In the field of welded pipe,the main defect of the weld is the position of the weld.When dealing with weld position defects,how to deal with inter-crystalline corrosion is an unavoidable problem.So what is the inter-crystalline corrosion?

When unstable Austenitic stainless steel with a carbon content of more than 0.03% is heated between 425 and 815℃,or slowly cooled through this interval temperature,under the action of corrosive media,the corrosive phenomenon between grains is called inter-granular corrosion.Stainless steel that produces inter-crystalline corrosion will be disconnected along the grain boundary when subjected to stress,and the strength will almost completely disappear.This is one of the most dangerous cases of stainless steel.The corrosion resistance of stainless steel that produces inter-crystalline corrosion will also slowly decrease until the corrosion resistance is lost.

What are the ways to relieve inter-crystalline corrosion?

1.Adjust the chemical composition of the weld and add stabilizing elements to reduce the possibility of chromium carbide formation,such as adding titanium or niobium.In stainless steel,the internal carbon content is generally large,so the carbon will spread to the grain boundary and bind to chromium to form a compound.

2.Reducing the carbon content in the weld can reduce and avoid the formation of chromium carbide,thus reducing the tendency to form grain boundary corrosion.The carbon content is less than 0.04%,which is called “ultra-low carbon” stainless steel,which can avoid the formation of chromium carbide.Reduce the excess amount of carbon in the weld,so as to improve the mass fraction of chromium in the weld and ensure corrosion resistance.

3.Control the resistance time in the dangerous temperature zone to prevent overheating,fast welding and cooling,so that the carbon is not lated.

Bright annealing is an indispensable step in the production of industrial welded pipes to improve the quality of welded pipes to high standards.We take Hangao’products as an example to learn how to reduce the inter-crystalline corrosion of pipes in bright annealing.

The equipment quickly heats the pipe to the specified temperature online,and then quickly cools it to less than 100℃ under gas protection.The heating power supply to heat the conductor itself by using the induction current generated under the action of a high-frequency magnetic field,which has the characteristics of significant energy saving,non-contact and fast speed.Heat exchange and hydrogen are used for cooling in the cooling section.Because graphite has good thermal conductivity,hydrogen transfers heat to the external water pipe for cooling.Multiple combinations enable stainless steel pipes to achieve rapid cooling.

For more product information,you can click Intelligent Bright Annealing Machine,Intelligent Insulation Type Bright Annealing Machine.

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