114 Questions
EASY Why is internal treatment of water essential in boilers?
to prevent boiler failure due to remaining impurities
What is the main purpose of internal water treatment in low-pressure steam heating boilers?
to prevent scale formation
What is the result of not treating internal water in boilers?
boiler failure
What is the primary function of internal water treatment in high-pressure boilers?
to monitor chemical and impurity levels
What is the purpose of precipitating feedwater hardness in internal water treatment?
to limit scale formation
What is the range of the pH value?
0 to 14
What is the purpose of internal water treatment in low-pressure hot water boilers?
to focus on pH control and corrosion prevention
Why is internal water treatment more extensive in high-pressure boilers?
due to high make-up water requirements
What causes pitting in the boiler and condensate lines?
Dissolved oxygen
What is the purpose of a deaerator?
To remove dissolved oxygen from the boiler feedwater
What is the byproduct of the reaction between oxygen and sodium sulfite?
Sodium sulfate
Why is hydrazine no longer commonly used as an oxygen scavenger?
It is highly toxic
What is the advantage of using DEHA as an oxygen scavenger?
It has very low toxicity
What type of amine is fed directly to the boiler?
Neutralizing amine
What is the purpose of filming amines?
To create a thin coat on piping surfaces
What is the function of molybdate?
To inhibit corrosion
What happens to dissolved oxygen as water temperature increases?
It decreases
What is a problem associated with using sodium sulfite as an oxygen scavenger?
It increases the concentration of dissolved solids
What does the pH of water indicate?
The degree of acidity or alkalinity of water
What is the pH level of neutral water?
7
What is the result of water being acidic or excessively basic?
More boiler corrosion occurs
What is the typical pH range for boilers to limit corrosion?
8.5 to 10.5
What is caustic embrittlement also known as?
Caustic cracking
What is the result of caustic embrittlement?
Both a and b
What is caustic gouging?
A type of corrosion caused by sodium hydroxide
What is the result of caustic gouging?
The affected metal becomes progressively thinner
What is the main cause of foaming in boiler water?
Organic material
What is the purpose of continuous surface blowdown?
To remove impurities from the boiler water
What is the purpose of molybdate in boilers and closed loop cooling systems?
To precipitate an inert passivating barrier layer on the metal surface
What is the recommended concentration range of molybdate in boiler water?
75-125 ppm
What is the effect of scale formation on heat transfer in a boiler?
It reduces heat transfer
What is the estimated increase in fuel costs for a 0.1 cm scale thickness?
9%
What is the purpose of adding sodium phosphate to boiler water?
To precipitate calcium and magnesium compounds in a different form
What is the recommended phosphate residual in boiler water?
20-40 ppm
What is the purpose of chelants in boiler water treatment programs?
To trap and hold metallic ions
What is the purpose of organic compounds like starch in boiler water treatment?
To condition and disperse soft scale
What can happen to boiler tubes if scale deposition results in local overheating?
They will overheat, bulge, and eventually rupture
What is the purpose of intermittent bottom blowdown in boiler water treatment?
To remove soft scale and sludge from the boiler
MEDIUM What is the result of high water temperatures on the solubility of oxygen?
Oxygen becomes less soluble
What is the purpose of scavenger chemicals in boiler feedwater?
To react with oxygen and prevent corrosion
What is a disadvantage of using sodium sulfite as an oxygen scavenger?
It increases the dissolved solids concentration in the boiler
What is a characteristic of filming amines?
They create a thin coat on piping surfaces
What is the purpose of neutralizing amines in boiler water treatment?
To neutralize acids formed in the condensate
What is the function of molybdate in boilers?
To protect the boiler against general corrosion and oxygen pitting
Why is hydrazine no longer commonly used as an oxygen scavenger?
It is toxic and requires special handling
What is the advantage of using DEHA as an oxygen scavenger?
It has very low toxicity and high volatility
What is the result of oxygen pitting in the boiler and condensate lines?
It causes highly localized corrosion
What is the purpose of a deaerator in boiler water treatment?
To remove dissolved oxygen from the water
What is the primary reason for internal treatment of boiler feedwater?
Because external treatment cannot remove all impurities
What happens to the steel in a boiler when a caustic buildup forms under a deposit?
The magnetite layer is stripped off the wall
What is the main consequence of not treating internal water in boilers?
Scale formation and corrosion
What is the effect of a high concentration of dissolved and suspended solids in boiler water?
It causes foaming within the boiler
What is the purpose of controlling the concentration of dissolved and suspended solids in the boiler water?
To prevent foaming
What is the primary method of preventing caustic embrittlement?
Limiting the boiler water NaOH concentration to the minimum required
What is the typical pH range for boilers to prevent corrosion?
9-11
What is the typical pH range for boilers to limit corrosion?
8.5 to 10.5
What is the purpose of providing the right level of alkalinity in boiler water treatment?
