We are facing intermixing of shell side medium into tube side in Breech lock heat exchanger in DHDT unit. During maintenance of the exchanger, the shell to tube sheet gasket (sprial wound gasket) was found damaged. The gasket was replaced and hydotested as per procedure. We understood that this type of problem is being encountered in most Refineries. I would like to know whether any specific improvement needs to be done on internals of Breechlock heat exchangers. Has anyone used Camprofile gasket instead of spiral wound gasket for shell to tube sheet gasket?