Oakum
Oakum can be used to seal cast iron pipe drains. After setting the pipes together, workers pack oakum into the joints, then pour molten lead into the joint to create a permanent seal. The oakum swells and seals the joint, the "tar" in the oakum prevents rot, and the lead keeps the joint physically tight.
Today, modern methods, such as rubber seals (for example, gaskets or o-rings) are more common.
Welding defect
A root crack is the crack formed by the short bead at the root(of edge preparation) beginning of the welding, low current at the beginning and due to improper filler material used for welding.Major reason for happening of these types of cracks is hydrogen embrittlement. These types of defects can be eliminated using high current at the starting and proper filler material. Toe crack occurs due to moisture content present in the welded area,it as a part of the surface crack so can be easily detected. Preheating and proper joint formation is must for eliminating these types of defects.