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Right choice is (a) True

For explanation I would say: There is no such single MATERIAL that can be USED in all environment CONDITIONS and all temperature ranges. So, it is important to select a proper metal or alloy for a particular corrosive service. It prevents or reduces the corrosion DAMAGE of the metallic structure.

The correct CHOICE is (b) IMPRESSED current supply

The best I can explain: Impressed current supply is used as the corrosion prevention for REDUCING maintenance COSTS of big metallic structures such as highways and bridges. It also used to reduce the corrosion of reinforced STEEL.

Correct option is (c) BENZOIC ACID

The best I can explain: Inhibitors are the chemical compounds that decrease the CORROSION rate of metal in a specific environment. Benzoic acid is used as an inhibitor for STEEL in water.

Right answer is (c) Surface preparation and selection of primary and top coatings

To elaborate: Factors to consider for organic coatings are:

i. Surface preparation USUALLY is DONE by sandblasting

ii. Selection of primary coatings for strong ADHESIVE bonding

iii. Selection of top coating for APPEARANCE and corrosion RESISTANCE.

Right option is (b) Copper/copper sulfate reference ELECTRODE

The EXPLANATION is: Copper/copper sulfate reference electrode is used for cathodic protection surveys. The potential of a structure is DETERMINED with a high-resistance VOLTMETER. This electrode has the advantages of low cost, good accuracy, and ruggedness.

Right answer is (c) The storage TANK of H2SO4

To explain: Impressed METHOD current is an external supply of POWER to provide electrons to metallic structure that needs to be protected. The storage tank of H2SO4 requires the HIGHEST current DENSITY per sq. feet due to the high corrosiveness of acid.

The correct option is (c) External impressed current SUPPLY and sacrificial ANODE

The explanation is: CATHODIC protection is achieved by supplying ELECTRONS to the METAL structure to be protected. Types of cathodic protection are i. External impressed current supply ii. Sacrificial anode.

Correct choice is (c) Organic amines

To explain I WOULD say: Adsorption-type inhibitors are the type of inhibitors that ADSORB on the surface of CATHODE or ANODE and alter its surface. Organic amines are examples of adsorption-type inhibitors.

Correct CHOICE is (a) Arsenic and ANTIMONY

Best explanation: Hydrogen-evolution poisons are the inhibitors that retard the rate of evolution of hydrogen gas in an ACIDIC ENVIRONMENT. Arsenic and Antimony are examples of hydrogen-evolution poisons.

Right CHOICE is (a) True

The best I can explain: Stress-corrosion cracking is a combination of stress and a CORROSIVE ENVIRONMENT. Uneven temperature distribution leads to INTERNAL stress and results in stress-corrosion cracking FAILURE.

Right answer is (a) True

The best explanation: In general, coatings should not be used where the environments WOULD RAPIDLY ATTACK the substrate material because one defect or small AREA of EXPOSED metal would result in rapid degradation.

Correct choice is (a) True

To elaborate: A thin coating of metallic, inorganic, and organic material can PROVIDE a satisfactory barrier between the metal and its ENVIRONMENT. Because it minimizes the exposure of native metal to the corrosive environment.

Correct ANSWER is (a) Commercially PURE metals

To elaborate: Commercially pure metal such as aluminum (99.5+ PURITY) is used for HANDLING hydrogen peroxide. Alloys result in the decomposition of hydrogen peroxide DUE to the catalytic action of alloying elements.

Correct option is (c) Short DRYING time, ADEQUATE wettability and it contains rust-inhibitive pigments

For explanation I would say: CHARACTERISTICS of primary coatings are:

i. It contains rust-inhibitive pigments

ii. Adequate wettability

iii. Short drying time.

Correct choice is (B) COATINGS PRODUCED by CORRODING the metal surface to form an adherent protective layer

The explanation: Chemical CONVERSION is one of the surface coating methods in that coatings are produced by corroding the metal surface to form an adherent protective layer.

Right CHOICE is (a) 2% boron trifluoride

To explain: Inhibitors are very SPECIFIC to a PARTICULAR metal, environment, and the concentration of an environment. 2% boron trifluoride inhibitor is used for steel in 80% pure SULFURIC acid.

