Design of Pipeline Ball Valve
Design and manufacture of pipeline ball valve
The pipeline ball valve is based on the needs of users. In order to meet the requirements of anti vulcanization stress cracking in vulcanization environment, we strictly comply with the relevant standards of NACE from the aspects of design, material selection, manufacturing, testing, surface treatment and painting. The pipeline ball valve series not only has a wide range of materials, but also the internal parts are made of nickel plated or 316 materials, and the sealing ring is made of special polymer materials. Alloy steel valves are not only anti-corrosion, anti vulcanization, strong capacity, fire prevention, anti-static, good sealing performance, applicable to a wide range of pressure and temperature, complete with full bore and reduced bore, and can be equipped with a variety of driving devices. It is an ideal valve choice for chemical industry, petroleum refining, natural gas production and transmission systems.
For China, pipeline ball valve is in the golden age. China, which accounts for one quarter of the world's population, had less than 20000 kilometers of long-distance pipelines in 2000, less than 1% of global pipelines. After 2000, it has achieved rapid development. By 2009, it had 80000 kilometers of long-distance pipelines, accounting for 2.5% of the world's total, including 31000 kilometers of gas pipelines and 29000 kilometers of oil pipelines. There are more than 20000 pipeline ball valves in online service.
In the design and manufacture of pipeline ball valves, the emphasis on safety and reliability should not be excessive. And this concept should be implemented in the whole process of ball valve product design, process specification, part processing, type test, product test, quality control and after-sales service. Both long-distance pipelines and urban pipe networks are the supply line of energy and the lifeline of the national economy. Global underground oil and gas pipelines and pipe networks, like the above ground transmission and distribution grid, are the basis for the survival of urban industry and civil use. Without this energy supply line, the function of modern cities will stop immediately.
1. The design of valve body can be divided into full welded valve body design and split valve body design.The fully welded valve body is designed with cylindrical structure and spherical structure. The cylindrical structure is double welded, with large heat input during welding, complex residual stress, and large axial and radial deformation. The spherical structure is spliced by four welds. Now, due to the progress of technology, the left and right valve bodies are hot forged and formed, and the middle single weld can be welded and formed to reduce the input of linear energy and reduce the axial and radial deformation.
Split structure is generally composed of valve body and left and right connectors. The connecting body and the valve body are connected by bolts. The thickness of the connecting flange and the connection strength of the bolt should be designed by analogy with the flange equivalent to the inner diameter of the valve body. Its connection strength must prevent the connection relaxation caused by pipe stress, so that the seal fails. The valve body is in contact with the connecting surface, and there is no gap in the middle. The seal must meet the fire safety requirements, and the combination seal of rubber O-ring and spiral wound metal gasket is adopted. The material of the valve body is forgings, and ASTM A105 is selected for the temperature above -29c °- ASTM A350 LF2 is selected below 29c °. For welded valve bodies, there shall be special restrictions on the chemical composition, carbon content, carbon equivalent, sulfur, phosphorus and other elements of A105 or LF2 materials. Forgings shall be accepted according to the standard of class III forgings, and 100% non-destructive testing shall be done. Dye inspection and ultrasonic testing shall be done at the welds.
Most valve bodies of ball valves in gas transmission pipelines use A105 and a105n balls. Most of the valve bodies of ball valves in oil pipelines use A105 and ball 316.
2. The sealing seat and the sealing seat adopt a combined sealing structure, that is, the initial "sealing" of metal to metal, to prevent the entry of solid particles; Rubber, PTFE plastic, nylon, peek and other soft seals are used as secondary seals to ensure zero leakage. However, due to the damage of soft sealing materials caused by the accidental introduction of foreign matters in the pipeline, the pipeline ball valves are equipped with emergency sealant injection systems to obtain temporary sealing requirements.
The rubber rings used for sealing have circular, triangular or other special shapes. Valve companies have their own design structure and process measures to prevent the rubber ring from being blown out or cut out during the switching process. For class 900 and above, materials with explosion-proof and pressure reduction (AED) characteristics should be selected as O-ring materials. PTFE sealing ring generally adopts cylindrical inlaid structure, and can also be made into barb shaped combined structure, in order to ensure that the sealing ring will not be blown out and cause sealing failure.
The material of the seal seat is the same as that of the valve body. It is electroless nickel plated and spring loaded to ensure the initial seal specific pressure. The spring can be spiral spring, plate spring or Belleville spring, and the material is Inconel X-750.
The valve seats at the inlet end and outlet end adopt symmetrical two-way sealing design. This piston type medium self sealing structure can be designed into "single piston action", pressure self releasing seal seat structure and "double piston effect" double sealing structure according to the needs of customers. The single piston effect means that the inlet end is sealed and the cavity pressure at the outlet end is automatically discharged.