What are Piping Strainers?
Pipeline piping strainers (or filters) stop debris including scale, rust, jointing compound, and weld metal, protecting processes and equipment. A strainer is a device that uses a perforated or meshes straining element to mechanically remove particulates from a flowing fluid or gas in a pipeline. Pipe strainers are crucial parts of piping systems because they shield expensive machinery from possible damage brought on by foreign particles carried by the process fluid. Strainer Filters and piping strainers have indistinguishable names.
Strainers stop pipeline debris like scale, rust, jointing compound, and weld metal, shielding machinery and processes from their damaging effects and lowering maintenance and downtime. To safeguard costly and essential downstream equipment like pumps, flow meters, steam traps, control valves, etc., it is imperative to use the right strainers at the right locations (often upstream).
Types of Strainers
- Permanent– According to how their bodies are constructed, strainers can be divided into two primary categories;
- Basket Type or T-Type.
Y Type Strainer:
The Y-type strainer gets its design and name from the way the filter leg joins the main pipe: at a diagonal angle. This kind can also be utilized in vacuum or suction situations and is frequently employed in pressurized lines, steam, liquid, or gas.
Y-shaped strainers typically require more regular cleaning because they can store less debris than basket-type strainers.
A blowdown valve can typically be installed in the strainer cap for situations where considerable amounts of debris are anticipated. This allows the strainer to be cleaned using the pressure of the steam without having to shut down the plant.
How to Install Y Type Strainer?
It is possible to install a Y-strainer with the screen element pointed downward in either a horizontal or vertical position (Downward flow). As a result, the material can be collected by the strainer screen at its lowest point.
A Y-type strainer should be put in horizontal steam or gas piping such that the pocket is in the horizontal plane. This prevents water from building up in the pocket, which could lead to erosion and impact how heat is transferred.
The pocket in liquid systems should point vertically downward. By doing this, it is made sure that when the flow is low, the removed material won’t be pushed back into the upstream pipework.
Although it is best to put strainers in horizontal lines, this is not always practicable. Instead, if the flow is downhill, strainers can be installed in vertical pipelines, where the debris will naturally fall into the pocket.
The strainer would have to be installed with the pocket opening pointing downwards, and the debris would tumble back down the pipe, making installation impossible with upward flow.
Basket Type Strainer or T-Type:
The vertically oriented chamber of a T type, Basket type, or Pot type strainer is often larger than that of a Y type strainer. The basket type strainer is the favored kind for liquid applications since, size for size, the pressure drop across it is lower than that across the Y-type due to its larger free straining area. The basket-type strainer is also used on larger diameter steam pipelines since it has a better capacity for holding debris than Y-type strainers.
Only horizontal pipes can accommodate basket-type strainers, and the base of larger, heavier basket strainers needs to be supported.
The cover of a basket-type strainer can be removed for maintenance, giving specialists quick access to the filtering element in case it needs to be replaced (due to accumulated debris). A sizeable amount of condensate may accumulate when basket-type strainers are employed on steam systems. To remove condensate, strainers made for use in steam systems typically contain a drain plug that can be equipped with a steam trap.
The duplex form of basket strainers, which consists of two parallel basket strainers with diverting valves, is also an option. It is better to use a duplex basket-type strainer for demanding chemical and abrasive applications. It is constructed so that the process won’t be interrupted to allow for strainer cleaning.
Automatic Self-Cleaning Strainers are employed in situations where manual cleaning is neither convenient nor practicable, which may occur if the installation needs to be cleaned frequently or is in a hard-to-reach area. Particulate builds up on the element’s surface and is expelled from the strainer using the differential pressure between the system and atmospheric pressure, or by applying whichever pressure is necessary for the backwashed fluid to exit the strainer body. The backwashing procedure, which uses a little amount of filtered fluid, can take anywhere from a few seconds to several minutes, depending on the design and strainer size.
A temporary Strainer protects equipment and instrumentation during startup time. After a new plant is installed, the strainer is often left between a set of flanges for a while. For ease of installation or removal, installing a spool piece that is at least as long as the strainer is advised. Temporary strainers come in three fundamental designs: the conical type, the basket type, and the plate type.
Materials Used for Construction:
Cast iron, bronze, carbon steel, stainless steel, and plastic are the most often used materials for the bodies of Y type strainers and basket strainers.
Due to its inexpensive initial cost, cast iron is the most used material for strainer bodies. It is utilized in systems where the water is not under a lot of pressure, is not very hot, and is not subject to a lot of mechanical or thermal shock. Along with a range of different products and processes, cast iron is generally used for bigger size potable water lines and numerous non-potable water systems.
For brackish, saline, and marine service, bronze is the material of choice. Potable water services are frequently provided by it. Its price is twice as much as cast iron.
When high temperatures and pressures are present and resistance to thermal and mechanical shocks is necessary, carbon steel is employed. Where there are fire risks, carbon steel components are the preferred choice of materials.
