MDMT and Brittle Fracture

Brittle fracture at low temperatures can be a major problem with carbon steel and many alloys, if not properly considered in the design stage, and verified with testing. Steel is normally ductile, which is a property that makes it ideal for pressure vessels, structures, machinery, and many other applications. Ductility basically means that when stressed, the material will bend before it breaks. This allows the material to absorb stress and makes it stronger. However, at colder temperatures, steel can sometimes lose its ductility and become brittle, which means complete fracture can occur at much lower stresses than normal. This could obviously lead to catastrophic failures of vessels or any steel equipment. Brittle fracture is what sunk the Titanic!

The ASME code accounts for this by requiring Charpy impact testing for certain combinations of materials, thicknesses, and minimum design temperatures (MDMT). This is a destructive test that breaks a material sample and measures its impact strength at a given temperature. With proper design and impact testing when required, an ASME Code stamped pressure vessel will never fail due to brittle fracture. Contact us if you have any questions about brittle fracture or the ASME Code.