Out-of-Tolerance Pressure Gauge on a Hydrostatic Test
A supplier hydrostatically tested five API 6A valve bodies at 7,500 psi for three minutes using a 0-10,000 psi analog gauge. The test record shows a passing result. During records review, the inspector finds that the gauge calibration was due five days before the test. The calibration laboratory report shows that when the gauge was later checked, it read 2.5 percent low at 7,500 psi. The supplier's procedure requires gauges accurate within 1 percent of full scale and calibrated within the past 12 months. The valve bodies have passed final dimensional inspection and are ready for shipment.
1. Is the original hydrostatic test valid? Explain the effect of the gauge error on the actual test pressure.
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The original test is not valid as documented. The gauge was out of calibration at the time of the test, and the later check shows a 2.5 percent low reading at 7,500 psi. If the gauge read 7,500 psi while indicating low, the true pressure may have been higher than intended, or the error may have caused an inaccurate pressure hold; either way the recorded value cannot be accepted as proof of the required test pressure. The procedure also requires accuracy within 1 percent of full scale and current calibration, and neither condition is met. The test record is therefore unreliable, and the lot cannot be accepted on the basis of that test.
2. What corrective action is required before the five bodies can be accepted?
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The supplier should quarantine the five bodies, raise a nonconformance report, and repeat the hydrostatic test using a calibrated gauge that meets the procedure and is within its calibration interval. The inspector should witness or verify the retest, including gauge identification, calibration date, test pressure, hold time, and any permanent deformation or leakage check. If the gauge error could have produced an over-pressure condition, the supplier should evaluate whether the bodies were subjected to pressure above the allowable test limit and inspect for damage. Acceptance should be based on a valid retest, not on a paper calculation correcting the old gauge reading.
3. What broader quality-system issue should the inspector examine, and how should it be reported?
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The broader issue is gauge control and test equipment recall. The inspector should determine whether other tests used the same gauge during its overdue period, whether the calibration recall system failed, and whether spare gauges are controlled. The supplier should review test records back to the last valid calibration date and retest any affected product. The inspector should report the nonconformance, the affected lot, the retest results, and the supplier's corrective action. If multiple tests are affected, the inspector should consider a supplier corrective action request and increased surveillance of test equipment until the recall system is verified effective.