Case Studies

The Dangers of Operating Pumps at Low Capacity

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Operating at low flow places the machine under a great amount of duress. It is always wise to have a mental picture of what is happening within the passages of the machine to understand why this is the case.

The days have long passed where pump vibrations were viewed as a matter of mechanical balance. Now, we recognize that even if the pump had perfect mechanical balance, it would still exhibit vibrations.

The intensity of this remnant vibration turns out to be flow related with its minimum level being at or around best efficiency point (BEP).

Source: https://www.pumpsandsystems.com/dangers-operating-pumps-low-capacity

Wireless Condition Monitoring Optimizes MTBR

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Working in partnership with the plant condition monitoring team, the PIEs installed a total of nine SDOF (Single Degree of Freedom) wireless vibration sensors on the pump and drive.

Alerts, advanced analysis, and automated reporting help to improve maintenance strategies and critical asset decision-making.

A power plant in Southeast Australia had recently experienced chronic high vibration amplitudes on a critical multistage boiler feed water pump. Given the criticality of the pump and the risks associated with catastrophic pump failure, the power plant contacted Hydro Australia for support.

In collaboration with Hydro, Inc.’s wireless condition monitoring team, Hydro Australia was able to provide the power plant with a significantly improved IIoT-based monitoring system. This would assist the plant by closely monitoring the status of its asset, making the best possible decisions for equipment maintenance, and ensuring equipment availability

Source: https://www.pumpindustry.com.au/wireless-condition-monitoring-optimises-mean-time-between-repair

Wear in Centrifugal Pumps

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Illustration of wear at the volute lip.

Centrifugal pumps are sometimes used in environments where the pumped product contains suspended solids. While some pumps are specifically designed for solid handling or slurry applications, normal centrifugal pumps do not contain features to prevent performance degradation from the impact of solids.

There are a few key signs that a conventional centrifugal pump is suffering from erosive and abrasive wear. Here are assessment and mitigation strategies to be considered and applied when this occurs.

Particles are a problem in a centrifugal pump due to the way the machine adds velocity to the liquid as it passes up the impeller channels. In general, the higher the speed at the tip of the impeller, the more energy that is imparted to any particle that is suspended within the liquid. This energy can then cause damage to anything it impacts.

Source: https://www.pumpsandsystems.com/wear-centrifugal-pumps 

Engineering a Long-Term Solution

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Figure 1. The pump as received

Many pumps in operation today were designed and manufactured decades ago. As plants require increased capacity, pump systems are expected to meet these higher process flow demands. Without an impeller rerate or change in speed, this increased capacity can be achieved in one of two ways. The individual pumps can supply more flow to the system, resulting in operation out on the pump curve. Alternatively, capacity can be increased by operating more pumps in parallel; in this case operation is pushed back on the curve, as operating another pump in parallel requires less flow from each individual pump to meet total system demand.

Either operational change results in a move away from the pump best efficiency point (BEP). As a result, the original designs and hydraulic characteristics no longer effectively meet plant requirements and detrimental effects from hydraulic instability can occur.

By way of example, this article will discuss a fertilizer plant in the Gulf of Mexico that had a boiler feedwater pump unit that was experiencing performance problems after a significant plant expansion project. Unfortunately, it was not the first time this particular unit had experienced a loss of capacity; the pump had been in operation only 18 months prior to the current issue.

 

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Root Cause Analysis Uncovers Casting Defects

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Efficiency and reliability are at the forefront of a successful pumping system. As such, unplanned outages can be a detrimental disturbance to the overall operation. In this case, the end user’s high pressure multistage  BB5 barrel pump was experiencing severe vibration, unstable performance, and failure in the field leading to unit shutdown.

This particular unit, used in boiler feedwater operations, is critical to the plant’s uptime and throughput. Furthermore, continued failures can cause growing costs due to inevitable maintenance and repairs, often overlooking a long term solution. With each unplanned outage, the plant could face a significant loss in capital.

Previously, the pump had been running for six months before experiencing catastrophic failure, requiring a shutdown and removal for further analysis. Initially, the unit’s damaged components were repaired by welding, and the volute was reassembled and installed for use. Upon its installation, the power plant placed the unit back into service but encountered a second emergency shutdown after two months in operation.

Video: https://vimeo.com/362808909

Source: https://www.pumpsandsystems.com/root-cause-analysis-uncovers-casting-defects-critical-boiler-feedwater-unit