Leak testing 101 – Part 1

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Not too long ago, when you wanted a product to be leak-proof, you simply put it under water, made sure it didn’t bubble, and thereby concluded there were no leaks. Such “bubble testing” takes time and depends on the operator’s ability, making it totally inappropriate for the modern production environment. Also, it doesn’t generate the quantitative measurements that are the lifeblood of quality assurance engineering.

Dry-air leak testing methods—some of which can detect leaks as small as 0.01 standard cubic centimeters per minute (sccm)—are the methods most commonly used today by a wide range of industries—from medical devices, to automotive, to appliances, and aerospace, among others. These dry air methods enable quality managers to define leaks quantitatively.

“No leaks allowed” standards are concepts of the past. There are a variety of dry air leak test methods and best-practice techniques for each type of method, which will enable compliance to ISO 9001 and comparable quality management standards to be achieved. Generally speaking, these dry air leak test methods include;

  • Pressure testing
  • Differential pressure-decay testing
  • Mass flow leak testing

In addition, tracer gas testing and especially helium mass spectrometer leak testing, are used in more demanding applications where leaks as small as 10-5 standard cubic centimeters per second (sccs) must be detected in a production environment. If one truly understands leak testing application requirements and best practice techniques for these various leak test methods, the selection of which type of testing to perform is a rather straightforward matter.

The first step in designing a leak testing solution is to correctly define what the leak limits are. Leak testing applications laboratories begin with an engineering analyses of a specific application to determine and quantify how much a product or component can leak. Often, correlation studies are performed to verify if it is possible to use dry-air test methods instead of hydraulic fluids. Sample parts are tested as part of an initial engineering analysis. These determine the production requirements and leak standards to be achieved so that quality engineering of test solutions can begin. The first step in this process is to select the leak testing method that is the best match to application requirements.

In this “Leak Testing 101” series we will discuss the various dry air leak testing methods and the issues and techniques that affect testing costs and gauge repeatability and reproducibility (GR&R).

First, let’s take a look at the pros and cons of pressure-decay testing.

The big plus of pressure-decay testing—or at least the thought behind it—is that the leak detectors for pressure-decay leak testing have the lowest upfront cost. It is probably for this reason that the method is still in use, although in many applications the real costs of pressure-decay testing are actually much higher than many realize.

In the pressure-decay method for leak testing (see figure 1), a part is pressurized, the test circuit is isolated, and the pressure drop associated with a leak is measured. A transducer reads the pressure change. Calculations then convert these time/pressure readings into a measure of leakage rate. The higher costs of pressure-decay testing stem from the difficulties inherent in the test methodology. Pressure-decay leak testing is relatively difficult because measurements are highly vulnerable to changes in testing conditions such as drafts or temperature and there are often difficulties in determining the volume of test parts and test circuits, which must be known in order to calculate results.

Pressure Decay Method of Dry Air Leak Testing

Pressure Decay Method

Also, pressure-decay leak testing requires two measurements of pressure with sufficient elapsed time between measurements. When speed of testing is an issue, this built-in delay makes the pressure-decay method less desirable. More important, the two measurements and the time lapse significantly increase the potential for measurement error. The amount of time you need to wait between measurements varies. Sometimes, long intervals between measurements can make for extreme accuracy, but these long wait times are typically not practical. The larger the part volume, the longer it takes to measure the pressure drop. Moreover, very large flows are also impractical with pressure decay, because when pressure drops very fast, it will probably not be measured accurately.

Thus, although pressure-decay leak testing instruments have a relatively low upfront cost, the extra time it takes to perform testing (if the results are reliable enough for the given application) is another expense that needs to be factored in to overall cost. It can still be the best leak test method for a specific application, but the trend lines are in the other direction. Most applications now require tighter GR&R even for very low leak rates, often with large volume parts, and with a desire to keep test cycle times to the bare minimum to cut overall testing costs.When you factor all these considerations in, it often leads one to use other leak test methods instead.

