On-site installation of zirconium equipment

This post was last edited by nj1952 on 2017-8-1 at 17:39. The flanges, bolts, and nuts of this structure are made of bimetallic materials with different electrochemical series, and corrosion of the bimetallic materials (electrolytic corrosion) can easily occur in the gaps between them. The use of non-metallic gaskets can effectively prevent electrolyte intrusion. With the electrolyte isolated, bimetallic corrosion should not occur. The basic components of bimetallic corrosion (couple corrosion) include a cathode, an anode, an electrolyte, and a conductor; if any one of these components is removed, the couple corrosion will cease.

Thank you for answering my questions. Assuming that this non-metallic washer is not installed and coulombic corrosion occurs, which one will corrode first? Is it just this reason? For many carbon steel equipment units where flanges are connected using stainless steel bolts, should the washers be made of carbon steel or stainless steel?

1. Assuming that this non-metallic washer is not installed and thus galvanic corrosion occurs, which party will corrode first? Is it just this reason? (1) In a specific electrolyte solution, the electrode potential of the material is measured separately; materials with more negative potentials are base metals, while those with more positive potentials are noble metals. (2) In this electrolyte, the corrosion of base metals accelerates, while the corrosion rate of noble metals slows down. (3) In practical work, the electrode series is commonly used to determine the relative corrosion tendency of metals in a certain medium (for details, refer to relevant literature such as the \"Handbook of Metal Corrosion\"). (4) I believe that in this case, only this factor should be considered. 2. For many carbon steel equipment units where flanges are connected using stainless steel bolts, should the washers be made of carbon steel or stainless steel? (1) Carbon steel. (2) In the potential series, there is a large difference in potential between carbon steel and austenitic stainless steel (in the passive state); carbon steel acts as the anode, while austenitic stainless steel (in the passive state) acts as the cathode. (3) In industrial atmospheres or humid environments, galvanic corrosion typically occurs near the contact points, with the anode (carbon steel gasket) that is closer to the cathode (stainless steel flange) being the first to suffer corrosion. (4) Galvanic corrosion can be controlled through visual inspection. (5) Carbon steel gaskets are used to protect the bolts and nuts; damaged gaskets can be replaced easily, thus saving on costs.

The reply makes a lot of sense; thank you, I’ve learned* it too.