Written by Jerry Ratzlaff on . Posted in Thermodynamics

Temperature is described as the amount of heat or cold, but it is neither heat or cold.  In piping design, temperature is important because mechanical properties are affected by increases or decreases in temperature.  Most materials become more pliable as the tempearture increases.  For pressurized pipe, this means that ability to contain the pressure is decreased. In very low temperatures and cryogenic services, the material become brittle and can fracture if it is involved in a high vibration environment.  Additionally, as temperature increases and decreases, materials will expand and contract.  Carbon steel, for example, expands at a rate of about 1 inch per 100 feet per 100 degrees Ferenheit.  Long sections of pipe without expansion loops can look like spaghetti and come off their supports.  Concrete without provisions for expansion can buckle and fracture.  Large pressure vessels such as heater treaters should have one end "floating" to allow for expansion.  Temperature is abbreviated as T or TEMP.

Temperature is the measurement of the average speed of molecules that are moving around in an object. Molecules don't always travel at the same speed.  The faster they move the hotter they get, the slower they move the colder they get.  When they stop moving that is absolute zero.  Temperature is measured in celsius, fahrenheit, kelvin, and rankine.

Boiling Point of Water 100.00 212.00 373.15 671.67
Triple Point of Water 0.01 32.03 273.16 491.69
Freezing Point of Water at Sea Level 0.00 32.00 273.15 491.67
Absolute Zero - 273.15 - 459.67 0.00 0.00

Typical Units

Common units for temperature are as follows:



Celsius Farenheit
Kelvin Rankine

Temperature Conversion

Celcius to Farenheit

\(C=5/9 \;(F-32)\) 

\(F=9/5 \;(C+32)\)

Celcius to Kelvin



Farenheit to Rankine



Temperature Instruments

In piping design, temperature is measured several different ways.  On a Piping & Instrumentation Diagram, the typical instruments are:

Thermowell - Thermowells are used in temperature measurement and provide isolation from the temperature sensor and the process fluid.  This is important because the temperature element is usually a piece of wire or wires that need to be in the process.  It provides not only structural integrity but also protection to the temperature element.

Temperature Element - A temperature element is a piece of wire, such as an Resistance Tempearture Detector (RTD), that provides the input to a temperature transmitter or temperature switch.  

Temperature Indicator - A tempearture indicator is a temperature gauge.  It is a mechanical device, that contains two dissimilar pieces of metal joined together. Each piece of metal has a different coefficient of expansion.  This difference is calculated to turn a shaft to display the temperature of the process.

Temperature Transmitter or Temperature Indicating Transmitter - This is used to display the temperature in the equipment and send an analog signal to a computer for futher processing.  It might be used as an alarm in case the temperature gets outside normal operating conditions. 

Temperature Switch - A temperature switch is used to send a digital signal (yes or no, 1 or 0) to a computer for an action to be performed.  E.g. send an alarm, turn off a pump, etc.


Tags: Equations for Heat Transfer Equations for Thermal Conductivity Equations for Temperature Equations for Thermal Expansion