The knowledge about physical properties of pipe and pipe fittings material are very important for piping engineer in performing his task, whether as piping material engineer, pipe support engineer or as piping stress engineer.
There are four (4) physical properties of pipng material in this lesson:
- Density
- Thermal Conductivity
- Thermal Expansion
- Specific Heat
1. DENSITY |
Density is one of the physical parameter which plays an important role in all material states, whether solid, liquid, or gaseous. Density is the ratio of the mass of a material to its volume. The formula is: ρ = m/V, with unit of density as kg/cm3 or lb/in3. Below shows some of the density for some of material for reference only: |
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2. THERMAL CONDUCTIVITY |
Thermal Conductivity is the ability of a material to transmit energy in the form of the heat from a high-temperature source to a lower temperature and usually expressed as a coefficient of thermal conductivity, k. The lower the value of k, the more resistant the material is to the flow of thermal energy. Good insulators possess low coefficients of thermal conductivity. |
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Thermal conductivity depends on the temperature of the material. For example, the coefficient of thermal conductivity of carbon steel decreases as its temperature increases, which in turn decreases its ability to transfer heat energy. Meanwhile Austenitic stainless steels, the thermal conductivity will increase when temperature increase. |
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The following is the value of Thermal Conductivity for some of piping material commonly used in Oil and Gas Industry:
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3. THERMAL EXPANSION |
Thermal Expansion is the coefficient of linear expansion of material. It is a ratio of the change in length of material per degree of temperature, compare to a length at a given standard temperature (such as room temperature, or the freezing point of water). See formula below. |
The units of the coefficient are the length of growth per unit length per degree of temperature. Since it depends on the temperature, then the value of the coefficient varies with temperature. This coefficient of thermal expansion is critical in the flexibility analysis of the piping system, as shown on down below table. |
Δ L = α L Δ T |
Where,
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The units of the coefficient are the length of growth per unit length per degree of temperature. Since it depends on the temperature, then the value of the coefficient varies with temperature as we can see from below table, for reference only. |
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4. SPECIFIC HEAT |
Specific Heat is a measure of the quantity of heat required to raise the temperature of one gram of a material by one degree in Celsius. The unit are usually Calories or Joules per gram per Celsius degree. |
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In addtion to the mechanical and physical properties, pipe material can also have to some extent the Electrical Properties. This is basically the characteristic of a pipe metal that enables the flow of electric current through or in other words to conduct electrical current. There are four (4) types of electrical properties we will present here:
- Conductivity: Conductivity is the ability of a material to flow electrons and conduct current through a material. Represented by the symbol kappa and having the greatest value in metals, and Copper and Aluminium are the most commonly used due to having the greatest conductivity, where Aluminium has the highest conductance per unit length
- Resistivity: Resistivity is the measure of the resistance to the current flow. Material who has high resistivity do not charge electricity freely and therefore consider to be insulator, such as glass, Teflon, rubber and polymer
- Capacitance: Capacitance is the ability of body to store electrical charge. The amount of energy stored is proportional to the amount of stored charge. Capacitors store electrical energy in the form of electric fields between metal plates. The gap can be filled with air or some other dialectric medium such as ceramic, or polymer, which act as insulator as well as increase capacitance
- Piezoelectricity: The piezoelectric property of a material is its ability to store electrical charge because of a stress that is applied to it. In fact, piezoelectricity means electricity due to pressure. Material who has piezoelectric property normally have a high elastic modulus.
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