Max H3PO4 conc. in carbon steel pipe?

[Dellsmit]

I'm trying to find the maximum "healthy" concentration for phosphoric acid in carbon steel piping. We're currently using a sodium phosphate/phosphoric acid mixture as an iron corrosion inhibitor in our cooling water system. We currently dilute to 1ppm, but is there any industry experience with a safe high setpoint for phosphoric acid in carbon steel pipe?

 

[saxon]

dellsmit, Check Perry's Chem. Handbook, table 23-2, Ferrous Metals and Alloys, pp.:23-21. From what I see, I wouldn't use carbon steel.

saxon