In This Article
- 1.Why Strainers Are Essential in Process Piping
- 2.Strainer Types Compared
- 3.Mesh Size and Perforation Selection
- 4.Material Selection by Service
- 5.Pressure Drop and Monitoring
- 6.Codes and Standards
Why Strainers Are Essential in Process Piping
Particulate contamination — weld slag, mill scale, sand, rust and process debris — is the leading cause of premature failure in pumps, compressors, heat exchangers, meters, and control valves. A correctly specified strainer positioned upstream of these assets intercepts solids before they cause damage, eliminating unplanned shutdowns and extending equipment life. In most process plants, strainer selection is governed by ASME B31.3, API 598, and project-specific piping specifications.
Strainer Types Compared
| Type | Orientation | Cleaning Method | Continuous Operation | Typical Pipe Size | Best Application |
|---|---|---|---|---|---|
| Y-Strainer | Inline, angled body | Blowdown valve or manual removal | No (line must be isolated) | DN15 to DN300 | Steam, condensate, gas, instrument lines |
| Basket (Pot) Strainer | Inline, enlarged chamber | Manual basket removal | No (line must be isolated) | DN25 to DN600 | Pump suction, cooling water, fuel oil |
| Duplex (Twin) Strainer | Two parallel baskets | Switchover valve; one basket cleaned while other in service | Yes — uninterrupted flow | DN50 to DN600 | Critical continuous-service lines |
| Temporary (Startup) Strainer | Cone or flat screen in flange | Single-use, removed after startup | No — temporary only | Any | New pipework commissioning, pump startup protection |
| T-Strainer (Tee-Type) | Tee-section body, perpendicular blow-off | Blowdown valve | No | DN15 to DN200 | Steam lines, condensate return |
Mesh Size and Perforation Selection
Strainer element opening size is specified in mesh (wires per inch) or as an equivalent hole diameter in mm or inches. Coarser meshes capture large debris with minimal pressure drop and are used on pump suction and cooling water lines. Finer meshes protect meters, control valves and instrumentation but impose higher differential pressures and require more frequent cleaning.
- 3 to 10 mesh (6.7 to 2.0 mm): pump suction strainers, cooling tower circuits, large-bore water lines
- 20 to 40 mesh (0.84 to 0.42 mm): general process service, fuel oil, condensate return
- 60 to 80 mesh (0.25 to 0.18 mm): instrument root connections, control valve upstream protection
- 100 to 200 mesh (0.15 to 0.074 mm): fine chemical dosing, metering systems, precision instrument lines
- Perforated plate (2 to 6 mm holes): heavy-duty slurry, polymer, high-viscosity fluids where woven mesh would blind
Material Selection by Service
| Body Material | Screen Material | Service | Standard |
|---|---|---|---|
| Carbon Steel A216 WCB | 304 SS perforated / woven | General hydrocarbon, steam to 425 C | ASME B16.34 Class 150 to 2500 |
| 316 Stainless Steel | 316 SS woven mesh | Corrosive chemical, pharma, food grade | ASME B16.34 / 3-A Sanitary |
| Cast Iron ASTM A126 | 304 SS mesh | Water, cooling service, Class 125/250 | MSS SP-85 |
| Duplex 2205 | Duplex mesh | Seawater, chloride-rich process | NORSOK |
| Hastelloy C-276 | Hastelloy mesh | HCl, HF, strongly oxidising acids | ASME B16.34 / NACE MR0175 |
| Bronze / Gunmetal | 304 SS mesh | Marine, cooling water, compressed air | BS 5154 |
Pressure Drop and Monitoring
The pressure drop across a clean strainer is typically 0.05 to 0.3 bar at design flow velocity. As solids accumulate, differential pressure rises — most specifications call for cleaning or basket replacement when differential pressure reaches 0.5 to 1.0 bar, monitored by a differential pressure gauge or transmitter across the strainer. Duplex strainers allow switchover when the cleaning setpoint is reached without interrupting flow. For accurate sizing, reference the manufacturer Cv tables or ISO 6945 for strainer pressure-loss calculations.
Codes and Standards
- ASME B16.34: pressure-temperature ratings for metallic strainer bodies
- MSS SP-85: grey iron globe and angle strainers
- API 598: valve and strainer testing (shell hydrostatic, seat leakage)
- ASME B31.3: process piping — governs strainer placement and pressure class selection
- ISO 6945: pipeline strainers — specification and testing (international projects)
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