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Helium – Boiling – Melting Point – Thermal Conductivity – Expansion

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Helium-melting-point-conductivity-thermal-properties

About Helium

It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements.

Thermal Properties of Helium

Helium – Melting Point and Boiling Point

Melting point of Helium is -272.2°C.

Boiling point of Helium is -268.9°C.

Note that, these points are associated with the standard atmospheric pressure.

Helium – Thermal Conductivity

Thermal conductivity of Helium is 0.1513 W/(m·K).

The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.

Coefficient of Thermal Expansion of Helium

Linear thermal expansion coefficient of Helium is — µm/(m·K)

Thermal expansion is generally the tendency of matter to change its dimensions in response to a change in temperature. It is usually expressed as a fractional change in length or volume per unit temperature change.

See also: Mechanical Properties of Helium

Melting Point of Elements

Periodic Table of Elements - melting point

Thermal Conductivity of Elements

Periodic Table of Elements - thermal conductivity

Thermal Expansion of Elements

Periodic Table of Elements - thermal expansion

About Boiling and Melting Point

Boiling Point

In general, boiling is a phase change of a substance from the liquid to the gas phase. The boiling point of a substance is the temperature at which this phase change (boiling or vaporization) occurs. The temperature at which vaporization (boiling) starts to occur for a given pressure is also known as the saturation temperature and at this conditions a mixture of vapor and liquid can exist together. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition. At the boiling point the two phases of a substance, liquid and vapor, have identical free energies and therefore are equally likely to exist. Below the boiling point, the liquid is the more stable state of the two, whereas above the gaseous form is preferred. The pressure at which vaporization (boiling) starts to occur for a given temperature is called the saturation pressure. When considered as the temperature of the reverse change from vapor to liquid, it is referred to as the condensation point.

As can be seen, the boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100°C (212°F) at sea level, but at 93.4°C (200.1°F) at 1900 metres (6,233 ft) altitude. On the other hand, water boils at 350°C (662°F) at 16.5 MPa (typical pressure of PWRs).

In the periodic table of elements, the element with the lowest boiling point is helium. Both the boiling points of rhenium and tungsten exceed 5000 K at standard pressure. Since it is difficult to measure extreme temperatures precisely without bias, both have been cited in the literature as having the higher boiling point.

Melting Point

In general, melting is a phase change of a substance from the solid to the liquid phase. The melting point of a substance is the temperature at which this phase change occurs. The melting point also defines a condition in which the solid and liquid can exist in equilibrium. Adding a heat will convert the solid into a liquid with no temperature change. At the melting point the two phases of a substance, liquid and vapor, have identical free energies and therefore are equally likely to exist. Below the melting point, the solid is the more stable state of the two, whereas above the liquid form is preferred. The melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point.

See also: Melting Point Depression

The first theory explaining mechanism of melting in the bulk was proposed by Lindemann, who used vibration of atoms in the crystal to explain the melting transition. Solids are similar to liquids in that both are condensed states, with particles that are far closer together than those of a gas. The atoms in a solid are tightly bound to each other, either in a regular geometric lattice (crystalline solids, which include metals and ordinary ice) or irregularly (an amorphous solid such as common window glass), and are typically low in energy. The motion of individual atoms, ions, or molecules in a solid is restricted to vibrational motion about a fixed point. As a solid is heated, its particles vibrate more rapidly as the solid absorbs kinetic energy. At some point the amplitude of vibration becomes so large that the atoms start to invade the space of their nearest neighbors and disturb them and the melting process initiates. The melting point is the temperature at which the disruptive vibrations of the particles of the solid overcome the attractive forces operating within the solid.

As with boiling points, the melting point of a solid is dependent on the strength of those attractive forces. For example, sodium chloride (NaCl) is an ionic compound that consists of a multitude of strong ionic bonds. Sodium chloride melts at 801°C. On the other hand, ice (solid H2O) is a molecular compound whose molecules are held together by hydrogen bonds, which is effectively a strong example of an interaction between two permanent dipoles. Though hydrogen bonds are the strongest of the intermolecular forces, the strength of hydrogen bonds is much less than that of ionic bonds. The melting point of ice is 0 °C.

Covalent bonds often result in the formation of small collections of better-connected atoms called molecules, which in solids and liquids are bound to other molecules by forces that are often much weaker than the covalent bonds that hold the molecules internally together. Such weak intermolecular bonds give organic molecular substances, such as waxes and oils, their soft bulk character, and their low melting points (in liquids, molecules must cease most structured or oriented contact with each other).

 

melting-and-boiling-point-chemical-elements-chart

About Thermal Conductivity

The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.

The thermal conductivity of most liquids and solids varies with temperature. For vapors, it also depends upon pressure. In general:

thermal conductivity - definition

Most materials are very nearly homogeneous, therefore we can usually write k = k (T). Similar definitions are associated with thermal conductivities in the y- and z-directions (ky, kz), but for an isotropic material the thermal conductivity is independent of the direction of transfer, kx = ky = kz = k.

Thermal Conductivity of Metals

Transport of thermal energy in solids may be generally due to two effects:
  • the migration of free electrons
  • lattice vibrational waves (phonons)

When electrons and phonons carry thermal energy leading to conduction heat transfer in a solid, the thermal conductivity may be expressed as:

k = ke + kph

thermal conductivity - metalsMetals are solids and as such they possess crystalline structure where the ions (nuclei with their surrounding shells of core electrons) occupy translationally equivalent positions in the crystal lattice. Metals in general have high electrical conductivity, high thermal conductivity, and high density. Accordingly, transport of thermal energy may be due to two effects:

  • the migration of free electrons
  • lattice vibrational waves (phonons).

