Features of Anodes PU-5U (-10U, -20U), PRM 20, PM 15-80

Electrochemical protection against corrosion is based on the potential difference between anode metals and a protected object being in the operating area. Dissolution of anode provides the protection to the metal. Since majority of the metallic constructions are made from steel, anodes are manufactured from the metals with more negative potential in comparison with steel. There are zinc, aluminum and magnesium anodes. Magnesium and magnesium alloy anodes give certain advantages in comparison with zinc and aluminum anodes.

1. The potential difference of magnesium and steel is the largest, which affects the radius for protection: it is 10-200 m. Therefore, under similar conditions less magnesium anodes are used than aluminum and zinc ones..
2. There is no polarization which is accompanied with the decrease in electrochemical capacity.

Anodes PM-5U / PM-10U / PM-20U

These anodes function at soil resistance of less than 50 Оm•m. Electrochemical capacity is about 2,200 А•hour, and stationary potential of copper-sulphate electrode is 1,600 mV. For its effective work an anode is placed in a cotton bag with powder activator mixture consisting of a quarter of epsomite, a quarter of gypsum building plaster and a half of bentonite clay. Anodes PM-5U, PM-10U, PM-20U, are packed in an activator when manufactured and operate:

• with higher and more time stable potential;
• with no low-solubility films on the surface of the products;
• with decreased transition resistance "anode - soil";
• with even solubility over whole surface of anode

The anode is kept and transported with a conductor connected to it and in a bag with an activator in one more paper package bag which is taken away before the anode is mounted. The number of anodes and their service life (5 - 10 years) depend on soil aggressivity and anode weight. On average, PM-10U protects about 1 - 2 km of a pipeline. Anodes are mounted to protect a pipeline at the distance of 5 m from it either one by one or in a group of 5 - 15 anodes. A group arrangement of anodes is a number of single anodes connected with a drainage conductor and a test station. A single anode unit includes an anode + drainage conductor + test station.

1. – group anode units;
2. – a pipeline;
3. – KIP (test station);
4. – conductor.

"Pipe - soil" potential distribution curve along a pipeline protected by a group of anodes

Anodes PRM 20

These magnesium anodes with the weight of 20 kg are used to protect steel reservoir bottoms against corrosion caused by drainage water. Oil from some Russian and CIS oil fields contains an increased amount of mineralized water. With natural or industrial disintegration of oil emulsion, the water accumulated at the bottom of the reservoirs causes corrosion of the lower parts and bottoms. It is recommended to use PRM 20 at 0.3 % and higher salt concentration in drainage water. Running current gives protective potential after an anode is mounted in a bottom (cathode) - protector (anode) galvanic couple. Current runs from the anode to the bottom via electrolyte (drainage water) and limits or stops the corrosion of the bottom. Diagram for anode PRM-20 (made by Scientific Research Institute VNIIST):

Anodes PM 15-80

It is reasonable to use anodes to protect the pipelines in the soils with high corrosive activity, in the zones with stray currents and in the areas with corrosion spots at the pipe surface.

Advantages of anodes PM 15-80 are as follows:
• they work as an extended anodic rod in the soils with the resistance of more than 50 Оm•m;
• only one anode creates larger protective field;
• they are easy to mount.

An extended anodic rob is laid in one trench along the pipeline in accordance with three diagrams - anode is
• interrupted extended;
• uninterrupted;
• with two uninterrupted anodes.

Diagram for anode PM 15 - 80 (made by a Scientific Research Institute TatNIPIneft):

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