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Questions and Answers
What is the effect of dissolved oxygen in water used for boilers?
What is the effect of dissolved oxygen in water used for boilers?
- It has no impact on corrosion rates.
- It stabilizes metal surfaces against corrosion.
- It promotes the formation of scale deposits.
- It can cause pitting corrosion of steel surfaces. (correct)
How does temperature influence corrosion in boiler systems?
How does temperature influence corrosion in boiler systems?
- High temperatures have no effect on corrosion rates.
- Lower temperatures facilitate electrochemical reactions.
- Higher temperatures reduce the rate of corrosion.
- Corrosion rates generally increase with temperature. (correct)
What is one potential consequence of carbon dioxide in boiler feed water?
What is one potential consequence of carbon dioxide in boiler feed water?
- It completely removes all dissolved minerals.
- It enhances the stability of boiler metal.
- It can lead to the formation of carbonate scale deposits. (correct)
- It decreases pH, leading to less corrosive conditions.
Which of the following gases is known to have little effect on water used in boilers?
Which of the following gases is known to have little effect on water used in boilers?
How can suspended solids affect boiler systems?
How can suspended solids affect boiler systems?
What happens to the solubility of oxygen in water as temperature increases?
What happens to the solubility of oxygen in water as temperature increases?
What is a primary factor contributing to high temperature corrosion in boilers?
What is a primary factor contributing to high temperature corrosion in boilers?
What role does carbonic acid play in the context of boiler feed water?
What role does carbonic acid play in the context of boiler feed water?
What is the primary purpose of treating feed water in boilers?
What is the primary purpose of treating feed water in boilers?
Which component of feed water is pure and free from impurities?
Which component of feed water is pure and free from impurities?
Which type of water testing is essential for monitoring boiler water quality to prevent issues?
Which type of water testing is essential for monitoring boiler water quality to prevent issues?
What is the typical range for boiler water pH to help suppress corrosion?
What is the typical range for boiler water pH to help suppress corrosion?
What happens if feed water is not treated properly in a boiler?
What happens if feed water is not treated properly in a boiler?
Which of the following is NOT considered an impurity in feed water?
Which of the following is NOT considered an impurity in feed water?
What does the alkalinity of water indicate?
What does the alkalinity of water indicate?
From which water source is makeup water typically derived?
From which water source is makeup water typically derived?
What is the primary reason for using external treatment in a boiler system?
What is the primary reason for using external treatment in a boiler system?
Which combination treatment is known for its effectiveness in reducing hardness and silica in water?
Which combination treatment is known for its effectiveness in reducing hardness and silica in water?
What is the primary purpose of internal treatment in a boiler system?
What is the primary purpose of internal treatment in a boiler system?
What material is primarily used in cation exchange softeners to replace hardness ions in water?
What material is primarily used in cation exchange softeners to replace hardness ions in water?
Under what conditions is internal treatment typically utilized alone?
Under what conditions is internal treatment typically utilized alone?
What is caustic cracking primarily caused by?
What is caustic cracking primarily caused by?
Which statement about carryover is true?
Which statement about carryover is true?
How do scale deposits affect boiler operation?
How do scale deposits affect boiler operation?
What causes foaming in the boiler?
What causes foaming in the boiler?
Which minerals primarily contribute to the hardness of feed water?
Which minerals primarily contribute to the hardness of feed water?
What can result from large slugs of water carrying over with steam?
What can result from large slugs of water carrying over with steam?
What is a significant risk associated with scale in the boiler?
What is a significant risk associated with scale in the boiler?
What is a common cause of turbine damage in boilers?
What is a common cause of turbine damage in boilers?
What is the purpose of adding Na3PO4 in boiler water treatment?
What is the purpose of adding Na3PO4 in boiler water treatment?
What action should be taken if high phosphate levels are detected in boiler water?
What action should be taken if high phosphate levels are detected in boiler water?
Which chemical should be added to address low alkalinity in boiler water?
Which chemical should be added to address low alkalinity in boiler water?
What is the correct action when dissolved solids are detected at high levels?
What is the correct action when dissolved solids are detected at high levels?
To address the risk of caustic cracking, which chemical should be considered?
To address the risk of caustic cracking, which chemical should be considered?
If trace sources of chloride compounds are identified, what is the appropriate action to take?
If trace sources of chloride compounds are identified, what is the appropriate action to take?
Which chemical serves to condition sludge in a boiler system?
Which chemical serves to condition sludge in a boiler system?
What should be done when alkalinity levels are found to be high?
What should be done when alkalinity levels are found to be high?
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Study Notes
Water Impurities and Effects on Boilers
- Salts in water can lead to scale formation and corrosion, threatening boiler integrity.
- Contaminated feed systems often stem from saltwater intrusion via leaking condensers or evaporators.
- Dissolved gases, especially oxygen and carbon dioxide, can cause significant corrosion; oxygen leads to pitting, while carbon dioxide creates acidic conditions.
- Water can contain up to 9 ppm of dissolved oxygen at room temperature; solubility decreases as temperature rises.
- Carbon dioxide in water contributes to the formation of carbonate scale when in alkaline conditions with calcium and magnesium.
Impact of Suspended Solids and Temperature
- Suspended solids like mud, sand, and clay settle and create deposits that promote corrosion.
- Higher temperatures accelerate corrosion rates via increased energy driving electrochemical reactions.
- High-temperature corrosion occurs particularly when loss of circulation overheats metal in steam.
Types of Boiler Corrosion
- Caustic cracking arises from high alkalinity water contacting unstressed steel, typically seen around leaking joints.
- Carryover occurs when contaminants leave the boiler with steam; it can damage turbines and valve systems.
- Scale is formed from hardness in feed water, particularly calcium and magnesium, leading to reduced heat transfer and higher metal temperatures.
Importance of Feed Water Management
- Continuous feed water, which includes condensate, flash steam, and makeup water, is essential for steam production.
- Makeup water often contains impurities, requiring treatment to avoid issues like scale and corrosion.
- Feed water impurities are categorized into dissolved gases, dissolved solids, and suspended solids, each needing specific treatment.
Boiler Water Testing and Treatment Procedures
- Regular testing of boiler water is crucial to maintain system integrity and efficiency.
- pH testing is vital; optimal ranges (9.5 - 11.5) help suppress corrosion.
- Alkalinity testing ensures sufficient bicarbonate, carbonate, and hydroxide levels to prevent scale formation.
- High dissolved solids indicate a need for blowdown and fresh feed.
- Chloride testing helps identify leaks that may need rectification.
External Treatment Methods
- External treatment methods like softening, evaporation, and deaeration tailor feed water for specific boiler systems.
- Cation exchange softeners replace calcium and magnesium with sodium to reduce hardness without affecting total solids.
- The hot lime-zeolite process combines lime treatment for hardness and cation exchange to allow for comprehensive impurity reduction.
Internal Treatment Techniques
- Internal treatment deals with impurities directly within the boiler system.
- Used in conjunction with external treatments, it focuses on conditioning feed water hardness and preventing foaming.
- Especially effective when boilers operate under low or moderate pressure and utilize high-quality raw water.
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