POWER ENGINEERING 2A2 LATEST EXAMS SCRIPT
QUESTIONS AND ANSWERS SURE A+
✔✔What is carbonitriding? - ✔✔It is a hardening process where a source of carbon and
nitrogen is introduced into the furnace at a temperature above the transformation range
of the steel. A less severe quench is required but the resulting hardening effect is
comparable to carburizing.
Nitriding, alone, produces the hardest surface.
✔✔What does Quenching do to a metal? - ✔✔It increases strength and hardness and
decreases toughness and ductility. Steel with a carbon content of over 0.8% is heated
above the upper transformation temperature and held there to allow the formation of
austenite. The steel part is then quickly cooled by immersing it in a liquid such as water,
brine or oil.
✔✔What is tempering? - ✔✔It is the process of heating quenched steels to a specific
temperature below their lower transformation ranges, which forces the saturation of
carbon in the martensite to form back into a stable iron carbide (cementite) and ferrite
mixture, and then cooling the sample to room temp at a rate that prevents martensite
reformation. The primary purpose is to improve the mechanical properties of the steel.
The goals are to increase ductility and toughness with slightly reduced hardness.
,✔✔When selecting metal for pressure piping, which variables may need to be
considered? - ✔✔- Internal or external max pressure
- Max and Min temperatures
- Tensile and compressive loads
- Vibration and cyclic stress loads
- Chemical corrosion exposure
- Temperature gradients and thermal expansion stress factors
- Nozzle loadings (on flange connections)
- Impulse stresses (liquid slugging, hydraulic shock, physical collisions)
- Heat conductivity
Cost savings will always be a consideration if the design engineer has a range of metals
that can successfully meet a given spec.
✔✔What are the 4 methods of destructive testing? - ✔✔Tensile tests
Hardness tests
Impact tests
Proof tests
✔✔What are the seven methods of NDE? - ✔✔Visual
Magnetic particle
Liquid penetrant
Ultrasonic
Radiographic
Acoustical emission
Hydrostatic and pneumatic leak testing
✔✔what is the name of a tensile test mechanism? - ✔✔Extensometer
✔✔What shape of the specimen for a tensile test? - ✔✔The shape will be defined by
the standard or specification being utilized in the test. The shape is important as it
ensures the break occurs within the "gauge length" section; the cross section of the
specimen is reduced throughout the gauge length.
✔✔How is stress related to the cross-sectional area during a tensile test? - ✔✔As the
diameter reduces within the gauge length, the stress becomes greater because stress is
inversely proportional to the cross-sectional are under load.
✔✔What are the five points on a graph illustratrating the nominal stress and strain? -
✔✔Proportional limit
Yield stress
Proof stress
Ultimate tensile strength
Final instability point
, ✔✔What is proof stress? - ✔✔It is sometimes described as the yield stress of the
material. It is at the point at which the specimen has undergone a certain (arbitrary)
value of permanent strain, usually 0.2%. The stress at this point is known as the 0.2%
proof stress. This is used because the precise positions of proportional limit and yield
stress are often difficult to define and depend on the accuracy of the testing machine.
✔✔Describe ultimate tensile strength. - ✔✔The UTS is the point at which plastic
deformation becomes unstable and a narrow region (a neck) forms. It is the peak
(maximum) value of nominal stress during the test. Deformation will continue in the
necked region until fracture occurs.
✔✔What are the differences between elastic strain and plastic strain? - ✔✔Elastic strain
involves the stretching of a material within its elastic limit. The value of this (Young's
Modulus) can be found in engineering tables.
Plastic strain, or plastic flow, is irreversible deformation of a material. There is no
equation to relate the stress to plastic strain.
✔✔What is the difference between engineering strain and true strain? - ✔✔Engineering
strain is the most common way of expression, and is the ratio of the change in length to
the original length.
True strain is similar but is based on the instantaneous length of the specimen as the
test progresses.
✔✔What is hardness and what are some tests that have been developed? -
✔✔Hardness is a measurement of the resistance of a material to surface indentation.
Four common hardness tests:
Brinell
Rockwell
Vickers
Knoop
✔✔Brinell Hardness Test - ✔✔Uses the principle of a constant load applied for a period
of time, using an indentor with a predetermined diameter (usually 10 mm).
It can also be described as bulk hardness testing, since it averages out small
imperfections.
✔✔Rockwell Hardness Test - ✔✔The most widely used hardness test, which uses
either a 120° diamond cone for the Rockwell C test or a 1.6 mm ball for the Rockwell B
test. It applies two loads to a specimen and measures the difference in depth of
penetration between the minor load (10kg) and the major load (60, 100, or 150kg).