In the upcoming issues of this “Leak Testing 101” series I will discuss differential pressure-decay testing, mass-flow leak testing, temperature compensation issues, and many other topics. By the conclusion of Leak Testing 101, my goal is to bring all quality managers up to speed on the real factors that affect leak testing cycle times, costs, and reproducibility.

If you would like your specific questions on best practices for leak testing (and other testing topics) to be discussed in future articles, please leave your comments and suggestions in the Comments area below.

ABOUT THE AUTHOR

Jacques Hoffmann’s picture

Jacques Hoffmann

Jacques Hoffmann is founder and president of InterTech Development Co., a world leader in test-centric assembly specializing in automated leak and functional testing with mass flow, hydraulic, helium, or pressure decay technology (ISO-17025 accredited). InterTech Development Co.-engineered solutions are used by hundreds of quality management, product design teams, and manufacturers worldwide and the company’s worldwide support organization maintains offices in North America, Asia, and Europe.

Note:  The above article has been reproduced from an article written by the author for Quality Digest

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M-1075 leak detectors optimize leak and functional testing processes with advanced Ethernet IP- compatible instrumentation.

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InterTech M1075 – for unsurpassed leak testing speed and accuracy

InterTech M-1075 Leak Test instrumentation and functional test stands generate real time quality control data, facilitating the integration of manufacturing and management information systems.

The Challenge

  • Manufacturers want instrumentation designed to manage all their functional testing requirements. For high volume leak and functional testing they want instrumentation that simplifies integration with in house networks.
  • This includes integration to Manufacturing Execution Systems (MES) and Enterprise Resource Planning Systems (ERP). Instrumentation
  • Check out IDC design report DR130 for full details on how to optimize leak and functional testing processes with advanced Ethernet IP-compatible instrumentation. 

Follow the link at DR130_web site for unique engineering insights from leading leak detection experts.

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Achieve the Failsafe Standard Required for Home Medical Equipment – AND Control Costs

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Medical Devices for Home Use Must Achieve Fail-Proof Standards

Improved clinical outcomes are now possible in a growing number of applications where patients are able to safely operate medical devices in their home environments.

Unlike medical devices used in clinical settings where trained technical staff is usually on-hand to verify that devices are operating as designed, medical equipment designed for patients’ use in their homes must be more thoroughly tested and proven to be reliable before release to the patient’s home environment.

In practical terms, this means that testing during assembly must be more extensive and more sensitive, without adding significant cost

Challenge:

Multi-Valve, Multi-Port Testing
An example of this trend is dialysis machines designed for patient’s use in their home environments. Achieving fail-safe standards is complicated by the complexity of dialysis equipment. Multiple solenoid valves must be controlled with precision and many dozens of ports must be operable at all times.

Solution:

InterTech’s Multi-Channel MED75-COMBO Leak/Flow Test Instrument
A new multi-channel test instrument from InterTech performs more than 100 leak tests and flow tests, combining pressure decay and mass flow test methods, in under 10 minutes for each unit.

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The Five Rules of Effective Leak Testing

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Designing a leak-testing system that meets appropriate reliability and reproducibility standards requires a thorough understanding of relevant test methods and technologies. That knowledge base is rarely available in house.

Penny wise, pound foolish

It is a distressing fact that leak-testing missteps are all too common in the medical device industry. Unlike some industries that traditionally enlist experienced outside applications engineers to develop turnkey test systems, many device manufacturers try to keep this in-house under the misguided notion that they are controlling costs by not outsourcing the project. On the contrary, attempting to design a test system without an encyclopedic knowledge base of test methods and technology typically will add considerable cost to assembly and test operations. These are not trivial mistakes—they can increase production costs by 25%, sometimes more.

Here are five critical factors to bear in mind when developing cost-effective and accurate leak-testing systems. It’s my professional opinion that they are often overlooked by device manufacturers.

1. Leak test specifications should match real-world requirements

There are two ways that leak-testing specifications can be “off”— by being too loose or too tight. Always correctly identify the leak test specs. If they are incorrect, you will pay for it one way or another.

