Q.1: Give the general design rules which should be taken to control corrosion of
ID: 700800 • Letter: Q
Question
Q.1: Give the general design rules which should be taken to control corrosion of metals and alloys. Q.2: Give the general rules which should be taken to control or prevent the following types of corrosion: a. pitting, galvanic, crevice, Q.3: Shortly describe the different measures which should be taken to control the corrosiveness of aquatic environments. Q.4: Explain two effective methods used to control corrosion of metallic equipments in storehouse, discuss how they affect the corrosion process.Explanation / Answer
Q1) The general design rules taken to control corrosion of metals and alloys are
a) The design and structure should always be simple.
b) The complicated design consists of more angles,edges, corners etc must be avoided.
c) Bolts and rivets should be replaced by proper welding
d) Metal washers should be replaced by plastic washers as they do not absorb water. They also help in insulation
e) Corrosion in pipelines can be prevented by smooth curve.
f) Heat treatment like annealing can prevent stress corrosion.
g) Crevices (gap or crack) should be avoided between adjacent parts of a structure.
Ans2) General rules to control the following types of corrosion are
1) Pitting
a) Proper selection of materials with known resistance
b) Control pH, chloride concentration and temperature
c) Cathode and anode protection
d) Use higher alloys for increased protection
2) Galvanic
a) Avoid the contact of dissimilar metals. Instead, insulation can be used.
b). When two dissimilar metals are to be in contact, the anodic area must be as large as
possible and the cathodic area should be as small as possible.
3) Crevice
a) Joints should be welded instead of being bolted or riveted.
b) The contacts between metals and non-metals should be minimized.
c) Sharp corners, edges and packets should be avoided
d) Use fillers to fill gaps
Ans3) Different measures to be taken to control the corrosiveness of aquatic environments
a) Isolate the corroding metal from direct contact of sea water by paintings or other coatings.
b) Change the potential of the metal to the numerical value where corrosion ceases by impressed voltage or coupling to sacrificial anode
c) Use corrosion inhibitors to make the metal passive.
d) Change the pH of local environment by chemical dosing
e) Use a more corrosion resistant material
Ans4) The two methods to control corrosion of metallic equipments in storehouse are
1) Coating
2) Plating
Coating reduces the effect of corrosion by making a barrier between the corrosive metal and moisture in the environment
Plating is the electrodeposition of the metal on to the corrosive metal. This layer acts as a sacrificial metal layer which can protect the corrosive metal.
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