The correct answer is (b) Current enters it from the electrolyte

The best explanation: Metallic STRUCTURE can be protected when the impressed current is arranged to enter it from the electrolyte. Whereas current passes from metal to electrolyte, electrical contact with DISSIMILAR METALS, and connecting the positive TERMINAL of the power supply RESULTS in accelerated corrosion.

Correct ANSWER is (a) True

To explain I would SAY: Boiling seawater is less corrosive than that of hot seawater. Because the solubility of OXYGEN in seawater decreases with an increase in temperature. REDUCTION of oxygen results in severe metallic dissolution in many oxygenated corrosive SOLUTIONS.

The correct option is (b) True

For explanation: OXIDIZERS such as chromates, NITRATES, and ferric are one type of inhibitors that inhibit the corrosion of METAL and ALLOYS that demonstrate active-passive transition. Active-passive transition metals include iron and stainless steel.

Right answer is (c) Ceramics

The explanation is: Ceramics are the class of MATERIALS that POSSESS excellent corrosion and high-temperature RESISTANCE. But brittleness or LESS tensile strength is the primary limitation of ceramics.

The correct answer is (B) Excellent corrosion RESISTANT to fresh, SEAWATER and soil immersion

The explanation: Coal-tar coatings are excellent corrosion resistant to fresh, seawater, and soil immersion. Whereas its ABRASIVE resistance and stability of coating are its limitations.

Right option is (b) Coating metal is vaporized electrically to DEPOSIT on the metals to be coated

The EXPLANATION is: Vapor deposition is a METHOD of metal coating in that coating metal is vaporized electrically to deposit on the metals to be coated. It is usually used for HIGH strength PARTS for missiles and rockets.

Correct choice is (d) Stray current REFERS to extraneous direct current in the earth that usually encountered in cathodic PROTECTION systems and ACCELERATED corrosion will occur at the point where current enters the soil

For explanation: Stray current refers to extraneous direct current in the earth that usually encountered in cathodic protection systems and accelerated corrosion will occur at the point where current enters the soil.

Correct option is (b) Nickel, IRON, and titanium

The best I can explain: ANODIC protection can be used only for active-PASSIVE transition metals as it provides external current for the formation of a passive oxide layer. Active-passive transition metals include nickel, iron, aluminum, titanium, and its alloys.

Right answer is (d) Silverware, galvanized steel, and tin CANS

For explanation I would say: Sacrificial metals such as zinc, tin, and precious metals such as silver, gold, PLATINUM is used as metallic COATINGS for VARIOUS applications. Silverware, galvanized steel, and tin cans are examples of metallic coatings.

Correct choice is (c) USE of bus conductor and rearrangement of ANODES

For explanation: Stray current effect CAUSED due to the densely buried underground pipelines in the vicinity of the cathodic protection system. It can be prevented by the use of bus conductors and rearrangements of anodes.

The correct ANSWER is (c) Avoid sharp bends in piping systems and provide thicker SECTIONS to reduce impingement EFFECTS

Easy explanation: Erosion corrosion can be minimized by AVOIDING sharp bends in the piping system and provide a thicker section to reduce impingement effects. And the better material selection is also one of the factors to PREVENT erosion-corrosion.

Correct option is (b) Nickel and its alloys

To explain: Nickel and its alloys are the BEST combination of metal for the caustic ENVIRONMENT. METALS such as TITANIUM and high tensile strength STEELS are prone to caustic embrittlement.

Correct answer is (c) Stainless steels

For explanation I WOULD say: Stainless steels are the best COMBINATION of METAL for the nitric acid environment. Stainless steels readily form a passive oxide FILM in nitric acid. This minimizes or reduces the corrosion damage.

The correct option is (C) Either to act as SACRIFICIAL metal or to act as an effective barrier

Best explanation: Coatings are the relatively thin material portion on the surfaces of native metal to avoid DIRECT exposure to the corrosive ENVIRONMENT. The PURPOSE of coatings is either to act as sacrificial metal or to act as an effective barrier.

