According to ASTM B813, what is the specification for flux?

The specification for flux according to ASTM B813 emphasizes that it must be flushable in warm water. This property is vital because, after the soldering or brazing process, the flux residue needs to be effectively removed to prevent corrosion and ensure the integrity of the joint. Fluxes that can be easily rinsed away with warm water facilitate the cleaning process and encourage good maintenance practices. This characteristic also allows for better visual inspection of the joint after the process is completed.

The considerations surrounding the other statements are important as well. While some might be concerned about the flammability of flux, not all fluxes are designed to be flammable, and flammability is not a requirement for effective performance. Thickness is also not a specified criterion; instead, it is the functionality of the flux that matters, including its ability to protect the joint and clean the surfaces being soldered. Lastly, reusability of flux doesn't align with ASTM B813 specifications, which typically dictates that it's used once during the soldering or brazing process for maximum effectiveness and then removed.