When electrons and phonons carry thermal energy leading to conduction heat transfer in a solid, the thermal conductivity may be expressed as:

k = ke + kph

The unique feature of metals as far as their structure is concerned is the presence of charge carriers, specifically electrons. The electrical and thermal conductivities of metals originate from the fact that their outer electrons are delocalized. Their contribution to the thermal conductivity is referred to as the electronic thermal conductivity, ke. In fact, in pure metals such as gold, silver, copper, and aluminum, the heat current associated with the flow of electrons by far exceeds a small contribution due to the flow of phonons. In contrast, for alloys, the contribution of kph to k is no longer negligible.

Thermal Conductivity of Nonmetals

thermal conductivity - building materialsFor nonmetallic solids, k is determined primarily by kph, which increases as the frequency of interactions between the atoms and the lattice decreases. In fact, lattice thermal conduction is the dominant thermal conduction mechanism in nonmetals, if not the only one. In solids, atoms vibrate about their equilibrium positions (crystal lattice). The vibrations of atoms are not independent of each other, but are rather strongly coupled with neighboring atoms. The regularity of the lattice arrangement has an important effect on kph, with crystalline (well-ordered) materials like quartz having a higher thermal conductivity than amorphous materials like glass. At sufficiently high temperatures kph ∝ 1/T.

The quanta of the crystal vibrational field are referred to as ‘‘phonons.’’ A phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, like solids and some liquids. Phonons play a major role in many of the physical properties of condensed matter, like thermal conductivity and electrical conductivity. In fact, for crystalline, nonmetallic solids such as diamond, kph can be quite large, exceeding values of k associated with good conductors, such as aluminum. In particular, diamond has the highest hardness and thermal conductivity (k = 1000 W/m.K) of any bulk material.

Thermal Conductivity of Liquids and Gases

In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids. Because the intermolecular spacing is much larger and the motion of the molecules is more random for the fluid state than for the solid state, thermal energy transport is less effective. The thermal conductivity of gases and liquids is therefore generally smaller than that of solids. In liquids, the thermal conduction is caused by atomic or molecular diffusion. In gases, the thermal conduction is caused by diffusion of molecules from higher energy level to the lower level.

Thermal Conductivity of Gases

thermal conductivity - gasesThe effect of temperature, pressure, and chemical species on the thermal conductivity of a gas may be explained in terms of the kinetic theory of gases. Air and other gases are generally good insulators, in the absence of convection. Therefore, many insulating materials (e.g.polystyrene) function simply by having a large number of gas-filled pockets which prevent large-scale convection. Alternation of gas pocket and solid material causes that the heat must be transferred through many interfaces causing rapid decrease in heat transfer coefficient.

The thermal conductivity of gases is directly proportional to the density of the gas, the mean molecular speed, and especially to the mean free path of molecule. The mean free path also depends on the diameter of the molecule, with larger molecules more likely to experience collisions than small molecules, which is the average distance traveled by an energy carrier (a molecule) before experiencing a collision. Light gases, such as hydrogen and helium typically have high thermal conductivity. Dense gases such as xenon and dichlorodifluoromethane have low thermal conductivity.

In general, the thermal conductivity of gases increases with increasing temperature.

Thermal Conductivity of Liquids

As was written, in liquids, the thermal conduction is caused by atomic or molecular diffusion, but physical mechanisms for explaining the thermal conductivity of liquids are not well understood. Liquids tend to have better thermal conductivity than gases, and the ability to flow makes a liquid suitable for removing excess heat from mechanical components. The heat can be removed by channeling the liquid through a heat exchanger. The coolants used in nuclear reactors include water or liquid metals, such as sodium or lead.

The thermal conductivity of nonmetallic liquids generally decreases with increasing temperature.

About Thermal Expansion

Thermal expansion is generally the tendency of matter to change its dimensions in response to a change in temperature. It is usually expressed as a fractional change in length or volume per unit temperature change. Thermal expansion is common for solids, liquids and for gases. Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion. A linear expansion coefficient is usually employed in describing the expansion of a solid, while a volume expansion coefficient is more useful for a liquid or a gas.

The linear thermal expansion coefficient is defined as:

linear thermal expansion coefficient

where L is a particular length measurement and dL/dT is the rate of change of that linear dimension per unit change in temperature.

The volumetric thermal expansion coefficient is the most basic thermal expansion coefficient, and the most relevant for fluids. In general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions.

The volumetric thermal expansion coefficient is defined as:

volumetric thermal expansion coefficient

where L is the volume of the material and dV/dT is the rate of change of that volume per unit change in temperature.

In a solid or liquid, there is a dynamic balance between the cohesive forces holding the atoms or molecules together and the conditions created by temperature. Therefore higher temperatures imply greater distance between atoms. Different materials have different bonding forces and therefore different expansion coefficients. If a crystalline solid is isometric (has the same structural configuration throughout), the expansion will be uniform in all dimensions of the crystal. For these materials, the area and volumetric thermal expansion coefficient are, respectively, approximately twice and three times larger than the linear thermal expansion coefficient (αV = 3αL). If it is not isometric, there may be different expansion coefficients for different crystallographic directions, and the crystal will change shape as the temperature changes.

Summary

Element Helium
Melting Point -272.2 °C
Boiling Point -268.9 °C
Thermal Conductivity 0.1513 W/mK
Thermal Expansion Coefficient — µm/mK
Density 0.00018 g/cm3

Helium-periodic-table

Source: www.luciteria.com

 

Properties of other elements

Helium - Comparison of Thermal Properties

Periodic Table in 8K resolution

Other properties of Helium

 

Hydrogen – Boiling – Melting Point – Thermal Conductivity – Expansion

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Hydrogen-melting-point-conductivity-thermal-properties

About Hydrogen

With a standard atomic weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.

Thermal Properties of Hydrogen

Hydrogen – Melting Point and Boiling Point

Melting point of Hydrogen is -259.1°C.

Boiling point of Hydrogen is -252.9°C.

