Why must residual flux be removed from the outside of a brazed joint?

Removing residual flux from the outside of a brazed joint is critical primarily because flux can absorb moisture from the air, leading to corrosion of the pipework over time. When flux remains on the joint, it can create a damp environment that contributes to oxidation and the deterioration of the metal surfaces. This corrosion not only compromises the integrity and strength of the joint but can also lead to leaks, which are particularly problematic in systems that handle refrigerants or fluids under pressure. Ensuring that the joint is clean and free of any flux residue helps maintain the longevity and reliability of the installation while preventing potential failures that could lead to safety hazards or costly repairs.