Chemical compatibility in regards to hydraulic hose can be complicated, however it is necessary for the performance and hose life. When selecting a hose, you must consider the chemical compatibility of the hose inner tube, cover, fittings and O-rings with the fluid used.
Variables affecting resistance of a compound
Some of the variables that affect the resistance of a compound to a chemical attack are:
- Type of media transmitted: Most hydraulic hoses are capable of transporting petroleum oil and liquids with high-water contents, but synthetic oils require dedicated hose materials.
- Temperature of the media transmitted: Higher temperatures increase the affect of chemicals on compounds. The amount of increase depends upon the polymer and the chemical. A compound quite suitable at room temperature might fail very quickly at higher temperatures. It is important that you do not operate outside hose temperature limits.
- Service conditions: A rubber compound usually swells when exposed to a chemical. Within a given percent of swell, a hose tube may function satisfactorily if the hose is in a static condition, but may fail quickly if the hose is subject to flexing.
- Grade or blend of the rubber compound: Basic polymers are sometimes mixed or blended to enhance a particular property for a specific type of application.
Below is a generic overview of how some polymers can react with different chemicals or environmental factors, however there are many factors that might change the compatibility outcome:
|Chemical / Environmental Factor||Chloroprene||Nitrile||Butyl||EPDM||CPE|
|Flame Resistance||Very Good||Poor||Poor||Poor||Good|
|Petroleum Base Oils||Good||Excellent||Poor||Poor||Very Good|
|Diesel Fuel||Good to Excellent||Excellent||Poor||Poor||Very Good|
|Gas Permeation||Good||Good||Outstanding||Fair to Good||Good|
|Weather||Good to Excellent||Poor||Excellent||Excellent||Good|
|Ozone||Good to Excellent||Poor||Excellent||Outstanding||Good|
|Low Temperature||Fair to Good||Poor to Fair||Very Good||Good to Excellent||Good|
Extra caution required
Exercise additional caution when selecting a hydraulic hose for gaseous applications subject to permeation. Some fluids that raise concerns include:
- Liquid and gas fuels
- Fuel oil
- Natural gas
If gas permeates through the tube, consider pin-perforated covers to prevent gas build-up. Don’t neglect the potentially hazardous effects of permeation, such as explosions, fires, and toxicity. Refer to applicable standards for specific precautions involving fuels and refrigerants. For instance, Parker has engineered hoses for the transportation and refrigeration market that are specifically designed for these applications:
- Diesel fuels and antifreeze (Parker’s 213, 266, 201, 206, 611HT and 221FR hydraulic hoses)
- Compressed natural gas (Parker’s SS23CG hose),
- Liquefied petroleum gas (Parker’s SS23CG and SS25UL hydraulic hoses)
- Refrigerant (Parker’s 285 and 244 hose)
Phosphate ester is another chemical that needs distinct design elements. Nitrile or rubber is fantastic for petroleum-based hydraulic oil, but would not be compatible with a synthetic fluid such as phosphate ester, which requires EPDM. Special attention should also be paid to chemical compatibility of the outer cover as well. That is why Parker offers a line of phosphate-ester fluid compatible hoses that feature inner tubes and outer covers that resist aggressive aircraft hydraulic fluids.
When in doubt, ask the manufacturer
Each manufacturer should have a document regarding chemical resistance for each of the hydraulic hose and fittings they manufacture. Usually, the basis for the ratings includes actual service experience, the advice of various polymer suppliers, and the considered opinion of chemists. When in doubt, a sample of the compound should always be tested with the particular chemical it is to handle. Click here to reference Parker’s media guidelines in regards to chemical resistance.
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:
Decoding a Hydraulic Hose Layline
Five Most Important Factors You Need to Consider for Hydraulic Fittings
Hydraulic Hose 101: Fast Facts
Top 8 Reasons Hydraulic Hoses Fail
Top 5 Reasons Customers Choose GlobalCore Hose
Successful Hydraulic Hose Assembly Starts Here