Note that, these points are associated with the standard atmospheric pressure.

Hydrogen – Thermal Conductivity

Thermal conductivity of Hydrogen is 0.1805 W/(m·K).

The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.

Coefficient of Thermal Expansion of Hydrogen

Linear thermal expansion coefficient of Hydrogen is — µm/(m·K)

Thermal expansion is generally the tendency of matter to change its dimensions in response to a change in temperature. It is usually expressed as a fractional change in length or volume per unit temperature change.

See also: Mechanical Properties of Hydrogen

Melting Point of Elements

Periodic Table of Elements - melting point

Thermal Conductivity of Elements

Periodic Table of Elements - thermal conductivity

Thermal Expansion of Elements

Periodic Table of Elements - thermal expansion

About Boiling and Melting Point

Boiling Point

In general, boiling is a phase change of a substance from the liquid to the gas phase. The boiling point of a substance is the temperature at which this phase change (boiling or vaporization) occurs. The temperature at which vaporization (boiling) starts to occur for a given pressure is also known as the saturation temperature and at this conditions a mixture of vapor and liquid can exist together. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition. At the boiling point the two phases of a substance, liquid and vapor, have identical free energies and therefore are equally likely to exist. Below the boiling point, the liquid is the more stable state of the two, whereas above the gaseous form is preferred. The pressure at which vaporization (boiling) starts to occur for a given temperature is called the saturation pressure. When considered as the temperature of the reverse change from vapor to liquid, it is referred to as the condensation point.

As can be seen, the boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100°C (212°F) at sea level, but at 93.4°C (200.1°F) at 1900 metres (6,233 ft) altitude. On the other hand, water boils at 350°C (662°F) at 16.5 MPa (typical pressure of PWRs).

In the periodic table of elements, the element with the lowest boiling point is helium. Both the boiling points of rhenium and tungsten exceed 5000 K at standard pressure. Since it is difficult to measure extreme temperatures precisely without bias, both have been cited in the literature as having the higher boiling point.

Melting Point

In general, melting is a phase change of a substance from the solid to the liquid phase. The melting point of a substance is the temperature at which this phase change occurs. The melting point also defines a condition in which the solid and liquid can exist in equilibrium. Adding a heat will convert the solid into a liquid with no temperature change. At the melting point the two phases of a substance, liquid and vapor, have identical free energies and therefore are equally likely to exist. Below the melting point, the solid is the more stable state of the two, whereas above the liquid form is preferred. The melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point.

See also: Melting Point Depression

The first theory explaining mechanism of melting in the bulk was proposed by Lindemann, who used vibration of atoms in the crystal to explain the melting transition. Solids are similar to liquids in that both are condensed states, with particles that are far closer together than those of a gas. The atoms in a solid are tightly bound to each other, either in a regular geometric lattice (crystalline solids, which include metals and ordinary ice) or irregularly (an amorphous solid such as common window glass), and are typically low in energy. The motion of individual atoms, ions, or molecules in a solid is restricted to vibrational motion about a fixed point. As a solid is heated, its particles vibrate more rapidly as the solid absorbs kinetic energy. At some point the amplitude of vibration becomes so large that the atoms start to invade the space of their nearest neighbors and disturb them and the melting process initiates. The melting point is the temperature at which the disruptive vibrations of the particles of the solid overcome the attractive forces operating within the solid.

As with boiling points, the melting point of a solid is dependent on the strength of those attractive forces. For example, sodium chloride (NaCl) is an ionic compound that consists of a multitude of strong ionic bonds. Sodium chloride melts at 801°C. On the other hand, ice (solid H2O) is a molecular compound whose molecules are held together by hydrogen bonds, which is effectively a strong example of an interaction between two permanent dipoles. Though hydrogen bonds are the strongest of the intermolecular forces, the strength of hydrogen bonds is much less than that of ionic bonds. The melting point of ice is 0 °C.

Covalent bonds often result in the formation of small collections of better-connected atoms called molecules, which in solids and liquids are bound to other molecules by forces that are often much weaker than the covalent bonds that hold the molecules internally together. Such weak intermolecular bonds give organic molecular substances, such as waxes and oils, their soft bulk character, and their low melting points (in liquids, molecules must cease most structured or oriented contact with each other).

 

melting-and-boiling-point-chemical-elements-chart

About Thermal Conductivity

The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.

The thermal conductivity of most liquids and solids varies with temperature. For vapors, it also depends upon pressure. In general:

thermal conductivity - definition

Most materials are very nearly homogeneous, therefore we can usually write k = k (T). Similar definitions are associated with thermal conductivities in the y- and z-directions (ky, kz), but for an isotropic material the thermal conductivity is independent of the direction of transfer, kx = ky = kz = k.

Thermal Conductivity of Metals

Transport of thermal energy in solids may be generally due to two effects:
  • the migration of free electrons
  • lattice vibrational waves (phonons)

When electrons and phonons carry thermal energy leading to conduction heat transfer in a solid, the thermal conductivity may be expressed as:

k = ke + kph

thermal conductivity - metalsMetals are solids and as such they possess crystalline structure where the ions (nuclei with their surrounding shells of core electrons) occupy translationally equivalent positions in the crystal lattice. Metals in general have high electrical conductivity, high thermal conductivity, and high density. Accordingly, transport of thermal energy may be due to two effects:

  • the migration of free electrons
  • lattice vibrational waves (phonons).

When electrons and phonons carry thermal energy leading to conduction heat transfer in a solid, the thermal conductivity may be expressed as:

k = ke + kph

The unique feature of metals as far as their structure is concerned is the presence of charge carriers, specifically electrons. The electrical and thermal conductivities of metals originate from the fact that their outer electrons are delocalized. Their contribution to the thermal conductivity is referred to as the electronic thermal conductivity, ke. In fact, in pure metals such as gold, silver, copper, and aluminum, the heat current associated with the flow of electrons by far exceeds a small contribution due to the flow of phonons. In contrast, for alloys, the contribution of kph to k is no longer negligible.

