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Benefits of coal tar tape coating over Guniting (cement mortar)

We are working for an Inspection Agency and presently carrying out project supervision of laying of Dia 2100 mm Mild steel Pipeline for transportation of water for Irrigation purposes. It is being laid underground at a depth of 3.0 Mtrs.

For corrosion protection the pipe is being coated with Epoxy enamel from inside and out side with Coal tar Tape. The pipeline is in the verge of completion. However, the client has been advised by some consultant that the Guniting (Cement mortar coating) on the outer surface of pipe would have been better. In view of above we want to know which type of coating is better for the outer surface of Mild steel pipes used for water transportation laid underground.

Shakti Kumar Roy
Inapection Agency - Ahmedabad, Gujarat, India
2004

Dear Sir,

Tar is easily attacked by alkalinity in the environment and Cement is more compatible to alkaline influences. Tar will withstand Acidity much better than Cement will.

Your consultant probably has an idea of the environment the pipe will pass through. The advantage of Cement is that it may produce many times a thicker coating than the tar, so in a neutral environment, it may be a better idea, however if you nearer a sea coast, you may want to look into the use of salt resisting cement grades instead.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2004

It may please be explained as to how cement mortar coating can be given at the project site when the dia. of pipe is 2100mm or more. Practically, I think, this is not possible at factory shop. In that case, I feel, MS Pipe with coal tar tape wrapping is the best method to protect the pipeline against corrosion. Your comments please.

Vedula. Narsingrao
tar products - Bhilai, Chattisgarh, INDIA
2005

If Tar is already coated then only non polar coating material should be used for overcoating of tar,but as cement mortar is to be used it should consist water which is a polar solvent ;so one of way to use is to use Acrylic emulsion along with the cement mortar,or rather some part of water used in the mortar should be replaced by acrylic cementitious resin. This shall give good adhesion to the mortar over the tar.

Mohan Anjikar
- Nagpur, Maharashtra, India
April 9, 2010