Skip to main content

Boiler Scale Formation




Deposits on heating surfaces results by exceeding the solubility limits of the impurities dissolved in the feed water.
When feed water is heated or concentrated the impurities become insoluble & form deposits.
The greater the evaporation rate the greater the deposits.
Scale formation can lead to reduced efficiency of boiler and boiler tube catastrophic failure due to thermal stress.

Calcium Carbonate
Formed by thermal decomposition of Calcium bicarbonate at heat transfer surface.
Ca(HCO3)2 + Heat      ⟶    CaCO3 + H2O + CO2

Magnesium Silicate
Formed when there is sufficient amount of Magnesium and adequate amount of Silicate ions and OH Alkalinity is deficient.                                                  
MgOH+  +  HSiO3-   ⟶  MgSiO3  +  H2SO4    Which causes Acidic corrosion too.

Silica (SiO2)
Smooth glass like deposit.
Strongly Adherent.
Insulating.
Can only be removed by acid washing with Hydrofluoric Acid.
In High Pressure boilers silica can evaporate from the boiler as Silicic acid & cause deposits on turbine blades.

Copper
Copper deposits initiates Galvanic corrosion.   
Appears as bright red/orange.
Copper comes to the boiler by corrosion and/or erosion of condensate lines, feed pump impellers, tracing lines & etc.
Erosion of copper in condensate system can occur when the boiler is priming or foaming.

Sodium Chloride
Presence of NaCl causes foaming and Priming

Magnesium Chloride
Will break down into Mg(OH)2 HCl which will cause Acidic Corrosion.

Labels:

Comments

Post a Comment

Popular posts from this blog

Boiler Corrosion

Galvanic Corrosion Can occur due to Oxygen attack or contact of two dissimilar metals in an electrolyte (eg: Copper + Steel). Oxygen Attack (Pitting Corrosion) At the Anode: Metal goes into solution               Fe ⟶ Fe 2+ + 2 e -               OXIDATION At the Cathode: Oxygen is reduced           ½ O 2 + H 2 O + 2 e - ⟶ 2 OH -             REDUCTION The variables pH, temperature and the concentration of oxygen affect the rate of corrosion. To avoid this alkaline conditions are maintained in the boiler. Oxygen reacts with iron to give ferric oxide (rust) Fe 2 O 3 which will not protect the metal from further attack and metal is continuously dissolved. 4Fe + 3O 2 → 2 Fe 2 O 3 Hematite (ferric oxide) Oxygen corrosion is usually...
Post a Comment
Read more

Analog Addressable Fire Alarm System

Main Panel Block Diagram The fire alarm system continuously monitors the detectors. Detectors are divided into zones. (Using Software configuration file in the base board). Detectors are connected to the system through loops. (physically) The Loops are connected to the loop boards. Each Board can have 3 loops. Each loop can have 254 detectors. (Depending on the address size) Each Loop has an address and each device has an address given using DIP switches. (These are stored in the Software config file) Devices send digital data packets containing the Addresses and the Data. The digital data packets are sent digitally using analog signals through the twisted pair cables. ( Analog Addressable Signals ) ID address on DIP switches All addressable loop units must be given an address between 1-254 to be operational. The loop units located on the same physical loop must all have unique addresses. The address is set by a 8 pole DIP switch located on each addressable unit...
Post a Comment
Read more