obtained extending on both sides of the completed wall structure as in fig3 these weld joints 9 and 9 u2032 are illustrated in fig4 by dashed lines the weld joints 9 and 9 u2032 have the same substantially t shaped cross section as in the abovementioned first embodiment the advantage with the second embodiment is that no milling is required of the inner wall 2 u2032 thereby affording time and material savings in this embodiment the distancing elements 4 u2032 must instead be fixed in a suitable manner between the inner wall 2 u2032 and the outer wall 3 after which welding is realized on both sides of the wall structure in fig5 a portion of an outlet nozzle 1 according to the present invention is shown more precisely a portion of the inner wall 2 with associated distancing elements where this structure has been manufactured according to the abovementioned first embodiment these distancing elements are configured by milling according to fig5 the distancing elements are divided into a first set of distancing elements 4 a and a second set of distancing elements 4 b in which the second set is positioned somewhat displaced in the longitudinal direction of the.