Sentence:  ... he then heats one half of the <WSD>skelp</WSD> at a time in an air furnace, or other fire, and having so heated it, he passes the <WSD>skelp</WSD> between a pair of grooved rollers placed at the mouth of the furnace, for the purpose of uniting (or marrying, as he terms it) the edges of the metal ; that is, causing the edges of the open part of the <WSD>skelp</WSD> to be pressed together, and made to adhere and form a complete cylinder. 
Meaning of the word marked with <WSD> tags:  A narrow strip of rolled or forged metal, ready to be bent and welded to form a pipe.