Which of the following is an effect of cold working on metal pipes?

Cold working is a process where metal is shaped and deformed at temperatures below its recrystallization point, resulting in several significant changes to its physical properties. One of the primary effects of cold working is an increase in strength due to the introduction of dislocations and strain hardening within the metal's microstructure. As the metal is deformed, its crystalline structure becomes more densely packed with defects, resulting in increased resistance to deformation.

This increase in strength, however, often comes at the cost of ductility. The material may become more brittle, meaning it is less capable of undergoing plastic deformation before fracture. Therefore, while the strength of the metal is enhanced, the risk of brittleness also increases, making it important for a pipefitter to consider these properties when working with cold-worked metals.

The other effects noted in the alternatives, like increased ductility and malleability, are typically not associated with cold working; in fact, ductility tends to decrease. Cold working does alter material properties by increasing strength, but this comes with a potential for brittleness, making option C the most accurate choice regarding the effects of cold working on metal pipes.