Corrosion allowance - additional thickness

This may be considered slightly off topic but I have to ask. Potable or drinking water is transported in PE pipe with no requirement for corrossion allowance. Why are you considering any other material.

I know that with proper external protection and impressed current cathodic protection steel pipelines have very good life spans as Natural Gas transmission lines but of course they are not carrying Oxygen rich water. Cement lining makes for expensive installations as the pipe cannot be snaked into the trench after jointing. It has to be jointed in the trench so jequires joint pockets in the trench at considerable cost. Cement lining is used with mechanical joints and ductile iron pipe in the water industry in the UK, but the distance between joints is either 3 or 6m.