Steam Heater Caution
Transcript of Steam Heater Caution
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Possible Possible Possible Possible cause of damage cause of damage cause of damage cause of damage :::: Corrosion byCorrosion byCorrosion byCorrosion by inadequate inadequate inadequate inadequate water treatment.water treatment.water treatment.water treatment.
Main factors of corrosion Main factors of corrosion Main factors of corrosion Main factors of corrosion
1. Oxygen Corrosion - < Annexed 1 >
2. Scale and sludge deposit. - < Annexed 2 >
3. Condensate Corrosion ( Erosion ) - < Annexed 3 >
Attached Attached Attached Attached – –– – DamagedDamagedDamagedDamaged caused caused caused caused by corrosion by corrosion by corrosion by corrosion
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Possible Possible Possible Possible cause of damagecause of damagecause of damagecause of damage :::: Water Hammering & Thermal StressWater Hammering & Thermal StressWater Hammering & Thermal StressWater Hammering & Thermal Stress
Cause Cause Cause Causes of Water Hammering & Thermal stresss of Water Hammering & Thermal stresss of Water Hammering & Thermal stresss of Water Hammering & Thermal stress
< Water Hammering > < Water Hammering > < Water Hammering > < Water Hammering >
1. Improper draining of condensate in steam heater during shut down
2. Malfunction of vacuum breaker during shut down
3. Mushrooming supply of main steam
< Thermal Stress > < Thermal Stress > < Thermal Stress > < Thermal Stress >
1. Mushrooming supply of main steam
2. Improper warm up / start up of steam heater
3. Excessive steam pressure
Attached Attached Attached Attached – –– – DamagedDamagedDamagedDamaged caused caused caused caused by w by w by w by waterateraterater h hh hammering &ammering &ammering &ammering & t tt thermalhermalhermalhermal s ss stresstresstresstress
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1 > Oxygen Corrosion Oxygen Corrosion Oxygen Corrosion Oxygen Corrosion
Corrosion caused by oxygen in steam heaters (boilers) usually shows up as pits.Often the pits are covered by raised mounds of iron oxide. Sometimes the
corrosion appears to be superficial. However, this type of corrosion can penetrate
the tube wall and lead to failure.
The potential for oxygen pitting can be minimized by the addition of chemical
oxygen scavengers and the use of mechanical deaeration. Because most cases
of oxygen pitting take place when steam heaters are shut down.
It is important to pay careful attention to idle and stored steam heaters (boilers) to
ensure that damage does not occur.
Have to be a storage procedure suitable for your steam heaters (boilers).
4Fe(OH)2 + O2 + 2H2O - > 4Fe(OH) 4Fe(OH) 4Fe(OH) 4Fe(OH) 2 22 2
Fe(OH)2 + 1/2O2 + H2O - > Fe(OH) Fe(OH) Fe(OH) Fe(OH) 2 22 2
7.0 7.5 8.0 8.5 9.0 10.0 10.5 11.0 11.5 12.0
4
3
2
1
Fe
PH
< Fe(OH) < Fe(OH) < Fe(OH) < Fe(OH) 2 22 2 melting rate melting rate melting rate melting rate(ppm) > (ppm) > (ppm) > (ppm) >
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> Scale and Scale and Scale and Scale and sludge sludge sludge sludge Deposits Deposits Deposits Deposits
Scale and sludge deposits can form on steam heater heat transfer surfaces,resulting in efficiency loss and possible failure due to overheating. The most
common types of deposits, those formed by calcium salts, are due to the
presence of excessive hardness in the boiler water & steam.
Other minerals such as magnesium, silicates, and iron can also cause deposits to
form. In addition, iron returning from the corrosion of steam condensate systems
is a common cause of deposits.
Such excessive amounts of hardness or iron cannot be effectively treated with
chemicals alone. A clean, deposit- free steam heater is primarily the result of
maintaining high quality boiler water and, after proper pretreatment, utilizing
chemical treatment programs that condition the remaining low levels of
contaminants after proper pretreatment.
Kinds of Materials Kinds of Materials Kinds of Materials Kinds of Materials Corrosion Rate Corrosion Rate Corrosion Rate Corrosion Rate
Distilled water inc lude Co2
MgCl2
MgSo4
Mg(NO3)2
CaCl2
CaSO4
Ca(NO3)2
NaCl
Na2SO4
NaNO3
1.0
51.1
20.5
11.5
19.8
10.5
10.1
31.1
18.8
9.0
(%) >
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> C CC Condensate Corrosion ondensate Corrosion ondensate Corrosion ondensate Corrosion
When alkalinity is present in boiler water in the form of bicarbonate (HCO3- ) andcarbonate (CO3- ) and enters the steam heater, it breaks down to form carbon
dioxide (CO2). The carbon dioxide travels with the steam and condenses
throughout the system. When carbon dioxide condenses in the condensate
system, it forms carbonic acid (H2CO3) which reduces the pH and causes
corrosion.
Condensate corrosion can also occur when poorly deaerated boiler water(steam)
enters the steam heater and oxygen flashes with the steam. Since carbon dioxide
has a high vapor liquid distribution ratio, most of it condenses in the farthest
points of the condensate system. Vented condensate receivers assist in removing
some of the carbon dioxide to reduce the amount of acid formed. Condensate
corrosion causes severe metal loss and damage to equipment. The metal ions
lost to corrosion also return to the steam heater (boiler) where they can cause
deposition efficiency loss, and failure.
Chemical treatment programs which utilize neutralizing, filming agents, and
oxygen scavengers minimize the effects of condensate corrosion. The most
effective way to minimize the costs of treatment is to reduce the alkalinity in the
boiler water by demineralization, dealkalization, or reverse osmosis.
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> Water treatment injection limit & rate Water treatment injection limit & rate Water treatment injection limit & rate Water treatment injection limit & rate
>
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AHU STEAM HEATER OPERATING METHOD Annexed 5 > AHU STEAM HEATER OPERATING METHOD
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Annexed 6 > Precautionary measures to prevent corrosion in heating coil Precautionary measures to prevent corrosion in heating coil Precautionary measures to prevent corrosion in heating coil Precautionary measures to prevent corrosion in heating coil
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Annexed 6 > Precautionary measures to prevent corrosion i Precautionary measures to prevent corrosion i Precautionary measures to prevent corrosion i Precautionary measures to prevent corrosion in heating coil n heating coil n heating coil n heating coil