Equipment builders who specify hydraulic hoses that meet SAE and other industry standards have strong documentation that their choice of hose will meet or exceed published performance and life ratings. This assumes, of course, that the hoses are installed and maintained according to manufacturers’ recommendations.
But when it comes to developing new machines or improving on existing designs, engineers are pursuing higher levels of performance and reliability. Consequently, they push hydraulic hoses to higher standards of performance. Furthermore, more hostile operating conditions—especially higher ambient temperatures—require premium materials and construction changes in hoses that need to be properly measured and qualified before final inclusion in the assembly.
Testing Is Critical
For hydraulic hoses, it is extremely important to test not only the hoses themselves, but also the fittings and entire assembly for compatibility and durability. Performing sufficient testing minimizes potential failures. Doing so reduces downtime, increases safety, and reduces damage that causes failures. Of course, depending on the end-use application, certain testing standards must be met for some equipment to be considered in particular applications.
Consistent testing, in conjunction with audits, may be necessary to keep up with an industry in constant motion. Audits are useful for comparing products to industry standards and benchmarks. Some of the driving forces behind auditing or retesting your product include:
Material changes—Suppliers often make changes to their materials, from what is used to construct hoses and machines to the fluid running through them.
Manufacturing-process changes—New crimping processes, along with extrusion, can affect hose performance.
Application changes—These include any environmental changes that may affect the product, such as changes in fluid used, pressure changes, and temperature changes.
Construction and design flaws—Examples of these flaws are unsuitable crimping practices and bending hose to a smaller-than-recommended bend radius.
Improper assembly—Hoses and connectors may not have been specified for use together, or required fittings and clamps are not being used.
Incompatible environment—Pinching or rubbing during operation can cause a hose to fail from erosive wear.
Hose Test Methods
Several key test procedures for hydraulic and industrial hoses fall under the SAE J517 and J343 standards. These evaluations focus on environmental concerns and how hose assemblies will perform under different types of stress. Tests can come from manufacturers that maintain internal controls as well as distributors that have standards for the hoses they are marketing. Crucial tests include:
Dimensional checks—Each hose needs to conform to the dimensions specified for its respective 100R-series hose type. This is considered a quality check for post-production validation.
Proof/leakage tests—These tests apply pressure up to two times the maximum allowable working pressure (MAWP) to verify that the product will not rupture and that assemblies will not leak.
Change in length—When a hose is pressurized to the MAWP, it cannot exceed the percentage change listed in SAE J517 for that type of hose.
Burst test—This test features a constant increase in pressure inside a hose assembly until failure occurs. It determines the safety factor ratio of the product—a minimum of four times the MAWP is required to pass.
Cold bend—The cold-bend test soaks the hose assembly in a low-temperature fluid, after which the hose is flexed to the minimum bend radius. The hose cannot leak or fail at the leakage pressure stipulated in SAE J343 for that type and size of hose.
Impulse test—Impulse testing produces high- and low-pressure pulses on assemblies to simulate common machine usage and on/off cycles.
Oil resistance—Studies are performed to confirm that the hose and the materials the hose is made from can withstand prolonged exposure to the hydraulic fluid being used.
Electrical conductivity—Hoses and assemblies are checked for electrical resistivity and conductivity, which is a safety concern in many applications.
Vacuum—There should be no evidence of hose blistering or collapse after five minutes at the absolute pressure as specified in SAE J517.
In addition to these hoses and assembly tests, further evaluations can be conducted to optimize hose assemblies before they are installed into machines. Among these evaluations are:
Abrasion—This test measures durability and life of the product when rubbing occurs while in use. Changes in material can widely affect abrasion results.
High temperature to accelerate aging—Elevated temperatures can speed up the aging process, which can approximate the amount of time it will take for a hose to fail. This testing can be tricky, however, because higher temperatures cause varying reactions. Materials may undergo transitions over accelerated temperature range, and exceeding high-temperature recommendations can alter results.
Temperature cycling—This evaluates the behavior of components when exposed to varying temperature extremes. Cycling limits and frequency can be developed to closely mimic service conditions.
Vibration testing—Mechanical vibration is used to simulate how a component is affected when it undergoes constant fatigue or when shaken.
The Value of Auditing
Audits mitigate risk in sourcing parts by verifying quality and allowing companies to make informed sourcing decisions. Manufacturers need to focus on a list of important features that impact the performance of hose systems and compare those features to the benchmark data. Auditing verifies consistency of product design, dimensions, material properties, and overall component performance over time to guard against small manufacturing inconsistencies.
Auditing, whether internal or external, is crucial for companies that supply hydraulic and industrial hose assemblies. Developing an internal auditing program requires investment and commitment. Minimizing failures is worth the effort of creating an internal program, but external testing from a laboratory can be more efficient.
Companies often face bottlenecks internally that can delay product releases, resulting in lost revenues. External testing serves to decrease delays and benchmark against competitive products, accelerating revenues of new products in the market.
Jeremy Jackson is product testing engineer at Smithers Rapra, Akron, Ohio. For more information, call (330) 762-7441, or visit the company's site.