What is the purpose of using Trisodium Phosphate (TSP) before brazing a joint?

Using Trisodium Phosphate (TSP) before brazing a joint serves primarily to remove surface scale. Surface contaminants, including oils, dirt, and oxide layers, can adversely affect the quality of the brazing process. TSP acts as an effective cleaning agent that helps to ensure a clean surface that allows for better adhesion of the filler metal to the base materials. A clean joint promotes a stronger bond and enhances the overall integrity of the brazed connection.

While other options mention potential benefits related to brazing, such as creating a seal, enhancing flow, or reducing oxidation, these effects are indirect benefits of cleaning the surface effectively. Removing surface scale is critical because any remaining contaminants can lead to poor joint quality, increased chances of leaks, or ultimately, joint failure. Thus, TSP’s primary function in this scenario is making sure that the surfaces to be brazed are adequately prepared for the process, leading to optimum results.