When the specs are too tight—this is widespread across the medical device industry—devices and parts that, in fact, meet requirements will be rejected. Unnecessary rejects add cost in terms of the time and materials used to fabricate them as well as the engineering resources that go into redesigning systems to attenuate defect rates, which could be significantly reduced simply by optimizing the specs. That’s the least of it actually. Leak testers designed according to overly tight specifications will almost always create unnecessary costs. For example, these systems run test cycles that are as much as 40% slower than they need to be.

At the other extreme, poorly understood specs that end up being too loose are the stuff of headlines, resulting in product recalls, lawsuits, negative branding and customer flight. The impact of loosely defined specs is difficult to quantify, but it should compel companies to heed the consequences of product failures. What might not be understood as clearly is that taking precautions to the extreme by setting leak testing specs too tightly also has an impact.

It cannot be emphasized enough that the first step should always be to correctly define leak test specs so that appropriate test methods can be designed. That is the cornerstone of CGMP for any leakproof medical device. If accuracy requirements are not too high and testing can be done at relatively low pressure—at 10 psi for a plastic moulded part, for example—an upstream test usually will suffice. In medical applications where the leakproof requirement is 1 sccm or less or where the part must function at higher pressures, more-accurate downstream test methods involving added tooling and fixturing costs may be necessary. Downstream leak-testing systems that deploy mass flow transducers or other sensing technologies are not exposed to the test part pressure and, therefore, will provide an accurate measurement that is independent of test pressure.

2. Software integration is key

Assemblies built by in-house manufacturing engineers or with the assistance of outside machine builders who are not testing experts, per se, will typically require additional test stands. This expense could have been avoided if the code for high-speed data acquisition had been written correctly and tightly integrated with machine controls. The idea that you can cut customization costs by using generic machine control software and stringing together modules is a widespread misconception. I can think of numerous instances where additional hardware costs could have been avoided by using custom software engineering at about 10% of the cost. For example, a valve that typically takes 50 milliseconds to open with traditional software controls opens in one millisecond or less when best-practices leak testing solutions (data acquisition software tightly integrated to machine controls) are employed.

For low-cost products such as medical check valves and similar applications that require high-speed testing, the problems caused by reliance on generic testing software tend to be magnified. Control engineering programs that allow users to string together several functional units on a screen are not cost-effective for high-speed testing. There is a trade-off in data acquisition speed. While it’s easy to add function upon function to the software, you end up with extremely bloated and sluggish applications.

As incredible as it may seem, some medical device manufacturers are still trying to use Windows XP software or comparable programs created for office environments in their production plants. Real-time operating systems for industrial environments have been the proven superior alternative for more than a decade.

3. Calibrate the system, not just the instruments

Calibration and traceability of leak-test measurements should be simple. Complicated calibration methods, at best, slow down production; at worst, they are unreliable or inaccurate. CGMP guidelines require that leak test instrumentation and system software be able to adequately store data. This includes logging parts by serial number for subsequent analysis.

The most common calibration mistake medical device manufacturers make is assuming that an accurately calibrated leak detector ensures accuracy of the test system as a whole. A perfectly calibrated leak detector is useless if it is hooked up to fixtures that have seal creep or other problems compromising the integrity of the leak testing system. Before being calibrated, instruments should be connected to the test fixtures and to the automated production line where the parts will be tested and assembled.

4. Fixtures must meet leak-test specifications

An assembly and test system with off-the-shelf test fixtures that have been cobbled together typically will not meet gauge repeatability and reproducibility (R&R) requirements. This is especially true for applications with demanding leak testing specs and tight tolerances. Companies that try to get away with spending less on fixtures may, in fact, be adding weeks or months of engineering time as they rework their systems to get the gauge R&R right.

An infusion pump, for example, cannot be leak tested without the use of very precise fixtures that typically have a surface roughness lower than the 16 Ra of common off-the-shelf fixtures. A 2-L lapped finish is not cheap to machine, but if your test specifications require fixturing tolerances of 10% or less, then you probably won’t be able to avoid this expense. Thinking about fixture requirements correctly in the first place will save money and ensure that CGMP-quality standards are consistently achieved.

