Nitrogen is required under certain codes because it reduces the chances of contamination in structural welds. It’s something that some moron engineer wrote into a couple of code books without ever trying it himself. Based on what I know and have been told it is the equivalent of putting on white gloves to make sure your pictures don’t get dirty when handling them (Ya, it keeps it cleaner but not by much). And as I understand it, the reduction in contamination has more to do with water vapor in compressed air than the actual gas composition. They pull the same BS with air/carbon arc gouging now and then. But yes, it eats your consumables because pure nitrogen is not as effective at cooling them as air is and makes for a hotter cut from what I understand.
Having said that, some of the guys I know who do it for a living have gotten good enough with nitrogen in there plasma that it looks just like air cut. I have also seen one person do plasma cutting with pure oxygen for a special application (don’t try it at home, from what I understand there are special safety considerations) and that made the most incredible cut I have ever seen in my life.
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