The accompanying drawings illustrate these relations.

Fig. 1 shows diagrammatically a power station with distributing circuits for atramway system.

Fig. 2 shows the effect of the application of the new process to this example, and

Fig. 3 shows a power station with additional anode.

A tramway system with running rail 1 and contact line 2 is fed by a continuous cur rent generator 3. A return wire is shown at 4. From the wheels of the vehicle 5 there flows, besides the rail current 6, a straycurrent 7 through a water main 8 to the boiler house 9 of the power station, and from there to a condenser 10, that is, to a part of the total metallic mass M, M. The condenser 10 is anodic'relat-ively to the stream of water 11, so that its pipes are imperilled. The stray current finds its way along the path indicated in dotted lines to the point E, where incidentally a good grounding of the return pole is assumed to exist. Now if the potential of the metallic mass M, M were to be reducedto zero by connecting it"to the negative pole ofi the source of current, the danger of corrosion would of course be eliminated for the condenser 10, but the stray current 7 would at the same time be very considerably strengthened and might do harm on its way. Now in Fi 2 the condenser 10 is separated by insu ators 30 from the totality of the rest of the metal masses M, M, and-con nected through the regulating resistance 31 -With the return pole of the generator 3.

Consequently its potential is reduced below that of the suction pipe 32 and the flowing water 33. The condenser 10 and the nest of tubes located therein are cathodic relatively to the water 33 and are thereby protected. The potential of the entire metallic mass M, M isnot appreciably altered .and accordingly the totality of the potential relations of the power station is still maintained; only the machine part to be protected has been made cathodic. I

Fig. 3 shows the employment of the process with diversion of the anode current from the total mass M, M to a special anode 40 arranged in the stream of water and serving for consumption only, whereby the" other current parts of stray currents, of which 4.1 diagrammatically illustrates one, are relieved, and-the anodio attacks are diverted to this special electrode.

I claim:

In an electric current generating plant, a"-

tubular condenser thereat in the path of leakagecurrents and grounded by the water passing therethrough; means to electrically insulate the condenser from the rest of the plant, means including an electrical resistance to connect the condenser with the negativepotential of the plant, an anode in the path of the grounded leakage currents and in the grounding water passing from the condenser, and means to connectthe anode to metal masses in the immediate vicinity of the condenser, whereby the condenser is protected and the-destructive action of the leakage currents diverted to less important parts of the plant.

In testimony whereof I affix my signature.

' FRANZ VON WURSTEMBERGER.

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