Demolition Inspection of Casting Wellhead Valve in Sulfur - Containing Oil and Gas Field

Abstract: Due to the strong corrosion of hydrogen sulphide, the equipment and materials required to mine sulfur-bearing oil and gas fields must have good resistance to hydrogen sulfide corrosion. Therefore, the disassembly inspection of cast-in wellhead valves used in sulfur-containing fields in western Sichuan was carried out. The dismantled parts include handwheel, stem copper nut, bearing seat, thrust ball bearing, packing gland, packing ring and seal ring, Valve stem, bonnet, valve plate, valve body, bolts and nuts. Demolition results show that some parts of the wellhead valve structure design is not reasonable and improper material selection and other issues, thus reducing the wellhead valve resistance to hydrogen sulfide corrosion. Aiming at the existing problems of Valve Parts, a preliminary study was carried out and some suggestions for improvement were put forward. Key words: wellhead valve anti-corrosion inspection With the rapid development of our national economy, the domestic demand for energy increased sharply. As one of the important energy sources, the contradiction between supply and demand has become increasingly prominent. Obviously, accelerating the development of a complete set of technologies for high-sulfur oil and gas fields is a far-sighted strategic measure for China National Petroleum Corporation. It is not only necessary but also urgent. In the exploitation of sulfur-bearing oil and gas fields, due to the strong corrosion of hydrogen sulfide, equipment and materials are required to meet the requirements of hydrogen sulfide corrosion resistance. To this end, we conducted a demolition inspection study on the well-tapped cast-in-mouth valves in a large amount of consumption in western Sichuan sulfur-containing oil and gas fields (two valves were demolished together). Check the appearance of the pre-demolition inspection on the 1st valve: the valve body, bonnet, most of the outer surface of the bearing seat off; the valve body at both ends and bonnet obvious corrosion; bearing seat is partially corroded; stem The top is bright and free of eclipse; there is a dark deposit at the opening of the housing. 2 valve inspection: the body, the valve cover part of the fall off; both ends of the flange paint shed at the obvious corrosion; most of the bearing primer off, and a small amount of red rust; stem bright top Erosion, the middle part of a black sediment. Analysis and Suggestion for Disassembly Results Due to limited research funding, the number of wellhead valves in this dismantling inspection is limited. Inspection of the valve belongs to the early production of products, but from the assessment of the extent of corrosion, these valves have shorter service lives. Here, I proposed only some preliminary views, to obtain more accurate and reliable conclusions, remains to be census of large quantities of valves and research. 1, handwheel Handwheel is the opening and closing valve plate parts, cast steel, dismantling a good condition, but with a bronze nut mating surface with a large number of scratches phenomenon, handwheel design needs to be improved. Analysis shows that when assembling the handwheel, if there is a burr or bump in the hole of the handwheel and the assembly is not advanced, the worker in the field may forcibly assemble it, so that the copper nut will be brushed. It is recommended to design the inner hole of the hand wheel as the inner cone hole and the outer surface of the copper nut mating surface for disassembly and assembly. 2, Stem copper nut disassembled found that the trapezoidal thread of the stem copper nut intact, only with the hand wheel with the outer surface of the keyway is severely hair, causing assembly difficulties. Intuitive feeling is that the copper nut is too long, if the strength of the check, the length of the copper nut can be shortened, not only can save the amount of copper, but also reduce the amount of the corresponding stem material. Valves with this copper nut has the following advantages: (1) easy to disassemble; (2) with hydrogen sulfide medium isolation. Drawback is due to the exposed copper, vulnerable to man-made damage, which may lead to major accidents. Design should consider the prevention of artificial disruption. According to the American Technical Specification for Anti-Sulfur Valves MR? 01? 75, only aluminum bronze is allowed for the anti-sulfur copper alloy. However, the design of such a valve has in fact substantially sealed the hydrogen sulfide in the valve, and whether or not the copper nut on the stem permits the use of other non-sulfur resistant materials remains to be further discussed. 