Rubber lining Shore A Hardness

[Ponnada]

Hi,
We have mixed bed polishing vessels provided in our water treatment unit,to remove Anions and Cation load from the feed condensate by Ion exchange process.
These vessels are made of carbon steel material lined with NATURAL SOFT RUBBER with a thickness of 4.5 mm +/- 10%, and Shore A hardness of 65 +/- 5.(as installed was between 60-68 S-A)

After a period of 3 years we noticed the Shore A hardness of the rubber lining has reduced to 38-45 Shore A inside the vessel at all location.

Can any rubber expert kindly clarify me:

1. What could be reasons for rubber lining hardness reduction in a period of less than 3 years. ?
2. What is the general life of a Natural soft rubber ?.
3. Are there any alternate economical methods for lining these vessels, such as PTFE / GRP for such service ?
4. We plan to reline the vessel with rubber considering the rubber lining deterioration, but the same condition might repeat during operation.

Thanks

 

[EdStainless]

Are these ever exposed to any regeneration chemicals?
The change in hardness is either a result of incomplete curing or degradation of fillers.
Ambient temperature water exposure should have virtually no impact on the rubber.

That said the most common vessels for this service are GRP, not lined steel.

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Plymouth Tube

 

[Ron]

Natural rubber will swell in relatively constant contact with water. As the rubber swells, its density decreases, as does its hardness as measured by the Shore scale.
I would opt for a different lining...there are many that would suffice for this application. Epoxies, polyester coatings, urethane coatings....For water treatment, check a ceramic epoxy that's approved for potable water service.