Purpose of Boiler Water Tests

Purpose of boiler water treatment

• Prevent corrosion of boiler tubes and shell
• Prevent scale formation and hence maintain heat transfer rates.
• Control sludge formation within the boiler.
• Control foaming and priming. Prevent entry of foreign matter, oil etc. into the boiler via feed system
• Extend boiler survey to the maximum allowed.

FOLLOWING TESTS ARE CARRIED OUT:-

Boiler water tests are therefore done to ensure that the chemical levels are maintained as required.

Chlorides : This is a measure of presence of Chlorides, usually an indication of contamination of Boiler water with sea water.( Sodium Chloride / Calcium or Magnesium Chloride ) . This results in increased scale formation, acidity and boiler priming. 

Normal levels: Chlorides< 300 ppm. 

What to do if chloride content increases beyond normal value.?

Check for leakages of SW into the system, mainly from atmospheric condenser leak and rectify any leaks found. Blowdown at regular and frequent intervals and replenish with distilled water till chloride content becomes normal.

Alkalinity:- There are two measurements of Alkalinity

P Alkalinity – It measures Alkalinity due to Hydroxides and Phosphates. pH testing also determines Alkalinity but is less accurate method. If Alkalinity is too low than corrosion could occur. Too high Alkalinity may result in Foaming.

TOTAL ALKALINITY – It measures the Alkalinity of all the other boiler salts, including bicarbonates. Total Alkalinity should be less than 2x P Alkalinity. This may occur when large quantities of untreated feed is admitted in to the boiler.

pH: 9.8-10.2

Phosphates- A sufficient reserve of Phosphates should be present
in Boiler Water, to neutralize any Hardness salts. These salts would
deposit as scale on the heating surfaces if the phosphate reserves
are too low while too high reserves of phosphates may lead to foaming and excess production of sludge which if not removed, will deposit on heating surfaces

Normal Values of Phosphate: 15 – 25 ppm

Oxygen Scavengers:- These chemicals are added to chemically
deoxygenate the boiler water. Useful in closed feed system as the oxygen will enter the boiler water in open hot well. The test is carried out to find the levels of chemical reserve of Hydrazine used for the purpose of deoxygenating the boiler water. If the Chemical reserve is low, corrosion will occur, if the hydrazine level is high it will form ammonia which can attack copper alloys in the feed system

Normal values of Hydrazine: 0.05-0.1 ppm

TOTAL DISSOLVED SOLIDS:- This is a measure of all the dissolved solids in the boiler water including those from the chemicals added. This test is done by using a electrical conductivity meter but the sample should be neutralized before test as the alkaline sample will affect the TDS reading