The following information is an excerpt from Bürkert's Steam Site Guide, a free document to help process engineers to size, optimise and ensure the safe designs of their steam systems.
It is widely appreciated that steam velocity is an important factor in the life and maintenance of a steam pipe.
As steam velocity is such a practical issue, it is reasonable that it could form the basis of a sizing method for steam pipes.
For relatively short runs (less than 50m), velocities of 15 to 40 m/s are used in saturated steam applications.
As a general rule of thumb, 25m/s is adopted as a happy medium. For longer pipe runs, alternative pressure drop method are normally considered.
Higher costs for ancillaries such as strainers, isolation valves, pipe supports and insulation can dramatically and unnecessarily increase both the initial installation cost and the overall cost of ownership.
It can also have an effect on the steam systems' operational effectiveness. More condensate can be expected to form, due to the greater heat losses from the larger heat transfer area, requiring more steam trapping or the increased risk of wet steam being offered to the process.
The process itself dictates the mass of steam required at the point of use. If the required mass of steam travels through undersized pipework, you can expect an increase in steam velocity.
Steam and condensate travelling at high velocities can be very damaging, increasing the risk of erosion, noise, wire-draw and water hammer.
With an increase in velocity, you can also expect a higher pressure drop across the steam pipework, resulting in a lower than expected pressure at the point of use, hindering the application’s effectiveness.
An industrial food autoclave condenses 180 kg/h of saturated steam and the steam pressure is 3 bar g. Using the example table to the right, starting on the left hand side, find the steam pressure required and select the desired velocity. Trace a line horizontally across, until you reach a figure greater than the required 180 kg/h. From there trace a line vertically upwards and simply read off the pipe size, which in this example would be 32mm.
Download Bürkert's Steam Site Guide for a table of saturated steam pipeline capacities, as well as several other guides to designing systems for steam.
The guide is twenty four pages long and comprises nine sections: