mass itself is practically chemically inert the tube bed 1 and the tube 2 are completely protected from the damaging cooling water this essentially eliminates galvanic corrosion fig1 b and c show common variants of the coolant tube extension with flush end 1b and with projecting end not pressed outward 1c in each case 1a through 1c the tube end 3 being completely integrated in the coating 6 7 fig2 shows the layered construction of the coating in accordance with the invention details of the tube bed coating and the tube coating are shown in sections a and b fig2 a and 2b the tube bed 1 itself exhibits a primer 8 underneath the actual coating 6 the primer filling in smaller irregularities the polished surface of the coating 6 is initially protected by a sealant 9 that runs into the tube and forms the exterior layer in the tube coating the wall 2 of the coolant tube is initially provided with a primer 11 on the cleaned metal surface the actual coolant tube coating 7 adjusted elastically with respect to the coating for the tube bed is applied to this base 11 in the case illustrated the coolant tube 2 is not coated over its entire length but rather only in the entry area the coating running out conically in its entirety section b e g each of the layers projecting farther into.