Question

how we can define acid have corrosion nature

Answer 1

Corrosion is a natural process, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and stopping corrosion.  

In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfates. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal, and results in a distinctive orange colouration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term "degradation" is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases.  

Many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and chromate conversion, can increase a material's corrosion resistance. However, some corrosion mechanisms are less visible and less predictable.  

Answer 2

Acidic corrosion occurs in stone and metals that are prone of high salinity, chemicals, low oxygen and harsh environmental operating conditions. Acidic corrosion is a gradual destruction and wearing away of a material (e.g., metal) due to acidic compounds present in the environment. The acids may be those coming from soil, industrial air, water or toxic chemicals that react with the material they contact.

Corrosionpedia explains Acidic Corrosion

The cause of acidic corrosion in industrial equipment is due to an electrochemical reaction. Three conditions must exist:

A electric potential difference must exist on the metal surfaces where the acidic corrosion is occurring

A charge transfer must occur between conductors

A continuous conduction path exists between anodic and cathodic centers

An electrochemical reaction is a process in which electrons flow between a solid electrode and another substance such as an electrolyte. This flow triggers an electric current through the electrodes, causing the reaction to liberate or absorb heat.

Acidic corrosion of boilers and furnaces is sometimes caused by chemical cleaning