Recently we refurbished a 250 cubic meter acid water process storage tank for one of our clients.

The tank was in desperate need of repair and refurbishment due to the condition of the steel. The existing coating (applied several times by another company) continued to fail.

severe corrosion and coating delamination inside storage tank  Corrosion and coating delamination inside of storage tank

(Above: Showing the condition of the storage tank before blasting)

Severe storage tank corrosion

Corrosion of the tank was immediately evident. Major delamination of the existing coating and cracking in many areas were visible.

Severe corrosion pitting of the steel was also seen. Pitting corrosion impacts storage tanks that aren’t protected. Either with a lining, or they have incorrect or poor preparation. The lining becomes ineffective as it starts to peel away. Leaving the steel vulnerable to corrosion and the possibility of a breach. Thus, correct preparation and blasting to the required standard are so important.

Pitting corrosion is a form of localised corrosion. It produces holes and pits to the metal of the tank.

The pits themselves can assume many different shapes and sizes. These result in a localised loss of thickness across the steel. 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 needs taking into account.

Pitting corrosion inside of storage tank  Detail of pitting corrosion inside storage tank

(Above: Showing the extent of the corrosion pitting to the tank steel after blasting)

Preparation is key

Before blasting we installed a scaffold roof over the tank as it was open topped. 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.

We blasted the tank walls to SA2.5 standard from an internal scaffold tower. Removing the existing failed coating. Achieving a blast profile of over 140 microns. Good preparation ensures good adhesion of the coating.  Abfad uses solvent-free coatings for storage tank lining as they offer a lot of benefits to the client. Corrosion pittings are also filled during coating application.

We ensure we have the correct profile from blasting by blast inspection verification. We do this with a specialised instrument that measures the peaks and troughs of the blast. UT steel thickness checks were also carried out to verify metal thickness in the tank.

Blast verification checks to blast profile  UT thickness checks to the steel after blasting

(Above Left: Blast inspection verification, achieving an excellent profile for coating adhesion. Above Right: UT steel thickness checks carried out)

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 the preferred coating. It has superb chemical, assorted acids and water resistance.

We coated all wall sections and then inspected the finished coating for any pinholes or discontinuities. Repairing any found.

The floor area was then blasted to SA2.5 standard and the coating applied. Then inspecting for any coating discontinuities and repairing.

The nominal thickness of the coating was 1000 microns (1mm). We used paint inspection equipment to verify this.

All areas of the tank were now blasted and coated to the required standards including the tank hatch. Achieving full corrosion protection of the internal tank steel.

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 means the storage tank will have a longer operational lifespan. Aids in reducing maintenance. Reduces repair costs down the line. All lead to increased profits.

Paint thickness checks to completed solvent free coating  Paint thickness checks to completed tank lining

(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. They wanted to ensure the safety of other personnel working around the power station. Especially those working in confined spaces.

Along with our tank lining services, this is something Abfad provide to our clients. Particularly in power station environments.

To save costs for our client, we provided two small teams that could interlink. A three-man blast and coating team for the storage tank refurbishment. As well as a three-man confined space rescue team to assist and manage confined space safety for the plant.

The confined space safety team was available to support plant trade personnel during confined space entry. They could also assist with the tank refurbishment when not required elsewhere.

This is possible due to Abfad personnel being multi-discipline. Trained in specialist coating application, rope rescue and confined space entry and rescue.

In real terms, this was able to save our client thousands of pounds.

Completed solvent free coating on storage tank  Storage tank lining completed

(Above: Competed storage tank returned to service with complete corrosion protection)