Guidelines for The Preparation of Strainer Specification- Part 2

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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
Plate Material
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
Seamless Pipe
Viz., 106 Cr B
Stainless Steel


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.

Sr.No. Type of Strainer Pressure Rating End Connection Details Material /size range



Upto 250 PSI, 435°F Gun metal body
Screwed Ends Size 15 to 40 NB
Flanged Ends Size 50 NB & above
Upto 150 PSI, 400°F Cast iron body
Flanged Ends Size 50 NB & above
Screwed Ends Size below 50 NB
Class 800 Forged CS Body
Socket Weld Ends Size 15 NB to 40 NB
600PSI, 850°F Flanged Ends Cast Carbon SteelBody size50 NB & above
1400 PSI, 1004°F Socket Weld Ends Alloy Steel Body
Size 15 NB to 25 NB
2 Basket Type 150 Class & above Flanged Ends CS Body
Size 50 NB & above


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 viscosity of a fluid at working temperature is also to be specified since higher the viscocity higher the pressure drop.

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.