Expanding the application of titanium: the application of titanium in the flat valve of the high-pressure gas production wellhead
Natural gas is collected from underground and contains more or less sulfur. This sulfur-containing gas has varying degrees of corrosive effect on commonly used metal materials. At the same time, its high ejection pressure has strong scouring of equipment structural parts. Therefore, the material is required to have good comprehensive performance and excellent sulfur corrosion resistance. For example, the large area valve plate and valve seat as the sealing part of the high-pressure sulfur gas production wellhead are both very critical structural parts. : Flexible opening and closing, safe and reliable, resistant to acid corrosion media H2S-CO2-H2O and (20%-25%) HCI media corrosion; at the same time, as a wellhead opening and closing part, it must be hard, HRC>45, resistant to strong wear, Resistance to high-speed air erosion, high specific pressure abrasion resistance, low friction coefficient, small sealing ratio; tensile strength 40MPa-70 MPa. In the late 1980s, the Guangzhou Research Institute of Nonferrous Metals showed that the surface hardness, smoothness, and dimensional accuracy of the sealing assembly made of TC4 alloy after nitriding treatment reached the design requirements, and were superior to the products of Cameron Corporation in the United States. , The prepared sealing assembly: reliable sealing, small opening, and closing torque, and safe and reliable operation under high pressure.
Sealing component preparation process
TC4 flat valve seal preparation process: forging blank → stress relief annealing → mechanical processing and sealing surface grinding → shaping treatment → sealing surface grinding → ion treatment. Ion treatment is an important process in the preparation of high-performance sealing surfaces. The treatment parameters are: treatment temperature, 880℃-900℃ for valve plate, 840℃-860℃ for valve seat; treatment time 6h-8h; maximum heating Speed＜15℃/min; Maximum cooling speed＜18℃/min; reaction atmosphere N2＋H2 mixed gas, and adding trace oxygen, N2 content 66%-90%; working pressure 1.33MPa-1.73MPa; gas flow rate 100L/h-150L /h; The current density is 3mA/cm2-7mA/cm2. In order to ensure the dimensional accuracy of the sealing parts, in addition to the reasonable selection of processing parameters, the stability of glow discharge should also be improved. In addition, the furnace should be installed reasonably. Ion treatment can greatly improve the wear resistance and corrosion resistance of TC4 alloy while maintaining the toughness of the matrix and the infiltrated layer.
Seal performance
We have tested some performances of the four kinds of titanium alloy flat valve discs (Table 1), and all performance indicators meet or exceed the design requirements. The surface hardness and dimensional accuracy are higher than those of the American FMC-OCT discs of the same specification. , Create stable and reliable conditions for use. The processing effect is very repeatable, and there is no waste after treatment.
Field Test
We conducted a strength and tightness hydraulic test, torque test, surface static natural gas test, and wellhead dynamic natural gas production test on the assembled titanium alloy TC4 flat valve body, all of which reached or were better than the set value and expected effect.
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