Design and Application Prospects of Forged Steel Ammonia Valves

Design and Application Prospects of Forged Steel Ammonia Valves

Dec 15, 2020


Abstract
The safety of the ammonia refrigeration system is the focus of the ammonia refrigeration industry. Safe and energy-saving ammonia valves are the inevitable development of the industry. The innovative design of forged steel ammonia valves and their application prospects are discussed in this article based on safety performance and use requirements for liquid ammonia refrigeration systems.
 
In recent years, ammonia leakage accidents have occurred frequently in ammonia refrigeration enterprises, causing unnecessary casualties and economic losses, which draws attention to the ammonia refrigeration system. Preventing ammonia leakage accidents in the refrigeration system is the top priority in the safety of cold storage. Once an accidents such as chemical explosion, combustion or ammonia poisoning occur due to the characteristics of ammonia itself, which will cause serious economic losses and unstable factors to enterprises and society. Prevent ammonia leakage from valves in the refrigeration system by innovative, safe and energy-saving valve products, which not only guarantees the normal production and operation of the enterprise, but more importantly, guarantees the national and people's property not being lost, safety of operators and other operating personnel and the stability of society.
 
2. Difficulties in research and development of ammonia valves or globe valves
The globe valve is an important valve in the refrigeration system. Its technical difficulties are as the following:
(1) How to adopt computer aided design, the international advanced three-dimensional solid modeling design concept and from top to down design method, simulate and optimize the structure, greatly improve the circulation capacity, have obvious energy-saving characteristics and greatly reduce operating costs of the refrigeration system?
(2) How to select new materials and new processes for the valve body of the globe valve to further improve corrosion resistance and good impact toughness; optimize the valve body structure to make the globe valve structure advanced and have features of good body strength, good pressure resistance, low flow resistance coefficient, energy conservation, less consumption and good cleanliness of the inner cavity?
(3) What kind of sealing and sealing materials should be used to further improve the sealing performance of the valve?
 
2. The low temperature forged steel globe valve design process
A large number of market exploration and adjustments are carried out for the cryogenic forged steel globe valve. The refrigeration valve developed after the research is an upgraded product of the existing traditional valve. After consulting a large number of domestic and foreign related data, the embryo of the product was determined, and after discussion and research, it was decided to divide the product design process into four steps, as shown in the following. In order to ensure product quality, cryogenic valves must be subjected to a cold test P', so the simulation and thermal analysis of the temperature field of the packing box and the valve during the dynamic cooling process of the globe valve sample were carried out during the design process.
  • Determining product structure    
  • Determining the material for each part      
  • Determining the product drawing of each part through computer-aided design
  • Formulating product processing technology and required process tooling 
Table 1 Project development content
Serial number Development steps Development content
1 Determine product structure.
 
The valve body adopts a direct flow type Y structure; the shape of the valve body is manufactured by precision die forging; the valve and the system pipeline are connected by butt welding; the upper sealing structure with advanced metal to engineering plastic soft inverted seals is adopted. The valve disc and valve stem adopt a ball connection structure similar to the bearing structure.
2 Determine the material of each part.
 
The material of the valve body and bonnet is 16MnD; the valve stem is made of stainless steel; the sealing and packing materials are polytetrafluoroethylene; two O ring seals are added.
3 Specifically design valve sizes.
 
Computer-aided design is adopted, using international advanced three-dimensional solid modeling design concepts, designing parametric part models, manufacturing and assembling samples and using ANSYS finite element analysis software to carry out simulation and thermal analysis of the temperature field of the packing box and the valve during the dynamic cooling process of the globe valve sample; the specific size of the valve is finally determined.
4 Formulate processing technology and required process tooling of the valve.
 
After the specific size of the valve is determined, the technologist will write the processing file, and the model personnel will make the relevant model. The tooling designer will design and complete the technological equipment required for the trial production.
 
In the design process, the innovations are as follows:
(1) Because of the complex internal structure of the valve channel, water flow phenomena such as vortex, air hammer and dead water zones are generated when the fluid passes through the valve channel. These phenomena seriously endanger the working conditions of the system and are the main factors for the loss of the system head. The globe valve adopts computer-aided design, and all its components are parameterized models, and the structure is optimized by simulation. The three-dimensional model is shown in the Figure 2.
 
Figure 2 The three-dimensional model of the cryogenic forged steel globe valve
 
(2) The valve body material is made of 16MnD low temperature carbon steel by hot die forging, and the dendrites in the steel are broken. The internal metal is fully compacted and forged to reduce the internal defects of the forging, increase the internal metal density and improve the corrosion resistance and low temperature impact toughness.
(3) The valve body structure adopts a 45° angle between the center line of the inlet and outlet ends and the center line of the front end surface. The fluid channel is linear and has good surface quality, good cleanliness, low flow resistance to fluid and basic no pressure loss, which can save energy.
(4) Packing is one of the important sealing devices of the valve. After the refrigeration valve is operated, the packing design plays a vital role on obtaining the sealing effect without leakage at low temperature. This design adopts PTFE packing ring and adds two O rings for double sealing to achieve the effect of zero leakage.
(5) The connection between the valve stem and the disc is the key to whether the valve can be opened and closed flexibly and whether it can play a cut off effect. The connection between the valve stem and the disc of this project adopts a bearing like ball connection, which has good connection strength and flexible rotation.
(6) The valve connection method adopts the butt welding type, that is, the standard welding groove pattern is processed by mechanical methods at the inlet and outlet ends of the valve. The valve and the pipeline are directly welded during installation. Each valve can reduce 4 flanges, which can save a lot of raw materials and standard parts, and effectively reduce leakage of flange gaskets.
The cryogenic forged steel globe valve has advanced technology, reliable performance, large flow and low resistance, which improves the operating efficiency of the refrigeration system, has low installation costs, obvious energy conservation and consumption reduction. It is suitable for low-temperature media such as ammonia, fluorine, propane, and carbon dioxide, which has a long service life and fully meets the requirements for low temperature refrigeration conditions. Tested by General Mechanical and Electrical Products Testing Institute and National Pump and Valve Product Quality Supervision and Inspection Center, main performance indicators of the valve meet the requirements for GB/T 26478-2011 (ammonia globe valves and lift check valves).
 
Application prospects of cryogenic forged steel globe valves
As a new generation of refrigeration valve products, the cryogenic carbon steel globe valve has reached the zero leakage and has good safety performance. The application in engineering practice shows the following aspects:
(1) The structure of this series of products is reasonable. The flanges at both ends are reduced, and the weight is light. And the purchase price is over 30% cheaper than that of fimported similar products.
(2) During installation, the seamless pipe fittings are directly welded to the valve body entrance, which reduces the work of welding flanges and tightening bolts, reducing installation costs and worker wages.
(3) The valve has excellent working performance under ammonia refrigeration and low temperature conditions and meets the requirements of use.
(4) The structure of the valve body is novel, and the flow resistance is smaller than that of the traditional entering from the low end and coming out from the high end type; the energy conservation effect is significant.
The performance of this series of products fully meets the use requirements for ammonia refrigeration in low temperature conditions, and greatly reduces the operating cost of the refrigeration system, which bring greater benefits to corporate users and society.
 

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