To prevent corrosion
What is the result of caustic gouging?
The affected metal becomes progressively thinner
What is the primary reason for internal water treatment being more extensive in high-pressure boilers?
Greater risk of corrosion
What is the purpose of precipitating feedwater hardness in internal water treatment?
To keep hardness in suspension for blowoff
What is the purpose of continuous surface blowdown?
To prevent foaming and carryover
What is the result of a high pH level in boiler water?
Foaming and carryover
What is the main consideration for internal water treatment in low-pressure hot water boilers?
pH control and corrosion prevention
What is the effect of steam blanketing on the boiler metal?
It allows salts to concentrate on the boiler metal surface
What is the purpose of adding anti-foaming agents to the boiler water?
To control foaming and carryover
What is the typical location of caustic embrittlement on boiler tubes?
At the points where the tubes are rolled into sheets, drums, or headers
What is the primary reactant that forms a passivating barrier layer on the metal surface in boilers and closed loop cooling systems?
Molybdate
What is the main consequence of scaling in boilers?
Increased fuel costs and risk of tube rupture
What is the purpose of adding sodium phosphate to boiler water?
To prevent scale formation
What is the effect of local overheating on boiler tubes?
Tube bulging and eventual rupture
What is the purpose of chelants in boiler water treatment programs?
To trap and hold metallic ions
What is the recommended concentration range of molybdate in boiler water?
75 to 125 ppm
What is the purpose of organic compounds like starch in boiler water treatment?
To condition sludge and prevent deposition
What is the estimated increase in fuel costs for a 1 cm scale thickness?
70%
What is the result of not maintaining a sufficient phosphate residual in boiler water?
Increased risk of scale formation
What is the purpose of intermittent bottom blowdown in boiler water treatment?
To remove sludge and precipitated solids
What is the primary mechanism of caustic embrittlement?
Concentration of caustic under deposits
What is the purpose of adding sodium nitrate, lignins, and tannins to boiler water?
To prevent caustic embrittlement
What is the result of caustic gouging?
Progressive thinning of tube metal
What is the purpose of continuous surface blowdown?
To prevent foaming
What is the effect of high pH levels in boiler water?
Increased corrosion rates
What is the result of carrying over liquid water into the steam line?
Priming
What is the purpose of adding anti-foaming agents to boiler water?
To reduce foaming
HARD What is the effect of acidic or excessively basic boiler water?
Increased corrosion rates
What is the purpose of limiting NaOH concentration in boiler water?
To prevent caustic embrittlement
What is the result of concentrated caustic buildup under deposits in boiler tubes?
Caustic gouging
What is the primary reason for internal treatment of boiler feedwater in high-pressure boilers?
To remove impurities that were not removed by external treatment
What is the main purpose of precipitating feedwater hardness in internal water treatment?
To limit scale formation by keeping it in suspension
What is the primary function of internal water treatment programs in low-pressure steam heating boilers?
To focus on pH control and corrosion prevention
What is the main consequence of not treating internal water in boilers?
Boiler failure
What is the primary purpose of internal water treatment in low-pressure hot water boilers?
To focus on pH control and corrosion prevention
What is the main reason for stricter internal water treatment requirements in high-pressure boilers?
Higher risk of impurities causing damage
What is the primary function of internal water treatment programs in low-pressure steam heating boilers with respect to make-up water?
To reduce the need for make-up water
What is the main purpose of internal water treatment programs in boilers with respect to suspended solids?
To prevent suspended solids from adhering to the boiler metal
What is the primary mechanism by which oxygen scavengers like sodium sulfite and hydrazine prevent corrosion in boilers?
By reacting with oxygen to form a stable compound
What is the primary advantage of using diethylhydroxylamine (DEHA) as an oxygen scavenger over hydrazine?
DEHA is less toxic and has a higher volatility than hydrazine
What is the primary function of filming amines in boiler water treatment?
To create a thin coat on piping surfaces to protect against corrosion
What is the result of high water temperatures on the solubility of oxygen in water?
The solubility of oxygen decreases
What is the primary disadvantage of using sodium sulfite as an oxygen scavenger in high-pressure boilers?
It increases the dissolved solids concentration in the boiler
What is the primary purpose of neutralizing amines in boiler water treatment?
To neutralize acids formed in the condensate
What is the primary function of molybdate in boiler water treatment?
To inhibit general corrosion and oxygen pitting
What is the result of oxygen pitting in the boiler and condensate lines?
Localized corrosion of the metal surface, resulting in pitting
What is the primary purpose of a deaerator in boiler water treatment?
To remove oxygen from the water
What is the primary advantage of using scavenger chemicals in boiler feedwater?
They remove oxygen from the water, preventing corrosion
What is the chemical formula for the reaction product of molybdate and iron in boiler water treatment?
