Understanding the potential threats and performance issues your product may encounter in the field is critical to providing a quality product. As a laboratory testing expert, Jeff Andrasik has experienced a range of scenarios in which product failures have occured. We catch up with Jeff to speak about some common themes found in automotive and industrial hose failures and ways to identify those potential risks during your testing evaluations.
What is the most common failure mode you see in the lab?
The most common failure mode I see in the lab are assemblies not using the proper fittings with the hoses. There are a number of occurrences where the connection between the hose and the fitting fail, either a leak or a hose separation. However, there are a number of conditions that could contribute to hose failures. Construction or design flaws, improper assembly or changes in the surrounding operating system are just a few common factors that can contribute to hose failures.
What are some of the most common standard test methods for rubber hose testing?
Standards vary between industry application and individual component / system specifications. Some of the most common standards for automotive applications are SAE, ISO, ASTM, or OEM standards. For hydraulic or industrial hoses, SAE J517 and J343 are the most referenced standards.
What common tests are there in a laboratory environment for applying pressure to the hose?
There are 3 common test methods used to verify the hose and hose assemblies’ pressure range:
- Static (aka Leak Check or Proof Tests) which allows you to apply pressure up to the Max Allowable Working Pressure (MAWP) to verify the hose will not rupture and the assembly does not weaken
- Impulse tests are designed to produce a high pressure / low pressure effect on the assembly to simulate the pump being turned on and off.
- Burst tests require a constant increase in pressure inside a hose assembly until a failure occurs.
There are a range of temperature protocols. What is evaluated for each?
Temperature aging is used to accelerate tests and produce reactions so they occur in a shorter timeframe. Temperature cycling exposes a part to varying temperature extremes. Following these temperature tests, the performance of the hose is typically evaluated through a series of post-tests. For material testing, common post-tests include tensile and creep testing. Tensile testing helps to understand the tensile strength, hardness and elongation changes. Creep testing measures the change of extension, known as creep stain, under a constant load and is used to determine service life. For hose product testing, proof or burst testing is performed after the temperature exposure.
How long should I test to obtain the most accurate results?
Developing a test to evaluate a product after a specified period of time is easier than testing to failure and will likely provide enough data to determine the durability of your product. If you are following an industry standard, the test length is commonly stated in the procedure. Otherwise, the time it takes is to reach a certain change in property for the material is typically the length of the test.
Are there specific standards for fluid compatibility when using oil versus gas?
Fluid compatibility can be evaluated using ASTM D471 for various types of fluids including fuels, oils, coolants and cleaning agents. The main objective for fluid compatibility testing is to confirm that the part will withstand prolonged exposure to the fluid that would be present while in operation.
How do test requirements differ between automotive and industrial hoses?
One of the biggest differences between the two industries I have seen is vibration or flex fatigue testing. While both industry standards have testing that include pressure, temperature, vacuum, diameter changes, etc., the automotive industry adds a vibration or flexing variable to the testing methods. One reason for this is because the automotive industry is trying to simulate either engine roll or the vibration of the engine.
Is there a standard length to test a hose for the best results?
If testing a “coupon” sample, a typical length of hose is in the range of 18"-24”. However, we commonly test production parts in the lab. These parts come in all shapes and sizes.
What are some common end of life thresholds that are used for testing when you are not testing a system to failure?
For material testing, common properties that are measured and compared to original properties are tensile strength, elongation, hardness, and volume swell. For hose products, common properties are diameter changes and burst pressures.