Explore topic-wise InterviewSolutions in .

Correct ANSWER is (d) Surface roughening for mechanical BONDING, REMOVAL of dirt, rust, mill scale, welding flux, and other impurities

To EXPLAIN: Surface PREPARATION is a crucial part of the stability of coatings. It roughens the surface to obtain mechanical bonding, removal of dirt, rust, mill scale, welding flux, and other impurities.

The correct answer is (d) Bonderizing, parkerizing, and chromatizing

Easiest explanation: Bonderizing, parkerizing, and chromatizing are examples of CHEMICAL conversion. AUTOMOBILE bodies are best known for phosphatizing treatment. Anodized aluminum with a PROTECTIVE FILM Al2O3 is another EXAMPLE.

Right answer is (c) Synergistic EFFECT

The best I can explain: When two or more inhibiting substances are ADDED to a CORROSIVE system, the inhibiting effect is sometimes greater than that achieved by either of the two or more substances alone. This is called a synergistic effect.

Correct option is (c) Availability in extremely CORROSIVE conditions and low current requirement

Explanation: ADVANTAGES of anodic protection than CATHODIC protection is:

i.Availability in extremely corrosive conditions

ii. Low current requirement.

The CORRECT answer is (B) Arc-melted zirconium

To EXPLAIN I WOULD say: Arc-melted zirconium is more corrosion resistant than induction-melted zirconium because of more IMPURITIES in the latter. Hence arc-melted zirconium is used in an atomic-energy application.

Correct answer is (a) Vinyl and epoxy PAINTS

Explanation: A variety of paints are available in the market for VARIOUS corrosion APPLICATIONS. It includes asphalts, bituminous paints, red lead, iron OXIDE, titanium oxide, alkyds, vinyl, and epoxies. Among them, vinyl and epoxies are the class of paints that are widely used for corrosion applications.

Correct choice is (d) Coke BREEZE, gypsum, and bentonite

The explanation is: Coke breeze, gypsum, and bentonite are the materials that are used as backfill material AROUND the anode. These materials improve the ELECTRIC CONTACT between the anode and surrounding soil.

Correct choice is (c) Hot rolling of TWO metals together to GET a composite sheet

To EXPLAIN: Metal CLADDING is a method of hot rolling two metals together to get a composite sheet. High-strength aluminum alloys and commercial pure aluminum are rolled together to provide the corrosion barrier.

Right choice is (d) Calomel ELECTRODE

For explanation: The Calomel electrode is used to MEASURE the potential maintained during the operation. It is connected to the THIRD TERMINAL of potentiostat whereas metal and auxiliary cathode are connected to first and second terminals respectively.

The correct ANSWER is (d) Decreasing velocity, removing oxygen and oxidizers and CHANGING the concentration

To explain: Alteration of the environment is one of the measures to minimize CORROSION. Alteration of the environment includes

Changing mediums

Lowering temperature

Decreasing velocity

Removing oxidizers

Changing concentrations.

The correct option is (a) True

Easiest explanation: ANODIC protection is one of the CORROSION prevention methods that is BASED on the formation of a protective film on metals by external APPLIED anodic CURRENTS.

Correct choice is (a) True

The BEST I can EXPLAIN: An inhibitor is a chemical substance that added in SMALL concentrations to an ENVIRONMENT, to decrease the corrosion rate. It is also regarded as a retarding catalyst.

The correct answer is (d) Stress-corrosion cracking, pitting and intergranular corrosion

The best explanation: STAINLESS steels are more susceptible to localized corrosion such as intergranular corrosion, stress-cracking corrosion, and pitting corrosion than ORDINARY steels. Instability of oxide LAYER in severe corrosive conditions and sensitizing TEMPERATURE are the reasons for the susceptibility of stainless STEEL.

Right answer is (b) 11.5 to 30% chromium and 0 to 22% nickel

The BEST I can explain: STAINLESS steel is the generic NAME for a series of more than 30 different alloys with composition ranges from 11.5% to 30% chromium and 0 to 22% nickel and other alloying ELEMENTS.

The correct option is (a) Inner COATING – adhesion, intermediate coating – CORROSION protection and top layer – appearance

Easiest explanation: In general, MULTIPLE layered metallic structures CONSIST of inner coating for adhesion such as copper, intermediate coating for corrosion resistance such as nickel and top coatings for appearance such as CHROMIUM.

Correct answer is (b) A wire or powder through melting flame is blown onto the surface to be protected

The best I can explain: Flame spraying METALLIC COATING is a METHOD of metal coating in which a wire or powder through the melting flame is blown onto the surface to be protected. OXYGEN, acetylene, and propane are used for melting flame.

Correct CHOICE is (a) IMMERSING native metal in a solution of the metal to be plated

Explanation: ELECTRODE POSITION is an immersion of native metal in a solution of the metal to be plated with direct current passing through them. It is also CALLED electroplating.

Right option is (c) 1/4 inches

To explain: The approximate thickness of a wall should be twice that of the estimated CORROSION rate to meet the MECHANICAL requirements such as pressure, WEIGHT, and stress. Hence, the thickness of the given wall is 2*(1/8) = ¼ inches.

The correct ANSWER is (d) ELECTRODE position, flame SPRAYING, and cladding

Easiest EXPLANATION: Methods to apply metallic COATINGS are:

i. Electrode position

ii. Flame spraying

iii. Cladding

iv. Hot dipping

v. Vapor deposition.

Correct option is (c) Heat treatment to cause alloy formation by diffusion of one metal into the other

To elaborate: Diffusion COATINGS INVOLVE heat treatment to cause alloy formation by diffusion of one metal into the other. It is also called as surface alloying. It improves VARIOUS properties such as wear-RESISTANCE and corrosion resistance at the surface.

The CORRECT CHOICE is (d) Graphite, platinized TITANIUM, and silicon-iron

Explanation: Materials that can be used as an impressed-currents anode are:

Graphite

Platinized titanium

Silicon-iron

Steel.

Correct option is (d) Paints, varnishes and lacquers

To ELABORATE: Organic COATINGS are widely used to protect more METALS on a tonnage basis than other corrosion combating PROCESSES. Organic coatings include paints, varnishes, and lacquers.

The CORRECT choice is (a) True

The explanation is: Cladding is a GREAT economical advantage in that the corrosion BARRIER as the expensive material is backed up by inexpensive material by MINIMIZING corrosion.

Correct OPTION is (d) Sherardizing – zinc, chromizing – chromium and alonizing – aluminum

For EXPLANATION: Types of diffusion coatings:

i. Sherardizing – zinc

ii. Chromizing – chromium

iii. Alonizing – aluminum

iv. CARBURIZING – carbon

v. NITRIDING – nitrogen.

Correct answer is (a) Negative TERMINAL

Explanation: As the conventional ELECTRICAL theory states that CURRENT flows from (+) to (-), the STRUCTURE is protected if the negative terminal of the power supply is connected metallic structure.

Correct answer is (a) True

The explanation is: Cathodic PROTECTION is achieved by SUPPLYING electrons to the metal structure to be protected. It can be done by using IMPRESSED current in the range of MICROAMPERES per unit area of the metallic structure.

The correct OPTION is (b) Adsorption and phase layers

Easiest explanation: Inhibitors are the chemical compounds that decrease the corrosion RATE of METAL in a specific environment. INHIBITION can be CAUSED by both adsorption and phase layers on the metal surface.

Right OPTION is (a) True

The best I can explain: SINCE corrosion is a penetrating action, it is NECESSARY to make allowances for the REDUCTION in thickness in designing pipes and tanks to meet the MECHANICAL requirements of the service.