CORROSION INVESTIGATIONS IN PULPING AND BLEACHING MEDIA

Abstract

The thesis starts with introducing the process and conditions of paper making with a view to have an idea about the corrosivity of the liquors and possible candidate materials of construction. Since pulping and bleaching sections are among the more corrosion prone sections, the investigations were performed related to these sections. Accordingly, emphasis has been given on the description of pulping and bleaching section. A review of the literature has been presented in the first chapter dealing with corrosion aspects and materials performance in pulping and bleach plant and related liquors. The second chapter deals with the experimental aspects of the various laboratory and in-plant tests conducted. The next three chapters discuss and analyze the results of various tests done as a part of the present dissertation. Attempt has also been made to suggest possible materials of construction. The last chapter deals with the conclusion on the work and recommendations about the work that needs to be done in future. A brief idea of the above has been given in following paragraphs. Chapter -1 : Introduction This chapter introduces about paper making process and gives an account of corrosion prevailing in pulping and bleaching sections, being the more corrosive sections of a paper mill. A survey of the literature has been done to show various attempts made in past for controlling corrosion in pulping and bleaching sections by appropriate material selection or otherwise. The prevailing process conditions in pulping section indicate to be corrosive due to various sulphur compounds. In bleaching section it is mainly due to the application of oxidizing bleaching chemicals. Consequently following was proposed for investigation: 1. Construction of E-pH diagram for S-H20 and Fe-S-H20 system for the electrolyte having sulfide and thiosulfate in the amount as observed in pulping liquor. Long term immersion test in laboratory prepared pulping liquor at room temperature on mild steel, austenitic stainless steel 304L, 316L and duplex stainless steel 2205. This had to be followed by quantitative estimation of uniform and localized corrosion attack and the analyses of the result on the basis of liquor composition and E-pH diagram, wherever possible.( Chapter 3 )