Correct ANSWER is (d) M==>M^++ne, 2H^++2e=>H2 and O2+4H^++4e==>H2O

Easiest explanation: The common electrochemical reactions that occur during corrosion are:

M==>M^++ne (METALLIC reduction or anodic reaction)

2H^++2e=>H2 (HYDROGEN evolution or cathodic reaction)

O2+4H^++4e==>H2O (oxygen reduction or cathodic reaction)

The correct choice is (c) Platinum-clad electrode

The explanation: It is necessary to have an inert AUXILIARY CATHODE such as a platinum-clad electrode as the anode provides external electric current to passivates the metallic STRUCTURE.

Right option is (d) Prevent SCALING, destroy BACTERIA and reduce water hardness

Best explanation: Magic device or water-conditioning GADGETS are the devices to control water CORROSION. Purpose of these gadgets are

Prevent scaling

Destroy bacteria

Reduce water hardness

Reduces corrosion.

Correct answer is (d) Dissimilar METAL contact, different phases such as vapor spaces, and uneven HEAT and stress distribution.

Explanation: The DESIGN RULE to avoid HETEROGENEITY includes dissimilar metal contact, different phases such as vapor spaces, and uneven heat and stress distribution.

Correct option is (d) Magnesium, ZINC, and aluminum-tin

Easy explanation: Sacrificial ANODES are metals that have a very high negative potential, which PROVIDES high current output. Magnesium, zinc, and aluminum-tin are TYPICAL examples of sacrificial anodes.

Correct choice is (a) Riveting the tanks rather than welding

To explain: Certain design rules can reduce or MINIMIZE the effect of corrosion. That INCLUDES welding the tanks rather than riveting. This eliminates the formation of CREVICES at the riveting AREA and avoids crevice corrosion.

Right option is (d) BRIDGES, refrigeration equipment and ship HULLS

The explanation: Application of FLAME spraying include vessels of all kinds, bridges, ship hulls, refrigeration equipment, and many fabricated steel products. Low melting POINT metals such as zinc, tin, and lead are used.

The correct choice is (C) Sandblasting, chipping, wire brushing and FLAME cleaning

For explanation I would say: Methods for SURFACE preparation for coating APPLICATION are:

i. Sandblasting

ii. Wire brushing

iii. Flame cleaning

iv. Chipping

v. Scarping.

Right choice is (B) GALVANIC effect

For EXPLANATION: The localized attack on the base METAL due to the porosity of coatings is dueto two-metal corrosion or galvanic effect. Because metal coating and base metal are electrically connected in a CORROSIVE environment.

Correct answer is (a) Platinized TITANIUM

Explanation: Platinized titanium is an INERT anode that is both efficient and expensive in NATURE. It is finding increased applications in marine environments.

Correct choice is (c) SODIUM SULFITE and HYDRAZINE

Explanation: Scavengers are the type of inhibitors that removes corrosive REAGENTS from the solution. Sodium sulfite and hydrazine are EXAMPLES of scavengers. 2Na2SO3+O2==>2Na2SO4 is the scavenging action of sodium sulfite.

The CORRECT choice is (d) It has very high vapor pressure, inhibit atmosphere corrosion without being contact with the METAL surface and very effective in closed SPACES

For explanation I would say: Vapor-phase INHIBITORS are very similar to organic adsorption-type inhibitors. Characteristics of vapor-phase inhibitors are:

i. It has a very high vapor pressure

ii. Inhibit the ATMOSPHERIC corrosion without being contact with the metal surface

iii. Effective in closed spaces.

Correct CHOICE is (d) Weld rather than riveting containers, design systems for easy replacements of components that fail RAPIDLY, and avoid excessive MECHANICAL STRESS and stress concentration

Easy explanation: Design rules for corrosion preventions:

Weld rather than the riveting tank and other containers

Design systems for easy replacements of components that fails rapidly

Avoid excessive mechanical stress and stress concentration

Avoid electrical contact between TWO dissimilar metals.

Correct choice is (a) Tin

The explanation: Tin is the BEST combination of metal for distilled WATER. Tin or tin coatings are almost always CHOSEN as a container or PIPING MATERIAL for very pure distilled water.