Boiler Water Test

Boiler water tests:

1. Alkalinity test. [a.Phenopthelin (P) alkalinity test  b.Total (T) alkalinity test ]
2. Chloride test
3. Excess phosphate test
4. pH test 
5. Amerzine test (Hydrazine test)
6. Conductivity test (total dissolve solids test) 
7. Hardness test

Purpose of Boiler water Test:

1. To ensure that proper chemical treatment are maintained at all time.
2. To detect the presence of contaminants in the water that may damage the boiler and feed system.

How to collect water sample for test?

• Test sample must be cooled to 25°C with the help of sample cooler.
• Allow sufficient water to flow through sample line before taking the sample, this will clear it from sedimentation.
• Let the water overflow from sample bottle to prevent air being trapped.
• Keep the bottle air tight for testing.
• If sample is colored or turbid, filter paper should be used for testing.
• Try to take sample  from same point.
• Try to avoid the sample to contact with air,  this will change the dissolved Oxygen content.

Alkalinity test: 

This is to ensure that the boiler water prevent corrosion by neutralization of acidic gases.

Phenopthelin test [P-Alkalinity test]

This test is for finding amount of hydroxides in boiler water.

Procedure:

1. Take 100 ml of boiler water sample.
2. Add 10 drops of Phenopthelin.
3. Colour will change to Pink.
4. Now add N/50 Sulphuric acid, till colour will varnish.
5. The quantity of Sulphuric acid will indicate Phenopthelin alkalinity of boiler water.

Result:

P-Alkalinity in PPM=Drops of Sulphuric acid ×10

Total Alkalinity test: 

This test is to determine the amount of Hydroxide,Carbonate,Bi-Carbonate in boiler water.

Procedure:

1. With the above sample add 10 drops of Methyl Orange.
2. Colour will change to Orange.
3. Now add Sulphuric acid, till colour change to Pink.

Result: 

T-Alkalinity in PPM=Drops of Sulphuric acid × 10 

Hydroxides and Carbonates can co-exist together in a solution but Hydroxides and Bi-Carbonates cannot.

Chloride test:

This test is to know the amount of salt in boiler water. 

To minimize the chloride level and to adjust the blow down.

Procedure:

1. Sample after P-Alkalinity to be used.
2. Add 10 drops of Potasium Chromate.
3. Colour changes to Yellow.
4. Add N/35.5 Silver Nitrate (Ag NO3), till colour changes to Brick Red.

Result:

Chloride content =No. of drops of AgNO3 ×10 

Chloride content < 300 PPM

Phospate test: 

To control the scale formation due to hardness.(presence of Phospate sample means no hardness salts)

A reserve of Phospate should be maintained in the boiler water ready to neutralize any hardness salts which may enter.

Procedure:

1. Take 25 ml of filtered boiler water sample.
2. Add 25 ml of reagent Molybdate.
3. Then add one small spoon of stannous Chloride.
4. Colour will change to Blue.

Result: 

Use comparator to check the phospate.

40 - 60 PPM should be maintained. 

pH test: 

To control condensate pH value within limit.

To minimize corrosion in steam and condensate system.

Procedure: 

1. It is checked by using pH paper.
2. Dip the pH paper.
3. Use the colour comparator to check the pH.

Result: 

Should be 10-11

Hardness test: 

To check for salt causing "hardness "

Hardness test of boiler is not necessary when the Phospate is above the lower limit of control range.

Procedure: 

1. This test can be carried out by conductivity meter or by a standard soap solution.
2. Take boiler water in beaker.
3. Add soap solution and stir it for sometime.

Result: 

more foam formed, less is the hardness in boiler water. 

conductivity test: 

To measure the total amount of dissolved solids (T.D.S) including treatment chemicals.

(Excessive density leads to priming and deposits)

To remove dissolved and suspended solid by blowing .

1.Higher conductivity,  higher the hardness.

2.with the hardness test, have the general idea about conductivity. 

3000 micro siemens/cm for high pr. boiler 

400 micro Siemens/ cm for low pr. boiler 

Amerzine test (Hydrazine test) 

• To test for dissolved Oxygen content. 
• To know reserve Hydrazine (N2H4) ppm to prevent corrosion and aeration.
• To minimize Oxygen pitting and corrosion in boiler, steam and condensate system.

what do you do for preventing of Oxygen?

Oxygen scavenging chemical used for deaeration the water. 

Usually Sodium sulphate (Na2O3) or Hydrazine (N2H4) 

2Na2SO3 + O2 = 2Na2SO4

2N2H4 + O2 = 2H2O + 2NH3 

Excess dosage of Hydrazine lead to steam and condensate line corrosion due to Ammonia being produced as the  excess Hydrazine decomposed.

Fe3O4 --> Magnetite 

{some Hydrazine carried away to steam  line.  It forms layer on pipe line & it will give corrosion protection}