Abfad Limited were appointed to refurbish a 250 cubic meter acid water process storage tank for one of our power generation clients due to the condition of the steel of the tank and the breakdown of the existing coating, which had been applied several times by another company, but continued to fail.
(Above: Showing the condition of the storage tank prior to blasting)
Severe pitting corrosion
Corrosion of the tank was immediately evident with major delamination of the existing coating, cracking in many areas, and severe corrosion pitting of the steel was found. This type of corrosion is often found in many storage tanks that aren’t protected with a lining, or have incorrect preparation meaning the lining quickly becomes ineffective as it starts to peel away, leaving the steel vulnerable to corrosion. This is why correct preparation and blasting to the required standard is so important when lining any storage tank.
Pitting corrosion is a form of localised corrosion which produces holes and pits to the metal of the tank. The pits themselves can assume many different shapes and sizes, and result in a localised loss of thickness and can eventually result in failure of the steel. This type of corrosion is often considered to be one of the more damaging forms of corrosion.
The acid water process tank has a wide range of chemical fluctuation from PH 1 right up to PH 13, although the tank operating range would be at PH 6-9 for discharge the majority of the time.
(Above: Showing the extent of the corrosion pitting to the tank steel after blasting)
Preparation is key
This particular process water tank was open topped so a scaffold roof was installed prior to blasting operations, to help protect the working environment within the tank. Abfad Limited supplied all plant required for the project including a shot blast dust extraction unit and expended grit vacuum system to remove any grit from the tank into skips ready for waste disposal.
The tank walls were blasted to SA2.5 standard from an internal scaffold tower, removing the existing failed coating and providing a blast profile of over 140 microns to ensure good adhesion of the solvent free coatings that Abfad use for storage tank lining, corrosion pitting’s were also filled during coating application.
After blasting, blast inspection verification was performed to ensure that the correct profile had been achieved, along with UT steel thickness checks to verify metal thickness in the tank.
(Above Left: Blast inspection verification, achieving an excellent profile for coating adhesion. Above Right: UT steel thickness checks after blasting has been completed)
Solvent free coatings offer the best long term protection
A solvent free, two component polycyclamine cured lining system utilising advanced epoxy novalac technology with flake and fibre reinforcement was chosen as the preferred coating as it has superb chemical, assorted acids and water resistance.
Once the wall sections were coated all areas were inspected for pin holes or any discontinuities in the coating and these were repaired.
The floor area was then blasted to SA2.5 standard and the coating applied, inspected and any coating discontinuities were repaired. Nominal thickness of the coating was 1000 microns (1mm), this was all verified with paint inspection equipment.
All areas of the tank were now blasted and coated to the required standards including the tank hatch, ensuring that full corrosion protection of the internal tank steel was achieved.
The benefits of the solvent free single skin to the client are huge as this new internal lining acts as an effective barrier between the tank steel and the stored product, creating a corrosion resistant barrier. This ensures the storage tank has a longer operational lifespan and aids in reducing maintenance and repair costs down the line, all of which lead to increased profits.
(Above: Coating nominal thickness verified with paint inspection equipment)
Abfad always look to save clients’ money
On this project our client also requested emergency rescue and safety cover for other trades working in confined spaces in and around the power station.
Along with our tank lining services this is something Abfad regularly provide to our clients, particularly in power station environments. In order to save costs for our client we not only provided a three man blast and coating team for the storage tank refurbishment, but also a three man confined space rescue team to assist and manage confined space safety for the plant.
The confined space safety crew was on site and available to support plant trade personnel during confined space entry, as well as being able to assist with the tank refurbishment when not required elsewhere. This was possible due to Abfad personnel being multi-discipline, trained in both specialist coating application and rope rescue / confined space entry and rescue, in real terms this able to save our client thousands of pounds.
(Above: Competed storage tank returned to service with complete corrosion protection)