There are a number of very important steps that must be followed in order to ensure good brazing, one of which is that the parts to be joined must be clean before being assembled for brazing.   

Unfortunately, too many brazing shops overlook this important criterion. Instead, they depend on the brazing furnace to burn off any lubricants or to dissociate any oxides present on the parts, thus saving time (in their opinion). Their reasoning seems to be: “Oh, don’t worry about that. The furnace will clean up the parts.” Or they think: “Don’t worry about that. Just put more flux on the parts.” The latter is said if they are torch brazing or induction brazing out in air.  

Both statements are incorrect, and the actions can result in poorly brazed assemblies that either leak in service or do not have sufficient braze-strength to handle the service conditions to which they are going to be subjected.