3, bearing demolition inspection found that a small amount of bearing housing cavities black corrosion products may be related to the leakage of trace amounts of hydrogen sulfide, other parts (especially the internal thread) intact, non-corrosive. Bearing with riding screws for bearing positioning is not conducive to thrust ball bearing clearance adjustment. In highly corrosive gas conditions, riding screws rust easy to die, resulting in disassembly difficulties. This design is suggested to be improved at design time. 4, Thrust ball bearings tear down the thrust ball bearings have different degrees of corrosion. The place is actually isolated from the hydrogen sulfide medium, but from the structural design point of view, the copper nut only the lower ring without the ring, due to the atmospheric corrosive moisture and temperature difference between day and night, frosting and adhesion on the steel surface Of the dew, most likely from the adjustment nut and the gap between the copper nut into the bearing cavity, causing corrosion of parts of the bearing, and stem orientation (vertical or parallel to the ground), the degree of corrosion of the bearing is different. Therefore, structural design, thrust ball bearings should consider the sealing problem. 5, packing gland packing gland corrosion is more serious. Gland used to adjust the packing seal, especially in the case of a trace of hydrogen sulfide leakage, to be adjusted tight. If the gland rusting, the filler will not play a regulatory seal, which will seriously affect the performance of the valve. It is recommended that the gland be replaced with stainless steel with better corrosion resistance. 6, packing rings and seals removed two valves found at the valve stem there are five PTFE packing rings. A valve cover has a rubber seal has been deformed, while the other valve cover PTFE seals are basically intact. In addition, the stem nut has a small rubber seal is basically intact. Overall, PTFE packing rings and seals are not damaged, hydrogen sulfide good performance, while the rubber seal is aging, deformation. Proposed hydrogen sulfide valve flexible seal at the use of PTFE or more stable fluorine rubber for sealing material. 7, the stem under the stem removal intact, only a small amount of light rod surface corrosion and pitting, consider the valve in the strong corrosive hydrogen sulfide medium conditions for many years, can be considered stem material is basically qualified. The author believes that the stem of the work part of the stress size does not match; working slot root processing acute angle, easily lead to stress concentration, thereby inducing stress corrosion under high stress corrosion cracking of hydrogen sulfide. For this reason, it is advisable to check the stem design for strength. In addition, the root of the trapezoidal thread radius is to take the standard value or consider the stress corrosion factor and increase the root radius, is the design should pay attention to the problem. Valve stem is an important force of the valve, but also prone to stress corrosion cracking and failure of the valve parts. In stem design, detailed technical specifications should be drawn on material selection, manufacturing, heat treatment and structural design. 8, the cover removed under the valve cover in addition to corrosion, the basic intact. According to the Sichuan Petroleum Administration Investigation and Design Institute demolition inspection report, the valve cover material 45 steel, hardness 202 ~ 304HB, more than the standard 187 ~ 225HB. The main chemical composition of C, Mn, Si, P, S qualified, low content of harmful elements. The bonnet is one of the most important parts that come in contact with the hydrogen sulphide media and it is recommended to use forged parts instead. The following points are noteworthy. (1) bonnet cavity at all steps of the rounded corners are small, mechanical design is the natural fillet. Taking into account the valve cover in the hydrogen sulfide corrosive medium to withstand high stress components, machined by the sharp corners are prone to stress concentration and subsequent stress corrosion cracking, it is recommended to fully increase the design of the valve cover all the round Corner transition radius. This principle should be implemented in all the design of anti-sulfur equipment components. Cover the minimum wall thickness of the strength should also be checked, and the body to match. (2) If the valve cover heat treatment hardness is too high, will lead to H2S in the H2S stress corrosion cracking ring early failure. The valve cover of the dismantling the highest hardness of 304HB (equivalent to 33HRC), hydrogen sulfide medium pressure vessel is dangerous. Caused Key words: Sulfur-containing oil field Casting wellhead valve demolition inspection Research on the sulfur-containing oil field casting wellhead valve demolition inspection Previous: Change the control valve opening difference to solve the problem of bearing temperature is too high Next: Electronic expansion valve dynamic characteristics Identify the relevant links · To change the control valve opening difference to solve the problem of bearing temperature is too high · China has 23 cities GDP over 100 billion yuan · China is a big development is still the last word · Nearly 400 technical equipment will be eliminated · The most basic Abstract: Due