Magnesium Anodes by Applied Magnesium

Applied Magnesium research and development in galvanic anodes began in 1939, and by 1949 Applied Magnesium had introduced extruded magnesium anodes for use in water heaters. As time went on, Applied Magnesium learned more about the advantages of anodes with small diameters and high current output to weight ratios, and identified several other applications for extruded anodes. Today, Applied Magnesium offers a complete line of extruded anodes for specialized cathodic protection applications.

There are four primary areas where extruded anodes offer important advantages in cost, performance, and ease of installation:

Magnesium Anode Rods

Anode Rod Composition

Anode, one end plain, one end capped.

Anode rods are available as either the standard GALVOROD anode or the high current output GALVOMAG anode. GALVOLINE ribbon anode is manufactured with the high current output composition.

In most environments, the oxidation potential is 1.4 to 1.5 volts for GALVOROD and 1.6 to 1.7 volts for GALVOMAG (with respect to a copper-copper sulfate reference electrode). Because of its higher oxidation potential, GALVOMAG anodes of a given size deliver approximately 25% more current (milliamperes) than GALVOROD anodes of the same size. As electrolyte resistivity increases, the need for GALVOMAG anodes increases.

Current capacities for GALVOMAG and GALVOROD anodes are similar and will range from 450 to 550 ampere hours per pound, depending primarily on the operating rate (anode current density).

  
Anode Rod Sizes

Anodes in various diameters, both ends plain
  

 
Anode rods are extruded in twelve standard diameters ranging from 0.500" to 2.562". GALVOLINE ribbon anode is extruded as a 3/8" x 3/4" ribbon. Each anode has a steel core running lengthwise through its center.

Length Tolerances

Plain Anode Rods:

• Up through 4.999 ft: +1/8", -0"
• 5 ft through 19.999 ft: 1/4", -0"
• 20 ft and over: +1", -0"

Threaded Capper Rods:

• ± 1/4"

GALVOLINE Anodes:

• 1000 ft: +/-25 ft coils - random wound
• Coils are 32" OD x 18" ID x 8" transverse steel banded

Shipping Tolerances

• Rods: +/-3% of pieces ordered.
• GALVOLINE: exact number of coils ordered.

Packaging

• Rods: Cardboard cartons on wood pallets.
• GALVOLINE: Bare (banded) coils. Special packaging by quotation.
    

End Configurations & Adapter Caps

Anode, one end plain, one end with core wire exposed.

For magnesium anodes to provide protection, a positive electrical connection must be established and maintained between the anode and the structure being protected. To facilitate their use, anodes are furnished with various end configurations and/or adapter caps. The standard end configurations are:

1. Both ends plain (saw cut).
2. One end plain, one end threaded.
3. One end plain, one end capped.
4. One end counterbored with core wire exposed (1.030 diameter and larger only).
5. One end plain, one end with core wire exposed.
6. Core wire exposed on both ends.
7. Link-type anode, one end welded steel plug with 9"-12" anode sections joined with flexible connector to desired length.

Link-type anode

Threaded end standards

Threaded end standards

Extruded Magnesium Rod Anodes

Applied Magnesium Extruded magnesium anodes are available in many diameters and in lengths up to 25 feet. The anodes are available in either the standard GALVOROD alloy or in the high potential GALVOMAG alloy (see anode composition chart).

Extruded magnesium anodes are available in the following configurations:

1. With any size, length and type of lead wire. These anodes come standard with an epoxy cap to protect the wire to anode connection and are typically used for hanging in steel water tanks.
2. Threaded at one or both ends to fit a standard pipe coupling. The anodes can then be "coupled" together for long lengths.
3. Fitted with a steel cap at one end for "drive-in" anodes. These anodes are typically used for service risers and come with 5 feet or #12 THHN solid wire attached to the anode for connection to the riser. A stainless steel clamp is also available for attachment to the riser.

To order, specify the diameter, length, alloy and configuration of the magnesium rod.

Extruded Magnesium Ribbon Anodes

GALVOLINE extruded magnesium anode ribbon from Applied Magnesium is a flexible anode material generally used in high resistivity soils and water and can provide higher current outputs than other cast magnesium anodes due to it's greater surface area to weight ratio.

