In what way does contamination primarily affect corrosion resistance in a weld?

Contamination primarily decreases corrosion resistance in a weld due to the introduction of unwanted substances into the weld area, such as oil, dirt, rust, or other impurities. These contaminants can create localized areas in the weld where the desired metallurgical properties are compromised. When the weld is exposed to corrosive environments, the presence of these impurities can lead to galvanic corrosion or pitting corrosion, where the metal is selectively corroded. Additionally, contaminants can interfere with the formation of protective oxide layers, which are essential for maintaining corrosion resistance. Therefore, ensuring a clean welding environment is critical for achieving optimal corrosion resistance in welded joints.