to the strong corrosion of hydrogen sulfide, equipment and materials that require the exploitation of sulfur-bearing oil and gas fields must have good resistance to hydrogen sulfide corrosion. Therefore, the disassembly inspection of cast-in wellhead valves used in sulfur-containing fields in western Sichuan was carried out. The dismantled parts include handwheel, stem copper nut, bearing seat, thrust ball bearing, packing gland, packing ring and seal ring, Valve stem, bonnet, valve plate, valve body, bolts and nuts. Demolition results show that some parts of the wellhead valve structure design is not reasonable and improper material selection and other issues, thus reducing the wellhead valve resistance to hydrogen sulfide corrosion. Aiming at the existing problems of valve parts, a preliminary study was carried out and some suggestions for improvement were put forward. Key words: wellhead valve anti-corrosion inspection With the rapid development of our national economy, the domestic demand for energy increased sharply. As one of the important energy sources, the contradiction between supply and demand has become increasingly prominent. Obviously, accelerating the development of a complete set of technologies for high-sulfur oil and gas fields is a far-sighted strategic measure for China National Petroleum Corporation. It is not only necessary but also urgent. In the exploitation of sulfur-bearing oil and gas fields, due to the strong corrosion of hydrogen sulfide, equipment and materials are required to meet the requirements of hydrogen sulfide corrosion resistance. To this end, we conducted a demolition inspection study on the well-tapped cast-in-mouth valves in a large amount of consumption in western Sichuan sulfur-containing oil and gas fields (two valves were demolished together). Check the appearance of the pre-demolition inspection on the 1st valve: the valve body, bonnet, most of the outer surface of the bearing seat off; valve body at both ends and bonnet obvious corrosion; bearing seat is partially corroded; stem The top is bright and free of eclipse; there is a dark deposit at the opening of the housing. 2 valve inspection: the body, the valve cover part of the fall off; both ends of the flange paint shed at the obvious corrosion; most of the bearing primer off, and a small amount of red rust; stem bright top Erosion, the middle part of a black sediment. Analysis and Suggestion for Disassembly Results Due to limited research funding, the number of wellhead valves in this dismantling inspection is limited. Inspection of the valve belongs to the early production of products, but from the assessment of the extent of corrosion, these valves have shorter service lives. Here, I proposed only some preliminary views, to obtain more accurate and reliable conclusions, remains to be census of large quantities of valves and research. 1, handwheel Handwheel is the opening and closing valve plate parts, cast steel, dismantling a good condition, but with a bronze nut mating surface with a large number of scratching phenomenon, handwheel design needs to be improved. Analysis shows that when assembling the handwheel, if there is a burr or bump in the hole of the handwheel and the assembly is not advanced, the worker in the field may forcibly assemble it, so that the copper nut will be brushed. It is recommended to design the inner hole of the hand wheel as the inner cone hole and the outer surface of the copper nut mating surface for disassembly and assembly. 2, Stem copper nut disassembled found that the trapezoidal thread of the stem copper nut intact, only with the hand wheel with the outer surface of the keyway is severely hair, causing assembly difficulties. Intuitive feeling is that the copper nut is too long, if the strength of the check, the length of the copper nut can be shortened, not only can save the amount of copper, but also reduce the amount of the corresponding stem material. Valves with this copper nut has the following advantages: (1) easy to disassemble; (2) with hydrogen sulfide medium isolation. Drawback is due to the exposed copper, vulnerable to man-made damage, which may lead to major accidents. Design should consider the prevention of artificial disruption. According to the American Technical Specification for Anti-Sulfur Valves MR? 01? 75, only aluminum bronze is allowed for the anti-sulfur copper alloy. However, the design of such a valve has in fact substantially sealed the hydrogen sulfide in the valve, and whether or not the copper nut on the stem permits the use of other non-sulfur resistant materials remains to be further discussed. 