corroded spark plugs

anyone have trouble with corroded spak plugs on the 5.4 triton v-8 engines. Had mine replaced as preventitive maintenance at 85,000 miles supposed to last 100,000 by the advertisements and service manuals.
#3 cyclinder plug was corroded so bad that it broke off. Need to pull head to repair.

corroded from the inside out or from the outside? Do a leakdown test on the coolant, might have a bad intake or head gasket.