INDUSTRY NEWS
The acid test for sprayable coating on flue gas duct
Even after five years , the effects of acid , corrosion and intense heat have had minimal effect on a flue gas duct at Henkel power plant in Düsseldorf . The reason for this resilience is the ceramicreinforced , epoxy surface coating – LOCTITE ® PC 7255 – that was applied to the inside surface of the duct in 2015 to protect it against aggressive sulphur and nitrogen compounds as well as condensation water .
The performance of the coating was assessed during a recent two-week inspection of and as Operations ’ Assistant , Axel Olschinski , confirmed : “ LOCTITE PC 7255 met the demands of this endurance test and still shows very good chemical resistance .”
LOCTITE PC 7255 is a low friction epoxy that is sprayed onto the substrate and is therefore especially good for coating large surface areas and complex structures . It creates an ultra-smooth and high gloss finish that is resistant to both acids and alkalis and also protects against , abrasion , corrosion and , in particular , chemical attack .
In 2015 , two coats of this product , each at least 250 micrometres thick , were applied by Henkel maintenance engineers to the flue gas duct and within 24 hours the system was returned to full operation .
Protection against warm and humid exhaust gases
The coal-fired power plant provides the entire Düsseldorf production site with energy . As one of its steam boiler systems is operated with hard coal , the flue gas contains - among other things - sulphur and nitrogen compounds that must be scrubbed out in several steps .
The resultant warm , humid and purified flue gases are deposited as an extremely corrosive condensate on the surface of the flue gas duct . So , the aim of applying LOCTITE PC 7255 was to protect the duct to extend its service life , minimise maintenance and underpin production .
Spraying instead of coating
Before LOCTITE PC 7255 was used , it was common practice to shield the flue gas duct with sandwich panels . This method was both complicated and costly . The process of rubberizing the surface with bromobutyl rubber is time-consuming and expensive as the material needs to be adapted to suit the design of the duct . This is precisely where
LOCTITE PC 7255 proves to be particularly efficient and user-friendly : the protective layer can be sprayed on easily and quickly .
Even complex designs involving bends or coils pose no problem . A further advantage is the weight of the product : conventional methods require coatings of up to five millimetres , whereas a coating thickness of 500 micrometres is all that is required for LOCTITE PC 7255 .
Minimum changes in coating thickness
To determine , precisely , the resistance of the coating after five years , changes in colour were examined as a visual indication and the coating ’ s thickness and Shore hardness measured . Engineers were delighted to record that even with long term exposure to extreme corrosion , the thickness of the coating and Shore hardness had changed only minimally over time .
“ With LOCTITE PC 7255 , we create a sacrificial layer that prevents wear and tear of the base material . Thanks to this process , we cut down on costly maintenance work ”, explained Hans-Dieter Krause , Business Development Manager for Maintenance , Repair and Overhaul in Western Europe . “ This method also allows us , for example , to dispense with costly FRP coatings ”.
He concluded : “ Having the option of simply spraying the coating onto a surface and its resistance to adverse conditions saves costs and extends the service life . The plant can be restarted more quickly and remains efficient in the long term . LOCTITE PC 7255 has certainly passed our five-year endurance test and displayed an impeccable performance .”
For more information go to : www . henkel-adhesives . co . uk
20 MARCH 2021 read online : www . surfaceworld . com