Question 1

Boiler water test? Why phosphate reserve Why hydrazine required? How oxygen affects?

Accepted Answer

Boiler water lives on tests: chloride sets blowdown, phosphate eats hardness, hydrazine eats oxygen that pits steel. Chloride test reads salt in ppm — rising chloride orders blowdown before foaming and carryover. Phosphate reserve proves no hardness salts free: it neutralises incoming hardness into removable sludge. Hydrazine reserve proves dissolved oxygen scavenged — oxygen otherwise pits drums, tubes and condensate lines. Back them with condensate pH and conductivity: low pH corrodes steam sides while high conductivity betrays contamination. Surveyor follow-up: phosphate nil with chloride steady and oxygen reserve present — scale, corrosion or carryover threatens first?

Question 2

Scale formation on evaporater

Accepted Answer

Evaporator scale is density plus heat: control brine density and temperature and scale never gets a footing. Submerged coils near 60°C barely scale; hotter surfaces bake magnesium and calcium sulphate hard. Convert only about half the feed to distillate — brine pump or ejector must clear the rest continuously. Hold level on the brine weir and cap output at rating; excess evaporation thickens brine into scale. Dose polymer to flocculate salts into the brine or acid-clean periodically when soft carbonate films appear. Surveyor follow-up: output high with density climbing past limits — throttle feed, open brine or dose chemical first?

Question 3

Boiler water treatment is carried out in order to prevent scaling, to give alkalinity, to condition sludge, to remove traces of oxygen, to reduce risk of caustic embrittlement, to reduce risk of carry over of foam, to ne

Accepted Answer

Boiler water treatment exists for seven reasons at once, and every test on the ship maps onto one of them. Prevent scaling, and give the water the alkalinity that keeps the magnetite film intact. Condition sludge so it stays dispersible and is blown away instead of baking onto the tubes. Remove dissolved oxygen, the scavenger doing the work against pitting of the drum and tubes. Reduce caustic embrittlement, reduce foaming and carryover, and keep the deposits that cause overheating out of the water side. Surveyor follow-up: alkalinity right, phosphate nil and the water foaming — which of the seven has actually been lost?

Question 4

Mechanics of scale formation

Accepted Answer

Scale forms where a bubble hides the metal: heat soaks through, the water under it concentrates past saturation, and salt precipitates on the plate. A steam bubble forms on the heating surface and momentarily insulates the plate beneath it from the water. The water under the bubble gets locally overheated, and its dissolved salts concentrate past saturation. The concentrated salt then deposits on the plate as hard scale, and the layer grows from there. Calcium sulphate is the most dangerous of the formers — a hard tenacious scale that wrecks heat transfer and causes tube failure. Surveyor follow-up: scale found under a row of tube failures with the phosphate reserve in band — is it the film, the salt or the bubble?

Question 5

Scale forms in boilers due to the presence of various salts which come out of solution and deposit because of the effects of temperature and density

Accepted Answer

Scale forms because a bubble insulates the plate, the water under it superheats and evaporates, and the salts it held are left behind as scale. Salts are soluble in the boiler water only while conditions are normal; if the density is carried too high a salt may deposit and form scale. Calcium sulphate is the most dangerous scale former — a hard tenacious deposit that badly cuts the rate of heat transfer. In the simplest description, a steam bubble forms on the heating surface, the plate under it is momentarily insulated and overheats, and the water there boils off. The salts left behind by that evaporation are the scale, and the tube under them runs far above its design temperature. Surveyor follow-up: tube showing heavy scale with a hot spot opposite it — what is the scale doing, and what causes it there?

Question 6

The serious results caused by scale deposition are

Accepted Answer

Scale is a heat-transfer killer: less heat gets through, the tube runs hotter, and the tube fails — the scale is the warning, not the fault. Heat transfer drops sharply, so the same firing produces less steam and the combustion temperatures climb. The tube metal overheats, oxidises and finally bursts under the pressure behind it. Loss of efficiency follows, so more fuel is burnt for less steam and the exhaust temperature rises. Under-deposit corrosion and caustic gouging set in once the deposit is there, so removing scale is remedial, preventing it is the job. Surveyor follow-up: tube burst with scale found and the blowdown schedule met — is it the treatment, the feed or the blowdown?

Question 7

This covers non-toxic, small-scale, aqueous corrosion testing in a variety of different environments including fresh and sea water. Fracture and Mechanical Testing

Accepted Answer

Small-scale aqueous corrosion testing is how galvanic order is established — immerse coupled metals and let the least noble one tell you where the damage goes. Sea water is circulated, heated and stored within a vessel and is strongly corrosive because it is a good electrolyte. With dissimilar metals in sea water, galvanic action results and the more anodic metal corrodes — so the test is about coupling, not about one alloy alone. In the galvanic series for sea water, titanium sits at the noble end, with graphite, Monel, stainless steel, nickel, cupro-nickel, gunmetal, aluminium bronze and copper below. And anything in the table is anodic to the metals above it, which is exactly why cupro-nickel condenser tubes are fitted alongside a steel hull. Surveyor follow-up: steel hull with aluminium bronze fittings below it in the galvanic table — which metal corrodes, and how is it protected?

Boiler Water Treatment — Most Asked Questions

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