Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Weld Flux

Last updated: October 31, 2018

What Does Weld Flux Mean?

Weld flux is a chemical purifying agent, flowing agent or cleaning agent. It is commonly used in metal joining and metallurgy. It is a material used to promote the fusion of metals and is employed in welding. The primary purpose of weld flux is to prevent oxidation of the base and filler materials during the welding process.

Some examples of flux materials include:

  • Ammonium chloride
  • Zinc chloride
  • Hydrochloric acid
  • Borax

Corrosionpedia Explains Weld Flux

The main function of weld flux is to oxidize the base and filler materials during the welding process. Weld flux is a substance that is almost inert at average room temperature but can be intensely reducing when exposed to higher temperatures to prevent metal oxide formation.

Flux dissolves the metal surface oxides that facilitate the molten metal wetting and acts as a barrier to oxygen and minimizes oxidation. Fluxes are used to generate a surface for wetting the solder.

However, flux can contain bromine and chlorine and can remain corrosive after the soldering process, subsequently causing corrosion to the surface throughout production or operation. Therefore, testing and cleaning techniques have been developed to ensure that the surface remains noncorrosive after the process.

The most common tests are designed to identify the flux residues' corrosive properties under extreme conditions. During testing, a solder pellet is melted when it comes in contact with the flux over a metal sheet. Afterward, the solder is exposed to various humidity levels. The corrosion generated is then evaluated visually.


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