Expansion of the underlying ring brings {HEAD ~ the sealing material} into {TAIL ~ contact} with the surrounding tubular 
Expansion of the underlying ring brings { HEAD ~ the sealing material } into { TAIL ~ contact } with the surrounding tubular
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH