Lining Life of Rubber Linings In Bleach (NaOCl) Service
The life expectancy of any rubber lining is very difficult to predict and relies heavily on historical performance records. There are a number of variables that affect performance most of which are outside the control of either the manufacturer or installer. These include but are not limited to:
- Frequency of draining and refilling the vessel; usually fewer cycles result in longer lining life.
- Immersion frequency – when rubber lining dry out, they deteriorate at a faster rate than being continually submerged.
- Temperature of the solution – the lower the temperature the longer the life with the ideal being between 50º and 70º F. Conversely higher concentrations and storage temperatures shorten service life.
- Differences between the solution and outside temperature – high variations can lead to accelerated permeation. Applying a light colored coating to the outside of the tank can reduce these differences in temperature. Temperatures have been reduced between 20º and 50º F in this manner.
- The concentration of bleach can range between 15 to 20%; the lower concentration results in optimum service life. Higher concentrations reduce expectancy.
Bleach storage generates a very harsh environment that few, if any lining can resist over the years. Rubber has been shown to be the most efficient and economical membrane to use in these conditions and users have reported service periods of anything between 3 and 10 years with the average being about 7 years. It all depends on service conditions.
Repairs of rubber linings after exposure to bleach are usually temporary because of the permeation of bleach in rubber linings. Repairs are best made early in the life of the lining with repairs later being done as a method of protecting the vessel until a complete re-line can be scheduled. Because of the difficulty in determining the suitability of the repair bonding to rubber that has been in bleach service we do not recommend extending warranty for repairs.
In recent years we have developed a number of linings that promise longer life under these severe conditions. Our VE526CPEBC is a non-sloughing, non-sticky bleach resistant lining that has been in active service for about a year and a half without any signs of premature wear. Our EPDM is also being trialed with early results showing a marked improvement over standard chlorobutyls. Despite these encouraging signs, it has to be stressed that both linings have been in service for a relatively short time, so we are reluctant to suggest that they would last longer than our present range of products.