The welding seam can have {TAIL ~ any desired shape}, as long as it exhibits a sufficient length and strength, in order to ensure {HEAD ~ a permanent joining} of the sheets 
The welding seam can have { TAIL ~ any desired shape } , as long as it exhibits a sufficient length and strength , in order to ensure { HEAD ~ a permanent joining } of the sheets
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH