Hydrostatic Test Run With the Wrong Gauge and Cold Water

Test pressure. For a hydrostatic test the minimum is 1.3 times the maximum allowable working pressure, multiplied by the ratio of allowable stress at test temperature to allowable stress at design temperature. For this carbon steel vessel the stress ratio is essentially 1.0, so 1.3 x 300 = 390 psi is a reasonable calculation, subject to confirming the actual maximum allowable working pressure rather than assuming it equals design pressure.

Deficiencies:

1. Gauge range. The gauge must have a range such that the test pressure is within the usable band of the dial - broadly, the test pressure is not less than 1.5 times and not more than 4 times the gauge range. A 0-300 psi gauge cannot even read 390 psi. The correct range here is roughly 600-1000 psi full scale.
2. Gauge calibration. The sticker is 22 months old against a 12-month program, so the gauge is out of calibration and unacceptable. There is no evidence of an as-found check.
3. Water temperature. The metal temperature during the test must be at least 30 F above the MDMT, i.e., at or above 50 F. Water at 45 F fails this requirement, and the metal temperature was never measured; ambient air temperature does not establish metal temperature.
4. Single gauge at full scale. The gauge was pegged, so the actual pressure applied is unknown.

The test is not acceptable and cannot be recorded as a satisfactory hydrostatic test.

Disposition:

• Raise a nonconformance and do not authorize the test record.
• Treat the vessel as potentially over-pressurized. With the gauge pegged at its maximum, the true peak pressure is unknown and may have exceeded 390 psi. Require evidence of no permanent deformation: circumferential and longitudinal dimensional checks against pre-test readings, examination of welds and nozzle connections, and review of the pump and relief arrangement to estimate the maximum pressure the system could have produced.
• Drain and inspect for any evidence of distress before proceeding.

Before re-test:

• Install a calibrated gauge of correct range, with a current certificate, and ideally a second gauge or recorder for cross-check.
• Heat the water and verify metal temperature with a contact thermometer at several points, confirming at least 50 F before pressurization and throughout the hold.
• Re-confirm the test pressure calculation and the maximum allowable working pressure.
• Verify the test procedure addresses venting, pressurization rate, hold time, and examination of all joints and connections.

Before start: gauge identity, range, and calibration certificate; the second gauge or recorder; the test pressure calculation against the maximum allowable working pressure; water temperature and measured metal temperature at several locations; that all vents are open and the vessel is fully filled; that no lining, coating, or insulation hides joints; that the pump and any relief protection are set so the vessel cannot be over-pressurized; and that access to all joints is safe.

During pressurization: rate of pressure rise is controlled; no visible leakage or weeping at welds, nozzle connections, manways, or gaskets; the gauge responds smoothly; metal temperature stays above the minimum.

At hold: confirm the gauge reading equals the calculated test pressure, record gauge identification and reading, start and end times of the hold, and the metal temperature. Personally examine every accessible joint and connection, including the bottom head and skirt area. Note any leakage, sweating mistaken for leakage, or permanent set.

After: record the result, confirm controlled depressurization, and ensure the record you sign states exactly what you observed and when.