corrosion is explained through the process of refined metals convert into their other forms. Generally, it defines as electrochemical oxidation of metal in reaction with an oxidant chemical like oxygen or sulfates.one of the most well-known examples of corrosion is rusting. Corrosion degrades the useful properties of materials and structures including strength, appearance, and permeability to liquids and gases.
What are the main factors that cause corrosion?
- Inadequate maintenance and operational conditions
- Dissolved gasses that are available in water that fed to boilers
- Presence of oxygen in boilers
- PH of water that is fed to boilers, acidic or alkali conditions
What are the main effects of corrosion in the system?
- Reduce the life of the equipment
- Making holes and undesirable bulges on metal surfaces
- Metal pitting
- Increase operational costs
- Decrease the boiler efficiency and final yield
How to prevent corrosion in boilers?
- Adequate and suitable ways of treatments
- Proper PH control
- Scale and deposit control
- Efficient design
- Proper and on time oxygen and carbon dioxide control
Corrosion in boilers
Corrosion in boilers is because of oxygen reaction with the equipment metal. Acidic PH of the water is another reason for corrosion. The main reason that leads to corrosion in the surface of equipment metal is iron. The oxygen that is present in the media reacts with iron and the component produced will cause corrosion.
Corrosion generally occurs through a chemical or electrochemical procedure. Chemical corrosion occurs in dray gasses and the main influence of chemical corrosion is the oxidation of metals. The other form of corrosion or electrochemical corrosion occurs in solutions and through metal compounds and electrolytes and with paying attention to their surface charge and potential ionization and oxidation of metal is occurred in the anode.
The cathode is the part that depolarization occurs there and also reduction of oxygen and hydrogen cation:
In the picture below the mechanism of corrosion is shown:
There is another corrosion type that is named biocorrosion that the degradation of metal is a result of microorganism activities. Microorganism builds a biofilm on the surface of the metal and this media is a suitable place for their growth.
Types of Corrosion
There are several kinds of industrial corrosion but these 9 type is the most relevant:
- Pitting Corrosion
- Atmospheric Corrosion
- Erosion Corrosion
- Uniform Corrosion
- Fretting Corrosion
- Selective Corrosion
- Inter-granular Corrosion
- Stress Corrosion
- Corrosion Fatigue
How can we protect the equipment against corrosion?
There are several ways to control corrosion but these 5 methods are generally applied in systems:
(I) equipment and boilers material selection
(II) Suitable design
(III) Cathodic protection,
(IV) Suitable coatings
- Graphene, graphene oxide and reduced graphene oxide-based coatings
- polyaniline/polyvinyl chloride mixture
- Nano-hybrid epoxy coatings
- bio-based polymers
- inorganic coatings
- siloxane-based sol-gel coatings
- silica-titania hybrid
- iron aluminide coating
These groups of materials make a thin layer on the surface of the material and prevent the equipment from corrosion. Organic corrosion inhibitors are widely used in industry because of their effectiveness at a wide range of temperatures, compatibility with protected materials, good solubility and relatively low toxicity. This is a very important issue for researchers which is confirmed by an increasing number of papers.
Over the past years, many organic corrosion inhibitors have been developed.
In the acidic system, many chemicals used as inhibitor such as:
- nitrogen-base materials
- Sulfur-containing compounds
- acetylenic compounds
In neutral systems many chemicals used as inhibitor such as:
The mechanism of inhibitors is by decreasing or preventing the reaction of metal and through this phenomena, the corrosion rate will be decreased by:
- The process of ions or molecules adsorption on the metal surface
- Changing in cathodic or anodic reactions procedure
- Reducing the diffusion of materials in medium to the metal’s surface
- Reduction in electrical persistence of the metal
- Brycki, B. E., Kowalczyk, I. H., Szulc, A., Karczewska, O., Pakiet, M., & Aliofkhazraei, M. (2017). Organic corrosion inhibitors. In InTech Open(No. 1). Corrosion Inhibitors, Principles, and Recent Applications.
- Rani, B. E., & Basu, B. B. J. (2012). Green inhibitors for corrosion protection of metals and alloys: an overview. International Journal of corrosion, 2012.