Thermal Conductivity of Nonmetals

thermal conductivity - building materialsFor nonmetallic solids, k is determined primarily by kph, which increases as the frequency of interactions between the atoms and the lattice decreases. In fact, lattice thermal conduction is the dominant thermal conduction mechanism in nonmetals, if not the only one. In solids, atoms vibrate about their equilibrium positions (crystal lattice). The vibrations of atoms are not independent of each other, but are rather strongly coupled with neighboring atoms. The regularity of the lattice arrangement has an important effect on kph, with crystalline (well-ordered) materials like quartz having a higher thermal conductivity than amorphous materials like glass. At sufficiently high temperatures kph ∝ 1/T.

The quanta of the crystal vibrational field are referred to as ‘‘phonons.’’ A phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, like solids and some liquids. Phonons play a major role in many of the physical properties of condensed matter, like thermal conductivity and electrical conductivity. In fact, for crystalline, nonmetallic solids such as diamond, kph can be quite large, exceeding values of k associated with good conductors, such as aluminum. In particular, diamond has the highest hardness and thermal conductivity (k = 1000 W/m.K) of any bulk material.

Thermal Conductivity of Liquids and Gases

In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids. Because the intermolecular spacing is much larger and the motion of the molecules is more random for the fluid state than for the solid state, thermal energy transport is less effective. The thermal conductivity of gases and liquids is therefore generally smaller than that of solids. In liquids, the thermal conduction is caused by atomic or molecular diffusion. In gases, the thermal conduction is caused by diffusion of molecules from higher energy level to the lower level.

Thermal Conductivity of Gases

thermal conductivity - gasesThe effect of temperature, pressure, and chemical species on the thermal conductivity of a gas may be explained in terms of the kinetic theory of gases. Air and other gases are generally good insulators, in the absence of convection. Therefore, many insulating materials (e.g.polystyrene) function simply by having a large number of gas-filled pockets which prevent large-scale convection. Alternation of gas pocket and solid material causes that the heat must be transferred through many interfaces causing rapid decrease in heat transfer coefficient.

The thermal conductivity of gases is directly proportional to the density of the gas, the mean molecular speed, and especially to the mean free path of molecule. The mean free path also depends on the diameter of the molecule, with larger molecules more likely to experience collisions than small molecules, which is the average distance traveled by an energy carrier (a molecule) before experiencing a collision. Light gases, such as hydrogen and helium typically have high thermal conductivity. Dense gases such as xenon and dichlorodifluoromethane have low thermal conductivity.

In general, the thermal conductivity of gases increases with increasing temperature.

Thermal Conductivity of Liquids

As was written, in liquids, the thermal conduction is caused by atomic or molecular diffusion, but physical mechanisms for explaining the thermal conductivity of liquids are not well understood. Liquids tend to have better thermal conductivity than gases, and the ability to flow makes a liquid suitable for removing excess heat from mechanical components. The heat can be removed by channeling the liquid through a heat exchanger. The coolants used in nuclear reactors include water or liquid metals, such as sodium or lead.

The thermal conductivity of nonmetallic liquids generally decreases with increasing temperature.

About Thermal Expansion

Thermal expansion is generally the tendency of matter to change its dimensions in response to a change in temperature. It is usually expressed as a fractional change in length or volume per unit temperature change. Thermal expansion is common for solids, liquids and for gases. Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion. A linear expansion coefficient is usually employed in describing the expansion of a solid, while a volume expansion coefficient is more useful for a liquid or a gas.

The linear thermal expansion coefficient is defined as:

linear thermal expansion coefficient

where L is a particular length measurement and dL/dT is the rate of change of that linear dimension per unit change in temperature.

The volumetric thermal expansion coefficient is the most basic thermal expansion coefficient, and the most relevant for fluids. In general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions.

The volumetric thermal expansion coefficient is defined as:

volumetric thermal expansion coefficient

where L is the volume of the material and dV/dT is the rate of change of that volume per unit change in temperature.

In a solid or liquid, there is a dynamic balance between the cohesive forces holding the atoms or molecules together and the conditions created by temperature. Therefore higher temperatures imply greater distance between atoms. Different materials have different bonding forces and therefore different expansion coefficients. If a crystalline solid is isometric (has the same structural configuration throughout), the expansion will be uniform in all dimensions of the crystal. For these materials, the area and volumetric thermal expansion coefficient are, respectively, approximately twice and three times larger than the linear thermal expansion coefficient (αV = 3αL). If it is not isometric, there may be different expansion coefficients for different crystallographic directions, and the crystal will change shape as the temperature changes.

Summary

Element Hydrogen
Melting Point -259.1 °C
Boiling Point -252.9 °C
Thermal Conductivity 0.1805 W/mK
Thermal Expansion Coefficient — µm/mK
Density 0.00009 g/cm3

Hydrogen-periodic-table

Source: www.luciteria.com

 

Properties of other elements

Hydrogen - Comparison of Thermal Properties

Periodic Table in 8K resolution

Other properties of Hydrogen

 

What is Film Radiography – Real-time Radiography – Definition

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In general, RT is method of inspecting materials for hidden subsurface defects by using the ability of X-rays or gamma rays to penetrate various materials of various thickness. The intensity of the radiation that penetrates and passes through the material is either captured by:a radiation sensitive film (Film Radiography) or a planer array of radiation sensitive sensors (Real-time Radiography).

In general, RT is method of inspecting materials for hidden subsurface defects by using the ability of X-rays or gamma rays to penetrate various materials of various thickness. The intensity of the radiation that penetrates and passes through the material is either captured by:

  • a radiation sensitive film (Film Radiography)
  • a planer array of radiation sensitive sensors (Real-time Radiography).

