MDMT primarily influences the need for which testing?

• A. Wall thickness calculation
• B. Bolt size determination
• C. Impact testing requirements
• D. Temperature rating of seals

Answer: (C)

The main idea here is how the minimum design metal temperature (MDMT) dictates whether toughness at low temperatures must be demonstrated through impact testing. MDMT is the lowest temperature at which the material or vessel is assumed to retain ductile behavior and avoid brittle fracture in service. To ensure this toughness, impact testing—typically a Charpy V-notch test—is required when service or design temperatures approach or fall below the MDMT. If service temperatures stay well above MDMT, impact testing may not be required; when temperatures are at or below MDMT, confirming impact toughness becomes essential to satisfy the code.

Wall thickness calculations, bolt size determinations, and temperature ratings of seals are important in their own right, but they are not driven by MDMT in the same way toughness verification is.