BLOGS

                                              

 THE FAILURES OF CENTRIFUGAL PUMPS (PART 1)

 By: Cyrus

On so many platforms, ranging from the oil and gas , mining, water and food industries, pumps failure ranges from one level to the other. When the pump start to fail, the entire plant can be shut down.

With so much to learn, pump professionals learn to recognize and detect the most common causes of pump failure and detect the most common causes of pump failure and the root cause through analysis and troubleshooting.

Despite all the care and maintenance, the statement engineers face "the pump has failed" Taking the pump out of service for its inability to deliver the desired flow and head its one of the conditions. There are other conditions which include seal related problems, pump and motor bearings related problem, cavitation, leakages from pump casing, coupling misalignment, leakages from pump casing, very high noise and vibration levels related problems. When the symptoms occur a little care can save the plant from total shut down.

                                                    

                                                           The pump has failed

ANALYSIS OF PUMP FAILURE

It is very necessary to analyze the job site to see what went wrong and to disassemble the pump for a proper inspection. Getting a thorough examination of a pump application will include, an overview of the installation, the piping system, the alignment record done on the pump set, the amount of flow and head, water content and the pump type use for a particular application.

Disassembling of the pump, this task should not be perform by the customer. As a practice

it is recommended to have the job performed by an O.E.M (Original Equipment Manufacturer) or by an authorized maintenance and repair shop. An O.E.M will have strict guidelines on how motor evaluation and pump repair are performed. Authorized mechanics

can take a pump apart to assess the bearings accurately, the sealing system (mechanical seal / gland packing) impellers, accurate measurement of the internals/abrasive wear. After all measurement and factor is scrutinized, a course action can now be determine.

                                               

                                                Accessing a failed pump in a customer base

PUMPING OUTSIDE THE DUTY POINT

The BEP( this refer to as the Best Efficiency Point). This indicated on a pump curve. All pumps has a point at which its flow becomes optimally efficient. When operating a pump too close to the shut of head (left of the curve) or at runout (right of the curve) t6his can result in damage to the mechanical seal, damage to bearings, breakage of shaft. A pump should operate within 30percent of its BEP to avoid all forms of failures mention in this article. This will maximize  the pump life span and the rate of power consumption.

A customer purchase  a new pump and installation was done by the customer onsite. The pump was commissioned and running. The pump ran for a month and suddenly high vibration / noise set in.

The pump was shut down. The OEM receive a report about the faulty pump. An Engineer was sent to site few days after the distress call. A thorough investigation/inspection was carried out by the Engineer. The Engineer was able to troubleshoot the causes of the pump failure. A wrong installation and no coupling alignment was done on the pump set before the initial commissioning.

A new installation for the pump set and laser shaft system alignment initiated to remove the soft foot and misalignment condition from the system. Pump alignment readings were within tolerance . The Engineer instructed the customer to start the pump and see if the noise and the vibration will still be in the system. The pump ran so smoothly all noise and vibration were eliminated from the pumping system.

WATER INGRESS INTO THE MOTOR

Water can make its way through to a pumps motor, it is often assumed a manufacturing defect must have come from the factory. This is possible, more likely the culprit is a cable that has been cut or damage allowing water ingress.

Chemicals can play a role as well. Pumping acidic or basic chemicals can erode the rubber portion of the mechanical seal, o rings or gaskets.

                                                 Ingress of water to the motor

HAVING FULL KNOWLEDGE OF YOUR PUMP

It is paramount not to consider the pump itself during a failure analysis, but also what exactly is being pump, the installation process, the piping and finally the misalignment.

In the next article we will discuss more on how pump installation can affect the overall performance of a pump.