The zinalium coating consists of:
-a layer of zinalium two-phase 85-15 alloy deposited by metallization(minimum quantity:400g/m2)
-a bituminous painting(pore-sealer) of average thickness 70 microns.
The metallic zinalium coating offers active protection due to the galvanic action of the alloy. The mechanism has two effects:
Formation of a stable protective layer
In contact with the surrounding soil, the metallic zinalium slowly changes into a dense, adherent, impermeable and continuous layer of insoluble zinc salts. This forms a protective screen. The presence of aluminum increses the passivation effect even in highly corrosive soils, reducing the zinc consumption rate.
Whilst allowing galvanic protection and self-healing, the bituminous paint promotes the formation of a stable, insoluble layer of zinalium conversion products.
This mechanism occurs first.
One of the particular features of external zinalium coating is its capacity for restoring the continuity of the protective layer at points where it is locally damaged. The Zn++ ions migrate through the pore-sealer to plug the damage and are then converted into stable insoluble zinc products.
Advantages of the 400g/m2 zinalium coating
PAM decided to increase the quantity of zinalium to 400g/m2(instead of 130g/m2 of zinc prescribed in the standards). This considerably extends the time during which the zinc provides active protection to the pipe.
Field of use
Usually ductile iron pipe with 130 g/m2 or 200 g/m2 zinc coating, can effectively protect the ductile iron pipe against the general type of soil corrosion. However, under strong corrosive conditions, ductile iron pipe lifespan is shortened. Through the use of Zinalium coating, pipe life can be increased by 3-4 times. The ZINALIUM-based coating is compatible with more than 90 % ground types, which includes:
- Wet areas such as ponds, swamps, mud and low-lying areas
- Saline Land
- Clay with poor permeability
- Area with stray current, such as near rails, high voltage lines etc.
- Metal mining area with low resistivity
- Chemical plants, waste disposal, thermal power plants, dairy plants and other industrial parks and agricultural parks
The pipe and active coating layer must be isolated from the soil in case of exceptionally corrosive environment.