Have you ever bought a bag of chips only to find later that the crispy crunchy chips you were expecting have gone damp and bad due to a small leak in the packet? Now, imagine the same situation happens on components such as valves, combustion engines, gas appliances, sewerage pipes or medical equipment such as ventilators. It would not just give a bad impression, but it will also cause fatality as these components are not functioning as they should be.
For manufactured components used in industrial and pharmaceutical industries, even the slightest leak on the objects can lead to severe consequences, such as injuries and fatal accidents. Therefore, industries that are dealing with these products such as aircraft, automotive, pharmaceutical, appliances manufacturers employ leak testing techniques as part of their strict quality control procedure to ensure that the products are not compromised.
What is Assembly Leak Testing?
Leak testing detects the integrity and the completeness of the products, to ensure that they are welded well and manufactured to the required standard. Each product may have a specific allowable leak limit and this data must be provided to the system. When the quality standards are followed diligently, leak test ensures a 100% leak-free guarantee and well-made products for use.
Leak tests are traditionally done with hydrostatic testing. It involves filling the objects with water or dyed water and pressurizing the system to the specific test pressure. This method is most commonly used for pressure testing of pipelines and pressure vessels. It generally takes a specific duration of time to complete the test and there may be difficulties with draining the system and cleaning up after the test is completed.
Accelerating on the concept of ‘Necessity is the mother of Invention’, leak testing is the process of checking a system or object for leaks or a defect that might cause a leak.
A leak occurs when a liquid or gas flows through an object via a manufacturing defect such as a hole, crack, or weak seal. Leak testing is performed to detect that abnormality and to ensure the proper functioning and maintenance of industrial systems, operations, and products.
However, the size of a leak is difficult to measure, thus leakage rate here is an important factor to determine the severity of the leakage.
The leak rate (Q) is expressed as either a volume per unit time or the change in pressure (p) times volume (V) per change in time (t):
Q = (Δp x V) / Δt
Different Leak testing methods have their own sensitivity, expressed as the lowest leak rate that the varied leakage testing methods can detect. Highly sensitive methods are required to test highly leak-prone systems such as vacuum.
There are other considerations required for choosing a leak detection system which includes the size of the system, the type of material contained in the system, the rigidity of the container, the accessibility to the internal environment, the temperature, and the presence of any coatings on the surfaces.
When systems include a metallic containment, leaks may occur because of the encasing material becoming corroded with time or long-term exposure to ambient air. Consequently, leak testing may also detect the corrosion problem alongside leaks.
Leak testing verifies that a manufactured product meets predetermined specifications that allow the part or system to operate as per the standards. This process is vital to ensuring product quality and the safety of end-users.
Need for Leak Testing
Industrial requirements of leak testing are manifold that owes their necessity to the following aspects:
Ensuring High Product Quality
Leak test validates the quality and reliability of the component. Conducting leak tests on products and components before the assembly ensures that only high-quality products are used in the assembly line. This minimizes the chance of leakage and defects in the finished product.
Depending upon the requirement and nature of the product, the finished component can be subjected to leak testing before packaging and dispatch as final validation for leak-free goods.
A consistent leak testing process for every assembly stage helps in performing the root cause analysis during components failure and eventually reduces the post-abnormality actions to identify the cause of failure.
Customer Safety and Hazard Prevention
Leak testing is also commonly used for testing home and lifestyle appliances such as kitchen products, air conditioning, consumer electronics, valves, as well as other automotive or medical devices. If these devices do not adhere to absolute precision, they can have a huge impact on health and the environment.
For example, the smallest leakage in medical pacemakers can have fatal consequences. In the manufacturing of pipelines used in the chemical and process plants and storage tanks, a small leakage can expose dangerous chemicals to the environment which can prove to be hazardous.
Components and equipment that are used in other high-risk areas that involve explosions, fire, and operational hazards such as the oil and gas field, electrical equipment, and automotive should always be subjected to leak testing to ensure safety.
No False-Failures
While performing leak testing of a component, a leak-tight connection and seal for all ports and holes is applied to the test piece, irrespective of the test method.
