Piping Strainers: Applications, types, design standards, materials

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. Strainers are very important components in piping systems to protect costly equipment from potential damage caused by foreign particles carried by the process fluid.

The following figure shows various types of strainers normally used in Pump or Compressor Suction lines in the process piping industry.

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 as 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 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(Fig. 2)
• Basket Type strainers( Simplex & Duplex construction) (Fig. 3) and

Y-Type Strainers

This type of strainer got its name from the shape as it resembles the alphabet “Y”. They are low cost strainers and 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-Strainers (Fig. 2) are normally small, they must be cleaned frequently.

Basket Strainer / Bucket Strainers

Basket Strainer or Bucket Strainers are a closed vessel with a filter screen inside it. They have a high capacity to retain foreign particles and hence widely used. Basket strainers (Fig. 3) 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 (Fig. 3) and
• Duplex Style Basket Strainer (Consists of two parallel basket filters with by-pass Valves as shown in Fig. 3)
• 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 setting 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

Refer to Fig. 4 that shows typical cone and truncated cone type temporary strainers.

Design standards for Piping Strainers

Strainers or filters are normally designed following the below mentioned International Standards:

• ANSI B 16.34
• PED 97/23/EC: Pressure equipment design
• BPVC: ASME Boiler & Pressure vessel code, Section-VIII Div.1

Materials of Construction of Piping Strainers

Strainer Body

The body of the strainer can be made from

• Forging
• Casting( but flanges shall be an integral part of the body) or
• Fabrication

Common materials used for the strainer body are iron, steel, stainless steel, bronze, chrome molly, and plastics.

Piping Strainer Internals

Strainer internal must be corrosion resistant and they have to be in contact with dirt or debris continuously. Common materials used are

• Stainless steel
• Special care shall be taken for Produced water service
• copper and aluminum

End connections of Strainers

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 center line 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

Now-a days various strainer options are available to the user like

• Magnetic inserts
• Self-cleaning strainers
• Mechanical type self-cleaning strainers
• Backwashing type strainers
• Temporary strainers

Y type strainer on various fluid

Comparison between Filter and Strainer

Now a days, the terms filter and strainer are used interchangeably in industries. However there are differences between the two. The main differences between a Filter and a Strainer are tabulated below

Few more Resources for you..

Piping Design and Layout
Piping Stress Analysis
Piping Interface
Piping Materials