81. Excessive alkalinity of boiler water will cause ________.

Excessive alkalinity in boiler water, typically from high caustic concentrations, directly causes caustic embrittlement, which is intergranular cracking of boiler steel. This damage occurs in stressed areas and is distinct from reactions related to oxygen scavenging, calcium carbonate precipitation, or general scale formation, all of which are primarily associated with water hardness rather than excessive alkalinity.