Are the requirements for flash rust inhiitors higher at welded joints?

In steel structures, submerged arc welding represents a common connection method for pipelines. While other welding techniques exist on the market, their impact on submerged arc welding's application scope remains limited. Submerged arc welding offers numerous advantages for steel structures; however, the heating process during welding alters the composition of the welded area. Consequently, after application of water-based anti-rust paint, this region becomes highly susceptible to flash rust.

 How can submerged arc welding better prevent flash rust?

First, one must understand the root cause of flash rusting in submerged arc welding and its prevention strategies. What changes occur due to the heating process? The welding arc burns on the filler wire and workpiece, melting the flux into a molten pool and slag. Upon cooling, the molten pool forms the weld, while the slag provides mechanical protection on the weld surface. It undergoes metallurgical reactions with the molten metal, altering the chemical composition of the weld. When water-based anti-rust coatings are applied to welds, flash rust readily forms due to alterations in weld material composition and impurities. A common approach to mitigate flash rust issues involves adding flash rust inhibitors to water-based coatings. However, the altered weld composition makes conventional flash rust inhibitors ineffective at suppressing flash rust formation within the weld.

Flash rust inhibitors are responsible for developing the weld's chemical composition, preventing cathodic potential difference reactions within the weld and avoiding the ionisation of iron elements. They exhibit excellent anti-flash rust performance, such as in submerged arc welds and cast iron components, while also enhancing the adhesion and salt spray resistance of water-based coatings.