As a biopharmaceutical company in Ireland prepared for a pre-approval inspection at a newly built injectable production plant, the quality auditor posed a simple question that disrupted the production along the way: "Present the Y-strainer surface finish certificate from the WFI loop." Even though the strainer involved a sanitary design made of 316L stainless steel, fully polished, and appeared clean, the company had never had the surface finish of the strainer checked independently. No data was available on the Ra. The auditor instructed the biopharmaceutical manufacturer to take corrective action, requiring the problematic strainer to be substituted with another one for which documentation was available and which had electropolished finish certified as compliant with ASME BPE. This cost only hundreds of dollars, but this way the validation was delayed significantly. In pharmaceuticals, even a sanitary filter is not something that can be taken for granted. It is a component in contact with a pharmaceutical product and has to fulfill the same requirements regarding its material and finish as every valve, fitting, or piece of piping.
Summary: The components used in pharmaceutical products are sanitary filters and strainers or fluid-handling components that are built to eliminate every particle from large contaminants to microbes and other impurities in the fluids. The filters and strainers can get rid of impurities from fluids such as WFI (water for injection), cleaning steam, and other CIP products and have a body made using a 316L type of stainless steel and have polishing for making the contacting area smooth and removing any pit and crevices that may lead to further contamination in future.
Where Sanitary Filters and Strainers Are Used in a Pharmaceutical Process
A sanitary filter or strainer is utilized in a pharmaceutical fluid system to protect equipment or ensure product purity or sterility. The device's location in the process determines the filtration rate, material, and documentation that the sanitary filter or strainer will require. The most common applications of sanitary filters or strainers include water for injection (WFI) and purified water distribution loops (the strainers are located upstream from the WFI pump to protect pump impellers and downstream spray balls from pipe scale, welding slag, and construction debris, with a Y strainer with 316L perforated screens typically of 50-100 microns rating), clean steam systems (the strainers are located upstream of the clean steam trap and the sterilization point to prevent pipeline scale and rust debris to pollute the steam and sterilized surfaces, with the strainer body and the screens rated for steam temperature typically above 150 °C, while its elastomer seals should be compatible with thermal cycling during SIP operating), the return lines of CIP solution (the strainer located in the return line of CIP serves to capture product residues, gasket pieces, and contaminations washed out from the pipes during cleaning to avoid their return through the CIP pump and depositing it on the cleaned surfaces), product transfer and filling lines (the sterile filter cross section is typically 0.2 micron PTFE or PVDF cartridge in the sanitary steel house which stands as the final barrier between the product and the container thus ensuring that the delivered drug is sterilized), and vent and some pressurized gas lines (the hydrophobic filter on the vent of the WFI storage tank prevents bacteria and particles from outside from penetrating the tank during water level drop while the particulate filter on the line with compressed air or nitrogen ensures that gas coming in touch with the product is free from oil, water, and particles).
The ASME BPE standard defines the material, surface finish, and design requirements for every one of these components, and a pharmaceutical manufacturer's validation file must contain the documentation that proves each component meets the standard.
The Critical Distinction: Strainers vs. Filters
The terms strainer and filter are sometimes used interchangeably, but in a pharmaceutical context, they serve different purposes, they operate at different particle sizes, and they are designed and documented to different standards. The table below summarises the key differences.
