Guide to Chemical Protection Guide to Chemical Protection

Guide to Chemical Protection

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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 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. 

Removal of existing coatings

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, 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 SP5 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 CSC Services’ 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.  

DFT Testing

Chemical coating specifications will often require multiple coats of varying colours 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 the substrate. CSC Services use a digital coating thickness guage 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.

Images showing the micron testing at various stages of coating protection for chemical protection are shown below.

CSC Services can repair and reline a range of tanks and vessels. For advice and information on protective coatings that offer chemical protection call 0191 410 3444.

Micron testing of chemical protection coating
Micron testing of chemical protection coating
Micron testing of chemical protection coating
Micron testing of chemical protection coating