5. Component traceability is essential for recalls and quality assurance

The basics of cost control in test-centric assemblies (i.e., test-intensive assembly processes, often including leak testing) at various stages of product development are not always well understood.1 Device manufacturers with an eye towards QA and cost controls recognize that parts traceability and logging test data by part number must be an integral part of the leak-testing process.

Traceability data is essential for process optimization to streamline production. Storage of test data at each step of the production process is needed for statistical process control, which underlies most QA systems and ISO 13485:2003 compliance.

There are numerous affordable methods that make traceability painless: bar code labeling systems are commonly used and laser-marking systems sometimes can be added on. Archiving test data for analysis of process improvements will boost yield, minimize defects and ensure that products that may jeopardize patient safety are never released to market.

Ask the experts

The intelligence, dedication and expertise of your in-house engineering team or the contract machine builders designing your assembly chassis may be peerless. But will they be able to achieve the cost controls, accuracy and gauge R&R standards of applications engineers whose sole focus is on testing and who have solved an array of leak-testing challenges? Think of it this way: if you need life-saving neurosurgery, would you select a neurosurgeon who does a dozen or so operations a year or one who does a dozen or so operations a week?

The aforementioned examples of leak testing–related shortcomings and failures in the medical device industry are just the tip of the iceberg. Nothing can replace the knowledge base of testing engineers who design, customize and calibrate leak detectors on a daily basis and who have created hundreds of test-centric assembly systems. Reputable testing applications engineers will provide no-cost evaluations of your test system requirements and make recommendations on test technology required to meet ISO 13485:2003 and CGMP standards at the lowest possible costs to stipulated gauge R&R. Such evaluations are available both for existing assemblies and leak testing systems that are still on the drawing board.

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Real Time Monitoring Software

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For Optimizing Test Conditions In Leak Testing Applications

Real Time Monitoring software for optimizing test times and isolating problems in leak testing applications is now available from InterTech Development Company, arguably the world’s leading authority on test-centric assembly specializing in automated leak and functional testing. InterTech’s S3085 monitoring software helps provide users with the means to show real time traces of how their test instrumentation transducers are performing versus actual cycle times.

The InterTech S3085 Software enables data transfer between a PC and test instrumentation and can display test records from up to 8 InterTech M-10×5 test instruments. It has the facility to automatically calculate R&R percentages based on the number of trials performed. All data can be saved in a Microsoft Excel™ spread sheet file format, facilitating SPC analyses. Data can also be viewed on a monitor including data, shift, channel and test status. Fully Windows compatible with the ability to record two million test records, InterTech’s S3085 monitoring software costs US $1800.

Jacques Hoffmann, President and Founder of the worldwide InterTech Development Company comments that InterTech’s S3085 monitoring software provides users with the means to better understand and assess complicated testing phases in their applications in a real time manner. Hoffmann says, “Through InterTech’s leading edge approach to leak testing applications worldwide, we saw the need for software tools that could enable users to intuitively diagnose issues with their testing process through real time graphical displays, and this is why and how the InterTech S3085 monitoring software came to be developed.”

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Test-Centric Assembly

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Uptime Optimization Services

18 station chassis optimized for test centric assembly

Machine builders, automotive component manufacturers, and others seeking faster test-intensive assembly operations can now access InterTech Development Company’s Uptime Optimization consulting services that detail how to incorporate on-line calibration and validation of test technology, automation of temperature compensation during testing, and similar engineering that minimizes or eliminates previous needs to shut down test-centric assemblies for recalibrations. InterTech Development Company engineers estimate that a combination of solid state capabilities for online recalibrations can eliminate up to 60 minutes of assembly downtime in each 8-hour shift using machines with leak testing stations.

Jacques Hoffmann, President of InterTech Development Company comments that many assembly operations are straddled with mechanical type calibration and validation processes that are now obsolete. Hoffmann says, “Machine builders that are adding test technology as a secondary consideration in a larger assembly often do not know that they are using substandard leak testing technology that slows down production processes. One of the more straightforward ways to optimize production uptime is by adding electronically self-calibrating leak testers that automatically validate entire test systems while they are in operation. Another method is by using technology that can automatically adjust testing and interpret results correctly for parts testing at different temperatures, such that cooling of recently cast parts isn’t necessary. These are some of the ways in which InterTech Development Company can help machine builders and assemblers re-engineer processes to eliminate downtime.”

