Question 1

Typical HF Alkylation units operate with 1% to 3% water in the acid, equivalent to an HF-in-water concentration of 97% to 99% and the temperatures are generally below _________.

Accepted Answer

The answer of Typical HF Alkylation units operate with 1%...

Question 2

Corrosion rates of the anode can be high if there is a _______ anode to cathode ratio.

Accepted Answer

A small anode to cathode ratio means there is less anode surface area in relation to cathode surface area, resulting in higher corrosion rates on the anode.

Question 3

Which of the following materials are generally not suitable for HF service?

Accepted Answer

Both A and C. 300 and 400 series stainless steels have varying levels of resistance to HF, but it is generally recommended to use a material with better corrosion resistance such as Hastelloy, Inconel, or Monel. Carbon steel is not suitable for HF service due to its high susceptibility to corrosion.

Question 4

Which of these materials exhibit an endurance limit below which fatigue cracking will not occur?

Accepted Answer

Carbon steel exhibits an endurance limit, meaning there is a stress level below which it can endure an infinite number of cycles without fatigue failure.

Question 5

Exposure to high solution strength caustic can result in general corrosion or high corrosion rates above ________.

Accepted Answer

Exposure to high solution strength caustic can result in general corrosion or high corrosion rates above 150º F.

Question 6

_________ is a mechanical form of degradation that occurs when a component is exposed to cyclical stresses for an extended period, often resulting in sudden, unexpected failure.

Accepted Answer

Mechanical fatigue is the correct term for degradation due to cyclical stresses over time, leading to sudden failure.

Question 7

Nitriding begins above ________ and becomes severe above _______.

Accepted Answer

Nitriding begins at temperatures above 600º F and becomes severe above 900º F, making option B the best choice. Options A and D have incorrect temperature ranges for nitriding, while option C only includes the severe stage of nitriding and not the beginning stage.

Question 8

Which of these materials are not susceptible to Spheroidization?

Accepted Answer

Spheroidization is a process that occurs in steels where carbides are converted into spherical particles. Carbon steel and 9Cr-1Mo are susceptible to spheroidization, but 316 SS is not. Therefore, the best choice is C, 316 SS, because it is not susceptible to spheroidization.

Question 9

________ and _______ damage develop without applied or residual stress so that PWHT will not prevent them from occurring.

Accepted Answer

Blistering and HIC (Hydrogen Induced Cracking) are forms of damage that occur due to hydrogen presence and do not require stress to develop, hence PWHT (Post Weld Heat Treatment) does not prevent them.

Question 10

__________ is a change in the microstructure of steels after exposure in the 850º F to 1400º F range, where the carbide phases in carbon steels are unstable and may agglomerate from their normal plate-like appearance.

Accepted Answer

Spheroidization is the process where carbide phases in carbon steels become unstable and agglomerate, changing from their normal plate-like appearance to a more spherical form when exposed to temperatures in the 850º F to 1400º F range.

Question 11

Susceptibility to hydrogen stress cracking __________ with __________ hardness.

Accepted Answer

The answer of Susceptibility to hydrogen stress cracking __________ with...

Question 12

Corrosion protection in the boiler is accomplished by laying down and continuously maintaining a layer of _____.

Accepted Answer

The layer of magnetite acts as a protective barrier against further corrosion in boilers. Manganese, carbon monoxide, and carbonate do not provide corrosion protection in boilers.

Question 13

Application of a post-fabrication stress relieving heat treatment of about ______ is a proven method of preventing carbonate cracking.

Accepted Answer

The answer of Application of a post-fabrication stress relieving heat...

Question 14

Naphthenic acid corrosion is most severe in _________ flow; in areas of high velocity or turbulence and in distillation towers where hot vapors condense to form liquid phase droplets.

Accepted Answer

Naphthenic acid corrosion is most severe in two-phase flow, where hot vapors condense to form liquid phase droplets. This is especially true in areas of high velocity or turbulence, such as in distillation towers. Single phase and three phase flows may also be subject to naphthenic acid corrosion, but the severity is generally less than in two-phase flow. There is no such thing as negative phase flow.

Question 15

In piping and equipment, creep cracking can occur where high metal temperatures and _________ occur together. Creep cracking, once initiated, can progress rapidly.

Accepted Answer

Creep cracking can occur where high metal temperatures and stress risers occur together, and once initiated, it can progress rapidly. Pressures and velocities do not directly contribute to creep cracking.

Question 16

In fired heater tubes, dissimilar weld metal cracking forms primarily on the _______ of the material.

Accepted Answer

The answer of In fired heater tubes, dissimilar weld metal...

Question 17

Cooling water corrosion is a concern with water-cooled __________ and cooling towers in all applications across all industries.

Accepted Answer

Cooling water corrosion is a concern with water-cooled exchangers in all applications across all industries.

Question 18

At elevated temperatures, dissimilar weld metal cracking is aggravated by the diffusion of carbon out of the weld metal and into the base metal. The temperature at which carbon diffusion becomes a concern is above ________.

Accepted Answer

The temperature at which carbon diffusion becomes a concern is generally above 800º F.

Question 19

Soil corrosion of carbon steel can be minimized through the use of special backfill, coatings and _______.

Accepted Answer

Cathodic protection is a method of preventing or slowing the corrosion of metal surfaces by making it the cathode of an electrochemical cell. This can be achieved by applying a small electrical current to the metal surface or by connecting it to a sacrificial anode made of a more reactive metal. This method is effective in protecting buried carbon steel pipelines from soil corrosion. Coatings and backfill can also be used to further reduce corrosion, but cathodic protection is the most effective method for long-term corrosion prevention. Resistivity and temperature can influence corrosion rates but are not effective measures for minimizing soil corrosion of carbon steel.

Question 20

Ammonium chloride corrosion is the general or localized corrosion, often pitting, normally occurring under ammonium chloride or amine salt deposits. All commonly used materials are susceptible to ammonium chloride corrosion. A small amount of _________ can lead to very aggressive corrosion.

Accepted Answer

Water can dissolve ammonium chloride or amine salts, creating a corrosive environment that leads to aggressive corrosion.

Exam 1: Corrosion and Materials