| Characteristic | Sanitary Strainer | Sanitary Filter |
|---|---|---|
| Particle size removed | 25–100 microns (perforated screen) or 50–500 microns (mesh screen). Designed to catch visible debris — pipe scale, weld slag, gasket fragments, undissolved solids. | 0.1–10 microns (pre‑filter) or 0.2 microns and below (sterilising‑grade). Designed to remove microscopic particles, bacteria, and endotoxins. |
| Primary function | Protect downstream equipment — pumps, spray balls, heat exchangers, spray nozzles — from mechanical damage and clogging. | Ensure product purity and sterility. Protect the patient from microbial contamination and particulate matter in the final drug product. |
| Typical location | Upstream of pumps, on CIP return lines, on WFI distribution loops, on clean steam lines — anywhere mechanical debris is expected. | At the point of fill, on the WFI tank vent, on compressed gas lines, on bioreactor feed and harvest lines — anywhere sterility or purity must be guaranteed. |
| Cleaning method | The screen or basket is removable and is cleaned manually, ultrasonically, or in a parts washer. The housing is CIP‑cleaned in place. | The filter cartridge or membrane is disposable — it is replaced, not cleaned. The housing is CIP‑cleaned and SIP‑sterilised between filter changes. |
| Documentation | Material test report (MTR) for the body and the screen, surface finish certification, certificate of conformance to ASME BPE. The screen mesh size must be certified. | All of the above, plus the filter cartridge manufacturer's validation guide for bacterial retention, extractables, and integrity testing. The filter is a critical component in the sterile manufacturing process. |
| Cost (relative, per unit) | $200–$1,000 for a 1‑inch to 2‑inch sanitary Y‑strainer in 316L with electropolished finish and documentation | $500–$5,000+ for a sanitary filter housing plus the ongoing cost of replacement cartridges. A sterilising‑grade cartridge costs $50–$200 and must be replaced after each batch or after a validated number of uses. |
Types of Sanitary Strainers for Pharmaceutical Applications
In pharmaceutical applications, the most widely used sanitary strainer is the Y-strainer. Its Y configuration allows the fluid to go through a removable screen or perforated basket located in the angled part of the body. The screen collects debris, and the body can be unscrewed/unclipped for subsequent cleaning. The Y-strainer is compact and can be placed in both horizontal or vertical pipelines and allows for rather low pressure drop. The Y-strainer used in WFI or clean steam applications should be made from 316L stainless steel with electropolished surface, should be drainable, and should have Tri-Clamp connections. The screen used should be perforated 316L sheet with holes ranging from 1.5mm to 3mm or should be made from woven 316L mesh with specific micron rating.
A T-strainer, or a basket strainer, has a higher dirt-holding capacity than a Y-strainer and is utilized in lines with a greater debris concentration — such as the return limp from a large process vessel where product residues and fragments of the gasket will be expected. The basket is taken out from the top of the T-body, and it is usually mounted on the horizontal line. A duplex strainer consists of two strainer baskets located parallel to each other and is equipped with the diverting valve, which allows cleaning one basket while the other one is in operation — crucial for continuous processes where the line needs not shut down for maintenance of the strainer.
For a deeper look at how these components integrate into a complete hygienic fluid system, our article on what a sanitary fitting is explains the design and material principles that apply to every product‑contact component in a pharmaceutical process.
Installation and Maintenance: The Practices That Protect the Product
The installation of a sanitary strainer or filter in a pharmaceutical process is much more complicated than simply attaching it to a pipe. The arrangement has to be such that the instrument can be taken out for cleaning and inspection without causing contamination in the pipeline, and it has also to drain completely when the system is being emptied. Among the main rules for installation are orientation to drain (the y-strainer must be mounted with leg downwards in the horizontal segment of pipe, which makes the strainer completely drained once the system is emptied — if the y-strainer is installed horizontally or with the leg pointing upwards it can trap liquid causing contamination), accessibility for cleaning (the strainer has to be positioned such that it is possible to remove the screen, but not have to cut the pipeline for this — while a Tri-Clamp strainer can be removed within minutes without tools, butt welded strainer needs manual cutting and welding); monitoring the pressure drop (a pressure gauge across the strainer or filter tells directly about clogging of the screen — increasing the pressure drop means that the strainer has to be cleaned or the filter cartridge needs to be changed before the process flow is restricted) and keeping records of cleaning and replacements (the cleaning of the strainer screen or filter cartridge has to be one of GMP operations that need to be documented — the entry in the equipment log should include time, person, reason, as well as part number and lot number of the new component, and this information should be available for the auditor).
Maintenance of a sanitary strainer includes periodical screen inspection and cleaning. The frequency of cleaning is determined by the amount of debris the strainer receives. For example, a strainer on an entirely new WFI loop can be cleaned weekly, while a strainer on a clean and old system requires cleaning only once a year. The screen must be visually inspected for any breakage, as when there is a torn mesh or cracked perforated plate, which shall be exchanged once it is discovered. With a faulty screen, debris can move downstream, which is the reason why strainer is installed in the first place. The body shall also be visually examined for rust and corrosion, as well as rouging, which is a reddish-brown deposition of iron oxide which can form on stainless steel in water and steam systems. In case a strainer discloses signs of rouging, it must be electropolished or replaced, as rouging implies that the surface is no longer in its corrosion-resistant condition.
