Phenolic sour water stripper is having thermosyphon reboiler.unit capacity is to strip off 180 m3/hr phenolic sour water having H2S 0.3 wt % in feed and outlet striped water is having less than 30 ppm h2s.lp steam is used in reboiler.temperature is checked as 160 degree c at the inlet of reboiler.lp steam pressure is 3.5 kg per cm2 gauge. Stripper bottom temperature normally is operated at 130.5 degree celcius.tube bundle of reboiler is required to be replaced every year due to heavy corrosion observed in top portion of the tubes and severe thinning specially at steam inlet including severe pin holes/leakages.lp steam is in tube side.tube bundle metalurgy is CS.

Your views on Potential root cause and type of corrision is requested.

Thanks and warm regards,