Temporary Strainers: Protecting Equipment from Pipeline Debris During Startup
However carefully a new pipeline is fabricated, it is never perfectly clean on day one. Weld slag, grinding dust, mill scale, rust, gasket offcuts, bolts and even tools can be left inside the pipe. When the system is first flushed and started, that debris travels straight to the most vulnerable equipment: pump impellers and mechanical seals, control valve trim, flow meter internals and heat exchanger tubes. A temporary strainer, also known as a startup strainer, is the low-cost safeguard that catches this debris before it can do any damage.
This article explains what temporary strainers are, the main types, how to size and install them, and the best practices for monitoring and removing them once the system is clean.
What Is a Temporary Strainer?
A temporary strainer is a perforated or mesh screen element that is clamped between two pipe flanges, usually just upstream of a pump, valve, meter or other sensitive equipment. It has no housing of its own; the pipe itself contains it. A flat mounting ring sits between the flanges with a gasket on each side, and a handle or tab projects outside the flange so that installers can see at a glance where a strainer is fitted.
As the name suggests, it is intended for the commissioning, flushing and early operating period. Once the line has been cleaned and the debris load has fallen, the strainer is removed and the flange joint is reassembled with a spacer or new gasket. In some services temporary strainers are left in place permanently as a low-cost protective screen, provided the pressure drop and cleaning access are acceptable.
Why Temporary Strainers Are Essential
- Protect expensive equipment: A single piece of weld slag can destroy a pump seal or score a control valve seat. The strainer costs a tiny fraction of the repair.
- Avoid commissioning delays: Damaged equipment during start-up means rework, spare parts and schedule slip.
- Maintain warranties: Many pump and compressor suppliers require suction strainers during commissioning as a condition of warranty.
- Improve flushing effectiveness: Strainers collect debris in known, accessible locations rather than letting it settle in dead legs or equipment.
- Simple and economical: No separate body, minimal installation length and easy removal.
Types of Temporary Strainers
Cone Type (Witch’s Hat) Strainers
The cone strainer is shaped like a pointed hat and projects into the downstream pipe. Its conical shape gives a large screen area and the lowest pressure drop of the three types, making it the most common choice for pump suction and high-flow lines. It does, however, need enough straight pipe downstream of the flange to accommodate its length.
Basket (Truncated Cone) Strainers
Basket or truncated-cone strainers have a flat bottom and are shorter than full cones. They are used where available straight length is limited, while still offering a good open area and dirt-holding capacity. Debris collects inside the basket, which makes removal and cleaning straightforward.
Flat (Plate) Strainers
Flat strainers are simply a perforated disc, sometimes with mesh, held in the mounting ring. They are the most compact option and can be fitted where there is almost no straight length available. Their smaller open area means a higher pressure drop and faster clogging, so they suit lighter debris loads, small lines or tight installations. They are also the easiest style to use where flow may be bi-directional.
How to Size and Specify a Temporary Strainer
Open Area Ratio
The open area ratio (OAR) is the free open area of the screen divided by the internal cross-sectional area of the pipe. It is the main sizing parameter. An OAR of 100-150 percent is a common minimum for flat strainers, while cone and basket strainers are typically specified at 150-300 percent or more. Higher OARs give lower pressure drop and longer running time before cleaning, which is important when heavy debris loads are expected.
Perforation and Mesh Size
Select the opening size according to the equipment being protected. Typical choices are 1.5 mm to 3 mm (1/16 to 1/8 inch) perforated plate for general pump protection, often lined with 20-100 mesh for finer protection of valves, meters and instruments. Fine mesh should always be supported by a stronger perforated backing to resist collapse.
Pressure Drop and Collapse Strength
As debris accumulates, differential pressure rises rapidly. The strainer must be strong enough to withstand the maximum expected differential pressure without collapsing, because a collapsed strainer can release all its trapped debris, and the screen itself, into the equipment it was meant to protect. Specify a design differential pressure and confirm the strainer’s rating.
