We have this heat exchanger installed in our plant. There are two modules. In module-2 saturated steam is entering @200 Deg C and heating the air from 40 to 80 Deg C. Condensate from module-2 is given to module-1 which preheats the air entering in module-2 from ambient temp (30 Deg C) by 10 Deg C . Recently 1 tube in module-2 which is on module-1 side had punctured. When opened we found errosion in bottom part of tube. There is FT type steam trap in between steam & condensate module. Steam is entering from top & condensate coming out from bottom. this condensate is taken to inlet of module-1 which is at top & outlet from bottom. These radiators are having frequent failures and already replaced two for same reason. Please guide me what can be the reason.