What problem commonly occurs to the base metal when a refractory lining cracks?

When a refractory lining cracks, the primary concern is often related to dew point corrosion. Dew point corrosion occurs when moisture settles on the cooler surfaces of a vessel or structural component, particularly in situations where high-temperature processes occur. The presence of cracks in the refractory lining allows for the cooler substrate or base metal to be exposed to fluctuations in temperature, leading to condensation of moisture on the metal surface.

As this moisture condenses, it can react with contaminants or other corrosive substances present, particularly if there are any lingering process fluids or combustion by-products. This can lead to accelerated corrosion of the base metal, especially if the temperature reaches a point where dew point conditions prevail. Addressing the integrity of the refractory lining is crucial to prevent these corrosive effects and protect the underlying metal from degradation.

Understanding this mechanism is vital in the inspection and maintenance of pressure vessels, as it highlights the importance of maintaining intact refractories to protect the structural integrity and longevity of the vessel.