Piping Strainers: Applications, Types, Design Standards, Symbol, Materials, Selection

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. Pipe Strainers are very important components in piping systems to protect costly equipment from potential damage caused by foreign particles carried by the process fluid. Piping Strainers are also known as Strainer Filters.

The following figure shows various types of pipe 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 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 Pipe 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 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-Strainers (Fig. 2) are normally small, they must be cleaned frequently.

Basket Strainer / Bucket Strainers

Basket Strainers 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 (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 settings or times; Hence, the cleaning operation is never interrupted.

Temporary Pipe 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 which 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

Pipe Strainer Symbol

Depending on the pipe strainer type, symbols for pipe strainers are also different. Common pipe strainer symbols are shown below in Fig. 5.

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

Strainers 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 Piping Strainers

Strainers are connected to piping by the following end connection types

• Flanged
• Socket Welded 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 Maximum 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.
• The 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

Nowadays 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 Pipe strainer on various fluid

Selection of Pipe Strainers

The success of a specific type of pipe strainer solely depends on the proper selection of the piping strainer. The main parameters that affect the piping strainer selection process are:

• Flow Rate: A flow rate in excess of 150 GPM requires a basket strainer.
• The dirtiness of the flowing fluid: The basket strainer has more dirt-holding capacity as compared to the Y-strainers.
• Application Requirement:
  • A y-type pipe strainer is suitable for applications requiring frequent cleaning.
  • For continuous operation, the ideal choice will be a duplex basket-type pipe strainer.
• Strainer Orientation: For vertical orientation, Y-type is the only option.
• Pressure Loss: Basket strainers exhibit less pressure loss as compared to Y-strainers. That’s why when there is doubt a basket strainer can easily be installed. It will cost more but serve all the purposes.

Note that, purchasing a spare pipe strainer is always a good engineering practice to avoid unnecessary delays in cleaning and installation for line operation.

Pipe Strainer Dimensions

Dimensions of pipe strainers vary with respect to flange rating, end connection, and pipe strainer types. For flanged piping strainers, with an increase in flange rating the dimension and weight increase. Normally, the pipe strainer dimensions are vendor specific. This is the reason during the initial stages of piping design the length of piping strainers is kept as hold in piping isometrics. Later, when the specific vendor data is available the same is updated in piping isometrics and adjustments are made in piping length. The following table provides some typical pipe strainer dimensions and weights for Y-type and Basket-type strainers as samples. However, Final vendor details need to be verified.

Pipe Size (Inch)	Pressure rating	Y Type Strainer Length- Flange face to Flange Face (mm)	Y Type Pipe Strainer Weight (Kg)	Basket Strainer Length- Flange face to Flange Face (mm)	Basket Pipe Strainer Weight (Kg)
1/2″	150	170	3
3/4″	150	170	3.5	224	7
1″	150	185	5.5	225	13.5
1-1/2″	150	270	10	240	19
2″	150	275	16	315	27.5
3″	150	360	30	365	46.5
4″	150	435	50	445	70
6″	150	560	92	600	167
8″	150	655	180	715	310
10″	150	880	340	855	550
12″	150	970	385	1015	600
1/2″	300	175	3.5	–	–
3/4″	300	175	4.5	224	7.5
1″	300	195	6.5	232	14.5
1-1/2″	300	275	11.5	245	21.5
2″	300	315	18	321	29.5
3″	300	405	35.5	375	49
4″	300	490	65.5	455	92
6″	300	582	125	620	225
8″	300	730	233	740	405
10″	300	910	420	890	655
12″	300	1070	445	1050	700

Comparison between Filter and Strainer

Nowadays, 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

Filter	Strainer
A device that eliminates unwanted particles from the fluid is known as a filter.	Strainer also serves the same function.
The filtering medium in a filter is normally disposable.	Strainer uses a Reusable filter that is used again after cleaning.
The Filters normally filter out smaller particles (smaller than 40 microns).	Strainers remove comparatively larger particles ( larger than 40 microns)
Normally filters remove elements invisible to the naked eye.	Dirt removed by strainers is visible.
Filters remove particles by obstruction as well as chemical action.	Strainers remove particles by construction only.
Filters use soft media on hard surfaces to remove contaminants.	Strainers use hard mesh or rigid materials to remove debris.

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