Larger length & diameter water pipes are made by

ANS:C - semi-centrifugal casting.

Semi-centrifugal casting is a casting technique used to produce hollow cylindrical or tubular metal components with a uniform wall thickness. Here's an explanation of the process:

1. Preparation of Mold: A mold, typically made of sand or metal, is prepared with a cavity in the shape of the desired cylindrical or tubular component. The mold is mounted on a rotating axis.
2. Introduction of Metal: Molten metal is poured into the mold cavity while the mold is rotating. The centrifugal force generated by the rotation of the mold causes the molten metal to spread uniformly along the inner surface of the mold cavity.
3. Solidification: As the molten metal comes into contact with the cooler mold surface, it begins to solidify, forming a solid shell along the inner surface of the mold. The centrifugal force helps to push any impurities or trapped gases towards the center of the mold, away from the inner surface of the casting.
4. Cooling and Ejection: Once the metal has solidified sufficiently, the rotation of the mold is stopped, and the casting is allowed to cool further. Once cooled, the casting is ejected from the mold.

Semi-centrifugal casting allows for the production of cylindrical or tubular components with a uniform wall thickness and good mechanical properties. It is commonly used to manufacture components such as pipes, cylinders, and rings for various industrial applications, including pipelines, hydraulic systems, and machinery components. The process offers advantages such as reduced porosity, improved grain structure, and better dimensional control compared to other casting methods.