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Steam Lines Flushing: The Why and How

Flushing of steam piping is an activity which is often neglected but can damage the components of steam system. During installation of steam piping, scales, internal debris accumulate inside the steam pipes. It is highly recommended to flush out steam piping of all this debris before the steam pipes become functional.

Flushing can be defined as a pre-commissioning activity which involves pumping water or any other suitable medium in sufficient quantity and velocity through a given piping, completely filling that section in such a way that the flow of medium through the system will forcibly remove any loose rust, construction debris or mill rust from the system.

Basic Flushing Guidelines

Some basic guidelines should always be followed while carrying out the flushing activity.

  1. A detailed flushing plan should be made for each system which is to be flushed. Each plan should have detailed instructions about type of flushing, duration for which the activity should be carried out and a detailed advice on how the activity should be carried out.
  2. Flushing should follow the normal flow direction of the system wherever possible.
  3. Flushing should be carried out from highest elevation to the lowest.
  4. A commissioning engineer should supervise the flushing activity. The commissioning engineer should also inspect the cleaned system for any rust, sand construction debris etc. and sign the acceptance of flushed systems.
  5. Verify that sufficient flushing or circulating water is available to carry out the flushing activity.
  6. Flushing should never be carried out through smaller openings such as drains or vents.
  7. In order to avoid the corrosion of the system, it should be completely de-watered as soon as possible.
  8. Flushing should be performed through fully open flanges/ open pipe ends.
  9. Ensure that the pump capacity (volume and pressure) is sufficient to carry out the flushing activity effectively.
  10. Ensure that the required temporary piping, hose connections, blind flanges, temporary gaskets, temporary strainers, dummy spools etc. are installed before starting the flushing activity.
  11. Ensure that all the temporary fittings are removed after completion and acceptance of the flushing operation.
  12. Re-install the piping systems/lines with correct materials as per the specifications.
  13. Rectify any damage caused to the steam system during the flushing activity before the system is commissioned.
  • Type of mesh and cleanliness of temporary strainers should be verified prior to and during the flushing operation
  • In-line components such as control valves, orifice plates, positive displacement meters, turbine meters, rota meters etc. should be isolated or removed prior to flushing.
  • The removed/isolated instruments should be stored or protected properly.
  • In case of control valves with bye-pass lines, remove the control valve, flush first through the bypass line and then flush through the open block valves
  • In case of control valves without bypass, remove the control valve. Install temporary spool piece leaving the pipe system/ line unimpaired, or flush through the open ended block valves
  • In case of instrument connections (transmitters, gauges, local indicators, analyser traps etc.), remove the analyser probes, close the line block valves and disconnect the instrument leads at the block valves. Never fill the instruments with water.
  • In case of turbine meters and strainers, install a temporary spool in place or flush through the open ended block valves.
  • All safety valves should be spaded off or removed prior to flushing.
  • Ensure that the lines do not flush through exchangers, flame arrestors or rotating equipment.


The following systems should not be flushed -

  1. Process lines where operational difficulties will be caused because of presence of water.
  2. Instrument service lines should be service tested and blown with air. The air used should be free from oil.
  3. Steam supply systems should be drained after the hydro test and should be blown with steam.
  4. Condensate systems should also be hydro tested and drained after that. These should be blown with steam when available.
  5. Steam tracing lines should be service tested with steam with steam traps bye-passed or removed.


During the flushing activity, there can be a large number of construction personnel working around the system. Safety of these people should be taken into consideration while planning the flushing activity.

Though flushing activity is carried out with the help of water or other suitable medium, its purpose is to remove solid debris from the system. These solids coming out with a high velocity can cause serious injury. Hence, the area around the exit end must be free and at least one person from the team should be present there.