Failure analysis of a four-way flange erosioning in a KQ52 wellhead Christmas tree

Abstract

The wellhead Christmas tree uses top sand drainage during multi-stage sanding fracturing, and it fails at the four-way and gate valves. Due to the multi-stage sanding fracturing process of a wellhead Christmas tree in an oilfield, the connection between the four-way and the gate valve flange failed for many times during service. In this paper, the failure causes of four-way flange joints were analyzed by reading spectrometer, Rockwell hardness tester, optical microscope, scanning electron microscope, energy dispersion spectrometer and numerical simulation method. The results show that the chemical composition, hardness and grain size of the four-way flange and connecting gate valve meet the standard requirements; By microstructural characterization and energy spectrum analysis, it is confirmed that a large number of corrosion products are attached to the inner wall of the four-way valve and gate valve; During the wellhead Christmas tree fracturing, high-speed sand-carrying fluid flows into the pipeline through four-way, and high-frequency multiple impacts occur to the connection of the four way flange and gate valve. At the same time, a large number of eddy current are formed at the intersection of the four-way and the gate valve flow channel. A large number of corrosion products distributed in the passage of the four-way valve and gate valve cause corrosion accumulation under the action of eddy current, forming corrosion wear, and finally the connection between the four way and the gate valve is damaged by erosion wear and corrosion wear.