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11247 Erosion-Corrosion Failures in Wellhead Chokes

Product Number: 51300-11247-SG
ISBN: 2011 11247 CP
Author: Gladys Navas and Ioana Cristina Grigorescu
Publication Date: 2011
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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 CO2 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.

Key words: corrosion- erosion, channeling wear, wellhead chokes, failures, gas wells
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 CO2 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.

Key words: corrosion- erosion, channeling wear, wellhead chokes, failures, gas wells
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