Objective 5: Sampling and Testing Flashcards Preview

3B1-10: Internal Water Treatment of Boilers > Objective 5: Sampling and Testing > Flashcards

Flashcards in Objective 5: Sampling and Testing Deck (49)
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What measuring units are typically used?

Metric units



Parts per million


What is the relationship between PPM and mg/L?

PPM x solution density = mg/L


What is the relationship between PPM and mg/L for water?

PPM = mg/L

Since water's density is taken to be 1.0.


What are 11 Guidelines for Monitoring and Testing of Boiler Water?

1. Identified critical points in the boiler system from which to take and test samples
2. Time schedule for sampling and testing

3. Clear, detailed procedure and interpretation for each test

4. Established acceptable limits for each tested parameter

5. Comparison of test results against acceptable limits

6. Guidelines to maintain each tested parameter within acceptable range.

7. Schedule and procedures for control chemical injections

8. Acceptable training for relevant personnel

9. Regular reporting procedure of results

10. Forecasting steam production and corresponding make-up requirements

11. Emergency troubleshooting procedures for severe excursions


What are the Typically Monitored Parameters?

1. Phosphate
2. Sulphite

3. Alkalinity

4. Total Dissolved Solids

5. pH Measurement

6. Chloride

7. Iron

8. Dissolved Oxygen

9. Steam Purity

10. Sampling


What is the most common method to determine Phosphate Residual in the water?

Ortho-Phosphate Test


What may be considered an acceptable Phosphate Residual?

Depending on the plant, anywhere from 2.0 mg/L (for complex equilibrium program) to 20 or 30 mg/L (for coordinated program).


Ortho-Phosphate Test

A measured amount of boiler water is mixed in a tube with specific amounts of reagents (one of which is molybdate). The water will turn a blue colour, with the depth of colour corresponding to the amount of phosphate in the water. The tube colour is then compared against standard coloured tubes, which are each marked to represent a specific mg/L or ppm of phosphate.


What instrument can be used for a more sophisticated and complete determination of all phosphate components?



Where is the feed point for sulphite?

1. Deaerator
2. Between the deaerator and the boiler


What is the typical sulphite residual maintained?

10-20 mg/L


What is the Sulphite Test Process?

1. Get a fresh sample of boiler water which has had as little exposure to air as possible, cooled to room temperature
2. Phenolphthalein indicator is added to the water, turning it red

3. Sulphite indicator is added until the water becomes clear, indicating an acceptable pH

4. Sample is titrated with potassium iodide-iodate solution until a faint permanent blue colour appears

5. The mL of titrant used is multiplied by a factor


What are the 3 Alkalinity Tests?

1. P Alkalinity
2. M Alkalinity

3. OH Alkalinity


P Alkalinity

P stands for Phenolphthalein, which is a titrating indicator that changes colour at a pH of 8.3 and used to indicate half of the carbonates plus all hydroxides in the water.


M Alkalinity

M stands for Methyl, which is a titration indicator that changes colour at a pH of 4.3 and is used to indicate the TOTAL amount of alkalinity (i.e. carbonates + hydroxides + bicarbonates) in the water.


OH Alkalinity

OH stands for Hydroxide and is a calculated alkalinity: 2P - M = OH. It gives only the amount of hydroxide alkalinity in the water and is often referred to as the caustic alkalinity.


Which Alkalinity Reading is generally used for control?

M Alkalinity


What are the methods of controlling Alkalinity?

1. Adjusting Phosphate Feed
2. Adding Caustic Soda

3. Boiler blowdown


What are the acceptable limits of Total Alkalinity?

0-2 MPa: <350 mg/L
7-10 MPa: <100 mg/L


Explain the process of Alkalinity Testing

1. Phenolphthalein indicator is added to a boiler sample which then turns red
2. Sample is titrated with sulphuric acid until the sample becomes clear - the endpoint for P Alkalinity

3. Methyl orange is added to the same sample, which then turns orange

4. Sample is titrated with sulphuric acid until it turns red - the endpoint for M Alkalinity


Boiler Conductivity

The ability of water to conduct an electric current


Specific Conductance

The measure of the exact amount of electricity that can be conducted by a particular sample


What is relationship between the amount of dissolved solids and conductivity?

The specific conductance indicates the amount of total dissolved solids in the water.


What are the units of specific conductance?

µ mhos/cm: micro-mhos per cm
µ S/cm: micro-siemens per cm


What is the approximate mathematical relationship between the specific conductance and the actual total dissolved solids in the water?

1.0 µmho/cm of conductivity = 0.9 mg/L of dissolved solids


Explain the process of Conductivity Testing

A measured amount of filtered boiler water is placed in a flask and then a probe from a conductivity meter is placed into the water. The meter passes a current between electrodes in the probe and then measures and indicates the current on a display that is calibrated to read in µmhos. Some indicate the total dissolved solids directly.


What is the main value of pH testing?

As a backup when alkalinity is used for control.


Why is pH Testing important?

Control of corrosion and the effectiveness of scale-reducing reactions are very pH dependent.


What are the acceptable pH ranges for boilers?

6 MPa: 9.0 - 9.6