Piping Strainers: Applications, types, design standards

What is Piping Strainer?

Piping Strainers (or filters) arrest debris such as scale, rust, jointing compound, and weld metal in pipelines, protecting equipment and processes. A strainer is a device that provides a means of mechanically removing solids from a flowing fluid or gas in a pipeline by utilizing a perforated or mesh straining element.
The following figure shows various types of strainers normally used in Pump or Compressor Suction lines in the process piping industry.

Stainer

Application of Piping Strainers

To ensure against the untimely shutdown of equipment, strainers should be installed ahead of pumps, loading valves, control valves, meters, steam traps, turbines, compressors, solenoid valves, nozzles, pressure regulators, burners, unit heaters, and other sensitive equipment. The most common range of strainer particle retention is 1 inch to 40 microns (0.00156 inches ).

Strainers in Sensitive Static Equipment:

Even though static equipment is normally not considered that sensitive, still sometimes strainers are installed near the following equipment.

- Heat exchanger
- Meters
- Steam trap
- Spray nozzles
- Strainers in Sensitive Dynamic Equipment

For the following sensitive and vibration-prone equipment use of a strainer is a must.

- Pumps
- Compressors
- Turbines
- Types of Piping Strainers/Strainer Types

Depending on the use, two types of strainers are found in industries.

- Permanent Strainers and
- Temporary Strainers
- Permanent Strainers

These strainers will be installed permanently in the piping system. Examples of permanent strainers are Y type strainers and Basket Type strainers( Simplex & Duplex construction) 

This type of strainer got its name from the shape as it resembles the alphabet “Y”. They are low-cost strainers and are used in pressurized lines with low debris or foreign particle concentration. They can be installed in horizontal or vertical lines keeping the filtering element towards the ground. As the retaining capacity of Y-Strainer slow-cost is normally small, they must be cleaned frequently.

Basket Strainer / Bucket Strainer

Basket Strainer or Bucket Strainers are closed vessels with a filter screen inside them. They have a high capacity to retain foreign particles and are hence widely used. Basket strainers are used only in horizontal lines; mostly for liquid services with high flow capacity. Bucket strainers can be independently supported like equipment in case their weight is more, or they can be supported inline from pipe supports. As they resemble the alphabet “T” of the English language, they are often termed as T-Strainers.

Basket Strainers are of three types

- Simplex Style Basket Strainer and Duplex Style Basket Strainer
- Automatic Strainers

Basket filters can be easily cleaned by opening the top cover. Duplex Basket strainers are cleaned online when the pipeline is in operation simply by diverting the flow to the other filter.

Automatic strainers have self-cleaning baskets that are controlled by using pressure drop settings or times; Hence, the cleaning operation is never interrupted.

Temporary Strainers

Temporary strainers are used for a small period of time. Examples of temporary strainers are

Cone type strainer and Truncated Cone type strainer

Strainers are connected to piping by the following end connection types

- Flanged
- SW or Threaded
- Screens or Filters for Piping Strainers

Two types of screens used in strainers :

- Perforated screens
- Mesh screens
- Perforated screens

- Perforated screens or strainers are formed by punching a large number of holes in a flat sheet of the required material using multiple punches. These are relatively coarse screens and hole sizes typically range from 0.8 mm to 3.2 mm Mesh screens

- Fine wire is formed into a grid or mesh arrangement. This is then commonly layered over a perforated screen, which acts as a support cage for the mesh.

Mesh Screen terminology: e.g. 3 mesh screen We shall always ask the process to give Max. allowable pressure drop at % clogged condition.

- Mesh screens are usually specified in terms of ‘mesh’; which represents the number of openings per linear inch of screen, measured from the centerline of the wire.

- Mesh is not the only thing to be asked for but hole size is also important.

- Corresponding hole size in the mesh screen is determined from knowledge of the wire diameter and the mesh size.

Selecting Mesh Size for Piping Strainers:

- While selecting the proper mesh size the following factors must be considered.
-The maximum particle size that the downstream equipment can handle safely.
- The working temperature and pressure ranges.
- The maximum allowed pressure drop.
-The fluid service or nature of the conveyed fluid.
- Strainer options

Y type strainer on various fluid

                                          

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