Principle of Operation

Radiographic testingThe radiation source can either be an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137). The choice between X-rays and gamma radiation depends on some factors such as thickness, contrast level and etc. For example X-rays typically work with lower amount of energy than gamma rays. The thickness is another parameter which influences the results. For example, at thicknesses more than 50 mm, the use of gamma rays increases significantly.

Radiation is directed through a part and onto film or other imaging media. The resulting radiograph shows the dimensional features of the part. Both in X-rays and gamma radiation as radiation passes more through the material the darker the film becomes on the image produced and, on the contrary, the more the ray is absorbed by the material the lighter is the image in those spots. Therefore, possible imperfections are indicated as density changes on the film in the same manner as a medical X-ray shows broken bones.

Radiographic testing is commonly used for weld verification in various industrial applications. In manufacturing, welds are commonly used to join two or more metal parts. The effects of welding on the material surrounding the weld can be detrimental —depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. For example, the base metal must reach a certain temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold the parts together, or cracks may form in the weld causing it to fail. Defects usually encountered include incomplete penetration, incomplete fusion, undercutting, porosity, and longitudinal cracking. These defects could cause a structure to break or a pipeline to rupture. Welds may be tested using NDT techniques such as industrial radiography or industrial CT scanning using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing, magnetic particle inspection or via eddy current.

Advantages and Disadvantages

Advantages:

  • It has a very few material limitations.
  • Detection of internal defects for thick materials (e.g. pipelines).
  • Minimal or no part preparation is required.
  • One of the major advantages of RT is its documentation capability. RT provides images of the object under inspection.
  • The probability of misinterpretation of results is minimized since each image can be reviewed by multiple operators.

Disadvantages:

  • The impact of radiation to health and environment can be considered as one of major disadvantages of radiographic testing since a few seconds of being exposed to radiation can result in sever injuries.
  • High degree of skill and experience is required for exposure and interpretation.
  • The high voltage needed to create X-rays is dangerous for human health also.
  • It is quite expensive method.
  • Ineffective for planar defects and for surface defects.
References:

Materials Science:

  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
NDT

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What is Radiography Testing – Definition

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Radiography testing (RT) involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. It is one of the conventional NDT methods which has been in use over decades and is still being used by companies around the world.

Non-destructive testing, NDT, is a very broad group of structural or material inspections and as the name implies, these inspections do not destroy the material/structure being examined. NDT plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause serious accidents such as, planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of troubling events.

This concept is extended, and known as Non-Destructive Evaluation (NDE), when combined with an assessment of the significance of any defects found. However, they are both terms often used interchangeably. Some testing methods must be conducted in a laboratory setting, others may be adapted for use in the field. Several commonly employed NDT techniques and their characteristics are described below.

Radiography Testing

Radiography testing (RT) involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. It is one of the conventional NDT methods which has been in use over decades and is still being used by companies around the world.

  • X-rays, also known as X-radiation, refers to electromagnetic radiation (no rest mass, no charge) of high energies. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers (3×1016 Hz to 3×1019 Hz), corresponding to energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. The distinction between X-rays and gamma rays is not so simple and has changed in recent decades.  According to the currently valid definition, X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus. X-rays can be generated by an X-ray tube, a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity. Upon striking the target, the accelerated electrons are abruptly stopped and X-rays and heat are generated.
  • Gamma rays, also known as gamma radiation, refers to electromagnetic radiation (no rest mass, no charge) of a very high energies. Since the gamma rays are in substance only a very high-energy photons, they are very penetrating matter and are thus biologically hazardous. Gamma rays can travel thousands of feet in air and can easily pass through the human body. Gamma rays are emitted by unstable nuclei in their transition from a high energy state to a lower state known as gamma decay. In most practical laboratory sources, the excited nuclear states are created in the decay of a parent radionuclide, therefore a gamma decay typically accompanies other forms of decay, such as alpha or beta decay.

In general, RT is method of inspecting materials for hidden subsurface defects by using the ability of X-rays or gamma rays to penetrate various materials of various thickness. The intensity of the radiation that penetrates and passes through the material is either captured by:

  • a radiation sensitive film (Film Radiography)
  • a planer array of radiation sensitive sensors (Real-time Radiography).

Principle of Operation

Radiographic testingThe radiation source can either be an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137). The choice between X-rays and gamma radiation depends on some factors such as thickness, contrast level and etc. For example X-rays typically work with lower amount of energy than gamma rays. The thickness is another parameter which influences the results. For example, at thicknesses more than 50 mm, the use of gamma rays increases significantly.

Radiation is directed through a part and onto film or other imaging media. The resulting radiograph shows the dimensional features of the part. Both in X-rays and gamma radiation as radiation passes more through the material the darker the film becomes on the image produced and, on the contrary, the more the ray is absorbed by the material the lighter is the image in those spots. Therefore, possible imperfections are indicated as density changes on the film in the same manner as a medical X-ray shows broken bones.

Radiographic testing is commonly used for weld verification in various industrial applications. In manufacturing, welds are commonly used to join two or more metal parts. The effects of welding on the material surrounding the weld can be detrimental —depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. For example, the base metal must reach a certain temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold the parts together, or cracks may form in the weld causing it to fail. Defects usually encountered include incomplete penetration, incomplete fusion, undercutting, porosity, and longitudinal cracking. These defects could cause a structure to break or a pipeline to rupture. Welds may be tested using NDT techniques such as industrial radiography or industrial CT scanning using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing, magnetic particle inspection or via eddy current.

Advantages and Disadvantages

Advantages:

  • It has a very few material limitations.
  • Detection of internal defects for thick materials (e.g. pipelines).
  • Minimal or no part preparation is required.
  • One of the major advantages of RT is its documentation capability. RT provides images of the object under inspection.
  • The probability of misinterpretation of results is minimized since each image can be reviewed by multiple operators.

