How To Choosing The Right Screen Element Of Strainer
Strainer Definition and Purpose
Strainers are used normally for the protection of pipeline and petroleum process equipment installed downstream of the strainer. The equipment protected by our strainers is generally more expensive than the total installation cost of a strainer. Also this equipment is critical to the pipeline or process operation.
Strainers use perforated and/or wire mesh media for straining purposes. These materials are “two dimensional”, meaning they do not have a “Depth” or “Dirt Holding” capacity. This means that when a debris particle is caught in the straining media the opening is blocked or plugged. This results in reduced available opening for flow. Strainer sizing and selection are critical to insure your cleaning cycle time, particle size retention and pressure drop requirements are achieved.
Introduction:
One of the most important design considerations when purchasing a strainer is specifying the perforation or mesh size of the straining element. The straining element (commonly
referred to as a screen for WYE strainers and a basket for basket strainers) is a mechanical filter which removes and retains particles too large to pass through yet allows the flowing media (liquid or gas) to pass unobstructed. This process is illustrated in Figure 1. By cleaning the flowing media, the straining element helps to protect expensive downstream equipment such as pumps, meters, spray nozzles, compressors, and turbines.
The Strainer should be should always be installed ahead of pumps and other expensive, downstream equipment to help ensure proper protection and trouble-free operation. This even holds true for "clean lines" to protect against scale and accidentally introduced items such as: tools, gaskets, nuts, or bolts.
Determining Opening Size
In general, screen openings should be approximately one-half the diameter of the largest allowable particle. The largest allowable particle is defined as the size of particle that can pass through downstream equipment without causing damage. For example, if the maximum allowable particle is 1/16 inch than the screen opening would be specified at 1/32 inch. In addition to the size of particles, the quantity of debris in the flowing media must also be considered when determining the appropriate opening size.Straining elements can only be used to remove insoluble floating impurities. The most common range of particle retention is 1 inch down to 40 microns (.0015 inch). See Figure 2 for a comparison of sizes for a variety of common particles.
Determining Opening Size:
A common mistake is to specify a screen opening that is to small for the application. This can lead to overstraining and should be avoided for the following reasons:
• Maintenance costs are significantly increased due to excessive cleaning requirements.
• Pressure drop is increased dramatically.
• The straining element may become damaged and fail.
In some applications requiring finer filtrations, it may be advisable to strain in gradual steps. This is accomplished by placing progressively smaller straining elements in series.
Construction Material:
Irregardless of the strainer housing material being used, the most common construction material used for straining elements is stainless steel. This is due to the inherent resistance to corrosion stainless steel provides. As such, standard construction material for all straining elements is Type 304 stainless steel. Other materials (316 SS, 316L, and Monel) are available upon application.
Screen Types:
In general, strainer elements are available in three types: perforated, wire mesh, and reinforced wire mesh lined.
Perforated:
We offers a wide range of perforation sizes. To make the selection process easier, we recommends a standard perforation size suitable for general service for each type of strainer. The standard perforation size has been determined to provide the best balance of open area ratio (OAR), hole arrangement, and gauge thickness that results in the least amount of pressure drop. Please refer to each strainer's specification sheet for standard perforation size recommendations. Additionally, Table 4 presents a general guide for selecting straining element sizes for water, steam, oil, gasoline and air.
60degC Staggered Round Hole Arrangement
Wire Mesh:
For finer straining applications, down to 40 micron, wire mesh straining elements are available. our utilizes a mono-filament, plain square weave that exhibits large OAR and very low flow resistance. Other types of weaves, such as plain Dutch and Twilled Dutch weave, are also available upon request. As with perforated straining elements, We has developed standard mesh sizes suitable for general service for each type of strainer. Unsupported wire mesh straining elements are only suitable for strainers under 2 inches in size, constructed of 20 or 30 mesh, and operating within low pressure applications (under 200 psi). For larger strainers, finer mesh sizes, and higher pressure applications reinforced mesh lined screens must be used.
Wire Mesh Lined:
In most cases, wire mesh straining elements are reinforced with a heavier gauge, perforated metal backing to provide additional support. Our standard perforated metal backing is 5/32 inch which provides excellent support without significantly diminishing the OAR.
Wire Mesh with
Perforated Backing