3, bearing demolition inspection found that a small amount of bearing housing cavities black corrosion products may be related to the leakage of trace amounts of hydrogen sulfide, other parts (especially the internal thread) intact, non-corrosive. Bearing with riding screws for bearing positioning is not conducive to thrust ball bearing clearance adjustment. In highly corrosive gas conditions, riding screws rust easy to die, resulting in disassembly difficulties. This design is suggested to be improved at design time. 4, Thrust ball bearings tear down the thrust ball bearings have different degrees of corrosion. The place is actually isolated from the hydrogen sulfide medium, but from the structural design point of view, the copper nut only the lower ring without the ring, due to the atmospheric corrosive moisture and temperature difference between day and night, frosting and adhesion on the steel surface Of the dew, most likely from the adjustment nut and the gap between the copper nut into the bearing cavity, causing corrosion of parts of the bearing, and stem orientation (vertical or parallel to the ground), the degree of corrosion of the bearing is different. Therefore, structural design, thrust ball bearings should consider the sealing problem. 5, packing gland packing gland corrosion is more serious. Gland used to adjust the packing seal, especially in the case of a trace of hydrogen sulfide leakage, to be adjusted tight. If the gland rusting, the filler will not play a regulatory seal, which will seriously affect the performance of the valve. It is recommended that the gland be replaced with stainless steel with better corrosion resistance. 6, packing rings and seals removed two valves found at the valve stem there are five PTFE packing rings. A valve cover has a rubber seal has been deformed, while the other valve cover PTFE seals are basically intact. In addition, the stem nut has a small rubber seal is basically intact. Overall, PTFE packing rings and seals are not damaged, hydrogen sulfide good performance, while the rubber seal is aging, deformation. Proposed hydrogen sulfide valve flexible seal at the use of PTFE or more stable fluorine rubber for sealing material. 7, the stem under the stem removal intact, only a small amount of light rod surface corrosion and pitting, consider the valve in the strong corrosive hydrogen sulfide medium conditions for many years, can be considered stem material is basically qualified. The author believes that the stem of the work part of the stress size does not match; working slot root processing acute angle, easily lead to stress concentration, thereby inducing stress corrosion under high stress corrosion cracking of hydrogen sulfide. For this reason, it is advisable to check the stem design for strength. In addition, the root of the trapezoidal thread radius is to take the standard value or consider the stress corrosion factor and increase the root radius, is the design should pay attention to the problem. Valve stem is an important force of the valve, but also prone to stress corrosion cracking and failure of the valve parts. In stem design, detailed technical specifications should be drawn on material selection, manufacturing, heat treatment and structural design. 8, the cover removed under the valve cover in addition to corrosion, the basic intact. According to the Sichuan Petroleum Administration Investigation and Design Institute demolition inspection report, the valve cover material 45 steel, hardness 202 ~ 304HB, more than the standard 187 ~ 225HB. The main chemical composition of C, Mn, Si, P, S qualified, low content of harmful elements. The bonnet is one of the most important parts that come in contact with the hydrogen sulphide media and it is recommended to use forged parts instead. The following points are noteworthy. (1) bonnet cavity at all steps of the rounded corners are small, mechanical design is the natural fillet. Taking into account the bonnet is in hydrogen sulfide corrosive medium to withstand high stress components, sharp corners formed by mechanical processing is likely to produce stress concentration and subsequent stress corrosion cracking, it is recommended to fully increase the valve cover design all the round Corner transition radius. This principle should be implemented in all the design of anti-sulfur equipment components. Cover the minimum wall thickness of the strength should also be checked, and the body to match. (2) If the valve cover heat treatment hardness is too high, will lead to H2S in the H2S stress corrosion cracking ring early failure. The valve cover of the dismantling the highest hardness of 304HB (equivalent to 33HRC), hydrogen sulfide medium pressure vessel is dangerous. Caused Key words: Sulfur-containing oil field Casting wellhead valve demolition inspection Research on the sulfur-containing oil field casting wellhead valve demolition inspection Previous: Change the control valve opening difference to solve the problem of bearing temperature is too high Next: Electronic expansion valve dynamic characteristics Identify the relevant links · To change the control valve opening difference to solve the problem of bearing temperature is too high · China has 23 cities GDP over 100 billion yuan · China is a big development is still the last word · Nearly 400 technical equipment will be eliminated · The most basic The mechanical knowledge of a large gathering

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