Disadvantages:

  • The impact of radiation to health and environment can be considered as one of major disadvantages of radiographic testing since a few seconds of being exposed to radiation can result in sever injuries.
  • High degree of skill and experience is required for exposure and interpretation.
  • The high voltage needed to create X-rays is dangerous for human health also.
  • It is quite expensive method.
  • Ineffective for planar defects and for surface defects.
References:

Materials Science:

  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
NDT

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What is Magnetic-particle Inspection – Definition

by
Magnetic-particle inspection is one of NDT processes for detecting surface and nearsurface imperfections and material discontinuities. This method is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with fine ferromagnetic particles (either dry or suspended in liquid).

Non-destructive testing, NDT, is a very broad group of structural or material inspections and as the name implies, these inspections do not destroy the material/structure being examined. NDT plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause serious accidents such as, planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of troubling events.

This concept is extended, and known as Non-Destructive Evaluation (NDE), when combined with an assessment of the significance of any defects found. However, they are both terms often used interchangeably. Some testing methods must be conducted in a laboratory setting, others may be adapted for use in the field. Several commonly employed NDT techniques and their characteristics are described below.

Magnetic-particle Inspection

Magnetic-particle inspection is one of NDT processes for detecting surface and nearsurface imperfections and material discontinuities. This method is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with fine ferromagnetic particles (either dry or suspended in liquid). These are attracted to an area of flux leakage and form what is known as an indication, which is evaluated to determine its nature, cause, and course of action, if any. Although this technique reveals the location of the defects, it is often unable to determine its depth.

The piece can be magnetized by direct or indirect magnetization. Direct magnetization occurs when the electric current is passed through the test object and a magnetic field is formed in the material. Indirect magnetization occurs when no electric current is passed through the test object, but a magnetic field is applied from an outside source. It has the major drawback of requiring to magnetize (and frequently demagnetize) the component.

References:

Materials Science:

  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
NDT

We hope, this article, Magnetic-particle Inspection, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about materials and their properties.

What is Ultrasonic Testing – Pulse-Echo Method – Definition

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Ultrasonic testing is a broad group of NDT techniques based on the propagation of ultrasonic waves in the object or material tested. The most commonly used ultrasonic testing technique is pulse echo, wherein high-frequency sound wave beams (normally ranging from 1-5 MHz) is introduced into a test object and reflections (echoes) are returned to a receiver from internal imperfections or from the part’s geometrical surfaces.

Non-destructive testing, NDT, is a very broad group of structural or material inspections and as the name implies, these inspections do not destroy the material/structure being examined. NDT plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause serious accidents such as, planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of troubling events.

This concept is extended, and known as Non-Destructive Evaluation (NDE), when combined with an assessment of the significance of any defects found. However, they are both terms often used interchangeably. Some testing methods must be conducted in a laboratory setting, others may be adapted for use in the field. Several commonly employed NDT techniques and their characteristics are described below.

Ultrasonic Testing

Ultrasonic testingUltrasonic testing is a broad group of NDT techniques based on the propagation of ultrasonic waves in the object or material tested. The most commonly used ultrasonic testing technique is pulse echo, wherein high-frequency sound wave beams (normally ranging from 1-5 MHz) is introduced into a test object and reflections (echoes) are returned to a receiver from internal imperfections or from the part’s geometrical surfaces.

The basic method of ultrasonic testing is transforming a voltage pulse to an ultrasonic pulse using a transducer. Transducers used for traditional UT consist of a piezoelectric crystal enclosed within a plastic or stainless steel housing. The piezoelectric crystals expand when electrically charged, thus generating an acoustic wave. The signal travels through the object with respect to its geometry and existing defects and then is either transmitted to another transducer or reflected back to the original transducer. Defects are detected if they produce a change in the acoustic impedance in the path of the ultrasonic beam. An open crack filled with air has very low acoustic impedance so it reflects virtually all the acoustic energy incident on it. Hence, the sound waves travel through the material and are reflected back from cracks or flaws. Defects and flaws affect its way and a small portion of the pulse will be sent back to the transducer/receiver before it hits the end of the object.

Since the speed of sound in the parent material is known, the reflected sound energy is then displayed versus time and analyzed to define the presence and location of flaws or discontinuities.

Advantages and Disadvantages of Ultrasonic Testing

The advantages and disadvantages of ultrasonic testing method are as follows:

Advantages:

  • UT is flexible, portable and has high penetration depth.
  • High sensitivity, permitting the detection of extremely small flaws.
  • It is applicable in wide range of industries
  • Some capability of estimating the size, orientation, shape and nature of defects.
  • Unlike radiographic testing, there is no health or environmental risk involved

Disadvantages:

  • It requires highly-trained operators and requires careful attention by experienced technicians.
  • Unable or not efficient in detecting planar defect that are in parallel with the direction of sound wave
  • Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.
  • Can be very expensive
References:

Materials Science:

  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
NDT

We hope, this article, Ultrasonic Testing – Pulse-Echo Method, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about materials and their properties.

What is Liquid Penetrant Testing – Definition

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Liquid penetrant inspection (LPI), also called dye penetrant inspection (DP), is a widely applied NDT method, which is used to check surface-breaking defects in all non-porous materials (metals, plastics, or ceramics).

Non-destructive testing, NDT, is a very broad group of structural or material inspections and as the name implies, these inspections do not destroy the material/structure being examined. NDT plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause serious accidents such as, planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of troubling events.

This concept is extended, and known as Non-Destructive Evaluation (NDE), when combined with an assessment of the significance of any defects found. However, they are both terms often used interchangeably. Some testing methods must be conducted in a laboratory setting, others may be adapted for use in the field. Several commonly employed NDT techniques and their characteristics are described below.

