Boiler Water Treatment - Part B:MEO CLASS2 A COMPREHENSIVE GUIDE frequently asked questions included

Summary

This video provides an in-depth exploration of boiler water testing, focusing on key issues such as corrosion, scaling, and carryover that affect boiler performance. The script covers different types of corrosion (pitting, stress, crevice, caustic) and explains essential boiler water tests like alkalinity, chloride, sulfide, and phosphate. The testing processes are clearly explained, detailing the chemical reactions involved and the measurement techniques. This comprehensive guide is designed for individuals looking to understand how to maintain boiler efficiency, prevent damage, and prepare for technical exams in the field.

Takeaways

• 😀 Corrosion in boilers is a major issue, and it occurs through various processes like pitting, stress, and crevice corrosion.
• 😀 Pitting corrosion is a localized form of corrosion, caused by factors such as acidity, low dissolved oxygen, or poor metal structure.
• 😀 Stress corrosion is caused by a combination of heavy stress and a corrosive environment, leading to cracks and eventual failure in the boiler tubes.
• 😀 Crevice corrosion occurs when water gets trapped in cracks, creating a potential difference that accelerates corrosion and material degradation.
• 😀 Caustic corrosion and caustic embrittlement are caused by high concentrations of caustic soda, leading to the formation of fractures in boiler materials.
• 😀 Carryover refers to the contaminants (solid, liquid, or gas) that exit the boiler with steam, which can cause operational issues like valve clogging and turbine imbalance.
• 😀 Priming is the carryover of water droplets in steam, which can result from improper boiler construction or fluctuating steam demand.
• 😀 Scaling occurs when suspended particles form thick layers on boiler surfaces, reducing heat transfer efficiency and overall boiler performance.
• 😀 Boiler water testing includes alkalinity tests (PL, TL, and M Alkalinity) to measure levels of hydroxides, carbonates, and bicarbonates in the water.
• 😀 Chloride testing is essential to detect saltwater leakage into the boiler system, which could indicate damage or contamination from the feedwater system.

Q & A

What are the three major problems that can occur in a boiler?

The three major problems that can occur in a boiler are corrosion, carryover, and scaling.

What is pitting corrosion, and what causes it?

Pitting corrosion is a localized form of corrosion that occurs when the protective coating of metal breaks down. It can be caused by the presence of acidity, low dissolved oxygen, high chloride concentrations, poor application of protective coatings, or irregularities in the metal structure.

How does stress corrosion cracking occur in a boiler?

Stress corrosion cracking occurs when the combined action of mechanical stress and a corrosive environment breaks down the protective film on the metal. The residual stresses within the metal propagate the cracking, which can eventually lead to failure of the material.

What is crevice corrosion, and how does it form?

Crevice corrosion occurs when water gets trapped in a crack or crevice in the metal surface. The velocity difference between water flowing over the surface and the trapped water inside the crack creates a potential difference, leading to the breakdown of material and the expansion of the crack.

What is caustic corrosion, and how is caustic embrittlement different?

Caustic corrosion occurs due to the presence of caustic soda (sodium hydroxide) at high pH levels, which accelerates corrosion. Caustic embrittlement, a more severe form, happens when high concentrations of caustic soda cause intercrystalline fractures, especially in areas with cracks or surface flaws.

What is carryover in the context of boiler water, and why is it a problem?

Carryover refers to contaminants (solid, liquid, or gas) that are carried along with steam from the boiler. It can cause damage to equipment such as control valves, turbines, and superheaters, leading to unbalanced turbine blades, reduced heat transfer, and overall reduced boiler efficiency.

How does foaming in a boiler affect its operation?

Foaming occurs when a thick layer of steam bubbles forms on the water surface inside the boiler. This can cause inaccurate readings of water levels, making it difficult to maintain the correct boiler water level and leading to potential operational problems.

What is the purpose of the alkalinity test in boiler water?

The alkalinity test measures the presence of hydroxides (OH-), carbonates (CO3-), and bicarbonates (HCO3-) in the boiler water. This is important for maintaining proper water chemistry and preventing corrosion or scaling in the system.

What is the difference between phenolphthalein alkalinity (PL) and total alkalinity (TL)?

Phenolphthalein alkalinity (PL) measures the presence of hydroxides and half of the carbonate ions. Total alkalinity (TL) measures all forms of alkalinity, including hydroxides, carbonates, and bicarbonates, providing a complete picture of the boiler water's alkalinity.

What is phosphate hideout, and why does it occur in a boiler?

Phosphate hideout is a phenomenon where the phosphate ion concentration in boiler water decreases when the boiler load or pressure increases, causing phosphate to precipitate. As load or pressure decreases, the phosphate returns to the solution, fluctuating the phosphate levels in the boiler water.