For high temperatures and pressures, chrome-moly steel is employed. Due to its resistance to corrosion and contamination as well as its ease of cleaning, stainless steel is the ideal material for bodies, baskets, and screens.
Types of Screens Used:
There are commonly 2 types of screens used, they are:
- Perforated Screen-
These are created by utilizing numerous punches to create plenty of holes in a flat sheet of the necessary material. After rolling into a tube, the perforated sheet is spot welded together. The normal range of hole sizes for these moderately coarse screens is 0.8 mm to 3.2 mm. Perforated screens are thus limited to the removal of common pipe debris.
- Mesh Screen-
An arrangement of fine wire is made into a grid or mesh. This is then frequently laid over a perforated screen, serving as the mesh’s support cage. Compared to perforated screens, mesh screens allow for the production of substantially smaller hole sizes. It is possible to drill holes as small as 0.07 mm. They are then employed to filter out tiny particles that would ordinarily pass through a perforated screen. Mesh, which refers to the number of apertures per linear inch of the screen measured from the center line of the wire, is typically used to describe mesh screens.
Applications of Piping Strainers:
Pumps, loading valves, control valves, meters, steam traps, turbines, compressors, solenoid valves, nozzles, pressure regulators, burners, unit heaters, and other sensitive equipment should all have strainers installed in front of them to prevent premature equipment shutdown. 1 inch to 40 microns is the most typical range for strainer particle retention (0.00156 inches ).
Strainers can be installed near delicate static equipment. Even though static equipment is typically not thought to be so sensitive, strainers may occasionally be positioned close to subsequent equipment- meters, heat exchangers, spray nozzles, and a steam trap.
Along with that, strainers are also equipped with sensitive dynamic equipment. The use of a strainer is required for the following delicate and vibration-prone equipment: pumps, compressors, and turbines.
Industries that require constant protection from particles are the greatest candidates for y strainers. A y strainer is most frequently utilized in steam applications. A y strainer can easily withstand the intense pressure that steam applications experience because of its form.
In liquid applications, Y strainers are frequently utilized. Two extremely typical particle kinds that represent a serious threat to liquid applications are sand and gravel. Y strainers assist in the protection of equipment that would otherwise be damaged or clogged by various undesired particles when used in conjunction with water handling applications.
Using Y strainers with natural gas and air applications is advantageous as well. Natural gas and air environments have high pressure levels, much like steam applications. These applications must withstand high temperatures as well, which our strainers can do with ease.
The components and customization of these strainers must be done individually due to the wide range of industries and applications where a y strainer can be employed. For applications involving steam or natural gas, for instance, it would be better to choose a y strainer manufactured of chrome-moly steel because carbon steel does not perform well in extremely high temperatures or pressures.
Design Standards for Piping Strainers:
Typically, strainers or filters are created per the following International Standards: ANSI B 16.34, PED 97/23/EC: Pressure equipment design and BPVC: ASME Boiler & Pressure vessel code, Section-VIII Div.1.
Custom-made pipeline strainers can be created with a variety of connections and ports, unusual alloys, unique coatings, and design specifications regarding differential pressure, flow velocity, and particle holding capacity.
Strainers Body: The body of the strainer can be manufactured from fabrication or forging casting, but the flanges must be an integrated part of the body.
Piping Strainers Internals: Internal parts of the strainer must be resistant to corrosion and must frequently come into touch with trash or dirt. Stainless steel is a common material. Copper and aluminum in the produced water service must be handled with special care.
Piping Strainers End Connections: The following end connection types are used to attach strainers to pipes- threaded SW or flanged.
Selection of Piping Strainers:
Only the sensible decision of the piping strainer determines the success of a certain kind of pipe strainer. The following factors are the primary determinants of piping strainer selection:
Flow rate: A basket strainer is necessary for flows greater than 150 GPM.
The flow of the fluid’s filth: Comparing basket strainers to Y-strainers, the basket strainer can contain more dirt.
Application: Y-type pipe strainers are appropriate for situations that call for frequent cleaning.
The best option will be a duplex basket-type pipe strainer for continuous operation.
Strainer Orientation: The Y-type is the only choice for vertical orientation.
Pressure Loss: Compared to Y-strainers, basket strainers lose less pressure. Because of this, a basket strainer may be readily placed when in doubt.
It is also important to consider the mesh size of the strainer. The following elements need to be taken into account while choosing the right mesh size:
- The largest particle size that downstream machinery may safely handle.
- The acceptable pressure and temperature limits.
- The greatest pressure decrease permitted.
- The fluid service or fluid character is being delivered.
