Boiler (MEP) — Most Asked Questions

5 questions asked about boiler (mep) across the General and Fn 6 papers, heaviest first.

1. 1 Boiler feed pump type

   Revise Theory asked 4 times · across 3 examiner banks · 2 wordings merged General

   Also asked: “Type of boiler feedwater pump”

   Answer

   Feed pumps are multistage centrifugals for pressure with positive-displacement backing where suction runs dry.

   • Multistage centrifugal stacks impellers for boiler pressure with overhung or ring-section builds.
   • Close-coupled motor pumps serve small duties; staged ring pumps serve the main feed range.
   • Positive-displacement plunger or screw sets back them where suction lifts and turndown defeat centrifugals.
   • Prove by discharge pressure against steam pressure plus control margin with auto changeover tested.

   Surveyor follow-up: feed pressure sagging at full firing — stages worn, suction starved or control valve, and what proves it?

   Full theory: Boiler Plant Working Flow

2. 2 How to change the boiler water level gauge glass?

   Revise Theory asked 3 times · across 3 examiner banks General

   Answer

   Change gauge glasses shut-and-drained: isolate steam and water, vent, renew glass with fresh seals, prove by blow-through.

   • Shut steam and water cocks to the gauge and open the drain — never pull a glass under pressure.
   • Remove the defective tube with guards and handling against scald and cuts, cleaning seats for new seals.
   • Fit the new glass with correct packings, leave cocks shut until boxed up, then crack open slowly to warm through.
   • Prove level by drain-and-refill blow-through with both cocks open — false level kills more boilers than leaks do.

   Surveyor follow-up: new glass fitted with old seals and full pressure slammed on — leak, crack or false level first?

   Full theory: Normal Operation, Load Control, and Watchkeeping

3. 3 why you need to remove oxygen from boiler feed water and how to remove?

   Revise Theory asked 3 times · across 3 examiner banks · 2 wordings merged Fn 6

   Also asked: “what chemical you add in boiler water to remoce oxygen”

   Answer

   Dissolved oxygen pits boilers from inside: strip it mechanically, scavenge it chemically, and prove a reserve.

   • Oxygen attacks drums, tubes and condensate returns as deep pits that burst under pressure.
   • Deaerate feed by heating, cascade and venting — high-pressure plants demand a proper deaerator.
   • Dose hydrazine to hold 0.02–0.1 ppm reserve with feed O₂ below 10 ppb; it breaks to ammonia and nitrogen helping alkalinity.
   • Guard the magnetite film with pH 8.6–9.0 and sludge conditioning — acid water strips what oxygen starts.

   Surveyor follow-up: reserve hydrazine nil with feed O₂ in limits — dose, vent or blow down, and what pitting follows delay?

   Full theory: Boiler Water Treatment, Testing, and Blowdown

4. 4 To prevent corrosion in the boiler feed system by maintaining the boiler water's alkaline condition

   Revise Theory asked 2 times · across 2 examiner banks · 2 wordings merged General

   Also asked: “To prevent corrosion in the boiler feed system by maintaining the boiler water’s alkaline condition”, “To prevent corrosion in boiler and feed system. —”

   Answer

   Keep the boiler water alkaline: alkalinity suppresses the acidic corrosion of the feed and boiler steel, and phosphate ties up the hardness.

   • Below 14 bar, sodium carbonate precipitates the salts and provides the alkalinity; magnesium sulphate acts as a sludge conditioner.
   • For medium pressure, sodium carbonate with sodium phosphate and sludge conditioners is used, and above 42 bar a deaerator is required.
   • An oxygen scavenger is added so that a magnetite layer can form on the steel — that layer is the protection, not the chemical itself.
   • At 42 bar and above, sodium carbonate dissociates, so sodium hydroxide is preferred for better controllability; note it attacks the magnetite, which is why congruent treatment is used.

   Surveyor follow-up: low pH in the drum after a deaerator change — which protection has stopped working?

   Full theory: Boiler Water Treatment, Testing, and Blowdown

5. 5 Type of boiler feed pump...(said multistage centrifugal pump

   Revise Theory asked 2 times · across 2 examiner banks General

   Answer

   The feed pump is centrifugal and multistage: each stage adds a little pressure, and together they lift the feed from the deaerator to the drum pressure.

   • A multistage centrifugal pump builds the high delivery pressure in series stages rather than in one impeller, which keeps the pump compact.
   • The suction is from the deaerator, which is the only feed source that can be at feed pump inlet pressure without cavitation.
   • In the arrangement usually quoted, a centrifugal feed pump and an auxiliary reciprocating feed pump stand by, the centrifugal running and the reciprocating taking over.
   • Because the boiler above 42 bar requires a deaerator, the pump type follows from the pressure the ship needs, not from preference.

   Surveyor follow-up: feed pump changeover to the reciprocating under load — what must be proved on the suction side?

   Full theory: Boiler Plant Working Flow

Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.