API 571 Certification (Corrosion & Materials) Practice Test

What type of welding is a concern with corrosion in dissimilar metal welds?

1. Welding carbon steel to aluminum

2. Welding nickel alloys to 300 series stainless steel

3. Welding cast iron to carbon steel

4. Welding carbon steel to 300 series stainless steel

The correct answer is: Welding carbon steel to 300 series stainless steel

Welding carbon steel to 300 series stainless steel is indeed a significant concern when it comes to corrosion in dissimilar metal welds. This is primarily due to the differences in their electrochemical properties, which can lead to galvanic corrosion. When two dissimilar metals are in contact in the presence of an electrolyte, the more anodic metal (in this case, carbon steel) can corrode faster than it would on its own, while the more cathodic metal (300 series stainless steel) is protected. The difference in thermal expansion and the potential for microstructural changes due to the heat of welding can also exacerbate the situation. Carbon steel and stainless steel have different coefficients of thermal expansion, which can lead to thermal stresses and potential cracks at the weld interface. In environments where moisture or corrosive elements are present, these factors can severely compromise the integrity of the weld. Understanding the corrosion mechanisms at play in dissimilar metal welds is crucial for material selection and welding processes to ensure longevity and performance in various applications.