Automation 101: Automated Leak Testing Methods

You’ve heard “automated leak testing methods” mentioned on the plant floor or maybe you have been involved with your product’s current leak testing procedures. Either way,  if you want to learn more about the overall topic in detail, we’re here to help. In this article, we cover the basics of manufacturing leak testing, a variety of different test methods and considerations for automating leak test processes that apply to any industry or product.   

Manufacturing Leak Testing: Defined 

Let’s start by defining leak testing in industrial manufacturing. Technically speaking, there is no such thing as “impervious” in the world of material science: With enough pressure, heat, speed or force, particles of tiny sizes can pass through any common plastic, metal, glass, paper or wood material. For this reason, special engineering evaluations must be employed to define the permissible level of leakage that can occur in a material while still performing as intended.  

You might next ask what “as intended” means. This is both a question of design intent as well as regulatory compliance. For example, on any given over-the-counter pill container, you’ll notice both a threaded cap and an adhesive seal. The threaded cap serves as a general dust guard (as well as child safety device, in many cases), and the adhesive seal as a much higher level of protection against contamination and spoilage between the time of manufacturing and purchase. In addition, the container itself is designed to protect the contents from foreign contaminants. On top of the manufacturer’s interests of quality and safety in their products, separate regulatory bodies such as the FDA have requirements around these types of seals so as to ensure a consistent expectation of safety across all manufacturers making similar products. 

From this example, we now see that the intent of the container and each seal varies by purpose as well as according to the regulations it’s intended to satisfy. These various requirements all translate back to permissible leakage limits that are to be tested against during the manufacturing process.  

No matter the industry, there is likely a regulatory body requiring testing, or a third-party agency prescribing testing. In the U.S. alone, nearly everything you purchase or consume falls under a federal or federally recognized authority. Here are a few examples: 

• The EPA governs devices that may leak environmentally impactful emissions.
• The FDA and USDA govern food and pharmaceutical industries.
• OSHA governs workplace safety and industrial hygiene, involving things such as bloodborne pathogen disposal containers.
• FMCSA (Federal Motor Carrier Safety Administration) governs freight containers. Producing parts, containers, or devices into markets regulated by bodies such as these all require some level of leak testing to be considered compliant, safe, and allowable for use.  

If leakage limits are determined and integrated into engineering designs up front, then why do we need to test?  Good question. There are several answers. In short, we test to achieve the following goals:

• Customer satisfaction 
• Quality assurance 
• Risk mitigation 
• Regulatory compliance   
• Audit and recall defense 

Automated Leak Testing Methods

Now that we understand what leak testing is and why it’s so crucial, let’s look next at how leak testing can be performed in an industrial manufacturing process. Then we’ll address how to automate these methods.  

Leak testing an industrial product can be distilled down into three categories: 

Noncontact testing: Using optical, x-ray, acoustical or other visual/sound inspection techniques, leaks in certain containers or assemblies can be discovered indirectly, without contact of the test subject. Non-intrusive tests tend to be inexpensive and low resolution, more for locating leak sources once a leak has already been identified, instead of proactively testing for potential leak points or leak rates.    

Hydraulic testing: Using fluids such as water or glycerin, leaks can be tested and found hydraulically by submerging the test subject and monitoring for either inflow or outflow. A good example of a hydraulic test is to fill a test subject with compressed air, submerge it in a water bath, and look for bubbles emitting from a leak point. Hydraulic methods are a middle-of-the-road approach to leak testing, offering a blend of cost economy to medium resolution leak detection.    

Pneumatic testing: Using various inert gases, pneumatic testing can more accurately measure leak scenarios of smaller leak rates and with higher precision than either noncontact or hydraulic testing methods. Pneumatic tests can evaluate both inward and outward leaks with high fidelity, and even quantify the exact amount of the leaked media. Pneumatic testing offers the highest resolution and precision measurement of leak points and leakage rates.  

A Closer Look at Pneumatics

With pneumatic methods being our best bet for industrial leak testing, we’ll continue on to discuss the three most common methods of performing these tests in an automated manufacturing environment.  

1. Pressure Decay 

The pressure decay method consists of charging the test part with a prescribed pressure of compressed gas, and then monitoring any drop in pressure within the part over a fixed period of time. If the pressure measured inside of the part decreases during the test, a leak to the atmosphere would be suspected. For parts where a certain amount of leakage is acceptable, the difference between initial and final pressure readings is used to determine pass/fail.  

2. Vacuum Decay 

The vacuum decay method consists of pulling a vacuum on a test chamber, in which the test part resides and is sealed. The vacuum level in the chamber is monitored for any increase in pressure (or decrease of vacuum) over a fixed period of time. If the chamber’s vacuum level decreases, a leak through the part that added air into the test chamber would be suspected. As with the above test, if a certain leakage rate is acceptable, the difference in initial and final vacuum readings determines pass/fail.  

3. Mass Flow  

The mass flow test is used for parts that are either quite large or cannot structurally withstand static pressure or vacuum. In this test, a flow of air or inert gas is sent through the test part. The amount of gas sent to the part is precisely measured against the amount of gas that escapes the part, compared to the allowable leakage rate, and this difference is used to determine pass/fail.

How to Automate Leak Testing

Automated machinery can be built to perform any of the above testing methods, to a wide range of semi-automatic to fully-automatic levels. At its most fundamental level, automating a test procedure consists of human handling of the part and test connections, while the machine performs the test itself, displaying pass/fail results upon completion.  Adding layers of automation on top of this foundation can include: 

• Automatic part inspection to test for proper assembly
• Robotic part handling from a continuous or batch process feed into the machine
• Data recording and archiving of test results
• Automatic rejection of parts that have failed testing
• Autonomous machine calibration and “self-checks,” and more.  

When considering automation options for your leak testing project, organize your interests into process objectives based on what existing production challenges you want to address. Some examples include:   

• Improve test reliability or eliminate “false positives.” This introduces industrial controls to make your test more resilient, repeatable and consistent  
• Bolster product quality through the use of automated safety checks and inspection tools built into the leak test machine. This assures that the test subject is ready for the test and avoids time lost to tests that are bound to fail 
• Remove human error. By automating handling, positioning, testing, results recording and pass/fail determination, you free up operators to perform other tasks. 
• Reinforce your paper trail by automatically and safely capture digital records of test results that can be used for customer service, regulatory compliance, audit response and internal continuous improvement needs.

Automated Leak Testing Methods for You

With that, you’re up to speed on the general topic of automated leak testing. Have more questions or would like to discuss an automated leak testing application? Please contact us for a complimentary application review or see our website here for more information.