Explore topic-wise InterviewSolutions in .

The correct OPTION is (B) AUSTENITIC STAINLESS STEELS

Explanation: Austenitic stainless steels are the types of stainless steels that are attacked by magnesium at its melting. Liquid magnesium preferentially leaches out nickel from this alloy from the iron matrix.

Correct answer is (C) Leathers, rubbers and bare and coated METALS

To elaborate: Materials that are USUALLY attacked by fungus are leathers, rubbers, and bare and coated metals. Though the attack of fungus on materials may not affect many mechanical properties it DETERIORATES the APPEARANCE of materials.

The correct answer is (c) By producing deposits, by influencing ANODIC, CATHODIC reactions and PROTECTIVE surface films

Explanation: The process that affects the corrosion behavior of metals by BIOLOGICAL activity are:

i. By directly influencing anodic and cathodic reactions

ii. By influencing protective surface films

iii. By creating a CORROSIVE environment

iv. By producing deposits.

The correct choice is (b) Oxygen

The EXPLANATION is: Percentage or relative amount of oxygen in the environment is taken into account to classify the microorganisms into aerobic and aerobic bacteria. The ANAEROBIC attack is pre-dominate in underground CORROSION DUE to the non-availability of oxygen.

The CORRECT option is (d) Production unit, transportation, storage, and refinery OPERATIONS

Explanation: The Petroleum industry is one of the most AFFECTED industries with CORROSION. The GENERAL areas of the petroleum industry that faces corrosion problems are production unit, transportation, storage, and refinery operations.

Right answer is (C) Crevice and PITTING corrosion

Easiest explanation: Crevice and pitting corrosion are the types of corrosion that dominate due to backfill such as stones, CINDERS, wood, and metal. Because these foreign particles result in the FORMATION of crevices.

Correct choice is (c) Aluminum, magnesium, TITANIUM, and iron

To ELABORATE: Aluminum, magnesium, titanium, and iron and their alloys are the PRIMARY materials regarding the construction of aircraft. These are selected based on a HIGH strength-weight ratio for materials and high ratios of payload to vehicle weight.

Right option is (d) Cast iron, stainless steel, and galvanized steel

Explanation: Cast iron, stainless steel, steel, and galvanized steel are widely used for handling freshwater. Metals such as copper, brass, aluminum, monel, and cupronickels are also used with the factors of TEMPERATURE, contamination, and LONGER LIFE.

The correct option is (d) Oxygen content, hardness and CHLORIDE content

To explain I would say: FACTORS that AFFECT the corrosivity in freshwater are:

i. Oxygen content

ii. Hardness

iii. Chloride and SULFUR content.

The CORRECT CHOICE is (d) Zirconium and its alloys, stainless steels, Inconel and Incoloy

For EXPLANATION: Zirconium and its alloys, stainless steels, Inconel and Incoloy are the metals/alloys that are used for handling high-purity WATER in nuclear APPLICATIONS.

Right answer is (b) Breathing

The best explanation: Breathing results in rapid corrosion on the inside of large STORAGE tanks occurs when moisture-laden SALT air is drawn in. This can be PREVENTED by protective coatings for steels and blanketing with nitrogen or DRY air inside the tank.

Right ANSWER is (c) Applying COATINGS, use of inhibitors, CATHODIC protection and substitute materials

To ELABORATE: Preventions to microbiological corrosion in soil:

i. Use of substitute materials such as asbestos and plastic

ii. Use of coatings such as asphalts and enamel

iii. Use of inhibitors and germicides

iv. Cathodic protection can be applied.

Correct option is (a) Alkaline SODIUM CHROMATE

For explanation I would say: Alkaline sodium chromate or sodium NITRATE is an effective inhibitor for the corrosion of DOMESTIC fuel oil tanks. The chemical FORMULA of sodium chromate is Na2CrO4.

Correct option is (c) Saline water, sulfides and organic impurities such as ammonia

The best I can explain: Oil and gas fields consumes a TREMENDOUS amount of iron and steel pipe, TUBING, CASINGS, pumps, and VALVES. Saline water, sulfides, and organic impurities such as ammonia are the impurities that are USUALLY present in oil and gas fields.

The correct choice is (b) Naphthenic acid

To elaborate: Naphthenic acid CAUSES rapid INTERGRANULAR stress CORROSION CRACKING of sensitized austenitic stainless steels in refinery operation. WHEREAS naphthenic acid is a combination of cyclopentyl and cyclohexyl carboxylic acids.

The correct option is (a) True

Best explanation: AMMONIA is used to control the pH of the WATER and to reduce chloride ACIDITY in the process STREAMS. It usually maintains a pH of 7 but it damages copper-bearing ALLOYS if the pH becomes 8 or more.

The CORRECT choice is (C) Monel, straight CHROMIUM steels, stellite, and copper-based alloys

The best I can explain: Metals that are usually USED for petroleum well VALVES and wellhead parts are straight chromium stainless steels, stellite, monel, and copper-based alloys.

Right answer is (a) Chlorides

The explanation is: Chloride IONS are the impurities that CONTAMINATE the brackish WATER due to the TIDAL action in rivers and bays near the ocean. The source of these chloride ions is sodium chloride in SEAWATER.

The correct answer is (C) Formation of brittle intermetallic COMPOUNDS, RESISTANCE to heat transfer and deposition of impurities in COOL areas

For explanation I would say: Conditions that are undesirable in heat-exchange systems handling liquid METALS:

i. Deposition of impurities in cool areas

ii. Resistance to heat transfer

iii. Formation of brittle intermetallic compounds.

The correct option is (a) True

The best explanation: WATER acts as an ELECTROLYTE and CAUSES corrosion in refining operations. This is because water tends to hydrolyze chlorides and other materials to form ACIDIC environments.

