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151.	As the metal dissolution within the crevice increases, the rate of oxygen reduction on adjacent surfaces increases.(a) True(b) FalseThe question was asked during an online exam.I'm obligated to ask this question of Eight Forms topic in section Eight Forms of Corrosion of Corrosion Engineering
Answer» Right answer is (a) True Best explanation: Metallic dissolution in the crevice cathodically PROTECTS the EXTERNAL SURFACE.Electrons TRANSFER from M==>M^+n+ne (in crevice) to compensate O2+H2O+4e==>4OH (adjacent surface).

152.	Which of the following combination results in crevice corrosion?(a) Metal and absorbent gaskets(b) Continuous weld metals(c) Metal and non-absorbent gaskets(d) Single metal pieceThis question was addressed to me during a job interview.The above asked question is from Eight Forms in division Eight Forms of Corrosion of Corrosion Engineering
Answer» Right option is (a) Metal and absorbent gaskets Best explanation: Metal and absorbent gasket combination results in the CREVICE corrosion. Absorbent gaskets ABSORB water VAPOR from surrounding and MAKE them stagnant at the metal–gasket interface. This results in crevice corrosion.

153.	Tarnishing of silver is an example of which type of corrosion?(a) Crevice corrosion(b) Pitting corrosion(c) Uniform corrosion(d) Erosion corrosionThis question was addressed to me during an interview for a job.I need to ask this question from Eight Forms in section Eight Forms of Corrosion of Corrosion Engineering
Answer» Correct answer is (c) Uniform corrosion Explanation: Outermost layers of SILVER undergoes a chemical reaction with hydrogen sulfide results in tarnish. This is known as the TARNISHING of silver. Metals like brass, copper, aluminum, silver, and MAGNESIUM undergoes tarnishing under VARIOUS corrosive ENVIRONMENTS.

154.	Which of the following chemical is responsible for the stains on silver?(a) Hydrogen peroxide(b) Hydrogen sulfide(c) Sulfur dioxide(d) Sulfur trioxideThis question was addressed to me in a national level competition.Query is from Eight Forms topic in division Eight Forms of Corrosion of Corrosion Engineering
Answer» Right choice is (b) HYDROGEN sulfide To elaborate: The stains on SLIVER is USUALLY due to the presence of hydrogen sulfide. It can be removed by the application of galvanic CORROSION. It can be done with silver-aluminum galvanic attachment in the presence of BAKING soda.

155.	Which of the following is/are the preventions of galvanic corrosion?(a) Avoid the unfavorable area effect of a small anode and large cathode(b) Select the close combination of metals in galvanic series(c) Select the far combination of metals in galvanic series(d) Avoid the unfavorable area effect of a small anode and large cathode and select the close combination of metals in galvanic seriesThe question was posed to me by my college professor while I was bunking the class.Enquiry is from Eight Forms in section Eight Forms of Corrosion of Corrosion Engineering
Answer» The correct choice is (d) Avoid the UNFAVORABLE area effect of a small ANODE and large cathode and SELECT the close combination of metals in galvanic series Easiest explanation: In industrial applications avoiding a dissimilar metal combination is impossible. But it can be minimized by avoiding the unfavorable area effect, selecting the close combination of metals. Proper material selection and regular INSPECTION are other preventive MEASURES.

156.	Pure metals are more corrosion resistant than commercial materials.(a) True(b) FalseI had been asked this question in homework.My question comes from Eight Forms in division Eight Forms of Corrosion of Corrosion Engineering
Answer» The correct answer is (a) True Explanation: In most of the CASES of corrosion, pure METALS are more corrosion resistant than commercial materials. This is DUE to the ABSENCE of galvanic effect and selective leaching in pure metals.

157.	Which of the following is used to visualize the heat flow and temperatures during welding?(a) Weld decay(b) Intergranular corrosion(c) Tablecloth analogy(d) Weld decay and intergranular corrosionThis question was posed to me in an online interview.The query is from Eight Forms topic in division Eight Forms of Corrosion of Corrosion Engineering
Answer» Correct ANSWER is (C) Tablecloth analogy For EXPLANATION I would say: Tablecloth analogy of heat flow and temperatures is used during WELDING. To visualize a mountain like a block with the rise and fall of each stripe represents the rise and fall of temperature in a welded PLATE.

158.	Which of the following is also known as under film corrosion?(a) Crevice corrosion(b) Filiform corrosion(c) Galvanic corrosion(d) Pitting corrosionI got this question during an interview.The origin of the question is Eight Forms in portion Eight Forms of Corrosion of Corrosion Engineering
Answer» Right CHOICE is (b) Filiform CORROSION The explanation is: Filiform corrosion is a special type of crevice corrosion. It is ALSO known as under film corrosion as it occurred under protective coatings or films.It USUALLY seen on food and beverage cans.

