It is commonly stated that “stainless steel pipe is non-magnetic”. This is not strictly true and is rather more complicated in the real situation. The magnetic properties of stainless steel pipe depended on the addition of the elements into the alloy. A basic stainless steel pipe has a ‘Ferritic’ structure and is magnetic such as 430 pipe,420 pipe and 410 pipe, formed from the addition of chromium – it can be hardened through the addition of carbon, making it ‘Martensitic’.
However, the most common stainless steels pipe are ‘Austenitic’ such as 201 pipe, 202 pipe, 304 pipe, 316 pipe– these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the pipes and makes it theoretically non-magnetic or weak-magnetic.
But due to improper smelting composition segregation or heat treatment, the Austenitic 304 stainless steel pipe will cause a small amount of Martensite or Ferrite in organizations.
In addition, the organization structure of 304 pipes will be to the Martensitic transformation after cold working, the greater the degree of cold, the more deformation Martensitic transformation, the more magnetic.
As the same stainless steel pipe, , there are no obvious magnetic induction when make it straight, but bent it into a rectangular or circular, the magnetic is more obvious especially the knuckle part .In this way, will with weak magnetic 304 stainless steel pipe.
How to detect the stainless pipe is magnetic or not. The magnet test is necessary to the pipe to get it to change the arrangement of the atoms to get ferromagnetic properties.In order to strengthen the performance of 304 stainless pipe, the magnetized 304 pipes have to be demagnetized before using.Then how to demagnetize 304 stainless steel pipe?there are two commonly using ways.
1 Direct current demagnetization
Connect the automatic demagnetizer’s power plug to a standard alternating current outlet and turn the unit’s power on, if needed. Set it on a non-metallic table.
Press the demagnetizer’s “trigger” button momentarily. The device runs through a demagnetization process automatically.
Test the demagnetized 304 pipe by attempting to pick up a staple or two. If the steel object is still magnetized, repeat the process.
2 Heating demagnetization
Place the magnetized 304 steel pipes in the furnace and close the door. Set the temperature to 770 degrees Celsius (1,417 degrees Fahrenheit). Turn the furnace
Note the time when the temperature reaches the set value. Allow the furnace to remain at that temperature for at least five minutes. Turn the furnace off and allow it to cool to room temperature.
Test the steel object by attempting to pick up staples. If it is still magnetized, repeat the process.
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