The world’s first production line leak detectors featuring electronic technology for self-calibration and system validation (CalVal) were introduced to assemblers by InterTech Development Company in 2004. Automated Temperature Compensation was developed and introduced by InterTech Development Company in 1995.

InterTech Development Company is a world leader in test-centric assembly specializing in automated leak and functional testing with mass flow, hydraulic, helium, or pressure decay technology (ISO-9001-2000 International Standards for Quality Management). IDC-engineered solutions are used by hundreds of automotive components manufacturers worldwide, among other assembly-intensive manufacturers. InterTech Development Company’s worldwide support organization maintains offices in North America, Asia, and Europe.

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Medical Device Testing – Some InterTech Insights

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Medical device – Current Good Manufacturing Practices

Which medical devices require leak testing, flow testing, crack pressure testing, electronic calibration or other medical device testing for strict adherence to cGMP?

Medical device cGMP requires stringent testing standards for a wide range of medical products and medical devices. A short list includes:

  • laparoscopic instruments
  • blood collection kits
  • IV bags
  • medical tubing
  • medical check valves
  • obturators
  • catheters
  • oxygen delivery systems
  • insulin pumps
  • pacemakers
  • syringes
  • medical and pharmaceutical packaging
  • pen injectors
  • implanted medical devices


Which tests are critical to the cGMP of medical check valves

Plastic medical check valves need to work automatically with control by a person or any external control. An important concept in check valves is the cracking pressure, which is the minimum upstream pressure at which the valve will operate. Typically the medical check valve is designed for and can therefore be specified for a specific cracking pressure.

cGMP of medical check valves usually involves both leak testing and crack pressure testing. The most economical solutions combine both types of tests at a single test stand and use multi-channel leak test instruments.

Which tests are required for cGMP of on-demand oxygen delivery systems?

The triggering sensitivity of demand oxygen delivery systems is critical to the functionality of this type of medical device. Vacuum levels must be precisely calibrated to preclude both false triggering or difficulty in triggering such that patients’ breathing can be in sync with normal respiratory cycles.

cGMPs require that each unit is both thoroughly tested for function and fully calibrated.

Calibration is usually two-fold—

1) a sensitivity calibration monitors the pulse volume while adjusting the sensitivity potentiometer, and

2) a manifold calibration monitors the pulse volume while the flow is manually adjusted.

There are a wide range of oxygen delivery system product designs. Generally speaking, cGMP testing of such medical devices will minimally ensure that the device does not trigger unintentionally, checks that all pulse settings meet required volume limits, and meet flow test specifications. Usually ensuring that these medical devices also work in low-battery conditions is part of the functional testing process

Why and how is testing critical to medical product and medical device GMP?

Unlike sampling, GMP (Good Manufacturing Practice as defined by 501(B) of the 1938 Food, Drug, and Cosmetic Act (21USC351) looks at the integrity of the manufacturing process itself that is used for medical device manufacture.

An extremely important part of GMP is documentation of every aspect of the process, activities, and operations involved with medical device manufacture. If the documentation showing how the product was made and tested (which enables traceability and, in the event of future problems, recall from the market) is not correct and in order, then the product does not meet the required specification and is considered contaminated (adulterated in the US).

Additionally, GMP requires that all manufacturing and testing equipment has been qualified as suitable for use, and that all operational methodologies and procedures demonstrate that they can perform their purported function. This bears on the integrity and FMP of a wide range of medical products and devices, such as leak testing blood collection kits and implanted medical devices such as pace makers, or flow testing obturators and other laparoscopic instruments, crack pressure testing of medical check valves, calibration of on-demand oxygen delivery systems, or functional testing such as the sufflation and insufflation capabilities of laparoscopic instruments.

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