Why can't stainless steel and carbon steel come into contact?
When conducting safety inspections in enterprises, it is often found that stainless steel pipes and carbon steel pipes are mixed together. When the enterprise is informed of the risks, some personnel do not take it seriously.
1、Standard basis for stainless steel and carbon steel materials not to come into contact
According to Article 4.3.3 of the General Code for Steel Structures (GB55006-2021), when stainless steel components are connected to carbon steel and low-alloy steel components using fasteners, insulation gaskets should be used for separation or other effective measures should be taken to prevent bimetallic corrosion, and the mechanical properties of the connection should not be reduced. Stainless steel components should not be welded to carbon steel and low-alloy steel components.
2、 The hazards of contact between stainless steel and carbon steel
Contact between stainless steel and carbon steel can result in carburization and intergranular corrosion. The phenomenon of carburization refers to the diffusion of carbon atoms from carbon steel to the surface of stainless steel. When the local carbon content exceeds 0.08%, chromium carbide is formed, resulting in chromium depleted areas at the grain boundaries of stainless steel and a 30% -50% decrease in material strength. Intergranular corrosion refers to the possibility that carbon steel welding rods may cause intergranular corrosion in stainless steel during the welding process. Corrosion that propagates along grain boundaries can significantly reduce the performance of the weld seam.
When stainless steel pipes come into contact with carbon steel pipes, especially in humid environments, electrochemical corrosion occurs between the two. When stainless steel comes into contact with carbon steel, there is a significant potential difference (over 500 millivolts), which can form a galvanic cell effect in humid environments. When they are in an electrolyte solution (such as water), a galvanic cell is formed, and this corrosion rate can reach 3-10 times that of when they exist alone, potentially causing a corrosion depth of 0.1-0.5 millimeters per year.
3、 Special Instructions
Industries such as petrochemicals may allow welding under specific conditions (such as using A302/A312 welding rods), but it is not advisable to use them under low temperature and high pressure conditions.
The construction industry strictly enforces this ban, especially for steel load-bearing structures.
