What is essential to do after cleaning the surfaces of pipes before joining them?

After cleaning the surfaces of pipes before joining them, applying flux to all surfaces to be joined is essential. Flux serves several important purposes in the brazing process. It helps remove any remaining oxides and contaminants that may be present after cleaning, allowing for a better bond between the base metal and the filler material. Additionally, flux protects the surfaces from oxidation during the heating process, which is crucial for achieving a strong and effective joint.

Using flux also facilitates the flow of the filler material into the joint by lowering the surface tension and allowing it to spread uniformly. This is particularly important in brazing, where the filler material needs to penetrate the joint closely and effectively to form a solid bond.

Other steps, while important in the overall process, do not directly follow the cleaning stage as immediately as applying flux. Thus, ensuring that all areas to be brazed are properly fluxed is critical for a successful join.