The objective of providing this tight connection is to isolate the component for testing, which can only be accomplished when all of the test ports and holes are sealed and leak-tight. By creating a leak-tight seal, chances of detecting a false failure that is caused by an improper connection or seal are reduced.
Methods of Leak Testing
Two of the most popular systems used in leak testers are pressure/vacuum systems and helium systems. Let us understand each system with its working principle-
- Pressure / Vacuum System for Leak Testing
While performing a pressure or vacuum leak test, the test piece and the reference volume are simultaneously evacuated or pressurised to a preset pressure. The air in the system is then allowed to stabilise with the supply valves closed and the Differential Pressure Transducer is automatically zeroed.
After the stabilisation, the pressure change in the test piece is compared to the pressure change in the reference volume, using the Transducer. The difference in volume is measured and if a leak is detected the difference will increase. An alarm limit may be set for a pass or fail decision. Here are a few methods used for a vacuum leak test.
- Pressurized Soap Bubble Test
In this test, the system or part to be tested is isolated and then pressurized. While the system is under pressure soapy water is applied to potential leak sites and is left there for a certain amount of time. The areas with soapy water are carefully observed as the leaks cause the soapy water to bubble.
The points at which bubbles are formed are marked so that they may be identified for repair. The pressurized soap bubble test is the easiest method for vacuum leak testing.
- Flexible Tape Test
For the parts that cannot be pressurized the flexible tape test can be used for locating leaks. A thin, flexible tape is put on the potential leak points of the test work.
Once the points have been covered the vacuum is pulled on the system and the tape at all the points is checked. A leak is detected on all the points at which the tape is sucked in or dented. In piping applications where PVC is used for inlet piping, the tapes can be kept in place to repair the vacuum leaks.
- Helium Systems for Leak Testing
A vacuum pump evacuates the test chamber and test piece simultaneously to a preset vacuum. At this preset level, the chamber and the test piece are isolated and the chamber is evacuated further to very low pressure. A positive pressure variation is therefore created between the test piece and the chamber.
Helium gas is then introduced into the test piece, often in a 10% concentration. A Mass Spectrometer analyses a sample from the chamber as the vacuum continues to be drawn.
The Mass Spectrometer measures the helium leakage and sets the pass/fail decision. The test piece pressure is often compared to the chamber pressure before dosing with helium, to avoid saturating the Mass Spectrometer in the event of a gross leak.
Factors to Consider while Choosing the Appropriate Leak test Method
Depending on their size, leaks can have various effects, which can be used for their location. All methods are based on the variation of a physical property measured on one side of the vacuum vessel wall while the pressure or the nature of the gas is changed on the other side.
Big leaks, involving large gas flow can generate mechanical effects, smaller leaks require finer methods.
The specification of the acceptable leak and the test method are the first parameters to take into consideration while choosing a leak test method. One must ask a few pertinent questions such as:
- How many points on the test subject need to be tested. How many points must be tested?
- What is the product life expected as per the company standards? What size is the component and what is its internal volume?
- What is the acceptable leak limit?
- Does the test sample have any hidden internal volumes that may affect the leak measurements?
- Is there inside access or is the test sample a sealed unit?
- Is the test sample rigid or flexible?
- Are parts present at ambient temperature?
- What is the surface finish of the sealing surface?
The industrial sector is pacing ahead with high sensitivity and low acceptance of the product abnormalities. This compelling market demand comes with the constantly changing environmental protection specifications, economic requirements, safety constraints, and requirements of quality products.
This drive has also alleviated stricter quality controls for leak testing across the manufacturing landscape regardless of the industry vertical. While there are varied leak testing methods, the right choice depends upon the production requirements.
Choosing the right test methodology demands industries to accurately consider all the other factors encompassing leak tests such as leak limits, component size, surface finish, etc. Mitigating the risk of a leak whether small, big or multiple is directly proportional to selecting the right testing method.
Bestech Australia provides solutions and products to facilitate reliable leak testing techniques. We partner with Furness Controls who has more than 40 years of experience in developing leak testing technology. The leak testers are suitable for leak detection in production components and sub-assemblies.
