This data-file is a calculator for steam pipe insulation, calculating heat losses and external temperatures of hot surfaces from first principles, as a function of the industrial insulation thickness. Higher energy prices incentivize additional insulation, although there can be diminishing returns.
The global market for insulation materials is $70bn pa, of which $10-15bn is for industrial insulation, especially around hot reactor vessels and pipeworks. Leading companies include Owens Corning, Rockwool, Johns Manville and Saint Gobain.
Why is industrial insulation needed? Let us imagine we have 100m of piping, carrying 5,000m3 of steam per hour, at 300ºC and 6-bar of pressure, perhaps from the steam generator at a thermal power plant. This equates to 10MWth of thermal energy. However without any insulation, the exterior surface of this pipe network will also be at 300ºC, which leaks 7% of the heat from the pipes, and creates a safety hazard.
The loss rate increases linearly when pipeline networks are longer AND when the flow rate of steam through the pipe is slower, as this creates a larger surface through which heat can leak and a longer time for heat leakage to occur per unit of heat that is conveyed.
Safety hazards. The burn threshold limit, set by OSHA and ASTM C1055 safety standards requires sufficient insulation to be added so that the external surfaces of most hot reactors will be below 60ºC. Moreover, an effect called “water hammer” can occur, if a pipe is losing too much heat at its surface, causing water to condense, and then the condensation droplets can become entrained in the steam flow and slam into valves or pipe joints.
The heat loss from steam pipes and other hot reactor vessels is calculated from first principles in this data-file. We consider the losses due to convection of air around the surfaces of pipes and due to radiation from the pipe surface. In turn, if we know the rate of heat loss, we can also back-calculate the surface temperature.
Insulation slows the loss of heat. Just 5cm of insulation is enough to slow the heat loss from our hypothetical steam pipe network above from 7% to 1%, and bring the outer surface temperature down from a dangerous 300ºC to a safe 55ºC. A nice rule of thumb is that each 50ºC increase in internal fluid temperature requires another 1cm of insulation thickness.
Diminishing returns are also shown in the data-file. The first 2cm of insulation reduces our thermal loss rate from 7% to 2%. The next 2cm reduces it from 2% to 1%. The next 2cm reduces it from 1% to 0.6%. Uninsulated surfaces and hotspots are therefore the best focus for industrial efficiency initiatives. But higher prices will therefore incentivize thickening the insulation
The numbers in this data-file depend on the steam flow (in m3/hour), pipe length (m), steam temperature (ºC), steam pressure (bar), pipe radius (m), insulation thickness (m), and coefficients for thermal conductivity of insulation, convective heat transfer and emissivity of the outer pipeline surface. The physics of heat losses, in kW, kW/m, kW/m2 and percentage terms can all be stress-tested in the data-file.