" Hot 12 % caustic solution is circulated as coolant in VCM reactors at temperature range between 90 - 105 oC cooled by HE. Carbon steel pipe line gets corroded and punctured on pipe part as well at joints very fast. Heated caustic solution is cooled in heat excahnger and surge vessel connected with vent pipe to atmosphere. Please indicate possible reason of failure of pipe line and suggest corrective action needed. We have now increased the concentration of caustic solution from 12% to 15%. Will it be helpful to minimise the corrosion?

Dear jc_chittora , Your Caustic Conc. = 12% circulated as coolant in VCM reactors Circulation Temperature range = 90 - 105 oC W.r.t. standard caustic soda service graph your caustic piping system is residing in a very sharp MOC transition region and if we consider upper temperature as 106C maximum residence then Carbon steel ( even though all welds, bends are well SR) is not a suitable choice and U have to go for suitable Ni base alloy like Hastealloy etc. CS piping will have accelerated corrosion and wil be consumed under your operating perspective. At 15% conc. your corrosion rate for CS can be lower than at 12% but w.r.t. temperature surge above 106Cand flow velocity it is advisable to use Ni base alloys. w.r.t. your experiment at 100C for 10%, 15%, 20% caustic solution well SR CS is OK. But probably you have used some coupons which are not properly SR or may be Non-SR which has given such result. Pl. chk back. regards