Class 2 (2nd Engineer) MEKM 📅 Apr 2024

Exam Question

With reference to large starting air receivers:

(a) Explain where corrosion is likely to occur and state why it occurs in these regions. (4)

(b) State how the incidence of corrosion in air receivers might be minimized. (4)

(c) If serious corrosion is detected in a starting air receiver and that receiver must be used. Explain how you, as Second Engineer, would determine the maximum pressure to which the receiver should be subjected. (4)

(d) State the further action a Second Engineer must take upon discovering such air receiver corrosion. (4)

Reference Answer

(a) Corrosion in large starting air receivers is most likely to occur in areas where moisture and oil accumulate or where stress concentrations exist. These areas include:
Bottom of the air receiver is the lowest point, where water and oil from the compressed air naturally settle and remain. The constant presence of moisture and oil creates a highly corrosive environment, leading to pitting and oxidation of the steel.
Around valve openings, drain and fusible plug areas often experience leakage or seepage of moisture and oil, concentrating corrosion at these points. The disruption of the protective paint layer during installation or maintenance further exacerbates the problem.
Imperfect welds can create stress concentrations and points of weakness where corrosion is more likely to initiate. Additionally, the welding process itself can alter the material's microstructure, potentially making it more susceptible to corrosion.

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