Tank Base Sealing

When & Why Tank Base Corrosion Occurs?

 

The industry has learned to protect the base of the tank from corrosion using cathodic protection and rectifying existing problems by installing a new floor if needed. With the base protected, the rim could at times be neglected.

The crevice at the interface between a steel tank and its base is where we see corrosion set in. Right at the chime angle. The main cause of corrosion is water ingress, sometimes exacerbated by poor drainage and sloping of the foundation towards the tank.

A sealant would prevent this water penetration. However, it is difficult to seal a steel tank to its foundation, typically concrete, as these dissimilar materials are subject to movement, expansion, and contraction at differing rates.

Storage Tank Displaying Water Ingress at the Base


"Solutions" or More Problems?

 

Cement, bitumen, asphalt, caulk, and other sealants have been tried for many years, typically proving to be temporary solutions due to poor adhesion and rigidity while the tank is in operation. In some cases, this tank base “protection” can do more harm than good.

Localized failures can effectively seal the moisture in, thus exacerbating the corrosion. As well as this, an inspection of these systems can prove difficult as devices cannot “see” the remaining steel thickness through the sealant.

 

Tank Base Corrosion


Microporous Membranes: More Than Just Roofing System

 


Originally developed for water- and weatherproofing roofs, tank maintenance engineers started noticing some features of these microporous membranes, which could prove useful on tank bases:

  • The application of the membrane system is straightforward, without the need for hot work or any specialist tools. Conditioner/primer is applied first to enhance adhesion, followed by the membrane with a reinforcement sheet, applied by brush. A two-coat system ensures there are no misses.
  • Unlike sealants, membranes prevent water ingress but do not trap moisture. Similar to human skin, their microporous nature allows the vapor to escape, leaving the underlying substrate dry and firm.
  • Membranes adhere very well to different substrates as they have been used on many roofing materials with great success for many years. Most carry globally recognized approval, such as ASTM D-6083, which is considered the benchmark for code related building product approvals related to the wind resistance and structural integrity of buildings and building components.
  • We know that most tank base protection systems fail due to their rigidity, however, membranes can accommodate the natural movement of the substrate and move in harmony.

Membrane In Action

 

Tanks at a refinery in France were suffering from water ingress. They had a polyester tank base sealing system in place, which was failing due to its rigidity. The failed system had resulted in water ingress, causing corrosion at the base of the tank.

Belzona 3111 was used to waterproof the tank base in 2004. The annular ring was subsequently inspected in 2007 and 2017, using nondestructive methods, and found to be in excellent condition.

 

Tank base sealing with a flexible membrane


The Future of Tank Corrosion Protection

 

These days we have a combination of aging structures that need preserving and new tank farms, where we are focusing on corrosion prevention. The industry needs to keep looking for alternatives to common maintenance techniques, such as the use of membranes over sealants.

What aids progress in corrosion management is the conversation. Material manufacturers, contractors, asset owners and operators, engineering design houses, testing houses, and classification societies among others can jointly facilitate continuous progress.

 

Belzona 3111 inspection in service