CSC Services refurbish tanks and vessels that operate in harsh environments. Across the UK power sector, tanks can be used for backwashing and rinsing, holding chemicals such as sulphuric acid and caustic soda.
Chemical compatibility is a key factor when a tank is commissioned, and this also needs to be considered when specifying protective coatings for refurbishment purposes. A chemical coating will need to be specified that will satisfy the requirements of both the chemicals used in the tank or vessel, as well as the needs of the substrate.
For the typical refurbishment of a chemical vessel, the existing lining would usually be removed using a range of techniques including shot blasting, induction disbonding and UHP water jetting techniques. The steel substrate’s profile is prepared using abrasive blasting techniques. This will be to a standard of cleanliness meeting ISO 8501-1:2007 Sa3, SSPC S5 and a minimum surface profile of 75 microns (3 mils), as specified in chemical coating system application procedures.
If there is any ancillary pipework, this process will also be applicable. CSC Services will often remove and transport ancillary pipework to their premises where abrasive blasting can be undertaken to achieve such same standards. Offsite work of this nature is used to minimise disruption and allows working operations to continue.
Alternatively, the latest dustless blasting techniques can be used. This is particularly useful for pipework in situ, in confined spaces.
Chemical coating specifications will often require multiple coats of varying colours that are applied until a minimum dry film thickness is achieved. For example, 1200 microns.
Dry film thickness (DFT) can be measured using two methods: destructive thickness measurement, where the coating is cut to the substrate using a cutter, and non-destructive coating thickness measurement, using techniques which do not damage the coating or substrate. CSC Services use a digital coating thickness gauge for this purpose.
Wet film thickness will be monitored during and after the application of each coat to ensure correct values are achieved, in accordance with the SSPC-PA2. The same testing procedures will be undertaken on the ancillary pipework, and full coatings records will be maintained and supplied.
Once fully cured, all ancillary pipework will be refitted. On completion, spark testing will be undertaken to ensure 100% coating coverage has been achieved to specification. The tank or vessel will then be returned to service.
The images below show the micron testing at various stages of coating protection for chemical protection.
