Abfad Limited were appointed to refurbish a 250 cubic meter acid water process storage tank for one of our power generation clients.
The tank was in desperate need of repair and refurbishment due to the condition of the steel. The existing coating had been applied several times by another company but continued to fail.
(Above: Showing the condition of the storage tank prior to blasting)
Severe storage tank corrosion
Corrosion of the tank was immediately evident with major delamination of the existing coating and cracking in many areas.
Severe corrosion pitting of the steel was found.
This type of storage tank corrosion is often found in many tanks that aren’t protected with a lining, or, have incorrect preparation.
The lining quickly becomes ineffective as it starts to peel away. Leaving the steel vulnerable to corrosion and the possibility of a breach.
Therefore, correct preparation and blasting to the required standard are 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. Eventually, this result’s in the failure of the steel.
Pitting 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. The tank operating range would be at PH 6-9 for discharge the majority of the time, but the full scale needed to be taken into account.
(Above: Showing the extent of the corrosion pitting to the tank steel after blasting)
Preparation is key
The tank was open topped so a scaffold roof was installed prior to blasting operations. This Helped protect the working environment within the tank.
Abfad Limited supplied all plant required for the project. This included a shot blast dust extraction unit and expended grit vacuum system. Any grit removed from the tank went into skips ready for waste disposal.
The tank walls were blasted to SA2.5 standard from an internal scaffold tower. The existing failed coating was removed and a blast profile of over 140 microns was achieved. This ensures good adhesion of the solvent-free coatings that Abfad use for storage tank lining. Corrosion pittings were also filled during coating application.
Once completed, blast inspection verification was performed to ensure that the correct profile had been achieved. UT steel thickness checks were also carried out 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 pinholes 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.
The nominal thickness of the coating was 1000 microns (1mm) and was 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.
This new internal lining acts as an effective barrier between the tank steel and the stored product. Stopping storage tank corrosion in its tracks.
Creating a corrosion resistant barrier ensures the storage tank has a longer operational lifespan. Aids in reducing maintenance. Reduces 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 an emergency rescue and safety cover team to ensure the safety of 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 team was on site and available to support plant trade personnel during confined space entry. They were also 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, rope rescue and confined space entry and rescue.
In real terms, this was able to save our client thousands of pounds.
(Above: Competed storage tank returned to service with complete corrosion protection)