Attributes & Outcomes Of High-Quality Bubble Point Testing For Filter Integrity

Fast, Easy, Cost-Effective Bubble Point Testing Of Filters In Industrial Applications Can Drive Down The Rate Of System/Product Inconsistency, Flaws, & Failure


Filter Integrity Testing Is An Essential Function Of Industrial Cleaning And Testing Service Providers

Any industrial testing and cleaning professional can confirm that particle size discrimination is the primary mechanism of particle removal employed by any filter in any system. In many systems, filters play a vital role in both protecting ongoing system function and ensuring a high level of purity (and even sterility) for materials passing through. Inappropriately sized, improperly installed, or otherwise flawed filters can and are frequently responsible for decreased system function, increased strain on (and deterioration of) essential system components, and total system failure [1].


Bubble Point Testing In Industrial Applications Improves Efficiency

A long-standing, preferred method of integrity testing, bubble point testing in industrial applications uses natural capillary rise to gauge relative values of the membrane’s largest pore size [2]. Because of the risks that problems of filter integrity pose to system operation and efficiency, industrial bubble point testing has become a critical tool for verifying that filter membrane/fabric and (by extension) that the manufacturing batch and/or installation process is flawless and fitted IAW SAE ARP901.

That said, failure to contract an experienced industrial cleaning and testing professional for bubble point testing of filters can mean failing to prevent (and even creating) the problems firms seek to avoid through regular testing. Contact the industrial cleaning and testing experts at Precision Fabrication & Cleaning or continue reading to learn the benefits and risks of bubble point testing and how high-quality bubble point testing administration can improve filter manufacturing and in-line filter function.


What Is Bubble Point Testing Of Filters?

Like other non-destructive, non-contaminating types of industrial cleaning and testing, bubble point testing in industrial applications aims to confirm the structural integrity and appropriate installation of the selected filter/system in compliance with specific regulatory standards (for example, IAW SAE ARP901) [3, 4]. There are a variety of different times for bubble point testing in industrial applications, the appropriateness of which depends on the specific industry, system, and filter function.


How Does Bubble Point Testing For Filter Integrity Work?

Generally speaking, bubble point testing in industrial applications calls for partially flooding the system with some fluid (sometimes water, though ethanol, iso-propanol, and n-propanol have lower surface tension and are preferential, as they present less risk of overpressurizing the system during bubble point testing) [5].

While all the pores in the filter membrane and the system’s downstream piping are filled with fluid, the filter surface and upstream piping are filled with gas. An experienced industrial cleaning and testing service provider then increases the gas pressure in the system slowly and incrementally, observing the system to pinpoint the point at which the first gas bubble entirely passes through (becoming separated from) the membrane. The pressure measurement at this, the “bubble point” sought after in any industrial bubble point testing procedure, is then plugged into the Laplace equation of capillary pressure to calculate the largest pore size.


What Is The Purpose Of Bubble Point Testing In Industrial Applications?

Specifically, the goals of bubble point testing for filter integrity include determining the largest pore-size in the filter membrane (looking for out-of-size or oversize pores) as well as identifying filter damage, ineffective seals, and/or system leaks [5]. Industrial bubble point testing professionals accomplish this by measuring the critical pressure of airflow (applied across the full thickness of the membrane/fabric) needed to force gas through the largest pore in the wetted filter [6].

This process constitutes both a fast and cost-effective form of integrity testing, and often only requires by-hand actions and taking hand-held measurements. It is not surprising, then, that bubble point testing is a popular method for estimating or confirming pass/fail acceptability of filter pores (based on known pressure values for acceptable pore sizes). That said, well-qualified industrial cleaning and testing service providers take precise measurements and account for variations in pore shape and distribution in their calculations [7].

Consequently, some industrial cleaning and testing service providers are able to be more exacting in their industrial bubble point testing procedures and more exact in their results.


Requirements For Conducting Industrial Bubble Point Testing

In filter manufacturing, bubble point testing of filters is a pre-shipment protocol verifying that filters’ pore sizing is consistent and IAW SAE ARP901. Likewise, in-system filter integrity verification using bubble point testing — both pre-use, in-process, and (especially for sterilization-grade filters) post-use — is critical to a wide array of manufacturing, food and beverage, aerospace, pharmaceutical, and bioprocessing firms. Nevertheless, in many industries, only post-use bubble point testing is mandated (with no more than about one-quarter of firms also conducting pre-use or in-system bubble point testing for filter integrity) [8].


Bubble Point Testing Functions & Benefits At Different Times During System Operation

  • Bubble point testing of filters pre-use/pre-sterilization: Safer than pre-use/post-sterilization bubble point testing; helps system operators ensure that filters’ design and installation is acceptable IAW SAE ARP901, yet avoids the risk of contaminating newly sterilized equipment through testing mismanagement.
  • Bubble point testing of filters pre-use/post-sterilization: The least common time for bubble point testing of filters; helps system operators determine whether sterilization processes damaged filters. Relying on manufacturers’ promised bubble point testing for pre-shipment materials is largely unrecommended [8].
  • Bubble point testing for filter integrity in-process: Though this requires temporary shutdown of continuously operating systems, it can detect system malfunctions (like leaks and ineffective seals). In-process bubble point testing for filter integrity also helps identify abnormally damaged filters or the expected, natural widening of filter membrane pores during extended use (which eventually will reach unacceptable levels); this helps system operators monitor system function and proactively maintain filter integrity [9].
  • Bubble point testing for filter integrity post-processing: The most common time for bubble point testing of filters (for 100% of firms across all industries), this may detect leaks and perforations that occurred during normal system operation; it helps indicate an immediate need for batch recall and reprocessing [10].


Only Proper Administration Of Bubble Point Testing Procedures Can Attest To The Appropriateness & Adequate Functioning Of Filters In Industrial Systems

Firms should not consider manufacturers’ pre-purchase bubble point testing sufficient evidence of filters’ appropriateness for their specific systems (or adequacy IAW SAE ARP901) [10]. Consequently, numerous guidelines (though not regulations) recommend pre-use and in-use bubble point testing by a well-qualified industrial cleaning and testing administrator as well as following the mandated post-use testing protocols.

That said, so long as all bubble point testing is conducted by a well-qualified industrial cleaning and testing service provider such as PFC, firms can expect that regular, high-quality bubble point testing of filters will result in a dramatic decrease in filter failure frequency. This is in addition to a notable reduction in the number and duration of shutdowns due to either filter manufacturing error or in-line filter failure.



  1. National Service Center for Environmental Publications (NSCEP)
  2. Researchgate

About PFC: Precision Fabricating & Cleaning is an innovative, highly qualified company with unique capabilities to accomplish a wide range of industrial testing and Precision Cleaning services, specializing in Hydrostatic Testing, Oxygen Cleaning Service, Cryogenic & Cold Shock Testing, Mobile Field Cleaning, Passivating/Passivation, High Purity Cleaning, Ultrasonic Cleaning, and so much more.

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