If boiler water chemicals are decreasing in one boiler and increasing in the other boiler, while both are steaming at normal rates, a leak probably exists in the __________.

Correct Answer: Option D — internal desuperheater flange

An internal desuperheater flange failure allows high-purity superheated steam or desuperheater steam to mix directly into one boiler's drum water, diluting or concentrating chemical levels disproportionately compared to the sister boiler, shifting chemical concentrations between parallel steaming units under normal load.