We are specifying pipes for a water injection system (high pressure - Rating 1500) with a physiochemical analysis of 36400 ppm chloride (CL). We need to use Carbon Steel pipe and to limit the corrosion,we use a corrosion allowance of 0.125 in, however, we think that this ppm of chloride are excesive. How we can calculate the corrosion allowance for this kind of fluid? Is it neccesary include some internal coating material or change the carbon steel to Alloy Steel?
in the presence of that much chloride, carbon steel pipe would be a bad choice. The idea that you could somehow accomodate its use by specifying 1/8" worth of allowance is poor practice because it assumes the corrosion rate is perfectly uniform, which is usually not the case in practice.
If you must use carbon steel in this application, it would be imperative to deoxygenate the feed water, buffer it to an alkaline pH, and spike the water with a silicate, chromate or tungstate corrosion inhibitor; even then, you would have no guarantees.
If you cannot condition the feed water, then you cannot use plain steel in this application.