QUESTIONS AND ANSWERS SURE A+
✔✔What is carbonitriding? - ✔✔It is a hardening process where a source of carbon and
nitrogen is introduced into the furnace at a temperature above the transformation range
of the steel. A less severe quench is required but the resulting hardening effect is
comparable to carburizing.
Nitriding, alone, produces the hardest surface.
✔✔What does Quenching do to a metal? - ✔✔It increases strength and hardness and
decreases toughness and ductility. Steel with a carbon content of over 0.8% is heated
above the upper transformation temperature and held there to allow the formation of
austenite. The steel part is then quickly cooled by immersing it in a liquid such as water,
brine or oil.
✔✔What is tempering? - ✔✔It is the process of heating quenched steels to a specific
temperature below their lower transformation ranges, which forces the saturation of
carbon in the martensite to form back into a stable iron carbide (cementite) and ferrite
mixture, and then cooling the sample to room temp at a rate that prevents martensite
reformation. The primary purpose is to improve the mechanical properties of the steel.
The goals are to increase ductility and toughness with slightly reduced hardness.
,✔✔When selecting metal for pressure piping, which variables may need to be
considered? - ✔✔- Internal or external max pressure
- Max and Min temperatures
- Tensile and compressive loads
- Vibration and cyclic stress loads
- Chemical corrosion exposure
- Temperature gradients and thermal expansion stress factors
- Nozzle loadings (on flange connections)
- Impulse stresses (liquid slugging, hydraulic shock, physical collisions)
- Heat conductivity
Cost savings will always be a consideration if the design engineer has a range of metals
that can successfully meet a given spec.
✔✔What are the 4 methods of destructive testing? - ✔✔Tensile tests
Hardness tests
Impact tests
Proof tests
✔✔What are the seven methods of NDE? - ✔✔Visual
Magnetic particle
Liquid penetrant
Ultrasonic
Radiographic
Acoustical emission
Hydrostatic and pneumatic leak testing
✔✔what is the name of a tensile test mechanism? - ✔✔Extensometer
✔✔What shape of the specimen for a tensile test? - ✔✔The shape will be defined by
the standard or specification being utilized in the test. The shape is important as it
ensures the break occurs within the "gauge length" section; the cross section of the
specimen is reduced throughout the gauge length.
✔✔How is stress related to the cross-sectional area during a tensile test? - ✔✔As the
diameter reduces within the gauge length, the stress becomes greater because stress is
inversely proportional to the cross-sectional are under load.
✔✔What are the five points on a graph illustratrating the nominal stress and strain? -
✔✔Proportional limit
Yield stress
Proof stress
Ultimate tensile strength
Final instability point
, ✔✔What is proof stress? - ✔✔It is sometimes described as the yield stress of the
material. It is at the point at which the specimen has undergone a certain (arbitrary)
value of permanent strain, usually 0.2%. The stress at this point is known as the 0.2%
proof stress. This is used because the precise positions of proportional limit and yield
stress are often difficult to define and depend on the accuracy of the testing machine.
✔✔Describe ultimate tensile strength. - ✔✔The UTS is the point at which plastic
deformation becomes unstable and a narrow region (a neck) forms. It is the peak
(maximum) value of nominal stress during the test. Deformation will continue in the
necked region until fracture occurs.
✔✔What are the differences between elastic strain and plastic strain? - ✔✔Elastic strain
involves the stretching of a material within its elastic limit. The value of this (Young's
Modulus) can be found in engineering tables.
Plastic strain, or plastic flow, is irreversible deformation of a material. There is no
equation to relate the stress to plastic strain.
✔✔What is the difference between engineering strain and true strain? - ✔✔Engineering
strain is the most common way of expression, and is the ratio of the change in length to
the original length.
True strain is similar but is based on the instantaneous length of the specimen as the
test progresses.
✔✔What is hardness and what are some tests that have been developed? -
✔✔Hardness is a measurement of the resistance of a material to surface indentation.
Four common hardness tests:
Brinell
Rockwell
Vickers
Knoop
✔✔Brinell Hardness Test - ✔✔Uses the principle of a constant load applied for a period
of time, using an indentor with a predetermined diameter (usually 10 mm).
It can also be described as bulk hardness testing, since it averages out small
imperfections.
✔✔Rockwell Hardness Test - ✔✔The most widely used hardness test, which uses
either a 120° diamond cone for the Rockwell C test or a 1.6 mm ball for the Rockwell B
test. It applies two loads to a specimen and measures the difference in depth of
penetration between the minor load (10kg) and the major load (60, 100, or 150kg).
