Pipe End Machining
Pipe end machining
Pipe end processing is the process of threading, sizing, thickening, strengthening heat treatment, chamfering and so on.
Pipe end thread turning is referred to as pipe end thread turning. The length of a single steel pipe produced by a steel pipe plant is usually less than 14m, and the service length of some steel pipes is often much longer than this length. For example, in geological drilling and oil drilling and production, the drilling depth is usually more than 1000m, with a maximum depth of 7000m; the pipelines used to transport oil, natural gas, water, alkali, minerals, etc. are several kilometers or even hundreds of kilometers long. Therefore, it is necessary to thread both ends of the steel pipe and connect the steel pipe with the corresponding coupling (adapter). Threaded connection requires high connection strength and good air tightness to prevent steel pipe fracture and transmission medium leakage. In order to meet the needs of various applications, various forms of screw threads have been developed in various countries, but the following three types are mainly used:
(1) dome triangle thread. It is characterized by simple thread processing. However, due to the uneven stress and deformation of the thread, the connection strength is low, and the sealing performance is poor only by the side sealing of the thread.
(2) partial trapezoid (bortrez) thread. It is characterized by high thread precision, high processing requirements and high connection strength, and high sealing performance relying on the side and top of the thread.
(3) straight connection thread. Its characteristic is that it does not need to take over, but the pipe end needs to be thickened, one end has external thread, the other end has internal thread, so it is difficult to process. High thread precision, high connection strength; relying on top and side sealing, good sealing performance.
The machining of the steel pipe end before turning the wire usually includes cutting the pipe, turning the outer circle, boring, chamfering and end face machining. These processes are generally completed on a special wire turning machine at one time, and some can also be completed on two machine tools. In order to ensure that the thread size meets the requirements of the standard, the pipe end thread of the pipe is used in the oil drill, and various instruments are required for strict inspection before delivery. The inspection items include screw torque, tooth height, tooth shape, thread length, taper, tight torque, etc.
The purpose of pipe end sizing is to reduce the ovality of steel pipe and ensure the dimensional accuracy of steel pipe after machining, which is mainly used for oil casing. After the casing is calibrated at the end, the number of black skin threads (threads left on the leaking surface) is small when the end threading, which can improve the yield.
Cold deformation technology is adopted for pipe end sizing, and two commonly used sizing methods are punch expanding and punch expanding + sizing ring compression. The effect of reducing the ellipticity of steel tube during punch expanding depends largely on the uniformity of steel tube wall thickness. For the hot-rolled pipe with serious wall thickness unevenness, such as the pipe rolled by the periodic mill (see the pipe rolled by the periodic mill), the surface quality of the pipe end deteriorates after the punch is expanded. Therefore, in order to eliminate the influence of uneven wall thickness and reduce the ovality of steel pipe, the method of punch expanding + sizing ring compression should be adopted. Because of the cold sizing, not only elastic deformation but also a small amount of plastic deformation occurs at the pipe end. After sizing, there may be residual stress of different degrees in the transition zone between expanding and non expanding. At the same time, there may be internal and external surface scratches caused by punch and sizing ring, resulting in slight stress corrosion. Therefore, the size accuracy of hot-rolled steel pipe should be improved as much as possible, and the method of pipe end sizing should be avoided.
Pipe end thickening is mainly used for oil pipe and geological pipe. Due to the thinning of the pipe wall after threading the pipe end, the threaded connection part becomes the weak link of the whole pipe body strength. In order to improve the strength of threaded connection part, the method of pipe end thickening is adopted to increase the pipe end wall thickness. In addition, the pipe end and tool butt welding connection, weld and its heat affected zone are the weak links of the strength. In order to improve the strength of the weld area, the pipe end thickening is generally used. The forms of pipe end thickening include internal thickening, external thickening and internal and external thickening.
The technological process of steel pipe thickening is: pipe end heating (in seam furnace or induction heater) → thickening (with horizontal forging machine or hydraulic forging machine) → cooling → inspection. According to the different size, thickening form and thickening compression amount of the thickened pipe, the heating times and thickening passes adopted are also different, one heating for one thickening, or one heating for two thickening. In order to eliminate the uneven performance between the thickened end and the pipe body caused by the thickening, the overall heat treatment is usually carried out after the steel pipe is thickened. The process parameters of tube end thickening mainly include: the heating temperature T of tube end before thickening, the temperature T of tube end after thickening and the deformation length L of tube end
T start = AC3 + (400-450) ℃ t end = Ar3 + (40-80) ℃ l end = (1.05-1.10) l
Where l is the calculated theoretical deformation length.
The failure of the drill pipe mainly occurs in the transition area between the thickened end and the pipe body, so the size of the transition area is very important.
The strength of the thread turning part of the tube end is one level higher than that of the tube body through the superheating treatment. The process of tube end strengthening heat treatment includes tube end heating, quenching (the medium is compressed air, water mist, etc.) and tempering.
Pipe end chamfering is used to transport mineral, gas, oil, water and other media, usually welded by steel pipes one by one. In order to facilitate the welding between pipes, chamfering is required for the outer corner of the pipe end (see Figure). According to the different purposes of the steel pipe, the α angle size and the ζ value of the blunt edge are also different, generally α = 30.. In order to ensure the accuracy of α and ζ dimensions after pipe end chamfering, it is required that the non roundness and wall thickness of steel pipe should be as small as possible. When the steel pipe plant processes the pipe end, the chamfering of the pipe end and the cutting of the steel pipe are carried out on the same machine tool. The advanced pipe cutting machine in the world has the function of chamfering. The processing of the oil pipe coupling is completed on a special machine tool, and other processes are similar to the pipe end processing except for the cutting off of the coupling material.
