Consider a pressure vessel fabricated from SA-240 Type 304 stainless steel. The fabricator decides to reduce the hydrostatic test from 1.3 × MAWP to 1.25 × MAWP to avoid gasket failure on a large manway. Is this acceptable?
Instead of UG-99, the repair organization must calculate the Maximum Allowable Working Pressure based on current corroded thickness (often called MAWP_remaining). The required post-repair leak test pressure is typically 1.1 × MAWP_remaining (or the original test pressure, whichever is lower). This ensures you are not overstressing an aged component. asme test
A vessel designed for -20°F using SA-516 Gr. 70 is hydro-tested outdoors in January at 35°F water temperature. While the water may not freeze, the vessel wall is at 35°F. The MDMT is -20°F, so this appears safe. However, the high stress concentration at a weld toe plus the hydrostatic test stress could initiate a brittle fracture if the material’s Charpy V-notch properties are not verified. ASME requires that the test temperature be at least 30°F above the MDMT unless a fracture mechanics analysis is performed. Consider a pressure vessel fabricated from SA-240 Type