CORROSION PROTECTION METHODS

Coating and Lining

Fittings and accessories shall be normally delivered internally lined and externally coated.

External Coatings

By agreement between manufacturer and purchaser, any one of zinc coating and may be supplimented by PE sleeving depending on the external soil conditions:

• Zinc with finishing layer of bitumen

• Zinc rich paint with bitumen finishing layer

• External polyethylene sleeving.

Internal Linings

By agreement between manufacturer and purchaser, any one of the following linings may be applied depending on the type of liquid transported :

• Portland cement (with of without additives) mortar.

• Blast furnace slag cement mortar.

• Sulphate resistant cement mortar.

• High alumina (calcium aluminate) cement mortar (not used for potable water).

• Cement mortar with seal-coat.

Bituminous Coating
Coating with bituminous finishing coat is provided over any ferrous casting to protect it against corrosion.

Coating is applied on the fittings after making the surfaces clean and dry. The coating material sets rapidly with good adherence and does not scale off.

In order that the fittings are to be used for conveying potable water, care is taken so that the inside lining does not contain any constituent soluble in such water or any ingredient which could impart any taste whatsoever to the potable water after sterilization and suitable washing of the mains.

Cement Mortar Lining

The D.I. fittings are provided with cement mortar lining, which has the following advantages:

• Reduces head loss at the fittings, reducing pumping costs.

• Prevents corrosion from inside, thus increases life of pipeline.

• Eliminates red water.

Zinc Coating
Ductile Iron Pipes & Fittings resist corrosion much better than steel pipes or even Cast Iron Pipes. Still D.I. pipe fittings all over the world are protected both by internal lining and external coating as additional protection from corrosion giving the pipes & fittings an assured service life of at least 100 years.

Due to bad handling the bituminous paint on the D.I. fittings may be damaged accidentally. But if the fitting is zinc coated the damaged zone becomes cathodic to the rest of the fitting and is progressively covered by zinc corrosion products. This self-healing mechanism is fairly rapid. The zinc coating first works as an active coating capable of restoring the protective layer at damaged points through galvanic protection and then operating as a dense passive coating, which is formed after laying.