I am using an Electric Boil Keggle made from a 1 in stainless nut and a 5500W ULD heating element. I'm getting rust on the base of the heating element, and some is transferring over to the stainless steel. Just wanted to get peoples thoughts.
Is this a problem?
Is there a way to avoid this?
Couple of things:
Firstly you have a water heater element. They ain't made for this duty.
Industrial process heaters are sheathed in super alloys like Inconel. Inconel is an austenitic stainless heavy in nickel and chromium.
It's possible your pot is 316 Stainless which is lower in Chrome than 304 and chrome is the only reason that Stainless is stainless. The chrome develops a passive oxide layer on the surface that resists oxidation and corrosion.
Simply put 304 is better for your application. It resists attack better.
But 304 is not the super alloy that Inconel is.
You can get SST to rust by stripping away the passive layer of chrome. Do that with Muriatic acid, various food acids, and of course with regular steel by abrading it against the SST surface. Also you can rust SST by heating it and a high temperature will flash off the chrome and if rust sets in before an new passive layer forms you get rust and pits. Which is why BBQ grill grates made of SST, rust.
You can remove the rust and re-establish that passive chrome oxide layer by soaking your SST in a solution of Citric acid. The solution strength is not terribly important nor is the temperature or time. Heat accelerated the process. You can buy citric acid on E-bay in powder form it is so common. You can even use lemon juice.
Too much time and even citric will take the chrome off, but that takes a very long time.
So you can manage the rust issue by passivating your SST pot with citric acid.
Preventing it is another matter altogether. I suggest you consider a different element. Maybe a Stainless steel CAMCO element. Though that too will eventually fail and start rusting but it won't happen overnight.
As to how this rust is "transferring" I suspect that it's literally falling off the element and the mere contact with iron oxide is attacking your pot.