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High ACN Content HNBR for high aromatic concentrations 

1. OBJECTIVE

Expose elastomer samples to fluids at specified temperature over an extended period of time, to observe the effects of the fluid exposure on the physical properties of the sample.

2. SCOPE

To measure the change in physical properties that occurs after an elastomer sample is exposed to fluids in a climate-controlled environment. Variables to measure include volume, mass, tensile, elongation, and hardness. Hardness change will be expressed in units, rather than percentage.  

Rubber samples to be tested include:  
HNBR-80A currently used as seals in many oil-well applications as a standard elastomer. It will be tested to establish a base line reference and to compare results with new alternative elastomers.    
HNBR-80D new elastomer exclusively developed to improve aromatic resistance and provide better performance in the field when exposed to light oil fluids.
CV75 (high performance FKM) its fluid resistance will be measured and compared against the other two compounds to determine if it is worth the price difference.  

Immersion Fluids include:  
Reference ASTM Oil: IRM-903
Homogenous oil mixture, oil well: FB-152-94-11B-14-5H  
Test Conditions: Temperature 50 ˚C at Atmospheric Pressure.  

3. NORMATIVE / DOCUMENTED REFERENCES

ASTM D471 – Standard Test Method for Rubber Property — Effects of Liquids
ASTM D412 – Tension
ASTM D2240 – Durometer Hardness
MSDS for chemicals involved    

4. INITIAL FINDINGS

4.1.  Customer complains about poor seal performance, short seal run life and loss of pressure.
4.2.  Some seals were returned to our facilities showing signs of compression set and swelling.
4.3.  Some seals from our closest competitors were also returned to our facilities for further analysis. These seals had clear signs of deterioration, swelling, compression set and loss of mechanical properties.
4.4. After the inspection of the seals, it was concluded that the swelling was due to the presence of aromatics in the production fluids, causing loss of properties and seal failure. A laboratory trial was conducted in order to look for an alternative compound able to withstand the demands of very aggressive oil-wells (high aromatic content) without compromising mechanical properties, and less expensive than a fluoroelastomer. 

 5. TEST RESULTS

5.1.  Initial Trial  This test was conducted using only elastomer samples from HNBR-80A, the standard elastomer; and the new elastomer HNBR-80D, designed to provide better aromatic resistance in the field. CV75 was not included in this test because based on its properties it is expected to perform well when exposed to the testing fluid.   Samples were exposed to IRM-903 Reference Oil; this oil is used in this type of analysis to establish quantitative comparison between the elastomers in terms of fluid resistance. The aromatic properties of the oil are specified in the ASTM D471.   Rubber samples were exposed to the reference oil for a prolonged amount of time, 1872 hours, and the changes in the properties were measured at certain intervals. See charts.  

 hnbr o-rings for aromatic concentrations

 high temperature hsn orings

This test results showed that the new compound HNBR-80D had better aromatic resistance and it is expected to perform better in the field when compared with the standard elastomer HNBR-80A.  As it is observed the change in volume due swelling was 12% on HNBR-80A, whereas HNBR-80D exhibited a very low swelling at 2% change in volume.  Similar behaviour is observed when hardness was evaluated. HNBR- 80D has better property retention when exposed to aromatic fluids.  

At this point of the analysis it was recommend doing a similar analysis, but using actual production fluid from a very aggressive oil well, in order to estimate the elastomer performance under circumstances close to the real application.      

5.2. Second Trial
This test was conducted using all three elastomer samples: HNBR-80A, HNBR-80D and CV75. The idea was to expose all available elastomers to the exact same conditions at the same time to determine how they will react under similar circumstances than those observed in the field.      

The fluid sample was provided by customer from the oil well: FB-152-94-11B-14-5H.  

All samples were immersed during 1344 hours (until saturation was reached) and the changes in the properties were measured at certain intervals in order to gather information and see how the elastomers were performing. The data collected was used to build the charts. See results and charts.  

 low temperature orings

 hnbr acn content

hnbr hsn orings

6. CONCLUSIONS   

After 1344 hours of exposure all compounds exhibited saturation.  

Although compound CV75 exhibited very good fluid resistance, evidenced on its change in Volume and Hardness, which were very low, the retention in mechanical properties was poor. Compound lost 14% of its tensile strength, whereas the hydrogenated compounds lost less than 6% in the same property. This is something to keep in mind when choosing the rubber compounds; if the seal’s exposure to mechanical stress is elevated, this may not be the best choice for that type of application. Besides, the cost of a CV75 seal may be several times higher than the hydrogenated options.   

Compounds HNBR-80A and HNBR-80D have both very similar “Original Properties” (before the immersion): Tensile, Elongation and Hardness.  This means that the changes done to create the new compound did not substantially affect the rubber mechanical behavior.  

Compound HBBR-80A exhibited a maximum of 20% change in volume and lost 11 Shore A hardness points, whereas HNBR-80D exhibited a maximum of 10% change in volume and only lost 5 points on Hardness.  Besides, the change in mechanical properties is close in both compounds but slightly better in compound HNBR-80D as well. This is a clear indication that new developed compound HNBR-80D is more suitable to withstand light oil applications where the aromatic concentration is expected to be high.  These results confirm that, under the same circumstances, the newly developed compound HNBR-80D will have a better performance than the standard compound.