Final answer:
The initial step in interlocking two joints of iron pipe is to inspect for corrosion, especially at junctions where different metals meet, leading to electrochemical reactions that may compromise the integrity of the iron.
Step-by-step explanation:
The first step of interlocking two joints of iron pipe is to carefully examine any existing Pb/Fe (lead/iron) or Cu/Fe (copper/iron) joints for signs of corrosion. In cases where different metals are jointed, such as a Pb-Fe junction, the less active lead serves as a cathode for the reduction of O2, promoting oxidation of the more active iron, which is at risk for corrosion. To minimize corrosion and extend the longevity of iron pipes, it is essential to assess any existing metal joints and consider using compatible materials that do not lead to rapid corrosion.