Pipe end processing is the process of threading, sizing, thickening, strengthening heat treatment, chamfering and so on.
Pipe end thread turning is referred to as pipe end thread turning. The length of a single steel pipe produced by a steel pipe plant is usually less than 14m, and the service length of some steel pipes is often much longer than this length. For example, in geological drilling and oil drilling and production, the drilling depth is usually more than 1000m, with a maximum depth of 7000m; the pipelines used to transport oil, natural gas, water, alkali, minerals, etc. are several kilometers or even hundreds of kilometers long. Therefore, it is necessary to thread both ends of the steel pipe and connect the steel pipe with the corresponding coupling (adapter). Threaded connection requires high connection strength and good air tightness to prevent steel pipe fracture and transmission medium leakage. In order to meet the needs of various applications, various forms of screw threads have been developed in various countries, but the following three types are mainly used:
(1) dome triangle thread. It is characterized by simple thread processing. However, due to the uneven stress and deformation of the thread, the connection strength is low, and the sealing performance is poor only by the side sealing of the thread.
(2) partial trapezoid (bortrez) thread. It is characterized by high thread precision, high processing requirements and high connection strength, and high sealing performance relying on the side and top of the thread.
(3) straight connection thread. Its characteristic is that it does not need to take over, but the pipe end needs to be thickened, one end has external thread, the other end has internal thread, so it is difficult to process. High thread precision, high connection strength; relying on top and side sealing, good sealing performance.
The machining of the steel pipe end before turning the wire usually includes cutting the pipe, turning the outer circle, boring, chamfering and end face machining. These processes are generally completed on a special wire turning machine at one time, and some can also be completed on two machine tools. In order to ensure that the thread size meets the requirements of the standard, the pipe end thread of the pipe is used in the oil drill, and various instruments are required for strict inspection before delivery. The inspection items include screw torque, tooth height, tooth shape, thread length, taper, tight torque, etc.
The purpose of pipe end sizing is to reduce the ovality of steel pipe and ensure the dimensional accuracy of steel pipe after machining, which is mainly used for oil casing. After the casing is calibrated at the end, the number of black skin threads (threads left on the leaking surface) is small when the end threading, which can improve the yield.
Cold deformation technology is adopted for pipe end sizing, and two commonly used sizing methods are punch expanding and punch expanding + sizing ring compression. The effect of reducing the ellipticity of steel tube during punch expanding depends largely on the uniformity of steel tube wall thickness. For the hot-rolled pipe with serious wall thickness unevenness, such as the pipe rolled by the periodic mill (see the pipe rolled by the periodic mill), the surface quality of the pipe end deteriorates after the punch is expanded. Therefore, in order to eliminate the influence of uneven wall thickness and reduce the ovality of steel pipe, the method of punch expanding + sizing ring compression should be adopted. Because of the cold sizing, not only elastic deformation but also a small amount of plastic deformation occurs at the pipe end. After sizing, there may be residual stress of different degrees in the transition zone between expanding and non expanding. At the same time, there may be internal and external surface scratches caused by punch and sizing ring, resulting in slight stress corrosion. Therefore, the size accuracy of hot-rolled steel pipe should be improved as much as possible, and the method of pipe end sizing should be avoided.
Pipe end thickening is mainly used for oil pipe and geological pipe. Due to the thinning of the pipe wall after threading the pipe end, the threaded connection part becomes the weak link of the whole pipe body strength. In order to improve the strength of threaded connection part, the method of pipe end thickening is adopted to increase the pipe end wall thickness. In addition, the pipe end and tool butt welding connection, weld and its heat affected zone are the weak links of the strength. In order to improve the strength of the weld area, the pipe end thickening is generally used. The forms of pipe end thickening include internal thickening, external thickening and internal and external thickening.
The technological process of steel pipe thickening is: pipe end heating (in seam furnace or induction heater) → thickening (with horizontal forging machine or hydraulic forging machine) → cooling → inspection. According to the different size, thickening form and thickening compression amount of the thickened pipe, the heating times and thickening passes adopted are also different, one heating for one thickening, or one heating for two thickening. In order to eliminate the uneven performance between the thickened end and the pipe body caused by the thickening, the overall heat treatment is usually carried out after the steel pipe is thickened. The process parameters of tube end thickening mainly include: the heating temperature T of tube end before thickening, the temperature T of tube end after thickening and the deformation length L of tube end
T start = AC3 + (400-450) ℃ t end = Ar3 + (40-80) ℃ l end = (1.05-1.10) l
Where l is the calculated theoretical deformation length.
The failure of the drill pipe mainly occurs in the transition area between the thickened end and the pipe body, so the size of the transition area is very important.
The strength of the thread turning part of the tube end is one level higher than that of the tube body through the superheating treatment. The process of tube end strengthening heat treatment includes tube end heating, quenching (the medium is compressed air, water mist, etc.) and tempering.
Pipe end chamfering is used to transport mineral, gas, oil, water and other media, usually welded by steel pipes one by one. In order to facilitate the welding between pipes, chamfering is required for the outer corner of the pipe end (see Figure). According to the different purposes of the steel pipe, the α angle size and the ζ value of the blunt edge are also different, generally α = 30.. In order to ensure the accuracy of α and ζ dimensions after pipe end chamfering, it is required that the non roundness and wall thickness of steel pipe should be as small as possible. When the steel pipe plant processes the pipe end, the chamfering of the pipe end and the cutting of the steel pipe are carried out on the same machine tool. The advanced pipe cutting machine in the world has the function of chamfering. The processing of the oil pipe coupling is completed on a special machine tool, and other processes are similar to the pipe end processing except for the cutting off of the coupling material.
