Calculate ASME B31.3 process piping hydrotest and pneumatic leak test pressure and hoop stress check. The test pressure should be 1.5 times the design pressure for hydrotest, or 1.1 times the design pressure for pneumatic test. An allowance should be made for the pipe design temperature.
Hoop stress can be calculated for either the minimum wall thickness (nominal wall thickness minus fabrication allowance), or the pressure design wall thickness (minimum wall thickness minus the corrosion allowance). Minimum wall thickness is recommended for new piping, or piping in as new condition. The pressure design wall thickness is recommended for corroded piping. The hoop stress should be ≤ 100% of yield for hydrotest, or ≤ 90% of yield for pneumatic tests. The test pressure should be ≤ 1.5 x the pressure rating for pressure rated components.
For piping systems with combined internal and external pressure during operation, the test pressure should be calculated from the internal pressure only. The hoop stress should be calculated from the pressure difference during testing. Use the workbook ASME B31.3 data tables to look up allowable stress data.
Note : The choice of high pressure versus low pressure service is at the discretion of the owner (section FK300). The ASME B16.5 Class 2500 pressure temperature rating for the material group is often used as a criteria.
Reference : ANSI/ASME B31.3 : Process Piping (2018)
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