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What is the best material of construction for chlorinated water?

Q: What is the best material of construction for chlorinated water (300PPM & 15PPM) -- SS316L or duplex?

A:

316L stainless steel is an acceptable material of construction for water at these levels of chlorine at room temperature.  Special attention needs to be paid to the following factors (taken from Tuthill, Nickel Institute Technical Series #14044, Reprinted from Journal American Water Works Association, Volume 86, Number 7, July 1994):

- procurement specifications and inspection that ensure full penetration welds;

- location of chlorine injection at the outlet rather than the inlet of water treatment plants handling manganese-bearing waters;

- injection of chlorine in a manner that ensures complete mixing in order to prevent high concentrations of chlorine from reaching the sidewalls of the pipe;

- designing distribution piping systems so there is minimal opportunity for moist chlorine vapors to come in contact with the inside or outside of stainless steel pipe;

- limiting the use of stainless steel in raw waters to lines that can be flushed with water periodically before sediment can collect and lead to undersediment corrosion;

- limiting the use of stainless steel in stagnant sections and lines in which flow is so low that the pipe is not flowing full;

- preventing or removing heat tint from circumferential welds when maximum resistance to microbiologically induced corrosion, crevice corrosion, or both is needed.

For working at high temperatures and/or where 316L stainless steel corrosion caused by chlorides (pitting, stress corrosion cracking, etc.) is an issue, a duplex stainless steel will offer improved corrosion resistance.

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