What is an acceptable level of residual magnetism in steel plate 2

[matschka]

We have a contractor who is producing 1.625 in. to 1.875 in. thick steel plate for a very large pressure vessel, Height 215.4 ft. Diameter, 130 Ft. with elliptical heads. They are using magnetic lifting devices after the forming process to move & transport the plates. The Base Material is SA738,Gr.B . Our client is concerned about residual magnetism in the plates affecting the welding of the plates together. What is an acceptable level of residual manetism that will not cause welding problems?

 

[JR97]

Matschka,

The rule of thumb we use is 3G or less is considered demagnetized which is what is listed in ASTM E-1444.

JR97

 

[SJones]

20 Gauss is considered the threshold value for the onset of arc blow. Bear in mind that measured levels of magnetism can increase substantially in the joint area when the individual parts are aligned for welding and as the structure size increases. If the fabricator is experienced, and normally uses magnetic lifting, they should be ready and geared up to apply appropriate measures for avoiding arc blow.

Steve Jones
Materials & Corrosion Engineer

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