To understand why stainless steels are passivated after welding, we need to first find out what is the exact meaning of a passive state and how and why welding affects this state in a negative manner. Passivation is of the utmost importance to keep the performance level of a stainless steel at the very top.
Brief Introduction to Passivation
Corrosion resistance is undoubtedly a key characteristic of stainless steel. Without it, the functionality of a stainless steel is dearly compromised. To make sure that the corrosion resistance of a stainless steel is maintained as much as possible throughout its use, the stainless surface is manipulated to be in a passive state. Long story short, passivation is the reason why stainless steels remain corrosion resistant for so long. To be in a passive state, a thin layer of chromium oxide has to form on surface of the metal. This is achieved through the process of passivation. If you are looking into chemical passivation, then you would find that alkalines, wetting agents, chelants, and organic or inorganic acids are used on a regular basis to polish the metal surface scrupulously. Since the metal surface is left exposed to an oxygen rich atmosphere, a uniform layer of chromium oxide develops on the surface.
Effectiveness of Passivation against Welding
Many people are unaware of the fact that stainless steels are often in a natural passive state. However, whenever the steel is manipulated or fabricated in any way, such as when it is welded, the natural chromium oxide film on the metal surface is tarnished. As a result of that, the corrosion resistance of the stainless steel weakens following welding. To restore the chromium oxide film on the surface of the metal, one needs to passivate the stainless steel. As a matter of fact, one of the main reasons why stainless steels need to be passivated is because of welding. As a metal is welded, it loses its free iron from the alloy and the overall structure of the metal surface is transformed considerably. In the heat affected zone of the weld, the chrome to iron ratio is significantly decreased. The iron that is free flowing on the metal surface of the stainless steel can facilitate corrosion/roughing.
Limitations of Passivation
Whether or not you use a proper weld determines the success of the passivation process. It is true that passivation eliminates most of problems that are related to welding. However, as mentioned before, the effectiveness of the passivation process relies heavily on the quality of the weld used. If intense discoloration takes place during the welding process, then passivation will do little good to the stainless steel. In addition to that, passivation is quite ineffective against the ill effects of sugared welds. As a final verdict, it can be said that passivation is the best solution to the problems created by welding. However, passivating stainless steels alone will not ensure the maximum productivity of the substance after the welding process.
Cougartron ProPlus for Electrochemical Weld Cleaning
Staying on the topic of welding, electro chemical cleaning is the best method to keep your welds neat and completely passivated. If you are looking for the latest and greatest system for electrochemical cleaning, then look no further than Cougartron’s ProPlus. This system uses the most advanced technology to provide you with a stellar service. It’s easy to use and gives you the best electrochemical cleaning and passivation that you could expect.
With this system you get IMMEDIATE passivation! In addition to that, you can use it safely without having to worry about health hazards, and it can be very conveniently transported. Last but not the least, the stunning outward appearance of Cougartron ProPlus combined with its unmatched functionality will leave you thoroughly satisfied with your investment.
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