US3445370A - Corrosion prevention device for irrigation pipe - Google Patents

Description

May 20, 1969 R. M. SHERMAN 3,445,370

CORROSION PREVENTION DEVICE FOR IRRIGATION PIPE Fild May 7, 1965 INVENTOR. ROGER M. SHERMAN ATTORNEYS United States Patent U.S. Cl. 204197 4 Claims ABSTRACT OF THE DISCLOSURE A cathodic system for preventing the corrosion of aluminum pipe including a sacrificial zinc wire located within the pipe and secured by anchoring means at the ends of the wire to the inside pipe wall.

This invention relates to a cathodic protection device for combating and inhibiting corrosion in piping.

Metallic structures installed underground, on the ground, in water, or otherwise in contact with an electrolytic medium are subject to corrosion due to a chemical reaction with non-metallic elements in the surrounding medium. The amount or degree of corrosion that takes place may be influenced by several factors such as the type of metal in the structure, the amount of impurities in the metal and the chemical nature of the nonmetallic medium.

Irrigation piping heretofore provided a particularly difficult corrosion problem because it is generally formed of relatively thin-walled aluminum material. This enables such pipe to be light and readily movable from place to place in conjunction with sprinkler systems. However, even a relatively small amount of corrosion on such piping can be sufficient to cause leakage and a severe weakening of the pipe.

When metal corrodes, it replaces hydrogen or another metal from a compound in the surrounding medium. The reactions take place simultaneously on the metal surface. In one reaction metal ions pass into solution and in the other hydrogen ions pass out of solution to form hydrogen gas. Since these two reactions cannot take place at the same point, there must be two kinds of areas on the metal surface: those which are anodic where metal dissolves, and those which are cathodic where hydrogen ions are discharged. Thus, for corrosion to take place a metal structure must have these dissimilar areas, and the interface between a metal and its environment cannot be entirely homogenous. This principle is borne out by the fact that pure, almost perfectly homogeneous, metals have an extremely high resistance to corrosion, even when exposed to highly acidic solutions.

In the normal production of aluminum irrigation pipe, the presence of metallic impurities, oxides and differences in crystal structure and physical strain cannot be avoided and therefore perfectly homogeneous material is not commercially available for use as irrigation pipe. It has been shown that two areas of different properties on the surface of a metallic structure will have different potentials and therefore their adjacent areas will form galvanic cells comprised of an anode area which dissolves metal into the solution and a cathode area that discharges hydrogen ions. There is a direct relationship between the quantity of current which passes through these cells and the amount of metal which is dissolved.

The basis for any electro-chemical treatment of corrosion is the electro-motive force series which is an arrangement of the elements in order of their dissolution tendencies. It must be recognized that this series is dependent on the electrolyte in use at the time of measurement. In

3,445,370 Patented May 20, 1969 ice other words, it may be said that every solution has its own electro-motive force series.

Water that flows through most irrigation piping systems usually has impurities containing various ions, and it therefore acts as an electrolyte Corrosive action may therefore take place on the inside surface of the pipe as described above when any One portion of the metallic pipe structure becomes anodic with respect to another part of the same pipe or with respect to some other object in the surrounding medium. During this electrolytic corrosive action metal in the anodic areas of the structure is electrochemically removed, and a weakening and eventually perforation of the piping results. It is wel known that corrosive structures can be protected by attaching an expandable material that is anodic with respect to the structure so that material will be dissolved from the sacrificial anode rather than from the structure itself. However, various attempts to provide such a cathodic system for irrigation piping have not been practical because of the unique requirement of the latter for mobility as well as economy and long life.

It is therefore an object of my invention to provide an improved cathodic system particularly adaptable for preventing corrosion in transportable piping systems.

A more specific object of the present invention is to provide a cathodic device for piping systems that may be contained within the piping but accessible for servicing from outside the pipe at predetermined locations. This is an important advantage because it locates the cathodic protective system Where it can be most effective and yet where it cannot be damaged when the pipe is handled over and over again during its normal life. In general, my corrosion prevention system comprises one or more sacrificial anodic wires each of which is supported within the pipe by an external member that may be helically wound on the anodic wire. The latter is anchored at its opposite ends at two spaced apart locations of each pipe section, and these connections, protected by fluid tight seals, are accessible from outside the pipe when servicing of the anode is necessary. Thus, the present invention solves the problem of providing an anodic device that is supported internally within the pipe, one that will provide adequate protection against corrosion for the entire pipe structure for long periods, and yet one which is easy to install and replace.

Another object of the present invention is to provide an anodic device for protecting pipes from corrosion originating from within the pipe that is particularly well adapted for ease and economy of manufacture.

Other objects, advantages and features of the invention will become apparent from the following detailed description thereof presented with the accompanying drawings in which:

FIG. 1 is a view in elevation of a typical pipe section with portions broken away to show an anodic device installed therein according to the principles of the present invention;

FIG. 2 is an enlarged view in section showing details of one end of the installed anodic device of FIG. 1;

FIG. 3 is an enlarged view in section showing an alternate form of anodic device according to my invention; and

FIG. 4 is a fragmentary view in perspective showing a pipe section having a pair of anodic devices according to my invention.

