400°C. Tube plate cracking typically starts at toes of boiler tube fillet welds and grows across the tube plate ligament from one boiler tube to another. Cracking has also occurred from centre-pop marks forming a small notch in the edge of the tube hole with expanded tubes. Ligament cracking is serious.
copper corossion Pitting of boiler drums and tube banks has been encountered due to metallic copper deposits, +4.
Intercrystalline cracking results only when all of the following are present: specific conditions of stress, a mechanism for concentration such as leakage, and free NaOH in the boiler water. Therefore, boiler tubes usually fail from caustic embrittlement at points where tubes are rolled into sheets, drums, or headers.
Unequal stresses on boiler tubes cause transgranular cracking. According to GE Water, "transgranular cracking primarily due to cyclic stress is the most common form of cracking encountered in industrial boilers." Cyclic stress, otherwise defined as a stress that changes over time in a repetitive fashion, eventually results in loose and leaky tubes or cracks.
reduce the efficiency of the boiler. Disadvantages of using hard water in boiler: The main destructive effects of using hard water in boilers are (i) formation of scales and sludges (ii) boiler corrosion (iii) caustic embrittlement and (iv)priming and foaming. Formation of scales and sludges is the main disadvantage of using hard water in boiler.
Embrittlement of boiler metal is normally referred to as caustic embrittlement or intercrystalline cracking. Failure of a boiler due to caustic embrittlement is normally undetectable during operating conditions; it generally occurs suddenly, with catastrophic results.
Dec 20, 2016 · Hot water boiler has a cracked heat exchanger and leaking water. We hope to be able to replace this boiler in the very near future.
Pitting is a type of extremely localized attack which can be difficult to detect. Pitting is a destructive form of corrosion that affects the water side of boiler tubes. Surface imperfections and deposits can serve as initiation sites for pitting, and a consequent breakdown of the protective scale.
Caustic embrittlement (caustic stress corrosion cracking), or intercrystalline cracking, has long been recognized as a serious form of boiler metal failure. Because chemical attack of the metal is normally undetectable, failure occurs suddenly-often with catastrophic results.
“intercrystalline cracking of steel” and is created by a combination of stress, leakage and the presence of sodium hydroxide, a highly caustic metallic base and alkali salt. The most vulnerable areas of a boiler tube for caustic embrittlement are “at points where tubes are rolled into sheets, drums, or headers.”