Water Impurities and Boiler Effects

Questions and Answers

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?

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?

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?

Nitrogen Signup and view all the answers

How can suspended solids affect boiler systems?

They settle and can promote corrosion cells. Signup and view all the answers

What happens to the solubility of oxygen in water as temperature increases?

It decreases. Signup and view all the answers

What is a primary factor contributing to high temperature corrosion in boilers?

Loss of circulation. Signup and view all the answers

What role does carbonic acid play in the context of boiler feed water?

It can contribute to corrosion. Signup and view all the answers

What is the primary purpose of treating feed water in boilers?

To remove impurities that can cause scale formation or corrosion Signup and view all the answers

Which component of feed water is pure and free from impurities?

Condensate Signup and view all the answers

Which type of water testing is essential for monitoring boiler water quality to prevent issues?

pH Test Signup and view all the answers

What is the typical range for boiler water pH to help suppress corrosion?

9.5 - 11.5 Signup and view all the answers

What happens if feed water is not treated properly in a boiler?

It may cause scale formation and increase blow down requirements Signup and view all the answers

Which of the following is NOT considered an impurity in feed water?

Condensate Signup and view all the answers

What does the alkalinity of water indicate?

Presence of alkaline substances like bicarbonate and carbonate Signup and view all the answers

From which water source is makeup water typically derived?

Natural bodies of water Signup and view all the answers

What is the primary reason for using external treatment in a boiler system?

To manage water impurities that exceed acceptable levels Signup and view all the answers

Which combination treatment is known for its effectiveness in reducing hardness and silica in water?

Hot lime-zeolite process Signup and view all the answers

What is the primary purpose of internal treatment in a boiler system?

To react with impurities and prevent issues like foaming Signup and view all the answers

What material is primarily used in cation exchange softeners to replace hardness ions in water?

Sodium ions Signup and view all the answers

Under what conditions is internal treatment typically utilized alone?

When good quality raw water and low pressures are present Signup and view all the answers

What is caustic cracking primarily caused by?

Water with high caustic alkalinity Signup and view all the answers

Which statement about carryover is true?

Solid particles in steam from carryover can erode turbine parts. Signup and view all the answers

How do scale deposits affect boiler operation?

They act as insulators and lower heat transfer rates. Signup and view all the answers

What causes foaming in the boiler?

Contaminants in the boiler water Signup and view all the answers

Which minerals primarily contribute to the hardness of feed water?

Calcium and Magnesium Signup and view all the answers

What can result from large slugs of water carrying over with steam?

Thermal and mechanical shock damage Signup and view all the answers

What is a significant risk associated with scale in the boiler?

It contributes to corrosion of metal surfaces. Signup and view all the answers

What is a common cause of turbine damage in boilers?

Carryover of contaminants with steam Signup and view all the answers

What is the purpose of adding Na3PO4 in boiler water treatment?

To prevent scale Signup and view all the answers

What action should be taken if high phosphate levels are detected in boiler water?

No action required Signup and view all the answers

Which chemical should be added to address low alkalinity in boiler water?

NaOH Signup and view all the answers

What is the correct action when dissolved solids are detected at high levels?

Partial blow down and take fresh feed Signup and view all the answers

To address the risk of caustic cracking, which chemical should be considered?

Na2SO4 Signup and view all the answers

If trace sources of chloride compounds are identified, what is the appropriate action to take?

Trace sources of leak and rectify Signup and view all the answers

Which chemical serves to condition sludge in a boiler system?

Al3AlO3 Signup and view all the answers

What should be done when alkalinity levels are found to be high?

Add sodium sulphite Signup and view all the answers

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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Description

This quiz focuses on the impact of water impurities on boiler operation and integrity. It covers topics such as the formation of scales due to salts, the effects of dissolved gases, and the roles of suspended solids and temperature in corrosion. Understand how various contaminants influence boiler performance and lifecycle.