Blower Vibration Above the Contract Limit at Provisional Acceptance
A 2,500 kW centrifugal process blower is mechanically complete. The contract adopts an ISO 10816-3 Zone B limit of 4.5 mm/s RMS and requires a four-hour stable run at operating conditions before provisional acceptance. At 3,000 rpm and 38 °C ambient, the motor NDE horizontal vibration is 4.8 mm/s RMS, dominant at 1X; the blower DE is 3.9 mm/s. Laser alignment before start-up showed 0.03 mm parallel offset and 0.02 mm/100 mm angularity. A soft-foot check shows 0.08 mm at one motor foot. When the discharge flange bolts are loosened, the flange moves 0.15 mm and vibration drops to 4.2 mm/s. The vendor says the reading is within API 610 tolerance and offers a 12-month warranty if the owner accepts now. The owner wants to start production and asks the supervisor to sign provisional acceptance with a punch list.
1. Should the supervisor accept the machine as meeting the contract? Give the reasoning and the technical significance of the symptoms.
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No. The contract acceptance criterion is 4.5 mm/s RMS under ISO 10816-3 Zone B, and the measured motor NDE value is 4.8 mm/s. The vendor's reference to API 610 is not the contractual standard for this blower, and a warranty offer does not change the acceptance criterion. A reading above the limit cannot be signed off as compliant.
The symptoms point to a correctable installation problem rather than an inherent machine limit. The vibration is dominant at 1X, which is consistent with misalignment or shaft distortion. The soft foot of 0.08 mm means the motor frame is being twisted when the hold-down bolts are tightened. The discharge flange movement of 0.15 mm when the bolts are loosened indicates pipe strain imposed on the casing. Both effects can raise 1X vibration and can change with temperature. The fact that vibration falls to 4.2 mm/s when the flange is relieved supports pipe strain as a contributor.
The correct conclusion is that the machine is not yet acceptable, but the cause is likely removable. The supervisor should not treat the 12-month warranty as a substitute for meeting the contract; a warranty covers repair costs, not lost production or the risk of repeated shutdowns.
2. What corrective actions and retest programme should be required before provisional acceptance?
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The supervisor should require a structured correction and retest. First, the motor and blower should be isolated and the soft foot eliminated: check all feet with a dial indicator or laser, shim to within the vendor's tolerance, and confirm that tightening each hold-down bolt does not change the foot load. Second, the discharge piping should be fitted without strain: the flange should be brought to the casing without pulling it into position, and the pipe supports should be adjusted so that the flange movement on bolt loosening is minimal. Third, cold alignment should be rechecked and a hot alignment check performed at operating temperature, because 38 °C ambient and heat from the blower can change the shaft position.
The machine should then be run for the full four-hour stable period at operating conditions. Vibration should be recorded at all bearings and in three directions, with a spectrum to confirm that 1X has fallen. Acceptance should be based on the contract limit of 4.5 mm/s RMS and on stable readings, not on a single spot reading. If the vibration remains above 4.5 mm/s after soft foot, pipe strain and alignment are corrected, the vendor should provide a root-cause analysis and a corrective plan; the supervisor should not accept the machine on a promise of future improvement.
3. The owner wants to start production immediately. What acceptance and commercial stance should the supervisor recommend?
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The supervisor should separate production need from contractual acceptance. Provisional acceptance should not be signed while the machine exceeds the contract vibration limit and the cause has not been corrected. Signing would transfer the risk to the owner and weaken the owner's position if the vibration later causes bearing or coupling damage.
A workable compromise is a controlled trial run under a written reservation: the owner may operate the blower for a defined period with enhanced vibration monitoring, but the acceptance certificate and the relevant payment milestone remain withheld. The vendor should be required to correct soft foot, pipe strain and alignment within an agreed period and to repeat the four-hour test. The reservation should state that operation does not constitute acceptance and that the vendor remains responsible for meeting the limit.
Commercially, the owner should withhold the acceptance milestone payment or retention until the retest passes. The 12-month warranty can be accepted as an additional protection, not as a substitute for the test. If production cannot wait, the owner should document the decision at management level and accept the residual risk knowingly; the supervisor should not sign a statement that the machine complies when the recorded data show it does not.