Boiler water tests

Corrosion and tube failure caused by water chemistry

Recommended ranges( Co-ordinated phosphate treatment for w/t boiler )

pH	- 9.6 to 10.3
PO4	- 4 to 20 ppm
N2H4	- 0.01 to 0.03 ppm
TDS	- < 150 ppm
Cond pH	- 8.6 to 9.0
Cl	- 20 ppm
O2	- 10 ppb
Si	- 10 ppb

Chlorides

• Measure 100ml of sample water into a casserole
• Add 10 drops phenol pthalein (RE 106)
• Neutralize with sulphuric acid
• Add 10 drops of Potassium Chromate
• Titrate Silver Nitrate untill sample just turns brick red
• ppm as CaCO₃= (ml x 10) ppm

TDS

• Measure 100ml of sample water into a casserole
• Add 10 drops of phenolpthalein
• Neutralise with TDS reagent (acetic acid)
• Temperature compensate then read off scale in ppm.

Phosphates

• Fill one 10 ml tube with distilled water
• Fill one 10 ml tube with boiler water tests.
• Add 0.5 ml sulphuric acid (RE 131) to each
  Add 0.5 ml Ammonium Molybdnate (RE130) to each
  Add 0.5 ml Aminonapthol Sulfonic acid (RE 132) to each
  Stir well between each addition
• Wait 3 minutes for calorimetric compaison

Alternately Vanado-molybdnate test

• Place 5 ml boiler water in 10 ml tube
• Place 5 ml distilled water in other 10 ml tube
• Top both to 10 ml with Vanado-molybdnate reagent
• Place in colour comparator and compare after 5 mins

Hydrazine

• Add 9ml distilled water to one tube
• Add 9 ml boiler test water to anouther
• Add 1 ml hydrazine reagent to each
• Use colour comparator

Alkalinity Phenolpthalein

• 100 ml filtered water
• Add 1 ml phenolpthalein
• If pH >8.4 Solution turns pink
• Add H₂SO₄ untill pink disapears
• Ml 0.02N H₂SO₄ x 10 = ALk in CaCO₃ ppm
• Measures hydroxides and carbonates in sample, bi-carbonates do not show up so sample should not be allowed to be exposed to the air for too long

Alkalinity Methyl orange

Bi carbonates do not show up in the phenolpthalein sample as they have a pH < 8.4. Bi carbonates can not occur in boiler but if suspected in raw feed then the following test.

• Take phenolpthalein sample, add 1 ml methyl orange
• If yellow, bi carbonates are present
• Add H2SO4 untill red
• Total 0.02N H₂SO₄ x 10 = Total Alk in CaCO₃

pH

• 100 ml unfiltered sealed water poured into two 50 ml glass stoppered test tubes
• Add 0.2 ml pH indicator to one ( pH indicator vary's according to required measuring range)
• Use colour comparator
• Due to difficulty of excluding air, electronic pH meter preferred

Sulphite reserve

• Exclude air at all stages
• 100 ml unfiltered water
• Add 4 ml H₂SO₄ + 1 ml starch
• Add potassium iodate-iodide untill blue colour
• ml Iodate-Iodide sol x 806 / ml of sample = SO₃ reserve in ppm

Ammonia in feed

• Only necessary where N₂H₄ used in blr
• Pour condensate sample into two 50 ml colour comparator tubes
• Add 2 ml Nessler reagent to one
• Wait 10 mins
• Use colour comparator