How Eagle Fittings Supports Pharmaceutical Filtration and Straining
Eagle Fittings produces Y-strainers and filter housings that comply with pharmaceutical industry regulations since they are made of 316L stainless steel that meets ASME BPE requirements. Manufacturing process of our sanitary strainers includes electropolishing product contact surfaces, fitting devices with Tri-Clamp ports for easy cleaning and removal, and providing with documentation package which includes material test report, surface finish certification, and certificate of conformance. Our strainer designs and production processes also comply with conditions for WFI, clean steam, CIP and product transfer purposes which makes them an integral part of pharmaceutical fluid systems.
For a comprehensive look at the broader range of hygienic fluid handling components, our article on pharmaceutical equipment pipes and fittings under BPE standards covers the full system of tubing, valves, and fittings that must all meet the same ASME BPE standard.
Frequently Asked Questions
What is the difference between a sanitary strainer and a sanitary filter?
The sanitizing strainer utilizes a filtrating apparatus to eliminate substantial particles — that is to say, particles 25 microns or more — although from here on all particles must be removed using the filter. It shields the equipment installed downstream from mechanical debris. The sanitary filter utilizes a disposable cartridge to filter minutiae including particles smaller than 0.2 microns. The strainer cannot be used repeatedly while the filter cartridge has to be replaced after every batch of filtration.
What material is used for pharmaceutical sanitary strainers?
316L stainless steel is used in combination with a controlled sulphur content of maximum 0.020%. The surface which comes into contact with the product is polished through electropolishing technique to a surface finish of 20 microns or better. The strainer too is made from 316L stainless steel and consists of a perforated plate or a woven mesh. The elastomer seals are made of FDA compatible EPDM, Viton, or PTFE depending on the requirements of the process fluid and the CIP/SIP chemicals used in the processing.
How often should a sanitary strainer be cleaned in a pharmaceutical WFI loop?
At the start-up stage of a newly installed WFI loop, the strainer may have to be cleaned on a weekly or even daily basis until the debris (pipe scale, weld slag, installation debris) is completely washed out. After the loop is matured and the load of debris is stabilized, the cleaning period may be extended to quarterly, semi-annual, or annual. The cleaning of the strainer depends on whether the pressure drop across it has reached certain level which is usually 50–100% higher than that of a clean strainer.
What is a sterilising‑grade filter, and when is it required?
A sterilizing-grade filter is a filter cartridge that has undergone strict tests to demonstrate its efficiency of filtering out a minimum of 107 colonies of Brevundimonas diminuta bacteria for every cm2 of the filtering surface in accordance with ASTM F838. It has a filter dimension of no more than 0.2 microns and is used as the last filtration step prior to filling sterile drug formulations into the containers. The filter has to be validated for the integrity prior and after usage, and documented in the batch record of the manufacturing procedure.
References
- ASME BPE — Bioprocessing Equipment Standard. The defining standard for the design, materials, surface finish, and documentation of pharmaceutical‑grade fluid handling components, including strainers and filter housings.
- FDA — Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing. Regulatory guidance on the use of sterilising‑grade filters, integrity testing, and the documentation required for sterile pharmaceutical manufacturing.
- 3‑A Sanitary Standards — Strainer and Filter Standards. The sanitary standards that define the design, material, and cleanability requirements for strainers and filters used in food, dairy, and pharmaceutical processing.
- Alfa Laval — Sanitary Strainers and Filters for Pharmaceutical Applications. Global manufacturer of hygienic strainers, filter housings, and process equipment for the pharmaceutical and biopharmaceutical industries.
Sanitary filters and strainers for pharmaceutical applications are a small component in a large and complex process, but they are a component that can stop a regulatory inspection, delay a validation, or — if they fail to capture the debris or the bacteria that they were designed to catch — compromise the sterility of a drug product that will be injected into a patient. The strainer in the WFI loop, the filter in the fill line, and the strainer in the clean steam trap all have to be made out of the same materials, and must have the same finish, ease of cleaning, and documents meeting the rigorous standards. It is necessary to install them properly, clean or replace them regularly, and keep a record of them in the logs. Eagle Fittings produces sanitary strainers and filter housings according to ASME BPE standard with 316L grade materials, electropolished finish, Tri-Clamp fittings, and necessary documentary evidence. After all, in the industry of pharmaceuticals, all components in contact with the final product must undergo the same sanitization and certification standards as the final product itself.
