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                    


       


 





  





  


TECHNICAL PAPER 


                


Figure 4: Schematic of chorine attack in the presence of alkali deposits under low oxygen partial pressure (reducing conditions) (M.A. Uusitalo, P.M.J. Vuoristo, T.A. Mantyla)


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309SS anchor. The chlorine penetrates the steel structure through the weaker grain boundaries and attacks the individual grains. The scale around each grain increases and wedges the grains apart to allow for even deeper penetration. This anchor was in operation for less than a year and most of the corrosion was evident in the area of the anchor where the temperature was within the sigma phase formation temperature of 425°C to 870°C.


   


Some anchor manufactures claim better performance of their anchors by a slow bending process rather than punching. Evidence of a punch technique is normally visible as a sharp indentation on the surface at each bend compared to a smooth surface on the inside of the curvature. Figure 7 is a good example to support the idea that corrosion is more likely to happen where a punch was used to form the bend. The areas around the bend were still fine with little corrosion whereas the inner part of the bend was heavily attacked by chlorine corrosion.


  


 


 





   





 


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 


         


 


 





   


  


Conclusion


Even though there may have been a time when metal anchorage was the simple solution to secure a lining to the steel shell, the ever increasing challenges of the modern process conditions requires a different approach to refractory lining design.


Metal anchors can be useful in securing refractory linings, but it can also be the main cause of a lining failure if not chosen well. In applications where chlorine is present it may well be argued that metal anchorage should be avoided and that solutions should be sought not requiring the use of metal. Design of vessels processing aggressive gas environments should rather be based on brick linings with domes or cones.


Through this three part series on anchor problems, an appreciation was hopefully created that anchor selection is a dedicated discipline within the design of a refractory lining.


Figure 6 left: Microscope image of 309SS exposed to chlorine in an area where sigma formation has occurred


 


Figure 5: Schematic of chorine attack in the presence of alkali deposits in the presence of oxygen (M.A. Uusitalo, P.M.J. Vuoristo, T.A. Mantyla)


   


 


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Figure 7: Microscope image of corrosion taking place in the area of an anchor bend


NOVEMBER 2014 ISSUE WWW.IRENG.ORG


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 





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


 





 





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