Liquid Penetrant Testing

Liquid penetrant inspectionLiquid penetrant inspection (LPI), also called dye penetrant inspection (DP), is a widely applied NDT method, which is used to check surface-breaking defects in all non-porous materials (metals, plastics, or ceramics). It is probably one of the most widely used NDT techniques. Test and pre-cleaned objects are coated with visible or fluorescent dye solution. Following a given time, ranging from 5 to 30 minutes depending on the material inspected, excess penetrant is removed from the surface, and a developer in liquid or powder form is applied. The developer acts as blotter, drawing trapped penetrant out of imperfections open to the surface. This developer absorbs penetrant drawn from discontinuities and reveals a vivid color contrast between the penetrant and developer (usually red on white). With fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce brightly, thus allowing imperfections to be readily seen.

LPI is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.

References:

Materials Science:

  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
NDT

We hope, this article, Liquid Penetrant Testing, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about materials and their properties.

What is Eddy-current Testing – Definition

by
Eddy current testing is one of most common electromegnetic testing NDT methods. It uses induced electrical currents to detect defects. Essentially, the technique uses a coil (ECT probe) carrying an alternating current as transducer.

Non-destructive testing, NDT, is a very broad group of structural or material inspections and as the name implies, these inspections do not destroy the material/structure being examined. NDT plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause serious accidents such as, planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of troubling events.

This concept is extended, and known as Non-Destructive Evaluation (NDE), when combined with an assessment of the significance of any defects found. However, they are both terms often used interchangeably. Some testing methods must be conducted in a laboratory setting, others may be adapted for use in the field. Several commonly employed NDT techniques and their characteristics are described below.

Eddy-current Testing

Eddy current testing is one of most common electromegnetic testing NDT methods. It uses induced electrical currents to detect defects. Essentially, the technique uses a coil (ECT probe) carrying an alternating current as transducer.  This produces an alternating magnetic field parallel to the axis of the coil which in turn induces eddy currents in the surface of the test object. These eddy currents set up a magnetic field opposing that produced by the coil, thus changing the impedance of the coil. Interruptions in the flow of eddy currents, caused by imperfections, dimensional changes, or changes in the material’s conductive and permeability properties, are detected.

Most eddy current testing is based on the measurement of the coil impedance, though it is possible to measure the magnetic field directly. ECT has a very wide range of applications. Since ECT is electrical in nature, it is limited to conductive material. There are also physical limits to generating eddy currents and depth of penetration (skin depth). In general, this technique is used to inspect relatively small areas and is therefore better suited for inspecting areas where damage is already suspected, it nevertheless has a variety of applications: from measuring material thickness to detecting corrosion damage. In nuclear power plants, eddy-current methods provide the best in-service inspection method for steam generator tubing. The following components are required to perform Eddy Current testing: an Eddy Current tester, a remote positioning device, and an eddy current probe drive control system.

The disadvantages of this technique are that it is sensitive to lift-off, it is a point test, so scanning is required for large areas, and it is generally limited to near surface defect of conducting materials.

References:

Materials Science:

  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
NDT

We hope, this article, Eddy-current Testing, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about materials and their properties.

What is Subsurface NDT Methods – Definition

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Subsurface methods, that can be used to detect defects that lie under the material’s surface, are especially Ultrasonic Testing and Radiography Testing.

The variety of techniques available can also be divided into two groups: surface methods, which are used to identify surface and near surface defects such as cracks and surface porosity, and subsurface methods, that can be used to detect defects that lie under the material’s surface.

Ultrasonic Testing

Ultrasonic testingUltrasonic testing is a broad group of NDT techniques based on the propagation of ultrasonic waves in the object or material tested. The most commonly used ultrasonic testing technique is pulse echo, wherein high-frequency sound wave beams (normally ranging from 1-5 MHz) is introduced into a test object and reflections (echoes) are returned to a receiver from internal imperfections or from the part’s geometrical surfaces.

The basic method of ultrasonic testing is transforming a voltage pulse to an ultrasonic pulse using a transducer. Transducers used for traditional UT consist of a piezoelectric crystal enclosed within a plastic or stainless steel housing. The piezoelectric crystals expand when electrically charged, thus generating an acoustic wave. The signal travels through the object with respect to its geometry and existing defects and then is either transmitted to another transducer or reflected back to the original transducer. Defects are detected if they produce a change in the acoustic impedance in the path of the ultrasonic beam. An open crack filled with air has very low acoustic impedance so it reflects virtually all the acoustic energy incident on it. Hence, the sound waves travel through the material and are reflected back from cracks or flaws. Defects and flaws affect its way and a small portion of the pulse will be sent back to the transducer/receiver before it hits the end of the object.

Since the speed of sound in the parent material is known, the reflected sound energy is then displayed versus time and analyzed to define the presence and location of flaws or discontinuities.

Advantages and Disadvantages of Ultrasonic Testing

The advantages and disadvantages of ultrasonic testing method are as follows:

Advantages:

  • UT is flexible, portable and has high penetration depth.
  • High sensitivity, permitting the detection of extremely small flaws.
  • It is applicable in wide range of industries
  • Some capability of estimating the size, orientation, shape and nature of defects.
  • Unlike radiographic testing, there is no health or environmental risk involved

Disadvantages:

  • It requires highly-trained operators and requires careful attention by experienced technicians.
  • Unable or not efficient in detecting planar defect that are in parallel with the direction of sound wave
  • Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.
  • Can be very expensive

Radiographic Testing

Radiographic testing (RT) involves the use of penetrating gamma or X-radiation to examine parts and products for imperfections. It is one of the conventional NDT methods which has been in use over decades and is still being used by companies around the world.

