Mechanical properties of pipe and pipe fittings are very important since it defines the response and the behavior of pipe material to the applied force. The followings are the brief explanation of the properties:
|1. MODULUS ELASTICITY|
|Modulus Elasticity is the ratio of normal stress to the corresponding strain for tensile and compressive stress in elastic region. This ratio is linear through a range of stress, known as Hooke’s law.|
|The material behavior in this range is elastic (meaning that if the applied load is released the material will return to its original shape). The value of the slope in the elastic range is defined as Young’s Modulus, which measured using tension test.|
Young’s Modulus, named after a British doctor, physicist, and Egyptologist, is a measure of the elasticity of the material. Young Modulus has a symbol of E. As you can see from the below table, the value of Young Modulus varies with temperature. The higher the temperature, the softer the material, and the lower its Young’s Modulus.
2. STRESS – STRAIN
|σ = E ε|
|Where, σ = Stress, Psi. E = Young’s Modulus, Psi. ε = Strain|
Stress is defined as the ratio of applied force per unit area, or F/A, while Strain is deformation of material due to stress. Below graph will show the releation between σ and ε. It can be seen that the Strain increases when Stress changes until it reaches the Yield Strength and eventually to the Ultimate Strength before fracture.
The table that showing the value of Yield Strength and Tensile Strength for some common material use in piping system, which was taken from ASME B31.3, is available on the Material Tab on this lesson.
|3. ELONGATION AND REDUCTION OF AREA|
|Percent Elongation is a measurement of how much the material will deform plastically and elastically before it rupture. It basically measures the ductility, where it relates to the amount of straining that a material undergoes when subjected to a stress.|
|Because, whenever the material experiencing strains, then it will also decrease the area of cross section, which called as Reduction of Area (RA). Below is the formula to calculate two of those changes, where Ao is the original cross section area, Af is final cross section area, L is the final length and Lo is the original length.|
2. PHYSICAL PROPERTIES
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.
One other thing needs to be considered is the fabricability characteristics such as the ability to be bent or formed, suitability for welding or other methods of joining, ease of heat treatment, just to name a few.
There are four (4) physical properties of pipng material in this lesson:
- Thermal Conductivity
- Thermal Expansion
- Specific Heat
|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.|
|2. THERMAL CONDUCTIVITY|
|Thermal Conductivity is the ability of a material to transmit 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.|
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.
The following is the value of Density and Thermal Conductivity for some of piping material commonly used in Oil and Gas Industry:
|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, Δ = Change of Length, in α = Coefficient of thermal expansion of the material, 1/oF. L = Length of Material, in Δ T =Temperature Change, oF.|
|4. SPECIFIC HEAT|
|Specific Heat is a measure of the quantity of heat required to raise a unit weight of a material one degree in temperature. It basically the ratio of a material’s mass per unit volume to that of water.|
3. ELECTRICAL PROPERTIES
Electrical Properties of piping material is basically the characteristic of a pipe metal that enables the flow of electric current through or in other words to conduct electrical current. In this lesson, we will talk about 4 of electrical properties for pipe metal, namely: