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? An Experiment was conducted in Lab to find out corrosion rate of carbon steel coupons in 10%, 15% and 20% NaOH solution at around 100 oC for 24 hours. Result : Loss in wt of corrosion coupon was more in 20% soln, less in 15% soln and it was less in 10% solution comparatively. Please comment?