Question 1

Sulfidation is primarily caused by ________ and other reactive sulfur species as a result of the thermal decomposition of sulfur compounds at high temperatures.

Accepted Answer

Sulfidation is caused primarily by H₂S and other reactive sulfur species as a result of the thermal decomposition of sulfur compounds at high temperatures.

Question 2

Conditions favoring carburization include a high gas phase carbon activity and _______ oxygen potential.

Accepted Answer

Carburization involves adding carbon to a material, typically through a high-temperature gas-phase reaction. To favor carburization, the gas phase carbon activity should be high, meaning there is an abundance of carbon available to react. However, the oxygen potential should be low, as oxygen can compete with carbon for bonding sites and impede carburization. Therefore, a low oxygen potential is preferred to create conditions that favor carburization.

Question 3

Cracking can occur at low caustic levels if a concentrating mechanism is present. In such cases, caustic concentrations of ________ ppm are sufficient to cause cracking.

Accepted Answer

According to the statement, low caustic levels can cause cracking if a concentrating mechanism is present. Therefore, even caustic concentrations as low as 50-100 ppm are sufficient to cause cracking in such cases. Options B, C, and D have higher caustic concentration ranges, which may not apply in cases of low caustic levels with concentrating mechanisms.

Question 4

Where is PASCC normally located?

Accepted Answer

PASCC (Polythionic Acid Stress Corrosion Cracking) is typically located adjacent to welds where the base metal has been sensitized due to the heat input during welding.

Question 5

Corrosion of the anode may be significantly higher ________ to the connection to the cathode, depending on solution conductivity.

Accepted Answer

Corrosion occurs when there is a flow of electrons from the anode to the cathode. When the anode and cathode are adjacent, there is a shorter distance for the electrons to travel, resulting in a higher corrosion rate compared to when they are parallel or perpendicular. The diagonal position does not affect the corrosion rate significantly. Therefore, B is the best choice.

Question 6

_________ corrosion rates are found in a gas oil desulfurizers and hydrocrackers than naphtha desulfurizers and hydrocrackers by a factor of almost "2".

Accepted Answer

The sentence states that the corrosion rates are "higher" in gas oil desulfurizers and hydrocrackers than in naphtha desulfurizers and hydrocrackers.

Question 7

All ________ based materials and low alloy materials, 300 Series SS and 400 Series SS are susceptible to Sulfidation.

Accepted Answer

The answer of All ________ based materials and low alloy...

Question 8

Damage from sigma phase appears in the form of ________.

Accepted Answer

Damage from sigma phase appears in the form of cracking. Sigma phase is a type of intermetallic compound that occurs in some stainless steels when they are exposed to high temperatures for extended periods of time. The presence of sigma phase can decrease the ductility and toughness of the steel, making it more susceptible to cracking.

Question 9

Alloys with nickel content above _________ are highly resistant to Cl SCC. The greatest susceptibility is 8% to 12% nickel.

Accepted Answer

The answer of Alloys with nickel content above _________ are...

Question 10

____________ is a form of environmental cracking that can initiate on the surface of high strength low alloy steels and carbon steels with highly localized zones of high hardness in the weld metal and HAZ as a result of exposure to aqueous HF acid service.

Accepted Answer

Hydrogen stress cracking is a form of environmental cracking that occurs in high strength low alloy steels and carbon steels with localized high hardness zones, often due to exposure to hydrogen-containing environments like aqueous HF acid service.

Question 11

Sulfuric acid promotes general and localized corrosion of carbon steel. Carbon steel heat affected zones may experience severe corrosion. Acid concentration, temperature, alloy content and ____________ are critical factors affecting sulfuric acid corrosion.

Accepted Answer

Velocity is a critical factor affecting sulfuric acid corrosion as it can influence the rate of corrosion by affecting the transport of corrosive agents to and from the metal surface.

Question 12

The extent and depth of decarburization is a function of temperature and ______.

Accepted Answer

The extent and depth of decarburization depend on both temperature and exposure time. As the temperature and exposure time increase, more carbon will diffuse out, resulting in a greater degree of decarburization. Pressure, material properties, and velocity are not significant factors in the decarburization process.

Question 13

With CO₂ corrosion, increasing temperatures _________ corrosion rates up to the point where CO₂ is vaporized.

Accepted Answer

Increasing temperatures can cause CO₂ corrosion rates to increase due to the increased acidity of the solution. However, once the temperature reaches a point where the CO₂ is vaporized, corrosion rates will no longer increase.

Question 14

Which of these materials are susceptible to brittle fracture?

Accepted Answer

All of the above materials are susceptible to brittle fracture, especially at low temperatures or when subjected to sudden impact or shock loading. This is because these materials have a relatively low toughness and limited ability to deform plastically before fracturing. Proper design and testing to ensure adequate toughness and ductile behavior are important to prevent brittle fracture.

Question 15

HCL acid corrosion is found in several units, especially _______ and ________, units, hydroprocessing units and catalytic reformer units.

Accepted Answer

HCL acid corrosion is most commonly found in crude and vacuum units due to the presence of chlorine in the crude oil and the use of hydrochloric acid in the refining process. It can also be found in other units, but these are the most susceptible.

Question 16

Spheroidization and graphitization are competing mechanisms that occur at overlapping temperature ranges. Spheroidization tends to occur preferentially above _______ while graphitization predominates below this temperature.

Accepted Answer

The answer of Spheroidization and graphitization are competing mechanisms that...

Question 17

Susceptibility to temper embrittlement is largely determined by the presence of the alloying elements manganese and _______.

Accepted Answer

The answer of Susceptibility to temper embrittlement is largely determined...

Question 18

Which of these materials is susceptible to 885º F embrittlement?

Accepted Answer

885º F embrittlement affects both 400 Series Stainless Steel and Duplex Stainless Steel due to the formation of embrittling phases at this temperature range.

Question 19

Improved resistance to erosion is usually achieved through increasing substrate ________ using harder alloys, hard facing or face-hardening treatment.

Accepted Answer

Increasing the substrate hardness will improve its resistance to erosion. This can be achieved through the use of harder alloys, hard facing, or face-hardening treatment. Composition and stress may also play a role in erosion resistance, but increasing hardness is the most effective method.

Question 20

Units where graphitization may be suspected are the FCCU and the _____ unit.

Accepted Answer

Graphitization is a phenomenon that occurs in equipment that experiences high temperatures and pressures, typically above 800°F and 500 PSI. The Fluidized Catalytic Cracking Unit (FCCU) typically operates at temperatures and pressures that are below the threshold where graphitization would occur. The Alky unit and Hydrotreater also operate at relatively low temperatures and pressures, so graphitization is not a concern. The Coker, on the other hand, uses very high temperatures and pressures in the process of converting heavy hydrocarbons into lighter products. As a result, it is possible for graphitization to occur in some of the equipment in the unit, particularly in the coke drums.

Exam 1: Corrosion and Materials