ASME Code Standards For Pressure Vessels And Piping Engineering Practice Test

Under UG-99, hydrotest pressure is MAWP × ?

MAWP × 0.9 MAWP × 1.0 MAWP × 1.5 MAWP × 1.25

Correct Answer:

MAWP × 1.25

Explanation:

Under UG-99, the hydrostatic test is used to verify the vessel’s strength and leak-tightness by applying a pressure higher than its operating limit. The code specifies a test pressure of 1.25 times the MAWP, which provides enough margin to reveal hidden flaws or leaks without pushing the material into plastic deformation or causing damage. This 125% level balances safety with practicality, ensuring the vessel can withstand pressures above its normal operating range while staying within safe stress limits. Using a lower factor like 0.9 or 1.0 would not give any margin above the MAWP, and a higher factor like 1.5 could introduce unnecessary risk of distortion or failure. Hence, 1.25 × MAWP is the standard hydrotest pressure per UG-99.

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