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Grigorescu I.C.,Simon Bolivar University of Venezuela | Navas G.,Instituto Universitario Of Tecnologia Dr Federico Rivero Palacio Iutfrp
NACE - International Corrosion Conference Series | Year: 2012

A detailed surface evaluation was performed for the components of two multistage centrifugal pumps for water injection in a Venezuelan oil production field. Several non-destructive methods were employed: visual inspection, die penetrant and replica extraction, followed by micro-morphological and chemical analysis by scanning electron microscopy (SEM) and energy dispersive X ray spectroscopy (EDX). The flow-induced degradation mechanisms varied depending on the pump component and their ranking, according to damage intensity, from high to low, was: i) severe erosion-corrosion in the balance bush system; ii) severe erosion-corrosion in the middle bush; iii) wear of variable intensity of the active face of wear-rings; iv) mild wear of the UNS-L13910 coated sliding bearings; v) axially oriented erosion of the contact surface between wear-ring and spindle; vi) high viscosity deposits of oil in the outlet stages; vii) spindle corrosion; viii) pitting inside impeller periphery slots; ix) deposition of crystallized salts. The criticality ranking fairly agreed with the performance history of the pumps. ©2012 by NACE International. Source


Navas G.,Instituto Universitario Of Tecnologia Dr Federico Rivero Palacio Iutfrp | Grigorescu I.C.,Simon Bolivar University of Venezuela
NACE - International Corrosion Conference Series | Year: 2011

The surface morphology and chemistry of two chokes for oil and gas condensate, which failed by leakage, were related to the flow pattern and material degradation mechanisms. In the choke for oil production, severe circumferential channeling develops near the screw connection between the nozzle and choke body, due to fluid leakage through the thread in imperfect contact. One of the channeling branches crossed the case wall producing leakage, this trajectory being enhanced by defects in the girth weld, inappropriately placed near the thread. Downstream, CO2 induced corrosion becomes the governing damage mechanism, being promoted by an almost stagnant back-flow in the annular gap between the nozzle and the choke body. In the second case, the corrosive fluid induces intense erosion-corrosion downstream the nozzle; the abnormal flow pattern is the consequence of the prior fracture of the nozzle. Toward the valve outlet, the damage turns into uniform COO2 corrosion, which is the typical degradation mode of the choke body. Both failures were enhanced by the inappropriate location of girth weld in the zones where the most intense erosion-corrosion damage occurs. © 2011 by NACE International. Source


Grigorescu I.C.,Simon Bolivar University of Venezuela | Navas G.,Instituto Universitario Of Tecnologia Dr Federico Rivero Palacio Iutfrp | Camacaro M.A.,University of the East Venezuela
NACE - International Corrosion Conference Series | Year: 2011

This paper summarizes the surface damage mechanisms that were observed in three double-screw pumps used for the transfer of high viscosity crude oil and their relations with pump operation conditions, flow characteristics and material defects. Erosion-corrosion governs the degradation of the screws; however the balance between chemical and mechanical damage varied according to local flow pattern and content of formation water, gas and solids. Along the screws, the thickness of the fluid film between threads and the inner surface of the pump case varies when excessive screw deflection occurs. Flow instability, mainly local gas compression - decompression, enhances the erosive attack with solid particles and intensify the fatigue inducing conditions. Contact areas between spindle and bearing or gears are corroded by the pumped fluid leaked through the mechanical seals, which viscosity is reduced due to the contained gas; clearances that developed in these corroded areas enhance fatigue. © 2011 by NACE International. Source

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