The correct OPTION is (d) Solution of STRUCTURAL metal, DIFFUSION of liquid into solid metal and intermetallic compound formation

To explain I would SAY: TYPES of liquid-metal corrosion are:

i. Solution of structural metal

ii. Diffusion of liquid into solid metal

iii. Intermetallic compound formation

iv. Mass transfer.

The CORRECT answer is (a) Sulfur-reducing bacteria

Easiest explanation: Sulfur-reducing anaerobic bacteria influences the corrosion behavior of BURIED steel structures. SO4^-2+4H2==>S^-2+4H2O is the general CHEMICAL REACTION of sulfur-reducing anaerobic bacteria.

The correct option is (c) Galvanized steels, electroplated steels and complete immersion of corrosion preventing PRIMER COAT

The explanation is: Types of steel COATINGS that are preferred for AUTOMOBILE PARTS are:

i. Galvanized steels

ii. Electroplated steels

iii. Complete immersion of corrosion preventing primer coat.

Right ANSWER is (a) True

Explanation: Liquid METAL corrosion is usually a physical effect rather than an electrochemical ATTACK. Electrochemical attack includes reduction and oxidation of hydrogen ions and metallic atoms RESPECTIVELY.

Correct CHOICE is (a) True

Easy EXPLANATION: The CORROSIVITY of a PARTICULAR solution depends on its composition. So, the corrosivity of SOILS varies over a wide range because of the variety of composition.

Right option is (d) BRASS, CUPRONICKELS and ARSENICAL admiralty metal

Explanation: Brass, cupronickels, and arsenical admiralty metal are usually used for heat exchangers tubes carrying WATER. Whereas carbon steels are unsuitable as it rapidly CORRODES by the cooling water.

The correct choice is (a) False

Best EXPLANATION: Sheltered CORROSION is the type of corrosion where moisture CONDENSES or ACCUMULATES and does not dry out for long periods of time. Corrosion on INSIDE of an automobile door and inside of a partially filled automobile gasoline tank are the examples of sheltered corrosion.

Right option is (C) Soft water

The best explanation: In HARD water, CARBONATES OFTEN deposit on the metal surface and protect it from corrosion. Whereas in soft water protective deposits do not form. HENCE, soft water is more corrosive than hard water and high-purity water.

The correct ANSWER is (c) Residual stresses, SELECTIVE weld metal attack, IMPROPER pickling, and heat treatment

The BEST I can explain: Corrosion DEFECTS that affect the reliability of tubing are:

i. Inadequate alloying

ii. Selective weld metal attack

iii. Improper pickling

iv. Residual stresses

v. Improper heat treatment.

Correct option is (d) Bacteria, fungi, protozoa, and nematodes

For explanation I WOULD say: Bacteria, fungi, protozoa, and nematodes are one of the MICROORGANISMS usually PRESENT in the soil. Biological activity that DIRECTLY or indirectly affects the corrosion of METALS is known as biological corrosion.

Right OPTION is (c) Temperature, VELOCITY, oxygen content and biological organisms

For explanation: The factors that AFFECT the corrosion of materials in SEAWATER are:

i. Temperature

ii. Velocity

iii. Oxygen content

iv. Biological organisms.

Correct choice is (a) True

Easy explanation: Biological CORROSION is a deterioration of a METAL by the corrosion process that occurs DIRECTLY or indirectly due to the activity of living organisms. This includes micro and MICROORGANISM.

Correct answer is (b) PERIODIC cleaning, reducing relative HUMIDITY during storage and applying TOXIC organic agents

The EXPLANATION is: Preventions for the GROWTH of mold on metal surfaces are:

i. Periodic cleaning of metal surfaces

ii. Reducing relative humidity during storage

iii. Applying toxic organic agents.

Right option is (a) HIGH strength-weight ratios for materials and high ratios of payload to the VEHICLE’s weight

The EXPLANATION is: High strength-weight ratio for materials and high ratios of payload to vehicle weight are the two prime considerations in SPACE VEHICLES and aircraft.

Right option is (C) Aerobic and anaerobic corrosion

For explanation I WOULD say: The anaerobic type of ATTACK is pre-dominate in underground corrosion. It is DUE to the non-availability of oxygen as it decreases with an increase in DEPTH.

The correct answer is (b) Electrical resistance

To explain: Electrical resistance is a good MEASURE of corrosivity of a corrosive solution. Higher electrical resistance lowers the corrosivity of a solution. Dry SOILS are generally not very corrosive DUE to HIGH electrical resistance.

Right choice is (d) Adding INHIBITORS, paints and other ORGANIC coatings and cathodic protection

The explanation is: Preventions methods that are usually employed on a BEAM of offshore drilling are:

i. Paints and other organic coatings

ii. Cathodic protection with sacrificial anodes or impressed currents

iii. Adding inhibitors.

Right OPTION is (a) True

To ELABORATE: Traces of titanium and magnesium in mercury can inhibit the CORROSION of iron in ferrous-based alloys. And it is reliable to USE carbon STEEL in mercury for up to 540°C.

Correct option is (b) Ammonia, sodium CARBONATE, sodium hydroxide, and sodium SILICATE

For explanation I would say: Neutralizers that are ADDED to petroleum to MINIMIZE corrosion are:

i. Ammonia

ii. Sodium carbonate

iii. Sodium hydroxide

iv. Sodium silicate and some organic INHIBITORS.

The CORRECT answer is (b) Solubility of the metallic STRUCTURE in LIQUID metal

For EXPLANATION: Solubility of alloying elements in metallic matrix has direct relation with CORROSION rate in liquid metals. Whereas liquid-metal corrosion is a physical effect rather than a chemical effect.