Pump and Motor Replacement Techniques for Pipeline Capacity Expansion

In liquids pipelines, the capacity of the pipeline may be limited by the pipe or by the pumping equipment. Assuming other external constraints such as tankage volumes, injection and delivery rate restrictions are not present, the capacity of an existing pipeline may be increased by several different methods: Pipe-based: • looping, • replacing with larger pipe, • requalifying to higher operating pressures, • adding drag reducing agent, • reducing the fluid viscosity, or • adding intermediate pump stations. In each of these pipeline capacity increase examples, the capacity of the existing pumps may be exceeded in two ways: 1. In flow rate, - the pumps are pumping well beyond their best efficiency point, or 2. In horsepower, - the power required to pump at the higher flow rates is greater than the capability of the existing motor. Therefore, to increase the capacity of a pipeline where the pumps are the source of the restriction, the following methods may be used: Pump-based: • adding more pumps, • trimming the pump impeller in the case of motor overloads, • modifying the pump to a higher capacity, • replacing an existing pump with a larger pump, • replacing the motor with higher horsepower motor, • increasing the speed of the pumps. A pump addition has the advantage of minimizing disruption to the existing facility and has the least impact on throughput, but at a higher cost than pump replacement. A pump impeller trim reduces the capacity of the pump, however, it can allow the pump to run at higher flow rates if the source of the flow limit is due to the motor rating. If the pump and/or motor need to be replaced, the new equipment will likely be larger and will not fit in the old location. The existing wiring, piping, foundations, baseplates, power and controls will therefore be affected by the pump and motor replacements. Careful design and planning will minimize the impact and cost of these replacements and reduce disruption to the ongoing operation of the station facilities. This paper discusses these options for pipeline capacity expansion, taking a practical approach with an emphasis on constructability and avoiding potential problems.