Question 45 MODE02 - Assistant MODU Engineer

The Correct Answer is C --- ### Why Option C ("Salt contamination") is Correct Testing auxiliary boiler water for chloride content is a critical operational procedure, particularly in a marine environment. Chloride ions ($Cl^-$) are highly corrosive under boiler conditions and must be strictly controlled. The primary source of sudden, high chloride contamination in a boiler system is the ingress of **seawater** (salt water), which is essentially a solution of sodium chloride (NaCl). Seawater leaks typically occur through failed condenser tubes or auxiliary heat exchanger leaks where the cooling medium is seawater. Because chloride is the key tracer element in sodium chloride, measuring the chloride level is the most direct and reliable way to determine if **salt contamination** has occurred due to a leak. --- ### Why the Other Options Are Incorrect **A) Total dissolved solids (TDS):** TDS is the measure of all dissolved inorganic and organic substances. While chloride contributes to TDS, a single test for chloride does not measure the total concentration of all solids (sulfates, carbonates, silicates, etc.). TDS is typically measured via conductivity. **B) Water hardness:** Water hardness is specifically defined by the concentration of multivalent cations, primarily calcium ($Ca^{2+}$) and magnesium ($Mg^{2+}$). These ions cause scaling and sludge formation. Chloride is an anion ($Cl^-$) and is not used to measure or define water hardness. **D) Chlorine contamination:** "Chlorine" (often referring to free chlorine, $Cl_2$, or hypochlorite, $ClO^-$) is typically associated with disinfectants used in drinking water. While chemically related, the boiler test specifically measures the concentration of **chloride ions ($Cl^-$)**, which are stable salts. In a boiler context, a high concentration of chloride ions signals salt (seawater) intrusion, not an overdose of oxidizing disinfectant.