Types of backfill in cathodic protection system
Types of backfill
The type of backfill used in the cathodic protection system in ground substrates depends on the type of cathodic protection system used. Due to the fact that the cathodic protection system exists in two types of sacrificial anode systems and impressed current anode systems, so two types of backfill materials are also used.
Sacrificial anode systems
The sacrificial zinc and magnesium anodes used to cathodic protection of structures buried in the soil are sometimes packed in a linen bag with a backing material. These materials reduce the local corrosion of the anode by preventing the anode from coming into direct contact with the soil. It also prevents the anode from becoming passive by reacting with salts in the soil. The backfill used improves the performance of the anode by creating a low-resistance environment around the anode. These materials are generally a combination of three types of gypsum gypsum, bentonite and sodium sulfate, and the percentage of their compounds depends on the environment used.
The following table shows the types of backfills according to the IPS-M-TP 750 standard:
Impressed current system
Impressed current anodes for cathodic protection of underground structures are usually surrounded by a carbon backfill. The purpose of using this support is:
- By reducing the resistance of the environment around the anode, it leads to an increase in the amount of current produced by the anode.
- As the anode level increases, the amount of current increases.
- Reduce anode consumption rate and thus increase anode lifetime.
Carbon backfill according to IPS-M-TP 750 standard is available in three types of 80% metallurgical coke, 90% petroleum coke and 95% special petroleum coke.
The chemical composition of these three types of backfill is specified in the table below:
Coal coke is generally used in shallow horizontal substrates. Petroleum coke or special petroleum is used for deep wells.
- Published in Articles, Educational, Scientific
Types of sacrificial anode system backfills and its applications
Types of backfill and its applications:
In cathodic protection systems of pipelines or underground structures buried in the soil, the anode used is not in direct contact with the soil. This is because the minerals and chemicals in the soil may interfere with the conductivity of the stream by creating a high-strength layer. To increase the efficiency of the anode, sometimes magnesium and zinc sacrificial anodes are provided in linen bags with a backfill. The backfill material quickly absorbs soil moisture and reduces electrolyte resistance, thus improving the practical implementation of protection. Backfill materials generally include gypsum plaster, bentonite and sodium sulfate. Depending on the environment in which the anode is placed, one of the types of backfill, which is considered in the table below, is used.
Table of combinations of different types of backfills according to IPS-M-TP-750 standard:
Due to its moisture retention properties, bentonite type A is used in areas where soil moisture is low.
Type B backfill is commonly used for sacrificial zinc anodes.
Type C backfill is useful for magnesium or zinc sacrificial anode in very wet or swampy soils to prevent the backfill from leaving the anode surface quickly.
Type D backfill, this type of backfill has low resistance and is used in areas where soil resistance is high to reduce the resistance of the anode to ground.
Dimensions of backfill bag
According to IPS-M-TP-750 standard, the diameter of the backfill bag must be at least 50 mm larger than the diameter of the anode. The backfill material should be tightly packed in the bag to prevent the anode from moving and to get enough coverage around the anode.
- Published in Articles, Educational, Scientific