“Hard water from well or even EPA approved to drink treated well can leave your pressure relief valves looking like this. I replaced one on my hot water tank and one on my boiler to avoid a possible larger issue later.”
“Photo indicates L100XL is not correct but perfect for my heater tank and exact model number SL100XL that matched my old valve. I also used teflon tape and pipe sealant on the threads into the tank for extra protection against leaks. No leaks so far. This valve is super important to prevent catastrophic tank failure. Test this valve annually.”