THE PROBLEM
The concrete gas storage tank at the Anaerobic Digestion site had suffered degradation as a result of exposure to hydrogen sulphide and biogenic sulphuric acid. Initially during our survey it was thought that the concrete had never been protected with a tank lining suitable for use within an Anaerobic Digester environment.
SOLUTION
We proposed the application of a tank lining with a proven history within the Anaerobic digestion market – Remmers Epoxy Universal. This tank lining is particularly suitable for relining concrete tanks as it is capable of crack bridging.
Preparing the surfaces
Initially all surfaces to be relined were prepared by method of High Pressure Water Jetting at 500 Bar (7,500 PSI) to remove degraded concrete. Following preparation it became apparent that a tank lining had been previously applied, but very poorly with large amounts of blow holes unfilled. As we always say you cannot fill blow holes with paint alone.
The discovery of existing coatings meant that the making good of the concrete prior to application of new tank lining had to be undertaken in two separate operations. To the exposed concrete areas a cementitious fairing coat was applied by method of trowel. This was sponge float finished in order to provide a good mechanical profile for the subsequent tank lining application.
Drying the tank
This fairing coat was allowed to set for an initial period naturally and then heating an dehumidification was introduced in order to dry the tank out and create the correct climatic conditions for tank lining application.
The previously coated areas were well adhered, so these were prepared by method of vacuum controlled diamond grinding to raise a surface profile for subsequent coatings to adhere to. As cementitious materials will not adhered to cured epoxy coatings these areas were made good by applying Remmers Epoxy MT100 with added Thixotropic powder to from a grout coat.
Spraying the epoxy
Once the correct moisture content of the substrate and climatic conditions had been achieved and records of this made Remmers Epoxy Universal was applied by method of airless spray to minimum thickness of 800 microns. This was further worked into the surface by rolling. This was verified using wet film thickness gauges during tank lining application of each coat.
Remmers Epoxy Universal is a tank lining that has extensive case histories of application in the Anaerobic digestion market, going back nearly 20 years. We have ourselves applied this tank lining in over 50 anaerobic digestion related tanks to good success.
Checking the tank lining
Following application of the tank lining as part of our standard quality assurance the new lining was checked for pin holing and porosity using a DC holiday spark tester. As witnessed with the previous poorly applied lining which could have been the cause of the lining failure, a single pin hole or break in the tank lining is a point of failure in an aggressive environment as found in the anaerobic digestion industry.
The whole project was completed in just over 3 weeks, with our team working two weekends and overtime to achieve the tight deadline for our client.
