Background
A copper mine in Peru's Andes region was experiencing premature failure of flanged steel pipe connections at its main tailings pump station. The pump station moved copper tailings slurry from the concentrator to the tailings storage facility via a 4km pipeline.
The pump station used three centrifugal slurry pumps running in series. The problem was at the pipe connections immediately adjacent to each pump β rigid steel flanged connections were cracking at the welds within 3β6 months of installation, causing slurry leaks that required emergency shutdown for repair.
Root Cause
Centrifugal slurry pumps generate significant vibration β both from pump imbalance and from the turbulent flow of abrasive slurry through the pump casing. This vibration transmitted directly through the rigid steel pipe connections to the pipeline structure.
At 3,800 meters altitude in the Andes, the mine also experienced thermal cycling β cold nights and warmer days. The steel pipe expanded and contracted with temperature changes. The rigid connections had to absorb this movement, adding cyclic stress to an already vibration-fatigued weld.
The combination of pump vibration and thermal movement was fatiguing the welds faster than the design anticipated.
Solution: Rubber Expansion Joints
Rubber expansion joints (also called flexible pipe connectors) were installed at the pump inlet and outlet on each of the three pumps β six joints total.
A rubber expansion joint is a short section of reinforced rubber body with flanged steel ends that connects to the pipeline. The rubber body can: - Absorb vibration β the rubber dampens pump vibration rather than transmitting it to the pipeline - Accommodate thermal movement β the rubber flexes to absorb pipe expansion and contraction - Compensate for minor misalignment β the rubber allows small angular and lateral offset between connected pipe flanges
Specification for this application: - Compound: EPDM/neoprene compound resistant to alkaline tailings slurry (pH 9β11) - Reinforcement: multiple plies of high-strength synthetic fabric - Pressure rating: PN16 (16 bar) β above the pump operating pressure - Diameter: 200mm (8") to match existing pipeline flanges - Movement accommodation: Β±25mm axial, Β±15mm lateral, Β±10Β° angular
Installation
The rubber expansion joints were retrofitted to the existing pump station during a planned maintenance stop. Existing rigid connections were removed and the expansion joints fitted in their place β same bolt pattern, no modification to the pump or pipeline structure needed.
Installation of all six joints took approximately 4 hours.
Outcome
Following installation, the cracking problem at the pump connections stopped entirely. At the 12-month inspection, no cracks were observed at any weld near the pump connections. The rubber expansion joints showed some surface scuffing from incidental contact with maintenance personnel and equipment β cosmetic only, no effect on function.
The expansion joints were estimated to have a service life of 4β6 years in this application before replacement would be needed β compared to the 3β6 month failure cycle of the rigid connections they replaced.
Secondary benefit: Noise level in the pump station decreased noticeably after installation β the rubber joints absorbed pump vibration that had previously been transmitted to the building structure and amplified.
Key Points
Vibration transmission through rigid pipe connections causes fatigue cracking. This is a predictable failure mode at pump connections. Rubber expansion joints prevent it by breaking the vibration transmission path.
Thermal movement and vibration are additive stresses. High-altitude operations with significant day-night temperature variation compound the vibration problem. Rubber expansion joints handle both simultaneously.
Compound selection matters for slurry applications. Alkaline tailings slurry (pH 9β11) attacks some rubber compounds. EPDM and neoprene resist alkaline environments; natural rubber does not. Specify the compound to match your process fluid chemistry.
Elephant Rubber supplied the rubber expansion joints for this project.