What is Pipe Flushing?
Pipe flushing is a process used to remove any impurities, such as dust, rust, mill scale, oil, grease, and other debris, from the interior of a pipe or pipeline system before it is commissioned. This process is usually used for pipes with a size of 10 inches or less and is not typically used for pipes with a size of 12 inches or larger, as the quantity of fluid required for flushing is too large to be practical.
Criteria for Pipe Flushing
In order to ensure that pipe flushing is successful, it is important to establish a detailed flushing plan before beginning the process. This plan should include the section of pipe that requires flushing, the quantity of fluid to be used, and the speed and direction in which the fluid should be pumped. Once these criteria have been established, the pipe flushing process can begin.
Types of Pipe Flushing
Depending on the fluid used for the operation, pipe flushing can be of two types:
- Chemical/Water flushing and
- Oil flushing
Pipe Flushing: Chemical/Water vs Oil Flushing: Chemical or water flushing is the most common method of removing debris and contaminants from piping and pipeline systems. This involves the use of plain water or water with chemicals. This helps ensure that the fluid flowing through the pipelines is free from any impurities.
Oil Flushing: A Necessary Step: While chemical or water flushing is the primary method used for pipe flushing, oil flushing is also necessary in some cases. This is usually done after chemical flushing and is used for lube oil systems. Oil flushing helps to ensure that the fluid is free from any contaminants and is ready for use.
Working Principle of Pipe Flushing
Pipe flushing is a process that is used to remove foreign particles, debris, and other unwanted elements from piping systems. The force of the flushing fluid passing through the pipes at high velocity is used to dislodge the unwanted elements, which then flow along with the flushing fluid, thus clearing the pipe and pipeline surface.
Velocity Requirements for Pipe Flushing
The velocity required for pipe flushing operations is determined in one of two ways. The first way is to decide on the velocity that will achieve a Reynolds Number (NR) of 4000 for Piping and of 3000 for Tubing 1/2″ and below. The second way is to ensure that the velocity is equal to or greater than the normal operating velocity of the fluid being used.
Pipe Flushing Criteria
When designing a pipe flushing plan, it is important to consider the criteria for successful pipe flushing. This article outlines the key guidelines for pipe flushing.
Flushing Medium: The recommended flushing medium for stainless steel pipes is potable or demineralized water with a chloride content of less than 20 ppm. For carbon steel or alloy steel pipes, plant water, potable water or any other approved flushing medium can be used.
Flushing Duration: For open-ended systems, pipe flushing should continue until clear water discharges for 5 minutes. In closed circuit loops, flushing should be stopped when the pump strainer is free from foreign materials and the water is clean.
Flushing Liquid Volume: In order to effectively flush the pipes, a sufficient volume of water should be available to fill the pipe and generate high velocity. In most cases, the water from the fire water distribution network is used for pipe flushing with a separate pump for generating the required velocity.
Pipe Flushing Standards
The standard for pipe flushing is ASTM D4174, with ISO 5910, ISO 28521, ISO 5911, SHELL DEP 31405030 being other notable standards in the industry.
Basic Guidelines for Pipe Flushing
When carrying out pipe flushing, there are certain considerations to keep in mind:
1. Developing a Detailed Flushing Plan: A detailed flushing plan should be developed to specify the types, steps, and duration of flushing.
2. Flushing Direction: Pipe flushing should be done using the normal operation flow direction.
3. Flushing from Highest to Lowest Elevation: Pipeline flushing should be done from the highest to the lowest elevation.
4. Supervision and Inspection: The pipe flushing activity should be supervised and inspected by a commissioning engineer.
5. Avoiding Smaller Openings: Flushing should be performed through fully open flanges/ open pipe ends and never be carried out through smaller openings such as drains or vents.
6. Selecting the Proper Pump Capacity: The proper capacity of the pump shall be selected for pipe flushing activity.
7. Fitting the Necessary Fittings: All required temporary fittings like a hose, blind flange, strainer, gasket, etc must be fitted before flushing and shall be removed immediately after completion of pipe flushing.
8. De-Watering and Drying: To avoid corrosion potential, the system shall be de-watered immediately after flushing and make it dry.