I have elements that still provide "some" resistance heating, and give very odd readings on an ohmmeter. On inspection, the casing is blown out, and the resistance wire is in the water, breaker not blown. Go figure.
The elements are "generic" so you do not have to worry about anything other than getting a "low watt density" one. You will recognize it because it has a "double" fold whereas the cheaper "high watt density" one are a single "U" shape.
Here are some exceptions: I have an electric water heater feeding into a gas Polaris for radiant floor heating and tap water. The electric unit does 95% of the work.
I have a trash can full of elements of every make, color and style and can say I am an expert in the destruction of elements. I have rewired the heater so that both 4500w elements are on together. The water is top quality but quite a bit of dissolved solids that build up on the element.
Element type 1] High watt density about 12" long various types of outer sheath - copper, nickel, no-name.
Type 2] Low watt density, a single fold back, perhaps 1/2 the watt density.
Type 3] Ripple element, able to dry fire, 10 year warranty. Super low watt density.
Expensive test results: Ripple elements are junk, usually sold by Camco. Customer No-service. Some blew out in a week, looks like the ripples cause stress points. Also blow out at the base. Poor mfg process most likely.
Low watt density. Used those most of the time. Some from Graingers with a nickel alloy sheath lasted 2 or three years plus. Others blow in a few months.
Went back to high watt density, got the longest life. My conclusion is that the calcium builds up on the low watt density elements until it becomes quite a good insulator, overheating the element internals.
The high watt density I am guessing gets hot enough to expand and crack the calcium layer, allowing it to self clean. A huge pile of stalagtites in the bottom of the heater seems to verify that.
They may look generic, but are anything but. Perhaps my use is extreme in the winter. I am about to pull the anode rod and see if its decayed. Websites say to change the rod every 5 years [?]