Step 3: Prepare the tank
For new buildings after final tank testing, the tanks must be fresh water washed and dried, especially if they have been in contact with seawater. All grease and oil must be removed from all surfaces and all hot work in the tank must be completed. Furthermore:
- Heating coils (if fitted) should be masked
- All cargo lines should be fitted and tested
- Cargo suction strums (if fitted) should be removed in order to give total access,
When conducting tank repairs, it is important to ensure that the tanks are clean and gas free.
Other factors to consider:
- Scale, debris and cargo residues must be removed from the tanks
- Any damaged lining must be prepared back to a firm edge or completely removed.
- Any damage to the steel (e.g. pitting) may need to be rectified e.g. by welding and/or grinding.
Step 4: Surface preparation
Again the lining Application Guidelines will stipulate the surface preparation requirements. Key areas to control include:
- Surface Profile - measurement on site should be undertaken by profile gauge or other instrument.
- Surface Cleanliness – the cleanliness Standards ensure that the substrate is clean and ensure a good adhesion of the lining
- Residual salt - If the surface salt contamination level is above the maximum that is permissible for the particular lining being used, further fresh water washing, blasting and cleaning will be required.
From the start of surface preparation to the final cure of the lining the environment in the tank should be maintained and monitored. Measurements should be taken in a variety of locations in a tank as factors such as the outside conditions may affect the environment in the tank such as direct sunlight on the outside of the tank raising the temperature of localised areas within the tank. Variables to monitor include:
Temperature Control – maximum and minimum air and steel substrate temperatures
Humidity Control – maximum and possibly minimum humidity levels
Ventilation Control – air change frequency and set-up inside the tank to avoid dead spots
Step 5: Apply the coating
The lining should be applied in accordance with the specific Application Guidelines and/or product Technical Datasheet, as provided by the lining product manufacturer.
Stripe coating is an essential part of good painting practices in cargo tanks. Typical areas where stripe coats should be applied include:
- Backs of stiffeners
- Cut outs i.e. scallops
- Areas of difficult access (corners)
- Ladders and hand rails
For optimum performance of cargo tank linings, close control of film thickness is essential. Over application may result in slow cure and solvent entrapment, whereas under application can lead to a poorly coalesced film and reduction in protection of the steel. Ensure strict adherence to the minimum and maximum thicknesses of both each coat and the overall scheme as stated in the Application Guidelines.
Once dry, the coating film thickness should be measured and rectified in accordance with the specification. The lining should also be checked for any holidays (non- continuous film) by either water testing or low voltage (wet-sponge) or high voltage (spark) testing as appropriate for the lining product/scheme applied (the lining manufacturer should be consulted). Any holidays identified should be addressed.
Some linings require a secondary heated post cure to achieve full cure and this should also be carried out according the manufacturer’s Application Guidelines and monitored to confirm that the required temperature has been achieved for the corresponding full period of cure.
By ensuring that all the above steps have been followed you will greatly increase the chance of successful application of your chosen tank lining and so deliver the performance and earning potential you are expecting
Learn more about the International range of Cargo Tank Coatings.
Contact us if you would like more information or contact our sales representatives in your local area here.