The campaign lives are extended and the risks of process gas leaks past seals are reduced by improved stave coolers that each hang together inside steel shelled furnaces by a single neck extended out through a steel jacketed collar. All the coolant circuits inside the stave cooler are collected and grouped together to pass inside through the one collar. The steel in the collar is matched to the steel used in the containment shell, and a matching steel weld seals them together. Thermal stresses are thereby prevented from accumulating over separation distances as a consequent of the steel's coefficient of expansion. A single point of penetration has no separation distance to another.