GALVOLINE magnesium ribbon comes standard in 1,000 foot reels and is also available as follows:

1. Cut to a specific length with any size, length and type of lead wire required.
2. With plain ends. The magnesium is then removed from the internal core and the core can then be mechanically attached or welded to the structure to be protected.

To order, specify the length and configuration of the GALVOLINE ribbon anode.

Applications

Structures in High Resistivity Electrolytes

GALVOLINE ribbon anodes offer minimum resistance
to earth per unit weight of anode installed.

The conventional GALVOMAG magnesium cast anode is an economical and dependable source of current in soils and waters of comparatively low electrolytic resistivity. However, at higher resistivities, the problem becomes supplying enough current for protection without installing an excessive weight of anodes.

The solution? The magnesium ribbon anode called GALVOLINE. A considerable departure from traditional sacrificial anodes, GALVOLINE ribbon anode offers the following advantages:

• Minimum resistance to earth per unit weight of anode installed. The GALVOLINE anode supplies from three to seven times as much current per pound of magnesium installed as does the conventional cast anode, so you get more milliamperes per pound for any weight of anode installed.

• Efficient current distribution along a pipeline reduces current requirements to a minimum. Whereas individual anode installations provide an uneven current distribution along a pipeline, the continuous ribbon anode provides uniform current along the pipeline.

• Fewer electrical connections. The number of electrical connections between the anode and the structure being protected is reduced to a minimum. Since the core wire is in contact with each incremental length of anode, the ribbon serves as its own collector wire, eliminating much of the wiring normal to the conventional anode installation. Given reasonably uniform corrosion of the anode ribbon and relatively light current drains (1-3 mA per running foot), connections made at intervals of 500-1000 feet are adequate. No chemical backfill is necessary.

• Easy mechanical installation. The ribbon is formable enough to permit storage in coils or on reels. If the reel is mounted on a tractor or truck, the ribbon anode can be fed from the reel to a wire laying plow for continuous mechanical installation. The ribbon can also be placed in special configurations such as helical, pancake, or hairpin coils, where interior surfaces of tanks, large pipes, or condensers are to be protected.

The nomograph at the end of this web page can be used in pipeline applications to determine current output per foot of GALVOLINE and anode life.

Gas Service Entrance Piping

A gas company's need to protect the pipe located between a gas main and a customer's gas meter can be easily and inexpensively met by a small diameter extruded magnesium anode. The amount of current required in this application is typically only a few milliamperes, easily supplied by a small extruded anode. Installation is a simple matter of driving the anode into the ground with a hammer. Both capped anodes (Figure 2) and counterbored anodes (Figure 7) have been used successfully in this application.

Prepolarization of Structures in Seawater

For cathodic protection of structures in seawater, it is best to first apply a high current density (30-50 mA/sq.ft) for a short time (5 days or more). This immediately arrests steel corrosion and precipitates a calcareous coating (CaCO₃ Plus Mg(OH)₂) from the seawater onto the steel surface. Once the calcareous coating has formed, the amount of current required to protect the steel is much less (2-3 mA/sq.ft) than before prepolarization (6-15 ma/sq.ft).

Extruded magnesium anodes supply a portable source of high current that can be used to prepolarize a corroding structure. The design shown in Figures 8 and 9 uses an extruded magnesium anode attached to the core of an aluminum sacrificial anode. The magnesium anode initially provides current at a rate of 1 to 2 amps per foot of anode in seawater. By the time the magnesium has been consumed, the calcareous coating has been formed on the steel. The aluminum anode then begins to operate but at a lower current output than would have been required if the calcareous coating had not been formed. The initial current blast from the magnesium serves to significantly increase the life of the aluminum anode.

Water Tanks

The use of extruded anodes for cathodic protection of water heaters is a universal practice. A 3/4" half-coupling welded into the top head of the water heater is typically used for anode installation. Caps DS-1W, DS-2W, and DS-3W can be screwed into the 3/4" half-coupling. DS-4W requires a 1" half-coupling.

Life Expectancy