An important design factor for steel pipe is toughness. Toughness is a measure of the resistance of the steel to brittle cracking including the ability to stop crack propagation. Once a crack initiates, the internal pressure tends to push the crack edges out, which directs energy to continue growth of the crack. Cracks are problematic since they are a source of leaks.
At low temperatures experienced in regions as such as Canada and Northern Europe, steel that is not sufficiently tough can fracture in a manner where the crack travels long distances — hundreds of yards or even a mile or more. A pipe with sufficient toughness will result in the crack being stopped in a distance of only inches since the pipe is tough enough to resist propagation of the crack. Toughness is measured using tests such as the Charpy Impact or the Drop Weight Tear Test.