【Daily Question】Chemical Engineering Principles 416: Boiler Caustic Cracking (August 29)
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This post was last edited by Zaihui Kangqiao on 2016-9-6 at 16:59. The Chemical Engineering Theory section is launching a \"One Question per Day\" activity starting today, aimed at helping everyone reinforce their basic knowledge in chemical engineering. Subsequent series will include those on \"Principles of Chemical Engineering\", \"Mass Transfer and Separation\", \"Thermodynamics in Chemical Engineering\", and \"Chemical Process Engineering\". We hope you will give it your active support! Wishing everyone a happy Christmas! Answers to the questions in the \"One Question per Day\" activity can be viewed directly; the thread will be closed after 1 day ! To encourage everyone’s continued participation this year! You get 3 wealth rewards just for participating, and an additional 4 wealth points if you answer correctly~~~ Short answer question: What are the three factors that cause caustic embrittlement in boilers? Answer: 1) The boiler water contains a certain amount of free alkali, which gives it corrosive properties ； 2) The boiler is riveted or expanded, and there are gaps in these areas, which lead to localized concentration of water quality ； 3) There is high stress in the metal.
Caustic embrittlement is a form of embrittlement that occurs due to the high concentration of sodium hydroxide (NaOH) in the medium, which accelerates the corrosion of steel. The mode of failure involves numerous fine, invisible cracks branching off from the main cracks that are visible to the naked eye. When a component suffers from caustic embrittlement, the steel in the area surrounding the cracks still retains good plasticity as well as brittleness. Caustic embrittlement generally occurs at the riveted and expansion-jointed areas of pressure-bearing components. The conditions for caustic embrittlement include: A) Loss of control over the pH level of the boiler water during operation, resulting in a high concentration of free alkalis in the water. B) Structural features in the boiler that allow for localized concentration of the boiler water, such as in the gaps between rivets and expansion joints; poor sealing in these areas can lead to high concentrations of water there. C) Tensile stresses in the metal that are close to its yield point. Caustic embrittlement is a type of intergranular corrosion, with the corrosion occurring along the boundaries between metal grains, resulting in extremely fine, crisscrossing cracks. Once caustic embrittlement sets in, the rate at which the metal is damaged accelerates. By the time cracks become visible, the damage to the metal has already reached a serious level. The consequences of caustic embrittlement can be severe – in mild cases it may cause the boiler to stop operating, while in severe cases it can lead to explosions.
1. Boiler water is corrosive, meaning it contains a certain amount of free alkalis. 2. The boiler has riveted or expansion-jointed areas, and there are gaps or leaks in these areas, which leads to a localized concentration of water quality and results in a high level of alkalinity. 3. The metal is subjected to extremely high stresses, close to the yield point, resulting in high stress concentration.
1. The furnace water contains a high concentration of caustic soda, NaOH. 2. The boiler is riveted or expanded, and there are gaps at these connection points, resulting in localized concentration of boiler water. 3. Metals have tensile stress approaching their yield point.
A. During boiler operation, the pH level of the boiler water gets out of control, with a high concentration of free alkalis present in the water. B. The boiler structure provides conditions that can lead to localized high concentration of boiler water, such as in the gaps around rivets and joints; due to poor sealing, boiler water tends to become highly concentrated in these areas. C. In metals, there is a tensile stress close to its yield point.
1) The boiler water contains a certain amount of free alkali, which gives it corrosive properties; 2) The boiler is riveted or expanded, and there are gaps in these areas, leading to localized concentration of water quality. 3) There is high stress in the metal
Higher alkali concentration, higher temperature, and tensile stress
1) The boiler water contains a certain amount of free alkali, which gives it corrosive properties； 2) The boiler is riveted or expanded, and there are gaps in these areas, which can lead to localized concentration of water quality ； 3) There is high stress in the metal.
1. Boiler water is corrosive, meaning it contains a certain amount of free alkalis. 2. The boiler has riveted or expansion-jointed areas, and there are gaps or leaks in these areas, resulting in a localized concentration of water quality with high alkalinity. 3. The metal has extremely high stresses, close to the yield point, with a high degree of stress concentration.
1. The boiler water contains a certain amount of free alkali, which gives it corrosive properties； The 2 boilers are riveted or expanded, and there are gaps in these areas, which lead to localized concentration of water quality ； There is high stress in the 3 metals.
1) The boiler water contains a certain amount of free alkali, which gives it corrosive properties； 2) The boiler is riveted or expanded, and there are gaps in these areas, which lead to localized concentration of water quality ； 3) There is high stress in the metal.