  • X-rays, also known as X-radiation, refers to electromagnetic radiation (no rest mass, no charge) of high energies. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers (3×1016 Hz to 3×1019 Hz), corresponding to energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. The distinction between X-rays and gamma rays is not so simple and has changed in recent decades.  According to the currently valid definition, X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus. X-rays can be generated by an X-ray tube, a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity. Upon striking the target, the accelerated electrons are abruptly stopped and X-rays and heat are generated.
  • Gamma rays, also known as gamma radiation, refers to electromagnetic radiation (no rest mass, no charge) of a very high energies. Since the gamma rays are in substance only a very high-energy photons, they are very penetrating matter and are thus biologically hazardous. Gamma rays can travel thousands of feet in air and can easily pass through the human body. Gamma rays are emitted by unstable nuclei in their transition from a high energy state to a lower state known as gamma decay. In most practical laboratory sources, the excited nuclear states are created in the decay of a parent radionuclide, therefore a gamma decay typically accompanies other forms of decay, such as alpha or beta decay.

In general, RT is method of inspecting materials for hidden subsurface defects by using the ability of X-rays or gamma rays to penetrate various materials of various thickness. The intensity of the radiation that penetrates and passes through the material is either captured by:

  • a radiation sensitive film (Film Radiography)
  • a planer array of radiation sensitive sensors (Real-time Radiography).

Principle of Operation

Radiographic testingThe radiation source can either be an X-ray machine or a radioactive source (Ir-192, Co-60, or in rare cases Cs-137). The choice between X-rays and gamma radiation depends on some factors such as thickness, contrast level and etc. For example X-rays typically work with lower amount of energy than gamma rays. The thickness is another parameter which influences the results. For example, at thicknesses more than 50 mm, the use of gamma rays increases significantly.

Radiation is directed through a part and onto film or other imaging media. The resulting radiograph shows the dimensional features of the part. Both in X-rays and gamma radiation as radiation passes more through the material the darker the film becomes on the image produced and, on the contrary, the more the ray is absorbed by the material the lighter is the image in those spots. Therefore, possible imperfections are indicated as density changes on the film in the same manner as a medical X-ray shows broken bones.

Radiographic testing is commonly used for weld verification in various industrial applications. In manufacturing, welds are commonly used to join two or more metal parts. The effects of welding on the material surrounding the weld can be detrimental —depending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. For example, the base metal must reach a certain temperature during the welding process, must cool at a specific rate, and must be welded with compatible materials or the joint may not be strong enough to hold the parts together, or cracks may form in the weld causing it to fail. Defects usually encountered include incomplete penetration, incomplete fusion, undercutting, porosity, and longitudinal cracking. These defects could cause a structure to break or a pipeline to rupture. Welds may be tested using NDT techniques such as industrial radiography or industrial CT scanning using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing, magnetic particle inspection or via eddy current.

Advantages and Disadvantages

Advantages:

  • It has a very few material limitations.
  • Detection of internal defects for thick materials (e.g. pipelines).
  • Minimal or no part preparation is required.
  • One of the major advantages of RT is its documentation capability. RT provides images of the object under inspection.
  • The probability of misinterpretation of results is minimized since each image can be reviewed by multiple operators.

Disadvantages:

  • The impact of radiation to health and environment can be considered as one of major disadvantages of radiographic testing since a few seconds of being exposed to radiation can result in sever injuries.
  • High degree of skill and experience is required for exposure and interpretation.
  • The high voltage needed to create X-rays is dangerous for human health also.
  • It is quite expensive method.
  • Ineffective for planar defects and for surface defects.
References:

Materials Science:

  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
NDT

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What is Visual and Optical Testing – Definition

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Visual inspection involves using an inspector’s eyes to look for defects, such as scratches, presence of debris, corrosion or oxidation. The inspector may also use special tools such as magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area. Visual and Optical Testing

Non-destructive testing, NDT, is a very broad group of structural or material inspections and as the name implies, these inspections do not destroy the material/structure being examined. NDT plays a critical role in assuring that structural components and systems perform their function in a reliable and cost effective fashion. Because NDT does not permanently alter the article being inspected, it is a highly valuable technique that can save both money and time in product evaluation, troubleshooting, and research. NDT technicians and engineers define and implement tests that locate and characterize material conditions and flaws that might otherwise cause serious accidents such as, planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of troubling events.

This concept is extended, and known as Non-Destructive Evaluation (NDE), when combined with an assessment of the significance of any defects found. However, they are both terms often used interchangeably. Some testing methods must be conducted in a laboratory setting, others may be adapted for use in the field. Several commonly employed NDT techniques and their characteristics are described below.

Visual and Optical Testing

Visual inspection involves using an inspector’s eyes to look for defects, such as scratches, presence of debris, corrosion or oxidation. The inspector may also use special tools such as magnifying glasses, mirrors, or borescopes to gain access and more closely inspect the subject area. In nuclear power plants, an  extensive fuel  inspection  programme  (including  e.g.,  visual  inspections,  oxide  layer  measurements,  eddy-current tests of control rods), is carried out under water and supervised by the regulatory body. So that visual testing are usually a part of the Post Irradiation Examination. Visual examinations are also very common in aircraft industry, where  over 80 percent of the inspections done to an aircraft are visual inspections, being often used as an initial screening method to detect gross defects and target subsequent testing by other methods.

References:

Materials Science:

  1. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
  2. U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
  3. William D. Callister, David G. Rethwisch. Materials Science and Engineering: An Introduction 9th Edition, Wiley; 9 edition (December 4, 2013), ISBN-13: 978-1118324578.
  4. Eberhart, Mark (2003). Why Things Break: Understanding the World by the Way It Comes Apart. Harmony. ISBN 978-1-4000-4760-4.
  5. Gaskell, David R. (1995). Introduction to the thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
  6. González-Viñas, W. & Mancini, H.L. (2004). An Introduction to Materials Science. Princeton University Press. ISBN 978-0-691-07097-1.
  7. Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
  8. J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
NDT

We hope, this article, Visual and Optical Testing, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about materials and their properties.