steam heater caution

8/17/2019 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

steam heater caution

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