There are certain significant details to keep in check while choosing a piping strainer for particular applications, they are:
Particle Retention Size: The permissible level of particle size and the performance tolerance must be determined since strainers are employed to protect downstream equipment or processes from particulate. For macro filtration applications where the retention efficiency is “nominal” or “approximate,” pipeline strainers are used. Applications needing precise efficiency in microfiltration are not suitable for pipeline strainers. Engineered particle testing and the establishment of a Beta Ratio characteristic of our filter cartridge and bag filter designs define such “absolute” efficiency. Pipeline strainers’ element retention is typically set at 1/4 to 1/3 of the largest acceptable particle size. The goal is to maintain the necessary particle size without being overly harsh or “over filtering,” which just makes element cleaning more frequent.
Due to many pipeline systems containing low-velocity regions, like the spaces between spray nozzle ports, tiny particles can gather there, clump together, and cause problems. This is one of the reasons it is preferable to place strainers and filters as close as possible to the region that needs to be protected, however much will rely on the physical properties of the particles in the system and their quantity.
The ratio of open area, which compares the total open area of the element to the cross sectional area of the input pipe, is used to calculate the relative element holding capacity. This ratio changes based on the strainer design from 2:1 to 6:1.
Physical Location: The ability to reach the strainer element is crucial; it needs to be secure, ergonomically convenient, and have the right clearances for removal. Same-side or 90° offset piping orientations can be accommodated by strainers that are specially made. Additionally, some designs aim to reduce the pipeline’s above-grade height. The goal is to make it safe and simple to exhaust and empty the basket chamber. The operator shouldn’t be put in an uncomfortable or risky position when the piece is removed.
The right choice of pipeline strainers ensures perfect process conditions and downstream quality while minimizing manpower, which improves safety and lowers operating costs. This is achieved by identifying important design parameters such as strainer configuration, construction material, and particle size to be removed while taking into account fluid velocity, differential pressure, and space limitations.
Fluid Velocity and Differential Pressure: The intended fluid velocity via a pipeline strainer runs from 3 to 8 FPS, with more viscous fluids operating at the lower end of the velocity range, though it varies slightly depending on the specific strainer design. As explained in our article Fluid Velocity and Differential Pressure, fluids can be transported via pipelines at higher velocities, but when the velocity across the screen reaches 8 FPS, it frequently harms crucial strainer element performance.
Due to particulate buildup, the open area of the element eventually becomes less than the cross sectional area of the inlet pipeline, increasing differential pressure dramatically.
To allow enough time to enter the vessel and clean the element, the size guidelines aim for an initial clean differential pressure of = 2 PSI and prompt for element cleaning when the differential pressure increases by about 5 PSI. Even though an element’s burst differential pressure may be in the 20 to 30 PSI range, deformation and the consequent failure to adequately seal may still occur at lower pressures. Fast-acting valves downstream of the strainer may also be a factor in pressure spikes known as “water hammers”. Always use the highest pressure and temperature—often referred to as the design pressure/temperature—to determine the strainer’s pressure class.
Symbols of Piping Strainers:
Some common shapes are as follows:
- Cone Temporary Strainer- It has a cone or a triangle shape in the middle of a straight line.
- Y Type Strainer- It is represented by a diagonal straight line emerging from the middle point of the straight line.
- T Type Strainer- It is similar to the Y type and has a line emerging from the midpoint, but the line in the T type is straight, forming a T shape.
- Basket Type Strainer- It has the shape of a half cylinder, forming in the middle.
Dimensions of a Piping Strainer:
Pipe strainer dimensions vary regarding flange rating, end connection, and pipe strainer kinds. As the flange rating changes, so do the size and weight of strainers for flanged pipework. Many times, a pipe strainer’s dimensions depend on the vendor. As a result, throughout the initial stages of piping design, the length of piping strainers is kept constant in piping isometrics. The piping isometrics are updated, and the piping length is modified, once the precise vendor data is later made available. The following table gives an example of some common pipe strainer weights and dimensions for Y-type and basket strainers. The final vendor’s information must be confirmed, though.
Difference between filters and strainers:
An apparatus known as a filter is used to filter particles out of a specific liquid or gas. A disposable medium for eliminating particles with particular micron sizes is included. While all filters are filters, not all strainers are filters. One kind of filter is a strainer. Larger particles are removed from a process stream using a strainer using a perforated plate or screen mesh. A Strainer’s main benefit is that it may be used again and again. Once it clogs, the filter screen must be replaced because it is only ever used once.
The media screen’s hole diameter, also known as the mesh size in the case of a strainer, appears to be the primary difference. To distinguish strainers from filters, there is no strict size distinction. Some filters can filter out particles as small as 1 m.
The resistance is another distinction. Typically, strainers offer a little barrier to liquid passage. When compared to the pressure drop over thick media filters or membrane filters, the pressure drop across the majority of strainers is quite minor.
The function is another distinction. Another downstream machinery (such as pumps and instruments) is shielded from harm by renegade garbage using strainers. To remove the particles from the fluid, a filter is used.
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