How should I expose photos of welding so the arc isn’t blown out?

There is nothing particularly special about photographing welding... it is very much like photographing fireworks.

The main thing is to stay back and use longer focal lengths to get the composition. Use smaller apertures like f/11 for adequate depth of field, and slower shutter speeds of around 1/125 to get spark trails. Use a tripod and remote release (not looking through the viewfinder) and shoot in small bursts. I would also be using full manual settings for this.

If you photograph the welder from the arc side the brightness of the arc will also illuminate the welder to nearly the same brightness and equalize your exposure. If you photograph the welder from the dark side the ambient and the arc will be very dissimilar; and you would need to add additional lighting on the welder (using flash)... this will actually help freeze/focus the welder in combination with the long SS for the spark trails, but complicates the setup and the work environment (you might need to add a lot of light from a short distance).

In any case you may need to use a fairly strong neutral density filter to allow slow enough shutter speeds. You can make a variable ND by stacking two linear polarizers which you can usually find used for cheap... they're not good for SLR camera's metering/autofocus systems and have largely been replaced by CPL's; but they are fine for a manual exposure/pre-focused situation like this, and they're fine for mirrorless use/cameras (i.e. live view photography).

You can also use welding glass as an ND filter, just secure it to the lens with rubber bands... #8 is about 10 stops, and #10 is about 13 stops. But it will have a strong color cast that will have to be corrected in post.

As long as your exposure is controlled there is little risk of equipment damage... the primary risk to humans is the strong UV emitted; but the glass of a lens, and the UV/IR sensor filter, eliminates most of that risk.