The problem of excessive vibration in series oil transfer pump systems

Thread Content

In a certain long-distance refined oil pipeline, the main pumping pumps (for pressurization) at each pumping station operate in series. Each station typically has 4 centrifugal pumps operating in series – pump No. 1 is usually of the BB1 type, while pumps No. 2, 3, and 4 are of the BB3 type – with at least one pump serving as a spare. The rated flow rate ranges from 130 to 1250 m3/h, the rated head ranges from 110 to 400 m, the rated power of the motors ranges from 330 to 1100 Kw, and the installation center height of these pumps is all above 225 mm; their rotational speed is 2970 rpm. This kind of situation is often encountered when individual oil transfer station pumps are in operation. When a single pump is running, its vibration levels remain within acceptable limits (below 3 mm/s), but once two adjacent pumps operate simultaneously, the vibration increases significantly; in some cases, the horizontal vibration of the pumps increases more noticeably than the vertical vibration. Could everyone please analyze what possible factors might be causing this issue? Additionally, pumps are manufactured in accordance with API standards, but for the management of vibration levels, we generally follow ISO standards, considering a level of 7.1 mm/s as normal (API standards require a lower value); an alarm is triggered when this value is exceeded, and levels above 11.2 mm/s are considered unacceptable. Is this approach to management reasonable? Please share any suggestions for improvement Additional note: Some single-stage, double-volute centrifugal pumps operate at low flow rates for extended periods of time. With a rated flow rate of 705 m3/h, during the first three years after they started operating with oil, the flow rate was usually between 230–280 m3/h (as there were many impurities such as sediment and welding slag at that time). The minimum flow rate specified by the pump manufacturer is 380 m3/h; at low flow rates, vibration increases significantly, but it remains within the range of 7.1 mm/s. The technicians at the oil transfer station did not pay enough attention to this issue. During a recent major repair when the pump was opened for inspection, it was found that the impeller had suffered severe erosion, resulting in its failure.