US1379582A - Berger - Google Patents

Description

F. VON WURSTEMBERGEH.

.raocsss FOR THE P R'OTECTION AGAINST ELECTROLYTIC DESTRUCTI APPLICATION FILED JULY 23.1920.

Patented May 24, 1921.

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UNTTED STATES PATENT FRANZ VON WURSTEMBERGER, OF ZURICH, SWITZERLAND.

Specification of Letters Patent.

Patented May 2st, 15221.

Application filed July 23, 1920. Serial No. 398,385.

T 0 all 20 7mm it may concern Be it known that T, FRANZ voN lVUnsrnM- BERGER, a citizen of the Republic of Switzerland, residing at Zurich, Hardturmstrasse 19, Switzerland, have invented certain new and useful Improvements in Processes for Protecting Against Electrolytic Destruction; and do hereby declare the following to be a clear, full, and exact. description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawing, and to letters or figures of reference marked thereon, which form a part of this specification.

The object of the present invention is a process forthe protection against electrolytic destruction of certain parts of apparatus which contain at least two liquidspacesand are constructed of different metals.

It has been ascertained that certain corrosions in the interior of tubes of heat exchanging apparatus, condensers etc. and generally of parts which are in contact with one of the liquid mediums, are the result of galvanic currents of low voltage, which are generated by the difference of potential, occurring in the space of the liquid medium between the exterior surface of the tube and the surface of wet parts of iron.

Such differences of potential are unavoidable when diiferent metals are used in the construction of such an apparatus. The currents generated in this way are very injurious to the metallic parts, if they have an oppo'rtunityto find their way into an extended system of electrodes such as a heat exchange apparatus consisting of a. quantity of tubes. In consequence of polarization and depolarization, the different parts of such electrodes are unequally exposed to the electrolytic attack, so that the whole destructive effect may be concentrated at certain spots and be the cause of their rapid destruction.

Referring to the drawings Figure 1 is a partial section of a condenser illustrating the corrosion currents.

Fig. 2 is a similar section showing one method of short-circuiting these currents.

Fig. 1 serves to explain these conditions for instance'in the case of an ordinary condensing plant. The tubes of brass 1 (of which only one is shown) are packed with rubber joints 2 in tube plates of brass (3) which are riveted to the iron shell l of the condenser 5. 6 is a supporting plate of iron in the interior of the condenser.

The steam space is to be considered also as a. space containing liquid because the steam is to be condensed therein. Assuming that the condensed steam may contain mpurities, such as a small quantity of salt, it will therefore be electrically conducting. The point of contact 7 between tube and supporting plate is not a metal to metal one, because the supporting plate and its holes will soon be covered with a layer of rust which prevents a metallic contact and possesses an electric conductibility only as carrier of an electrolyte. The tube or tubes on one hand, the supporting plate and shell on the other form in this way the electrodes of a galvanic cell. The path of the current will be that shown in Fig. 1 by a dash and dot line provided with arrows. The nest of tubes will be anodic relative to the circulating water in space 10 and is subjected to corrosions for this reason.

Protectors of zinc and iron used heretofore preserve the tubes from the harmful effect of such currents, by concentrating the destructive electrolytic action on the protectors themselves. The protecting effect is usually incomplete.

.Vith the new process which is the object of the present invention a much more effec tive protection is obtained by equalizing differences of potential which occur between parts of different metals at their contact with a liquid acting as an electrolyte, by means of well conducting, durable short-circuits between these metallic parts themselves which act as electrodes. In this way the wandering of currents into other circuits for instance such formed by liquids in other spaces and their respective metallic parts is prevented as well as any resulting electrolytic destruction of said parts. Galvanic electrical corrosions on the less precious metal itself in the first space are of course not eliminated, they occur in the highest degree there where the two different metals are nearest to one another therefore at the joints and the points of contact of the short circuits. They may be taken up by removable parts placed there to strengthen the exposed parts of the less precious metal.

In Fig. 2 an exemplification for carrying out the process according to the invention on a condenser is illustrated. The joint between the two dilferent metals is removed from 20 to 21 by choosing brass for the supporting plate instead of iron. The thick line 21 denotes a short-circuit joint made by soldering. Instead of the direct soldering of the joint a connection soldered to both metals may be adopted. 22 is a strengthening ring which serves to take up the electrolytic attack. short-circuit-joint between the latter and 23 is a well conducting the end cover 26. This joint being'outside of the waterspace a screw joint is sufiicient for a durable connection. The currents which will occur will follow the circular path indicated in chain-dotted lines. All other parts of iron or brass, especially the tubes are free from currents. v

Different kinds of short circuiting devices have already been proposed, but the fact that certain kinds of corrosions of the more electro-positive metal in one liquid space were of electrolytic nature and were caused immediately at their point of origin and rendered harmless through shortclrcultlng same. The meaning of more electro-posltive is used in the same sense that copper is more electro-positive than zinc and iron.

I claim: 1

'1. The method of protecting from electrolytic destruction certain parts of apparatus which contain at least two liquid spaces trolyte by connecting together those parts by well conducting durable short circuit de vices.

2. The method of protecting from electrolytic destruction certain parts of apparatus which contain at least two liquid spaces and are constructed of different metals, which comprises equalizing the differences of potential'that occur between any parts of different metals contacting with a liquid acting as an electrolyte by connecting together those parts by well conducting durable short circuit devices and providing removable strengthening elements of the less electropositive metal onits most'exposed places.

In testimony that I claim the foregoing as my'invention, I have'si 'ned no name.

g Y FRANZ Von WVURSTEMBERGER;

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