When it comes to undertaking the tank lining works adhering to the pre defined proposal and planning is essential. This can be challenging if factors outside of the applicators come into effect – such as weather risk or an unforeseen change in the working environment.
When changes in the developed plan occur communicating this changes to the client is critical as these can often have implications to safety, quality and program duration if not addressed. Adaptability when changes occur is something that we pride ourselves on. When changes and challenges do occur it will often involve referring back to technical documents or communication with the tank lining material supplier to understand what mitigation measures or additional steps need to be put in place.
Any change in scope are often identified as part of the testing and inspection regime developed for that particular tank lining installation. These would typically include the following;
Cleanliness – contaminants from the tanks usage if they have been in service must be removed before preparation for the new tank lining can commence. For example if a tank has been used for storing oils or hydrocarbons these must be washed away and the thoroughness of this checked using a UV Blacklight.
Surface profile – the majority of tank linings require a minimum surface profile or roughness to ensure optimum adhesion of the new tank lining. This must be checked, typically either using a surface profile needle gauge or Testex tape. This results are recorded and retained as part of our standard tank lining quality assurance.
Visual Preparation Standards – As per ISO 8501-1 there are internationally recognised preparation standards that are referenced by the tank lining manufacturer for their materials.
Soluble salts – something many tank lining contractors over look as soluble salts cannot often be seen, but an essential part of a thorough tank lining application. Soluble salts if left in place can cause premature tank lining failure through osmotic blistering as a result of moisture being drawn through the coating film as a result of osmosis.
Dust tape tests – following preparation a cleaning stage is undertaken, typically vacuuming or a washing operation. To verify that this has been effective a dust tape test is conducted at various locations throughout the tank and retained as part of the quality assurance records.
Climatic Monitoring – the tank lining manufacturer will specify the temperatures, relative humidity and dew point restrictions relating to their tank lining material. This need to be strictly adhered to in order to ensure adhesion and proper performance of the tank lining. These conditions are continually monitored through the tank lining application phase.
Wet film thickness checks – during application of most tank linings the applicator checks that the material is being applied to the correct thickness using wet film thickness combs. This is not possible with ultra fast gel time tank lining materials such as polyurea tank linings.
Dry Film thickness checks – the cured tank lining thickness is checked after each coat in order to inform the applicator if they need to adapt their methodology. These are logged and retained for the project quality file. Any areas below the required thickness must be rectified to ensure that each constituent layer is applied inline with the tank lining manufacturers technical documentation.
Porosity – a single pin hole in a tank lining is a point of failure through which moisture, oxygen and chemicals can attack the substrate you are protecting. To identify these on conductive substrates (metal and concrete) it is best practice to test the new lining using a DC Holiday Detector – commonly called a spark tester.
As well as the testing regime there are best practices when physically applying the tank lining. These include;
Stripe Coating – applying an additional coat to angles, edges, nuts and bolts where tank linings naturally are thinner as a result of gravity and surface tension of angles and edges.
Contrasting colours – it is best tank lining practice to apply each coat in a contrasting colour to the previous coat in order to ensure full coverage for each layer of the tank lining specification.
When plural spraying using fast setting materials such as polyurea tank linings the lining may be applied in multiple layers, but these are not typically considered separate coats so the same colour is used throughout.