Materials
Carbon steel and stainless steel 304 or 316 are standard. Monel, Hastelloy and other alloys are available for corrosive or seawater service. The material should be compatible with the process fluid and with the pipe material to avoid galvanic corrosion.
Specification Checklist
- Pipe size, schedule and flange rating and facing (RF, RTJ)
- Strainer type: cone, basket or flat
- Perforation size, mesh and required OAR
- Flow rate, fluid and allowable pressure drop
- Design differential pressure (collapse rating)
- Material of construction and handle/tag identification
Installation Best Practices
- Install the strainer as close as practical upstream of the equipment it protects, typically in the pump suction spool.
- For cone strainers, the preferred orientation is with the point facing upstream, so that flow passes from outside to inside and debris collects on the stronger outer surface. Pointing downstream makes cleaning easier but leaves the tip more exposed to collapse under heavy loading.
- Make sure there is enough straight pipe downstream of the flange for the strainer’s length.
- Design the piping with a removable spool so the strainer can be taken out without disturbing pump alignment.
- Install pressure gauges or a differential pressure gauge across the strainer to monitor loading.
- Tag and record every temporary strainer location in the commissioning register so none is forgotten.
Monitoring, Cleaning and Removal
During flushing and start-up, monitor differential pressure closely. A sudden increase indicates clogging and the strainer should be removed and cleaned before it collapses or starves the pump. Inspect the debris collected; the quantity and type tell you how clean the system is.
Once differential pressure remains stable through several cleaning cycles and little debris is being caught, the line can be considered clean. The strainer is then removed, the flange gap is closed with a spacer ring or the spool is replaced, and the joint is reassembled with new gaskets. For lines that will continue to carry solids in normal operation, replace the temporary strainer with a permanent Y strainer or basket strainer that can be cleaned without breaking the flanges.
Typical Applications
- Pump suction lines in refineries, petrochemical and chemical plants
- Compressor suction lines during commissioning
- Upstream of control valves, flow meters and turbines
- New pipelines, plant expansions and revamp projects
- Water and wastewater treatment plant start-up
- Power plant feedwater, condensate and cooling water systems
- Pipeline hydrotest and flushing operations
Common Mistakes to Avoid
- Choosing a flat strainer where a cone strainer fits, leading to rapid clogging.
- Not monitoring differential pressure, which can result in screen collapse.
- Leaving temporary strainers in service indefinitely without a cleaning plan.
- Fitting mesh that is too fine for the commissioning debris load.
- Losing track of strainer locations so that one is left installed unintentionally.
Temporary Strainers from Bliss Flow Systems
Bliss Flow Systems supplies the temporary strainer in cone, basket and flat styles for all common pipe sizes and flange ratings, in carbon steel, stainless steel and special alloys, with perforated and mesh-lined screens to suit your commissioning plan. We also supply the permanent strainers your plant will need once start-up is complete.
Frequently Asked Questions
What is a temporary strainer used for?
It is used during commissioning and start-up to catch weld slag, scale and other construction debris before it damages pumps, valves, meters and other equipment.
Which direction should a cone strainer face?
The preferred orientation is with the point facing upstream, so flow passes from outside to inside and debris collects on the outer surface. Some users point it downstream for easier cleaning, accepting lower collapse resistance.
What open area ratio is recommended?
Flat strainers are commonly specified at 100-150 percent open area, while cone and basket strainers are usually 150-300 percent or more for lower pressure drop and longer running time.
When can a temporary strainer be removed?
When differential pressure stays stable and very little debris is being collected after several cleaning cycles, indicating the system has been adequately flushed.
Can a temporary strainer be left in permanently?
It can in some clean services, but a permanent Y or basket strainer is usually better because it can be cleaned without dismantling the flange joint.
Conclusion
Temporary strainers are one of the simplest and most cost-effective ways to protect valuable equipment during the riskiest phase of a plant’s life: start-up. Choosing the right type, open area and screen size, installing it correctly, and monitoring differential pressure until the line is clean will help you commission faster and avoid costly damage.
Contact Bliss Flow Systems
For product selection, technical datasheets or a quotation, reach our engineering sales team at the office nearest to you, or send an enquiry through our contact page.