Steam Boilers are irreplaceable for operational purposes in manufacturing facilities. Plant managers ensure that the boilers are functioning seamlessly by taking every precaution. However, some issues in the steam boiler system are inevitable that need immediate action. One of such issues is corrosion and erosion that occurs in every component of the steam boiler, including piping. Corrosion can lead to overheating or failure of boilers, resulting in severe losses or injuries as well as extensive plant downtime. Poor quality of feedwater is a major cause of the corrosion, along with the temperature of water or steam, presence of oxygen, pH, quality of steam, flow velocity, the chemical composition of steel pipe, and oxide layer on the inside of pipe.
Corrosion in Steam Boilers:
The feed water used for the processing operations should not be of poor quality with any impurities, impacting the boiler performance.
Utilizing water for heat transfer and steam generating purposes requires attention to prevent problems arising due to corrosive gases like dissolved oxygen and carbon dioxide. The intensity of the gases attacking the steam boiler depends on the quantity of dissolved substances, water pH, and temperature.
Corrosion mechanisms in steam boilers are caused by collective depositions of ferric oxides and dissolved salts of calcium, magnesium, iron, copper, and aluminum. The deposit acts as thermal insulation in high heat transfer areas, leading to local overheating and extreme corrosion in steam boilers.
Causes of Corrosion in Steam Boilers:
Corrosion in steam boilers are caused due by various factors such as,
- Negligence in maintenance or/and reparation that halts the system from operating, resulting in production loss
- Increased fuel utilization and reduced efficiency in steam boiler
- Exceeding maximum metal resistance
- Extensive time period in reaching system parameters
Corrosion in Piping:
Corrosion in pipes, if overlooked, can eventually advance to the internal part of the metal, leading to pipe thinning and pipe failure. Additionally, corrosion by-products are transported through pipes that contaminate the fluid and cause erosion and further corrosion of piping and valves.
Corrosion of Steel:
Steel piping in steam boilers includes a considerable amount of steel and is exposed to rust in specific conditions. The oxidation of the metal surface by contact with air and water results in iron rust. Steel condensate recovery pipes are particularly at risk due to ample reagents for rust formation.
In properly maintained steam pipes, there is considerably less air and water present after startup. It consequently decelerates the spread of rust. It must be noted that less rust is formed in a closed condensate recovery system compared to an open recovery system. After shutdown, contaminated air in the steam boiler system results in extensive corrosion. Frequent shutdowns in boiler systems cause increased rusting of pipes with condensate remaining in the system during the shutdown.
Steam trap helps to eliminate condensate and keep the steam dry to prevent rust. Air vents release excess air from the steam boiler to decrease the possibility of rust formation. It is vital to manually drain condensate during shutdown that steam traps fail to drain.
Corrosion of Copper:
Because of its low installation cost and easy bending around the equipment and flanges, copper is used in tracing lines. However, high temperature and low pH value in condensate destroy the copper ions that dissolve in the condensate. Copper-filled condensate reaching the steam trap causes the lower pressure on the outlet side of the trap to flash into steam. It results in some copper ions precipitating and accumulating as solid build-up around the valve, causing the reduced temperature in the tracing line and orifice blockage. It is important to treat feed water and monitor pH levels to prevent corrosion of copper. Neutral pH between 7 and 9 and low dissolved oxygen content is ideal for copper.
Preventing Corrosion in Piping:
- Stainless steel is considered a corrosion-resistant metal due to a process termed passivation. Passivation is the formation of a thin oxide layer on the metal surface when introduced to the air. The oxide layer safeguards the stainless steel by naturally forming a resistant layer for corrosion and rust.
- Properly implementing steam traps and air vents during shutdown to avoid air and water from reacting.
- Adequate water treatment and monitoring of condensate pH level
- Draining the system of condensate during shutdown
- Selecting pipes and traps based on the needs and requirements of the system
Rakhoh Boilers is a leading thermal solution provider and steam boiler manufacturer in Pune since 1983. With our dedication and expertise, we have delivered over 3000+ efficient steam boilers in 26 countries worldwide. We manufacture a range of industrial steam boilers, waste heat recovery systems, thermic fluid heaters, and boiler accessories. We provide the best boiler services like steam trap assessment, energy audit, boiler automation, annual maintenance contract, etc.
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