Dear members, We have observed severe mouth thinning of one of the crude distillation unit overhead air fin cooler tubes.During initial period the OVHD pH went to low level causing the acid attack coupled with turbulance at the inlet .The attak takes place at the mouth and inside length up to 1 ft .Outlet tube mouth is very good condition. What are the method we can follow to avoid tube mouth thinning due to acid attack? Will insert help?If insert is put there is concern that pressure drop will be more to make the system worst?Is it true? Is any one tried to seal weld the tube to tube sheet to smoothen the surface thus by avoiding the turbulance? This is plug header type bundle and plugging is also a problem> Is there any proven method to plug the tube at the middle row of tubes due to limited accessibility from the top? regards, krish