6. Material of construction of Strainer and Strainer element
The material of construction of the strainer and strainer element must be keeping in view compatibility with the process fluid being handled. As a general rule MOC of strainer body is specified in line with relevant piping material spec code and the element material is specified at least equivalent or superior to the body material.
The following Table is prepared as a general guideline for specifying material, based on what is offered as Standard product of the manufacturer:
|Sr.No.||Type of Strainer||Body Material||Element Material||Remarks|
|Flat Disc||–||Carbon Steel/Bronze, Stainless Steel|
|Conical||–||Sheet material of SS, CS or Brass with SS Wire mesh|
|“T” Type||–||Carbon Steel/ Stainless Steel|
|“Y” Type||CS-A105 or A105 Galvanized||Stainless Steel||Size 15 to 40 NB Forged Construction|
|SS-A182 Gr F304,316,321
Bronze – ASTM B62
|SS-304,316,321||For potable Water and instrument air service|
|“Y” Type or Basket Type||CS-A216 Gr WCB
SS-A351 Cr CF 8
Cast Iron-A126 CLB
IS 210 Gr 20
IS 2002 Gr FG 200
|Stainless Steel||Size 50 to 100 NB Cast Construction|
|Basket Type||Pipe Material
A53 Gr B,A106 Gr B
A515 Gr 60, IS 2062
Is 2992 Gr 2A
|Stainless Steel||200 NB and above Generally for Utility Services Welded Construction|
|Duplex Type||Carbon Steel
Viz., 106 Cr B
|Cartridge Type||Same as Basket type Body Material||Honey Comb Wound With cotton, fibers glass, polypropylene, nylon yarn on GI/SS 304/SS 316|
For cast iron strainers, bolts, studs and nuts shall conform to ASTM A307 Gr B or equivalent where as for steel trainers, bolts and studs shall conform to ASTM A193 Gr. B7 or equivalent and nuts to ASTM A194 Gr. 2H or equivalent.
7. Pressure Rating and End Connection details
The pressure rating of the strainer shall be identical to that of other piping components used in a system such as valves etc. related to the specific fluid covered under the relevant piping Spec Code.
Similarly end connection details shall be akin to whatever applicable to inline piping components like valves as covered in the relevant Spec Code.
8. Layout aspects to be considered during Installation of Strainers
8.1. Y-Type Strainer to be properly installed as per flow direction. Sufficient clear space to be provided in all strainers to facilitate easy removal of mesh element for cleaning purpose.
8.2. In large basket type strainers cover to be provided with a davit arrangement for ease in opening. Alternatively, monorail beam to be envisaged in the layout.
8.3. Be low drains of basket strainers sufficient clearance to be provided for drainage.
8.4. For temporary cone type strainers break off flanges (spool piece) to be considered for ease in removal.
8.5. Temporary conical strainers are to be placed with the cone pointing opposite to the direction of flow.
9. Pressure Drop across a Strainer / Mesh Number
The mesh is effectively the number of opening per (25.4 mm) linear inch measured from the center of one wire to another one inch from it. Mesh numbers range from 2 to 400.
Hence the mesh number is an indication of the operative opening size, higher the mesh number smaller the opening and higher the pressure drop. Liquids which are more viscous when used with finer meshes create increased pressure drop.
Perforated plate strainers provide coarse filtration to above 150 microns. Finer filtering wire mesh elements are normally used, in conjunction with perforated plates for reinforcement. Wire mesh strainers can provide filtration down to about 40 microns.
Attachment – II gives an idea of aperture sizes based on various mesh numbers.
Numerically the service life of a strainer (between cleaning times) can be expressed as the ratio of open area of the strainer to the pipe cross section. Open area is determined by choice of perforations or mesh.
Basket type strainers shall have a minimum free flow area of 1.5 times the cross sectional area and all Y-type strainers would have a minimum free flow area of twice the bore cross sectional area.
Thus specifying mesh number would depend on :
a) The smallest particle size to be filtered
b) The allowable pressure drop
Generally the allowable pressure drop across a clean filter is specified as 0.01 kg/cm2 (g) and across la clogged filter as 0.5 kg/cm2 (g).
The data for Mesh No. and Pressure Drop if not given in the Process Licensor’s Documentation is to be confirmed with Process Department.
Vendors are to provide pressure drop versus flow rate curves for all the strainers for clean condition as well as 50% clogged condition.
9. Sample Strainer Specification
Before commencing on preparation of strainer specification the first step involves identifying the types of strainers and quantifying the number of strainers from the P&ID’S. Alternatively Strainers can be included in Piping MTO for quantification purpose.
The following gives the user an idea for the input sources for specifying a Strainer.
|Tag no||To suit Special Material Index & P&ID|
|Type||As per P&ID or to suit the purpose|
|Size mm NB Line Strainer||As per P&ID Line Size to be specified By vendor|
|Quantity (N.)||As per P&ID or Material Status Report.|
|End Connection||To suit Type & Size and Pipe Spec|
|Flange Facing and Finish||To suit Pipe Spec|
|Strainer Element Size (mm2)||To be specified by Vendor|
|Mesh Number||To be obtained from Process Dept.|
|Piping Spec||As per Line Designation / P&ID|
|Line Number / Location||As per P&ID|
|P&ID No.||As per P&ID|
|Manufacturer||Same as Vendor (To be incorporated at the time of Order Specification after receipt of LOI/Purchase order from clients).|
|Manufacturer Drawing No.||Same as above|
|Dimension face to face And center line to Bottom strainer||As per Piping Layout|
|Body Material||To suit Type & Size and Piping Spec.|
|Mesh Material||To suit Piping Specification (equivalent or superior to body material)|
|Flanges||As per Piping Spec|
|Gasket||As per Piping Spec|
|Bolting||As per Piping Spec|
|Plug||As per Piping Spec|
|Service Fluid||As per Piping Spec Index.|
|Design Flow Rate||To be obtained from Process Dept. Alternatively it can be obtained from the Process Data Sheet of the equipment for which the Strainer is warranted.|
|Design Pressure||As per Piping Spec Index.|
|Design Temperature||As per piping Spec Index.|
|Density at Operating Temp (Kg/m3)||To be obtained from Process Dept.|
|Viscosity at Operating Temp.||To be obtained from Process Dept.|
|Maximum Allowable Pressure Drop across clean filter||Generally specified as 0.01 kg/cm2(g). However the same to be confirmed with Process Department|
|Hydrostatic TestTest Pressure||1.5 times the Design Pressure|
For basket strainers on pump suction it is advisable to calculate the design pressure based on operating conditions to establish hydro test pressure at shop or site in order to avoid a robust strainer construction which may be unacceptable to layout.
The following special requirements are to be observed by Vendor.
1 Vendors are to provide pressure drop versus flow rate curves for all the strainers for clean conditions as well as 50% clogged condition.
2 Supporting of Large Strainers:
All basket strainers 200 NB and above are to be provided with leg supports and above 500 NB, 3 legs are required.
Depending on layout constraints and foundation requirement the limitation on the maximum distance between bottom face of leg support and center line of nozzle is to be specified as also the distance between center line of nozzle and drain plug.
3 Drains & Vents
All basket strainers are to be provided with drain plugs and vent cocks. If Valves are to be used and are not in vendors scope then vendor to be informed of the appropriate end connections required.
4 Tag No to be clearly identified.