Posted by Fluid Gas Handling Team
on Wednesday, August 30, 2017
The process for testing and evaluating hydraulic hose is defined by SAE and ISO Standards, which contains various test procedures including change in corrosion resistance, hose construction integrity, burst, and impulse test.
Salt spray test
The salt spray (or salt fog) test is a standardized and popular corrosion test method for hydraulic fittings used to check corrosion resistance of materials and surface coatings. Salt spray testing is an accelerated corrosion test that produces a corrosive attack to coated samples in order to evaluate and compare the suitability of the coating for use as a protective finish.
Most commonly, the time taken for oxides to appear on the fitting samples under test is compared to expectations, to determine whether the test is passed or failed. For instance, the plating on Parker’s hydraulic hose fittings
will meet or exceed 120 hours to white corrosion and 240 hours to red rust.
Stainless steel or advanced plating options are alternatives to avoid corrosion. Hose Products Division offers a variety of stainless steel fitting configurations as well as XTR coating
, which provides more than seven times the SAE standard protection.
A burst test is a hydrostatic pressure test of a hose assembly that determines the actual burst strength of the assembly. Any signs of leakage, bulging, coupling ejection or hose burst below the specified minimum rated burst pressure of the assembly are considered a failure.
Minimum burst values are used as one factor in the establishment of a reasonable and safe maximum work pressure. Maximum working pressure is one of the essential operating characteristics that a hose user must know and respect to ensure satisfactory service and optimum life.
The following are recommended guidelines regarding the maximum working pressure:
- Water Hose up to 150 psi - 3:1 ratio
- Hydraulic Hose for all other liquids, solid materials suspended in liquids or air, and water hose over 150 psi - 4:1 ratio
- Hydraulic Hose for compressed air and other gases - 4:1 ratio
- Hose for liquid media that immediately changes into gas under standard atmospheric conditions - 5:1 ratio
- Steam Hose - 10:1 ratio
For additional safety precautions and abrasion resistance, it is recommended to utilize a hose sleeve or guard
based on the application.
Cold flex test
Hydraulic hose manufacturers rely on cold flexibility tests, using guidelines such as ISO 10619, to design and rate their hydraulic hose products. When tested, the sample’s hose or cover should not crack; and when warmed to ambient temperature, the test piece should not leak or crack when subjected to proof pressure.
Rubber blends in typical hydraulic hose are rated for cold weather operation to –40° F (–40° C). However, a number of hose manufacturers offer a wide range of products suitable for lower temperatures such as Parker’s low-temperature hydraulic hoses
that are rated to –70° F (–57° C).
Impulse testing for hydraulic hose is one of the key predictions of hose life. Impulse testing involves the pressurizing or cycling of hose pressure, often times up to 133% of working pressure, at rates up to 1 cycle per second while the hose is held in either a 90° or 180° configuration. To pass the test, the hose must meet or exceed two times the minimum number of impulse cycles based on the applicable industry standard. Parker tests its GlobalCore 787 and 797 to twice the impulse (to 2,000,000 cycles). Although hoses are tested at higher than rated working pressures, it is for your safety and the life of the assembly to not exceed the published maximum working pressure of the hose and/or fitting.
A more severe version of this test involves holding one end of the hydraulic hose assembly while moving the other end of the assembly back and forth, most often referred to as the flex impulse test. Flexing applications are some of the most severe applications hose assemblies can face and a flexing impulse test is a very good indicator of assembly robustness.
Article contributed by Kyri McDonough, marketing services manager at Hose Products Division, Parker Hannifin.
Other related topics on hydraulic hose, hose application, and selection criteria:
The Love-Hate Relationship Between Hydraulic Hose and Chemical Compatibility
Decoding a Hydraulic Hose Layline
Five Most Important Factors You Need to Consider for Hydraulic Fittings
Hydraulic Hose 101: Fast Facts
Successful Hydraulic Hose Assembly Starts Here
Going to Extremes: A Closer Look at Hydraulic Hoses