Coatings & Linings

Internal Cement Mortar Lining (BF)

The method of application of the blast furnace cement lining is described below:

Homogeneous fresh mortar is prepared (CEMENT:SAND <1:3.5)
Required quantity of mortar is poured inside through a lance uniformly along the length.
Pipe rotates at about 700 rpm (changes with dia) which exerts a compaction force of 40g.

It protects from inside:

Cement mortar lining provides a physical barrier to the water and thus protects the pipe from corrosion and subsequent tuberculation .
Cement linings in iron pipes create a balanced pH environment at the pipe wall that prevents corrosion occurring.
The ground blast furnace slag content reduces the amount of soluble alkaline material in the mortar.
The blast furnace slag reacts with the free lime in the mortar to produce compounds with cementitious properties, reducing the level of alkaline materials able to leach out into the water.

It improves hydraulic flow characteristics:

Centrifugally applied cement mortar linings are smooth, which results in high flow coefficients (provide a higher Hazen William’s ‘C’ value of 140) and reduces frictional head loss and pumping costs
Additional vibration enables optimum compaction.
After spinning, the lining is cured for a sufficient time in a controlled atmosphere.
Process control ensures a controlled uniform thickness of mortar throughout the pipe.
The seal coat reduces the interaction between the water and cement. If the water is soft and aggressive or if there is high ‘residence’ time, it has been found that leaching from uncoated cement linings can in the certain conditions result in an undesirable rise in pH.
In gravity distribution networks, it helps to maintain enough residual pressure at tapping points.
Cement mortar linings help to maintain the same flow area and coefficient of friction over a long period of time.

Protection Mechanism of Zinc / Zinc Aluminium Coatings

1. Zinc coating provides a stable protection layer:-

In a Zinc coated pipe, the metallic Zinc in contact with corrosive soil slowly turns into a layer of zinc corrosion products, such as zinc oxides, carbonates, oxychlorides etc. which results in stable, dense, impervious, adherent layer which occupies almost exactly the same volume as the initially porous Zinc metal layer and uniformly covers the surface.

2. Self healing of damage:-

Zinc is electronegative to Iron and is therefore able to protect it sacrificially. If the pipe surface gets damaged during handling or installation the zinc coating acts as a cathodic protection system. The porous top coat of epoxy allows migration of Zinc ions and the Zinc transformation product fills the damage in the coating and prevents further corrosion of the exposed Iron. This process is often referred to as ‘self healing’.

Zinc Aluminium

How does it work?

The Zinc Aluminium coating provides increased longevity of the active corrosion protection layer. Zinc ions provide sacrificial galvanic protection to areas which may have been damaged during the transportation, handling or installation of the pipe. Once the pipe has been installed and is in contact with the surrounding soil the Zinc Aluminium forms a long term barrier through a stable insoluble protective layer. As mentioned above the pure Zinc coating provides galvanic protection for the ductile pipe which is 100% active however its effect can be rapidly depleted in very aggressive soils. In addition when the Zinc transforms too quickly the resulting passive layer can be of poor quality. The presence of aluminium in the coating slows down this conversion, by decreasing the rate at which the Zinc is transformed. It creates a more stable protective layer compared to Zinc alone, whilst allowing the sacrificial galvanic healing process to take place.

Coating Thickness

Electrosteel apply the Zinc-Aluminium coating at a rate of 400 g/m². The benefit of this thicker coating in terms of durability is significantly greater than simply the proportional increase in thickness, providing for protection in a wider range of soil

conditions.

Epoxy Topcoat

Electrosteel Pipes are finished with a tough, porous minimum thickness 100 microns epoxy coating. This semi-porous epoxy top coat is applied at a thickness that provides durability and robustness to the coating but also allows the galvanic action of the zinc to carry on taking place. Some of the additional benefits of this final coat are: