CORROSION IN PROCESS INDUSTRY

What is Corrosion 

Physio-chemical interaction between a metal and its environment which results in changes in the properties of the metal and which may often lead to impairment of the function of the metal, the environment, or the technical system of which these form a part.

Corrosion Science and Corrosion Engineering

Since corrosion involves chemical change, the student must be familiar with principles of chemistry in order to understand corrosion reactions. Because  corrosion processes are mostly electrochemical, an understanding of electrochemistry is also important. Furthermore, since structure and composition of a metal often determine corrosion behavior, the student should be familiar with the fundamentals of physical metallurgy as well.

The corrosion engineer , on the other hand,applies scientific knowledge to control corrosion. For example, the corrosion engineer uses cathodic protection on a large scale to prevent corrosion of buried pipelines, tests and develops new and better paints, prescribes proper dosage of corrosion inhibitors, or recommends the correct coating.

Corrosion Environment

Corrosion cannot be defined without a reference to environment. All environments are corrosive to some degree. Following is the list of typical corrosive environments:

• Air and humidity.                                                                                                              
•  Fresh, distilled, salt and marine water                                                                                
• Natural, urban, marine and industrial atmosphere.                                                           
• Steam and gases, like chlorine.                                                                                                 
•  Hydrogen sulfide.                                                                                                           
• Sulfur dioxide and oxides of nitrogen.                                                                        
•  Fuel gases.                                                                                                                                
•  Alkalies.                                                                                                 
•  Soils                                                                                                                                            

Corrosion factors

There are some following factors which cause corrosion                                                                      Temperature ,Potential Difference ,Heat Treatment ,Surface Condition ,Erosion Time,Pressure

Functional Aspects of corrosion

1. Impermeability: Environmental constituents

must not be allowed to enter pipes , process equipment, food containers, tanks , etc. to minimize the possibility of corrosion.

2. Mechanical strength:

Corrosion should not affect the capability to withstand specified loads, and its strength should not be undermined by corrosion.

3. Dimensional integrity:

Maintaining dimensions is critical to engineering designs and they should not be affected by corrosion.

4. Physical properties:

 For efficient operation , the physical properties of plants, equipment and materials, such as thermal conductivity and electrical properties, should not be allowed to be adversely affected by corrosion.

5. Contamination:

Corrosion, if allowed to build up, can contaminate processing equipment food products, drugs and pharmaceutical products and endanger health and environmental safety.

6. Damage to equipment:

Equipment adjacent to one which has suffered corrosion failure , may be damaged.

Cavitation Corrosions

Cavitation damage (sometimes referred to as cavitation corrosion or cavitation erosion) is a form of localized corrosion combined with mechanical damage that occurs in turbulent or rapidly moving liquids and takes the form of areas or patches of pitted or roughened surface. Cavitation has been defined as the deterioration of a surface caused by the sudden formation and collapse of bubbles in a liquid.It has been similarly defined as the localized attack that results from the collapse of voids or cavities due to turbulence in a liquid at a metal surface. Cavitation also occurs in areas of high vibration such as on engine pistons and piston liners.

          

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