Fe2(MoO4)3
What is the primary reason for using sodium phosphate in boiler water treatment?
To precipitate calcium and magnesium compounds as soft scale
What is the estimated increase in fuel costs for a 1 cm scale thickness in a boiler?
70%
What is the purpose of using chelants in boiler water treatment programs?
To trap metallic ions and make scales more soluble
What is the result of local overheating caused by scale deposition in a boiler tube?
The tube expands and bulges, potentially leading to rupture
What is the purpose of adding organic compounds like starch to boiler water treatment?
To coat scale precipitates and prevent them from adhering to boiler internals
What is the recommended concentration range of molybdate in boiler water?
75 to 125 ppm
What is the primary function of intermittent bottom blowdown in boiler water treatment?
To remove sludge and scale precipitates from the boiler
What is the result of not controlling scale formation in a boiler?
The boiler is at risk of overheating and physical damage
What is the purpose of using EDTA as a chelant in boiler water treatment?
To trap metallic ions and make scales more soluble
Study Notes
Importance of Internal Water Treatment
- Internal water treatment is essential to prevent boiler failure caused by impurities in the feedwater.
- Chemicals are added to the water after it enters the boiler to soften, deaerate, and condition the water.
Purposes of Internal Water Treatment
- Limit scale formation by precipitating feedwater hardness and keeping it in suspension.
- Ensure suspended solids in the boiler do not adhere to the boiler metal.
- Control the concentration of dissolved and suspended solids in the boiler water without causing foaming.
- Eliminate oxygen from the boiler water.
- Provide the right level of alkalinity to prevent boiler corrosion.
pH Control and Corrosion Prevention
- The pH value is a number between 0 and 14, indicating the degree of acidity or alkalinity of water.
- A pH of 7 is neutral, less than 7 is acidic, and higher than 7 is basic (or alkaline).
- Boilers are typically kept at a pH of about 9.5 to 10.5 to limit corrosion.
- Sodium hydroxide (NaOH) solution is often used to raise pH to the required level within the boiler.
Caustic Embrittlement and Gouging
- Caustic embrittlement occurs when metal under stress is attacked by a concentrated caustic solution.
- Sodium hydroxide (NaOH) can concentrate in areas of high heat transfer, leading to caustic corrosion.
- Caustic gouging is a form of corrosion that occurs when sodium hydroxide concentrates under deposits on tube surfaces.
- Preventing caustic embrittlement and gouging requires limiting boiler water NaOH concentration to the minimum required.
Foaming, Carryover, and Priming
- Foaming in the boiler is caused by a high concentration of dissolved and suspended solids in the boiler water.
- Foaming can lead to carryover, which is the entrainment of boiler water in the steam.
- Priming is a type of carryover that contains large volumes of water.
- Foaming can be controlled with continuous surface blowdown and the use of anti-foaming agents.
Oxygen Corrosion
- Dissolved oxygen causes pitting in the boiler and condensate lines.
- Oxygen scavengers such as sodium sulfite (Na2SO3) and hydrazine (N2H4) are used to combat oxygen corrosion.
- Sodium sulfite reacts with oxygen to form sodium sulfate (Na2SO4).
- Hydrazine is toxic and its use is decreasing.
Scale Formation
- Scale formation is caused by the reaction of dissolved solids in the boiler water with other ions.
- Scale reduces heat transfer, increases fuel costs, and can lead to physical damage.
- Chemicals such as sodium phosphate (Na3PO4) are added to prevent scale formation by precipitating impurities in a different form.
- Chelants are used to trap metallic ions and make scales more soluble.
Sludge Deposits
- The sludge produced by the precipitation of soft scale in the boiler must be conditioned to stay fluid and well dispersed.
- Organic compounds such as starch, tannin, lignin, and alginates are used to coat scale precipitates and prevent them from adhering to the boiler internals.
Importance of Internal Water Treatment
- Internal water treatment is essential to prevent boiler failure caused by impurities in the feedwater.
- Chemicals are added to the water after it enters the boiler to soften, deaerate, and condition the water.
Purposes of Internal Water Treatment
- Limit scale formation by precipitating feedwater hardness and keeping it in suspension.
- Ensure suspended solids in the boiler do not adhere to the boiler metal.
- Control the concentration of dissolved and suspended solids in the boiler water without causing foaming.
- Eliminate oxygen from the boiler water.
- Provide the right level of alkalinity to prevent boiler corrosion.
pH Control and Corrosion Prevention
- The pH value is a number between 0 and 14, indicating the degree of acidity or alkalinity of water.
- A pH of 7 is neutral, less than 7 is acidic, and higher than 7 is basic (or alkaline).
- Boilers are typically kept at a pH of about 9.5 to 10.5 to limit corrosion.
- Sodium hydroxide (NaOH) solution is often used to raise pH to the required level within the boiler.
