Which of the following discontinuities could be found in sand castings?

Pipe discontinuities in sand castings occur due to the shrinkage of molten metal as it cools and solidifies. When the metal cools, it contracts, and if there is insufficient liquid metal to fill the cavity created by the contraction, a void known as a pipe forms. This typically happens in the upper sections of the casting, where the material has already solidified while the lower sections are still liquid.

Understanding this specific type of discontinuity is essential in casting processes, as it can affect the overall integrity and mechanical properties of the final product. It's important to manage the gating and riser design properly to ensure that adequate metal is available to compensate for shrinkage, thus minimizing the occurrence of pipe.

The other types of discontinuities, like cavities, bubbles, and craters, originate from different causes such as trapped gas, inclusions, or surface irregularities. Each has its own implications for the casting process but does not relate to the unique phenomenon of shrinkage voids that result in pipe discontinuities.