Magnesium anode and its applications:
Magnesium is the most common material to protect structures buried in the soil. Magnesium anodes are also used for cathodic protection inside water tanks, heat exchangers, condensers, ship hulls, sea docks, etc. In addition to the amount of output current, the efficiency of magnesium anode also depends on the anode material and its chemical composition. Magnesium anodes are manufactured according to ASTM G97, B273, IPS-M-TP-750/1 standards. Magnesium anodes are produced in two types of standard voltage (1.7 V) and high voltage (1.75 V). The capacity of magnesium anode is 1230 ampere hours/kg. The efficiency of these anodes is 58% for standard voltage type and 49% for high potential. Magnesium anodes buried in the soil are usually used with backfill, which is an anode backfill compound that absorbs and retains moisture. One of the characteristics of magnesium anodes is the small amount of open circuit potential difference (1.7V vs. Cu/CuSO4- for high potential magnesium anode and 1.5V vs. Cu/CuSO4- for standard magnesium anode) compared to the protected structure (compared to current injection system ) which does not cause over protection, at the same time due to the limited flow, stray current is also prevented.
Chemical composition of standard and high potential magnesium anodes based on standards
(ASTM G97, B 273, IPS-M-TP-750/1)
standard magnesium anodes (High purity) and high potential (High potential) with round and D-shaped sections; For the protection of pipelines
standard magnesium anodes (High purity) and high potential (High potential) with round and D-shaped sections; For the protection of heat exchangers and condensers
Magnesium anode installation guide:
Magnesium anode for use in the soil to protect the pipeline is usually installed at a distance of at least 1.5 and at most 3 to 5 meters from the protected structure buried in the soil. This type of anodes are implemented in a batch or individually.
The depth of magnesium anode burial for underground pipes is such that the anode is installed parallel to the underground pipeline. The method of installing anodes is like a vertical surface bed.
Regarding the installation of backfilled anode, its plastic cover should be removed and submerged in water for 2-3 hours. Then install it in the ground. It is better to water around the magnesium anode at the time of installation, which will lower the resistance of the anode bed and improve its performance.
Design requirements:
- It may be connected to the structure under protection according to the design principles and execution plans of the anode directly without using a distribution box.
- According to the NACE-RP0387 standard, the insert used in magnesium anodes must be made of galvanized steel.
- Use non-chlorine water for immersing the anode.
- It is better to use soft soil without lumps and stones to return the surrounding soil to the Andean burial site.
- All distances, values and sizes announced are determined based on the design and executive instructions.
- According to the request of the customer, magnesium anode is also produced and installed in strip form.
- Magnesium anode should not be used in alkaline environments (with a pH higher than 5.9) and acidic environments (with a pH lower than 5) and at a temperature higher than 60 degrees Celsius.
- Magnesium anodes are also made in different shapes and sizes based on the customer’s design and request.
Magnesium anode containing carbon backing:
In order to protect the cathodic structures buried in the soil, it is very desirable to use the backfill around the anode. The function of the back strap material is:
1) Stability of anode potential
2) prevent anode polarization
3) reducing the resistance between the anode and the soil and increasing the output current of the anode
4) By creating uniform corrosion in the anode, it reduces the self-corrosion of the anode and increases its efficiency.
Usually, the back material is a mixture of gypsum, bentonite, and sodium sulfate.
Different chemical composition behind the galvanic anodes used in soil according to IPS-M-TP-750 standard
1) Backing compound (A) is suitable in areas with low soil moisture because the bentonite in it has water retention properties.
2) Backing compound (B) is commonly used for zinc anodes.
3) Backing compound (C) is suitable for magnesium and zinc anodes in very wet and swampy soils because it holds well around the anode.
4) Back strap compound (D) has a low specific resistance and is suitable for areas with high soil specific resistance in order to reduce the resistance between anode and ground.
According to the IPS-M-TP-750 standard, the granulation of the backing material should be such that 100% of its particles pass through a sieve with 0.84 mm holes (20 mesh) and 50% of its particles pass through a sieve with mm holes. 0.15 (mesh 100) remain. Also, the humidity behind the strap should not be more than 5% (if the humidity behind the strap is high, the anode will corrode during storage).
32-pound backfilled magnesium anode and the schematic of this anode’s accessories, including cable connection, epoxy resin, insert, backing material