Caustic Embrittlement and Gouging
- Caustic embrittlement occurs when metal under stress is attacked by a concentrated caustic solution.
- Sodium hydroxide (NaOH) can concentrate in areas of high heat transfer, leading to caustic corrosion.
- Caustic gouging is a form of corrosion that occurs when sodium hydroxide concentrates under deposits on tube surfaces.
- Preventing caustic embrittlement and gouging requires limiting boiler water NaOH concentration to the minimum required.
Foaming, Carryover, and Priming
- Foaming in the boiler is caused by a high concentration of dissolved and suspended solids in the boiler water.
- Foaming can lead to carryover, which is the entrainment of boiler water in the steam.
- Priming is a type of carryover that contains large volumes of water.
- Foaming can be controlled with continuous surface blowdown and the use of anti-foaming agents.
Oxygen Corrosion
- Dissolved oxygen causes pitting in the boiler and condensate lines.
- Oxygen scavengers such as sodium sulfite (Na2SO3) and hydrazine (N2H4) are used to combat oxygen corrosion.
- Sodium sulfite reacts with oxygen to form sodium sulfate (Na2SO4).
- Hydrazine is toxic and its use is decreasing.
Scale Formation
- Scale formation is caused by the reaction of dissolved solids in the boiler water with other ions.
- Scale reduces heat transfer, increases fuel costs, and can lead to physical damage.
- Chemicals such as sodium phosphate (Na3PO4) are added to prevent scale formation by precipitating impurities in a different form.
- Chelants are used to trap metallic ions and make scales more soluble.
Sludge Deposits
- The sludge produced by the precipitation of soft scale in the boiler must be conditioned to stay fluid and well dispersed.
- Organic compounds such as starch, tannin, lignin, and alginates are used to coat scale precipitates and prevent them from adhering to the boiler internals.
Importance of Internal Water Treatment
- Internal water treatment is essential to prevent boiler failure caused by impurities in the feedwater.
- Chemicals are added to the water after it enters the boiler to soften, deaerate, and condition the water.
Purposes of Internal Water Treatment
- Limit scale formation by precipitating feedwater hardness and keeping it in suspension.
- Ensure suspended solids in the boiler do not adhere to the boiler metal.
- Control the concentration of dissolved and suspended solids in the boiler water without causing foaming.
- Eliminate oxygen from the boiler water.
- Provide the right level of alkalinity to prevent boiler corrosion.
pH Control and Corrosion Prevention
- The pH value is a number between 0 and 14, indicating the degree of acidity or alkalinity of water.
- A pH of 7 is neutral, less than 7 is acidic, and higher than 7 is basic (or alkaline).
- Boilers are typically kept at a pH of about 9.5 to 10.5 to limit corrosion.
- Sodium hydroxide (NaOH) solution is often used to raise pH to the required level within the boiler.
Caustic Embrittlement and Gouging
- Caustic embrittlement occurs when metal under stress is attacked by a concentrated caustic solution.
- Sodium hydroxide (NaOH) can concentrate in areas of high heat transfer, leading to caustic corrosion.
- Caustic gouging is a form of corrosion that occurs when sodium hydroxide concentrates under deposits on tube surfaces.
- Preventing caustic embrittlement and gouging requires limiting boiler water NaOH concentration to the minimum required.
Foaming, Carryover, and Priming
- Foaming in the boiler is caused by a high concentration of dissolved and suspended solids in the boiler water.
- Foaming can lead to carryover, which is the entrainment of boiler water in the steam.
- Priming is a type of carryover that contains large volumes of water.
- Foaming can be controlled with continuous surface blowdown and the use of anti-foaming agents.
Oxygen Corrosion
- Dissolved oxygen causes pitting in the boiler and condensate lines.
- Oxygen scavengers such as sodium sulfite (Na2SO3) and hydrazine (N2H4) are used to combat oxygen corrosion.
- Sodium sulfite reacts with oxygen to form sodium sulfate (Na2SO4).
- Hydrazine is toxic and its use is decreasing.
Scale Formation
- Scale formation is caused by the reaction of dissolved solids in the boiler water with other ions.
- Scale reduces heat transfer, increases fuel costs, and can lead to physical damage.
- Chemicals such as sodium phosphate (Na3PO4) are added to prevent scale formation by precipitating impurities in a different form.
- Chelants are used to trap metallic ions and make scales more soluble.
Sludge Deposits
- The sludge produced by the precipitation of soft scale in the boiler must be conditioned to stay fluid and well dispersed.
- Organic compounds such as starch, tannin, lignin, and alginates are used to coat scale precipitates and prevent them from adhering to the boiler internals.
Learn about the importance of internal treatment of boiler feedwater to prevent impurities and boiler failure. Understand the process of adding chemicals to soften, deaerate, and condition the water.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
