Steam Boilers are the backbone for processing operations in industries. Plant managers take every measure to ensure the safety of the steam boiler and the operating personnel. One such measure includes maintaining the boiler tubes. Overlooking boiler tubes can lead to hazardous consequences like overheating and boiler failure. Examining the root cause of the boiler tube failures is crucial to reduce the possibility of future boiler issues. An overall assessment is required to examine the cause of boiler tube failure that is usually a cause of other boiler problems. Some of the most common boiler tubes that occur on steam boilers are as follows:
Waterside failure for boiler tube:
- Caustic Attack:
The caustic attack takes place due to excessive deposition on the boiler tube surfaces, leading to reducing the cool water flow in contact with the tube. As a result, it causes local under-deposit boiling and boiler water chemicals concentration. It leads to a caustic condition that corrosively attacks and breaks down protective magnetite if blended with boiler water chemistry with high pH.
It is identified by localized wall loss on the surface of the boiler tube that increases the stress and strain in the tube wall and impacts furnace wall tubes or any inclined tube. Preventing caustic attacks requires avoiding the accumulation of excessive deposits and maintaining boiler water chemistry for preventing the local formation of caustic in areas with chemicals concentrated. In some cases of caustic attack, the top of a sloped tube is related to the steam-water separation that is avoided by using ribbed tubes. Maintaining boiler water chemistry is ensured by appropriate feed water chemistry with phosphate boiler water treatments.
- Acid Attack:
The acid attack occurs due to poor process control of boiler chemical cleanings or inadequate cleaning of residual acid. The tube metal surfaces result in an irregular pitted appearance on the boiler tube and affect water wall tubes.
It is prevented by maintaining water chemistry, proper controls for boiler chemical cleanings, and assessing the chemical hideout.
- Hydrogen Damage:
Hydrogen damage in the steam boiler is the result of excessive deposition on boiler tube surfaces and boiler water with less pH excursion. Inappropriate water chemistry from condenser leaks with saltwater cooling medium leads to acidic contaminants that are concentrated in the deposit and causes under-deposit corrosion releasing atomic hydrogen that passes to the tube wall metal and reacts with carbon in the steel. It causes intergranular separation.
Hydrogen damage is detected by intergranular micro-cracking, ductility loss, and boiler tube material embrittlement. It leads to brittle catastrophic rupture. It usually takes place in regions of high heat flux and can be prevented by maintaining water chemistry and avoiding scaling on the waterside of the boiler tube.
- Oxygen Pitting:
Oxygen pitting occurs by the excess oxygen in boiler water that takes place during operation due to in-leakage of air at pumps or failure in boiler water treatment. It also occurs during extended out-of-service periods of steam boilers. Aggressive localized boiler tube corrosion and loss in tube walls are signs of oxygen pitting.
Proper layup procedures during steam boiler outages, enhanced oxygen control during steam boiler startups, and operations can prevent oxygen pitting.
- Stress Corrosion Cracking:
Stress corrosion cracking occurs due to the combination of high-tensile stresses and the presence of corrosive fluid. It results from cracks that propagate from the boiler tube. The corrosive fluid results from the carryover into the superheater from the steam drum.
Stress corrosion cracking is identified by a thick wall, brittle-type crack at locations of higher external stresses. Stress corrosion cracks are usually related to various secondary cracks branched with the main ruptured area. The ideal solution for stress corrosion cracking includes preventing water carryover control and flush after cleaning.
- Waterside Corrosion Fatigue:
Waterside corrosion fatigue occurs due to thermal fatigue and corrosion. Corrosion fatigue depends on steam boiler design, water chemistry, boiler water oxygen, and steam boiler operation, leading to the breakdown of the protective layer on the surface of the boiler tube that prevents the boiler tube from corrosion.
Waterside corrosion fatigue can be detected by wide transgranular cracks taking place adjacent to external attachments. It is prevented by minimizing the operational cycles, constraints on tubes, and reducing dissolved oxygen on start-up.
It is imperative to ensure regular maintenance of the steam boiler for optimal efficiency and productivity with hassle-free operations. Rakhoh Boilers are one of the renowned names as manufacturers of boilers in India with 38+ years of expertise in boiler manufacturing and thermal solutions. We manufacture a range of efficient and reliable industrial steam boilers, waste heat recovery boilers, thermic fluid heaters, and boiler accessories. We provide excellent boiler services like annual boiler maintenance, steam trap assessment, energy audit, boiler automation, fuel conversion, etc.
We are proudly catering to over 20 process industries in 26 countries worldwide.
Know more about our products and services by visiting www.rakhoh.com