Thereafter, {HEAD ~ a pouring aperture} is cut in {TAIL ~ the barrier layers} which span the opening 
is cut in
Thereafter , { HEAD ~ a pouring aperture } is cut in { TAIL ~ the barrier layers } which span the opening
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH