We have 10% NaOH caustic treaters to remove mercaptans in propane and butane. We donnot have merox or merichem catalyst. The regenerator reboiler to the lean rich caustic exchanger has very high levels of corrosion. The material is C Steel ie A105 and A106. The temperature 240F. We try and keep the contaminates Na2S lower than 1% but it seems to go to as high as 2.5%. We have a amine unit ahead of the caustic unit to prevent H2S. We feel the problems is due to COS hydrolysis to Na2S in the caustic. We also monitor Na2CO3 but we have no real operating targets. We are addressing the problem at the moment but ..... Comments and questions would be appreciated.