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 observed as localized pitting on a metal surface. (Pitting Corrosion) This form of corrosion can be reduced by: 1.by reducing the level of oxygen as far as possible using mechanical means which include deaeration and/or judi
Post a Comment
Read more

Polar Code

International Code for Ships Operating in Polar Waters IMO has adopted the International Code for Ships Operating in Polar Waters (Polar Code) and related amendments to make it mandatory under both the  International Convention for the Safety of Life at Sea (SOLAS) and the International Convention for the Prevention of Pollution from Ships (MARPOL). The Polar Code entered into force on 1 January 2017. This marks an historic milestone in the Organization’s work to protect ships and people aboard them, both seafarers and passengers, in the harsh environment of the waters surrounding the two poles. The Polar Code and SOLAS amendments were adopted during the 94th session of IMO’s Maritime Safety Committee (MSC), in November 2014; the environmental provisions and MARPOL amendments were adopted during the 68th session of the Marine Environment Protection Committee (MEPC) in May 2015.
Post a Comment
Read more