With reference to the drawing, FIG. 1 shOWs a section of irrigation pipe 10 of the type that is generally installed on the surface of the ground for sprinkling systems and the like so that it can be readily moved to different locations when required, Usually such pipe is made from a suitable aluminum alloy which, if unprotected, is vulnerable to corrosion due to the electrolytic effect of impurities in the water within the pipe. My cathodic device for providing the necessary corrosion protection comprises generally an elongated device 11 which extends within the pipe section from near one of its ends to near its other end for substantially the full lentgh of the pipe. With the pipe section made of aluminum, the device 11 must contain a material that is anodic with respect to it. Thus, a portion of the device 11 is essentially a wire 12 of pure zinc. Since the wire 12 must extend for almost the full length of the pipe section, the problem arose of providing it with adequate support and of maintaining electrical continuity through it as it is consumed as a sacrificial anode. This problem is solved in the embodiment of FIGS. 1 and 2 by hehcally wrapping the anodic wire 12 with a supporting wire 13 of a stronger metal such as steel. For example, I have found that steel wire of 16 gauge wrapped three turns per foot around an anodic zinc wire of 4;" diameter provldes suificient support to the anodic wire 12 and enables 11 last for a long period of use even under severe environmental conditions. Yet the two-wire combination of the sacrificial anodic wire 12 and a neutral but conduct1ve supporting wire 13 still is easy to handle during its installation within the pipe.

To secure the cathodic device 11 within the pipe sectlon as shown in FIG. 2, an anchoring means 14 is provided in combination with a circular opening 15 in the pipe wall near one end of the pipe. It includes machine bolt 16 having a hex head 17 which extends through the openmg 15 and into the pipe 10. The opening around the shank of the bolt 16 is sealed by a first washer 18 which may be made of any slightly yieldable material, such as rubber. A second, fairly large and more rigid washer 19 within the pipe 10 fits over the bolt shank and over the anodic device 11 looped around the shank. It is secured by a hex nut 20', the washer 24 thus holding the anodic device firmly against the inner pipe wall to assure good electrical contact. A similar attaching means 14a is provided for securing the other end of the anodic device 11 with the pipe.

Since the attaching bolts 16 are located near the ends of the pipe section 10, the anodic wire 12 may be easily replaced by merely disconnecting the pipe section temporarily and gaining access to the nut 20 from the end of the pipe. Under average conditions, the anodic zinc wire 12 will last from six to ten years when supported within the pipe by the wire 13, so the amount of servicing required is minimal.

As shown in FIG, 3 an alternate form of anodic wire may be used in accordance with the present invention. Here, I provide a composite wire 22 comprising a central core 23 of relatively stiff material for the necessary strength such as steel wire. Surrounding this core 23 is an outer layer or coating 24 of expandable material such as zinc that again provides the anode for my device. This wire may be connected in the same way to the inside of the aluminum pipe, as described above, by wrapping its ends around bolts, such as the bolt 16, that extend inwardly from the sides of the pipe.

An anodic wire 12 or 22 installed according to my invention is efiective to prevent a corrosive attack on the pipe which extends for a considerable area on both sides of the wire. Thus, it is not necessary for the wire to extend absolutely to the end of the pipe section, as shown in FIG. 1. In pipe up to 6" in diameter, I have found that one of my elongated anode devices within the pipe is sufiicient, but for pipe 6" to 10"- in diameter, two anode devices spaced 180 apart should be installed. In FIG. 4 is shown a typical arrangement Within such a pipe 25 wherein two such anodic devices 26 and 27 are installed in such a manner. In pipe 12" in diameter and larger, three anode devices spaced apart should be used for maximum corrosion protection.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. -A cathodic protection system for preventing corrosion to an aluminum pipe section comprising: a wire extending longitudinally, within said pipe section, said wire being of zinc material that is anodic with respect to the aluminum material of said pipe; and anchoring means attached to the ends of said wire for securing only said ends to the inside pipe wall near the opposite ends of said pipe section.

2. The system as described in claim 1 including supporting wire means helically wrapped around said zinc wire along its length.

3. The system as described in claim 2 wherein each said anchoring means includes a bolt having a head outside said pipe and a threaded shank extending inwardly through an opening in the pipe, sealing means between said bolt head and the outer pipe wall around said opening and a nut threaded on said bolt shank within the pipe for holding said zinc wire firmly against the inside wall surface of the pipe.

4. A cathodic protection system for preventing corrosion to a section of aluminum pipe, comprising: a plurality of sacrificial wires extending longitudinally within the pipe and spaced apart equally along its inner surface, said wires being of zinc and therefore anodic with respect to the aluminum pipe material; supporting wire means helically wrapped around each of said sacrificial zinc wires; and means extending through the wall of said pipe section at both ends for securing the ends of the sacrificial wires to the inner pipe surface.

References Cited UNITED STATES PATENTS 801,489 10/ 1905 Uthemann 204-197 2,190,824 2/ 1940 Cook 204-197 2,619,455 11/1952 Harris et a1 204-197 2,765,273 10/ 1956 Lobos 204197 3,037,926 6/1962 Ambler 204l97 3,109,510 11/1963 Phelan 138--103 3,232,857 2/ 1966 Caldwell 204197 OTHER REFERENCES Fahrney et al., Chemical & Metallurgical Engineering, July 1942, pp. 86 and 87.

JOHN H. MACK, Primary Examiner.

T. TUNG, Assistant Examiner.

U.S. Cl. X.R. 138-103

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