159.	Which of the following ions have a high tendency to pitting corrosion?(a) Chlorides(b) Bromides(c) Hypo chlorites(d) Chlorides, bromides, and hypochloritesThis question was posed to me during a job interview.My doubt stems from Eight Forms topic in section Eight Forms of Corrosion of Corrosion Engineering
Answer» Right ANSWER is (d) CHLORIDES, bromides, and hypochlorites To explain: In practical applications, most pitting failures are caused by chloride ions, hypochlorites, and bromide ions. OXIDIZING metal ions with chlorides are aggressive pitters. CUPRIC, ferric, and mercuric halides are extremely aggressive.

160.	Which of the following type of brasses is/are highly prone to localize or plug-type dezincification?(a) Low brasses(b) High brasses(c) Low and high brasses(d) Neither low nor high brassesThe question was asked in an online quiz.My question is based upon Eight Forms topic in portion Eight Forms of Corrosion of Corrosion Engineering
Answer» The CORRECT choice is (a) LOW brasses The explanation: The COMPOSITION of low brasses are usually 80% copper and 20% zinc. Low brasses are highly prone to localize or plug-type dezincification in alkaline, neutral, and slightly acidic ENVIRONMENTS.

161.	Which of the following corrosion test is most reliable to know the extent of pitting corrosion?(a) To measure the average depth of pits(b) To measure the maximum depth of a pit(c) Weight loss method(d) Weight gain methodI had been asked this question in quiz.I'm obligated to ask this question of Eight Forms in division Eight Forms of Corrosion of Corrosion Engineering
Answer» Right option is (b) To measure the maximum DEPTH of a PIT The best I can explain: The MEASUREMENT of maximum depth of pit would be a more reliable way of expressing pitting corrosion. As metal LOSS or metal gain (corrosion product) is very small and does not indicate the depth of penetration.

162.	Which of the following is a non-absorbent gasket?(a) Polyethylene(b) Isoprene(c) Teflon(d) Polyethylene and isopreneThe question was posed to me during a job interview.This is a very interesting question from Eight Forms topic in portion Eight Forms of Corrosion of Corrosion Engineering
Answer» Right choice is (c) Teflon The explanation: Teflon (CF2=CF2) is a non-absorbent GASKET. It is USED in the industrial application to minimize the crevice corrosion. Whereas polyethylene and isoprene (rubber) is absorbent to FLUIDS such as WATER and acids.

163.	Which of the following are the methods and procedures to minimize crevice corrosion?(a) Use of welded joints instead of riveted joints(b) Avoid sharp edges and stagnant areas(c) Removal of deposits frequently(d) Use of welded joints instead of riveted joints, avoid sharp edges and stagnant areas and removal of deposits frequentlyI got this question during an interview.I would like to ask this question from Eight Forms in chapter Eight Forms of Corrosion of Corrosion Engineering
Answer» CORRECT answer is (d) Use of welded joints instead of riveted joints, avoid sharp edges and stagnant areas and removal of deposits frequently Explanation: Combating or MINIMIZING CREVICE corrosion can be DONE as follows: L. Use of welded joints instead of riveted or bolted joints ll. Avoid sharp edges and stagnant areas lll. Regular inspection lV. Removal of deposits frequently V. Use of non-absorbent gaskets

164.	Which of the following ions that accelerate the dissolution rate of metals or alloys in a crevice?(a) H^+, OH^–(b) H^+, Cl^–(c) OH^–, Cl^–(d) OH^–, Cl^– and H^–The question was posed to me in semester exam.My doubt stems from Eight Forms topic in section Eight Forms of Corrosion of Corrosion Engineering
Answer» The correct ANSWER is (b) H^+, Cl^– Explanation: H^+ and Cl^– ions accelerate the dissolution rate of metals and alloys in the crevice. These are produced by hydrolysis of METAL chlorides. It accelerates corrosion because hydrogen ion decreases pH value (more ACIDIC) and CHLORIDE ion attacks the metallic surface in the crevice.

165.	What does the square bracket [] in the galvanic series indicates?(a) Most practical metal combinations(b) High corrosion-resistant metals(c) Low corrosion-resistant metals(d) Avoidable metal combinationsThe question was asked in class test.This is a very interesting question from Eight Forms in portion Eight Forms of Corrosion of Corrosion Engineering
Answer» The correct answer is (a) Most practical metal combinations For explanation: The bracket in the galvanic SERIES indicates the most practical metal combinations. This metal COMBINATION RESULTS in little danger of galvanic corrosion. Example: [ Monel, bronzes, COPPER, brasses]

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