| The cuttings and mechanical impurities existing in produced gas always lead to a series of pitting, fracture phenomenon of the crucial equipment and important fittings. Thus, the intrusive probe, elbow and the ball valve as the crucial vulnerable parts has been the research hot spot in the flow security area.Sand erosion directly endangered the ground equipment. Revealing the essence in the wearing process and mastering the characters of the erosive progress could encourage the development of the equipments, integrity assessment and safety management. This paper picks the probe, elbow and ball valve core as crucial vulnerable parts in gas gathering plant. Based on the surface reconstruction and erosion theory, experimental and numerical methods were constructed to study the wear characters on the surface loss of those vulnerable parts. Erosion evolution models which were used to describe the surface loss distribution were brought out and validated with experimental results. And a method that could correlate the wall surface loss of the pipe fittings between the intrusive probe was introduced. Besides, an erosion monitoring probe was developed and tested. The research includes the following components.(1) A feasible and reliable experimental method was introduced. An rate-controllable sand-burst equipment was established in order to simulate the sand-burst conditions in Sebei gas field. The wall thickness evolution of the typical vulnerable parts were quantified based on the spatial digitizer (Shining3D-Scanner) and the bundled software Geomagicll. Different sand-bursting rate, sand production, particle size, peak values and materials were studied. When the angle between the fluid flow and the upstream surface is 45°, both sides of the upstream surface on the intrusive probe shows almost same eroded condition. The most seriously eroded areas are always on the upstream edge. For the elbow, the seriously eroded area would spread in a lower speed toward the elbow outlet direction with the increaseing sand production and sand burst rate. For the ballvalve core, the seriously eroded area would spread unevenly on the upstream surface.(2) In order to find an optimum erosion model and grid form, a commonly used calculation platform Ansys Fluent was used. Erosion models like Alhert, Oka, E/CRC were comparatively studied among those erosion models. Comparisons between structured grid and unstructured grid were also proposed in the simulation as well as the examination of the grid independence. The results show that, Alhert erosion model is a suitable model to describe the surface evolution among those models in predicting the surface loss of a probe and elbow as relatively simple geometry were present. For the ballvalve core, the geometry is a little bit complex and the flow trajectories of the particles were affected, the predicting accuracy of the Alhert model is not that good. Surface evolution contribute a lot in the deviation of those models.(3) In order to overcome the influence of the surface evolution in the prediction. Modifications of the Alhert erosion model were implemented.As the transformation of the impact angle was found in section (1), parameters like sand burst rate and velocity distribution were integrated to build a new model. This model is good at predicting the surface evolution during the surface erosion.A clue correlating the gas-solid drag model was founded. The Alhert erosion model and the Gidaspow drag model were introduced here. The modified model could describe the wall surface evolution accurately in a specific range for the elbow and ball valve core and offer an accurate result in predicting the surface evolution. This implies that the the surface thickness loss affects the drag correlations qualitatively.Based on the surface reconstruction theory, the eroded surfaces of the crucial vulnerable parts were rebuild and compared with the original. The impact angles before and after the erosion were calculated. The results shows that during the test, the impact angle at the top of the probe became blunt first and then spread to the bottom. The impact angle of the elbow upstream surface did not change significantly, the impact angle increased only in the seriously eroded area. The impact angle of the ball valve on the upstream surface did not change significantly either.To study the influence of the eroded surface to the erosion rate in later progress. A dynamic mesh method was introduced to create the progress of the surface loss. The results shows that for the elbow, the internal velocity distribution leads to an increase in the erosion rate. For the ball valve core, the inlet of the valve cavity was expanded by sand erosion, however, the erosion rate decreases.(4) An optimal correlation searching function was brought out based on grey correlation theory in order to solve the problem that the intrusive probe can only detect the wear of itself but the pipe fittings around.The test results is good in reflecting the erosion evolution characters in different sand productions and sand production rates. When the relative position of the probe and the elbow (ball valve) is changed, the method still has a high precision.(5) Based on the results of section (1), an intrusive erosion monitoring probe was developed. The material selection, key components arrangement and data transmission were introduced.The sand-loading erosion tests and the sand-free tests were proposed to access its monitoring capability. The results show that the probe gives a reasonable signal in the sand-free tests, however, the disturbance came from the temperature variation made a tiny deviation here. The probe could detect the minimum metal loss (accuracy 16.7%) at the sand production of 0.02kg and the flow velocity of 3m/s. With the decreasing of the particle size and increasing of flow speed the monitoring accuracy increases. With the increase of sand production, the eroded area became more serious, and an accurate result is easier to access. |
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