Nickel-Molybdenum Passivation Layer

The passive layer on nickel-molybdenum alloys forms through reaction with oxygen and protects the material from corrosion. When welding, you need to be careful that this layer doesn't get damaged or undesirably altered by excessive heat input. If the layer is destroyed, it can lead to corrosion and cracking in the weld zone. Keep the interpass temperature within limits and ensure the weld has a chance to rebuild its protective layer after cooling. Post-treatment with acid or pickling can help clean the surface and support reformation of the passive layer, but don't overdo it.