Blockage on a Long Vertical Pumping Line
A 125 mm steel pipeline is placing 40 MPa concrete with 20 mm aggregate and 120 mm slump. The layout runs 15 m horizontal from the pump, through a 90-degree elbow, 25 m vertical, a 45-degree elbow, 70 m horizontal, another 90-degree elbow, and a 6 m rubber end hose. The pump is rated at 120 m3/h and is running at about 70 percent output. Over 10 minutes, the pressure gauge at the pump rises from 18 MPa to 28 MPa, output drops to about 20 m3/h, and the pipeline vibrates sharply at the first 90-degree elbow 15 m from the pump. The crew wants to add water to the hopper and increase engine speed. A worker is standing beside the end hose to watch discharge.
1. What is the likely problem, and what immediate actions should the operator take?
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The signs point to a partial blockage or restriction, most likely at the first 90-degree elbow or in the vertical section, because pressure is rising while output falls and that elbow is vibrating. The operator should stop pumping, reduce engine speed to idle, and follow the manufacturer's pressure-relief procedure before anyone touches the line. Do not add water and do not increase engine speed. Keep everyone away from the end hose and the elbow; a partial blockage can release suddenly and whip the hose. Notify the pump supervisor and the batch plant or quality control. Check slump and concrete consistency, but do not alter the mix at the pump without approval. If the pump has an approved reverse or pressure-relief function, use it only as the manufacturer directs.
2. Evaluate the crew's proposal to add water and increase engine speed.
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Adding water at the hopper changes the water-cement ratio and can reduce the 40 MPa strength, increase segregation, and make the blockage worse by separating aggregate. Increasing engine speed raises pumping pressure and can rupture the pipe or blow a coupling, especially with a partial blockage and 28 MPa already showing. Neither action addresses the root cause, which may be a dry or restricted elbow, a slump loss, or a pipeline layout problem. The correct response is to stop, relieve pressure, and inspect or clear the line using the approved procedure.
3. How should the line be cleared and restarted safely?
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Stop the pump, relieve pressure, and isolate the line. Barricade the area. Disassemble at the first elbow or at a joint downstream of the suspected blockage using the manufacturer's procedure, keeping personnel clear of the opening and wearing appropriate PPE. Catch and contain the concrete; do not hammer a pressurized pipe. Inspect the elbow and pipe for wear or hardened concrete. If the blockage is due to slump loss, coordinate with the batch plant for a suitable mix and do not add water. Before restart, re-prime the line, confirm couplings and safety pins, and restart at low output while watching pressure. If pressure rises again, stop and repeat the diagnosis rather than forcing the pump.