What does the factor of safety compare?

The factor of safety is a crucial concept in engineering that provides a measure of how much stronger a system is than it needs to be for an intended load or stress. It is calculated by comparing the maximum load that a material can withstand (the tensile strength) to the actual load or working stress that the material will experience in practical use.

When engineers design structures, components, or materials, they need to ensure that these elements can support expected stresses without failure. The factor of safety serves to account for uncertainties in load conditions, material properties, and potential flaws in manufacturing. By ensuring a greater tensile strength compared to working stress, engineers can mitigate risks of failure and enhance safety.

In contrast, the other options address different aspects of engineering considerations. The weight and cost effectiveness relate to economic decisions rather than stress comparisons, dimensions of pipes to their pressure ratings focus on material suitability for specific applications, and thermal expansion compared to cold shrinkage deals with material behaviors related to temperature changes. None of these options address the specific comparison used for calculating the factor of safety, which firmly ties back to comparing tensile strength with actual working stress.