A dynamic demagnetizing technique reduces magnetic arc blow in welds by reversing the magnetizing field dynamically.
Fremont, CA: The welding process can be halted if there's residual magnetism in pipes, causing poor quality and costly delays. The welding arc's magnetic field interacts with the residual magnetism field, causing the welding point to deflect away from it.
Welding: How Does It Work?
The arc blows are the most severe in steels with minimal magnetism. After fitting up, the magnetic field becomes concentrated in the pipe gap, reaching 1000 gauss. Welding processes affect this, with fields more significant than 30 gauss causing problems. Steel composition, especially high nickel content, influences arc blows a lot. Root welds are the worst, with magnetic shunting occurring as the weld progresses.
Why Do Pipes Magnetize?
Materials can be magnetized by the earth's magnetic field, magnetic clamps, and residual magnetism from inspections, plasma cutting, or material stress. It's an even, longitudinal field that affects the circumference of the pipe. It's also possible to observe induced magnetism in buried pipes by reversing the polarity.
Getting Rid Of Magnetic Arc Blow
If you remove or reverse local magnetism using external fields, you can fix arc blow problems. In the first option, you heat the material to Curie Point and cool it in a zero field, but it's unpractical for pipes or plates because of energy costs. As a second option, degaussing can reduce parts to zero but is slow and ineffective if the field strength isn't strong enough.
What Is Dynamic Demagnetizing?
A dynamic demagnetizing technique reduces magnetic arc blow in welds by reversing the magnetizing field dynamically. Its ability to compensate for magnetism at any level or direction makes it useful for pipe welding, steel building, shipbuilding, and LNG storage.
Ways to Reduce Arc Blow
Zeromag can reduce and even eliminate the impact of the arc blow, but you can do some simple things without it.
• It's easier to control a backward deflecting arc by welding towards the earth point, and you can use multiple earth points on pipes or circumferential strapping.
• Changing the arc drive parameters affects the level and incidence of arc interference.
• Avoid welding problems with AC or high-frequency AC supply. Using DC supplies can induce high magnetic fields, making removal difficult.
