Valve repair process, full understanding of the valve body material, in order to better valve repair, valve material, valve maintenance program, the following is related to the valve material of knowledge
First, the valve body material
The normal practice is required to control the body material of the valve user requirements, in particular, the special conditions or serious conditions with the valve. The valves of many common conditions require the use of ordinary basic materials, such as carbon steel and stainless steel. In most cases, the requirements of the body material is the same as the pipeline material (often called chromium molybdenum), mainly carbon steel, stainless steel, chrome molybdenum steel.
Carbon steel is probably the main valve to use general-purpose materials. In short, it is an ideal material for non-corrosive fluids. The carbon steel is widely used in the neat and condensing operation. Its optimum high temperature performance can be high as 800 ° F (425 ° C) continuous work, or even up to 1000 ° F (535 ° C) does not work continuously. Carbon steel has been used in common industrial valves, especially compared with other commonly used materials, the price of ordinary cheap.
Stainless steel corrosion resistance is very strong, as he may require for the 1000 ° F (535 ° C) or higher temperature conditions. The cost is slightly higher than carbon steel, but cheaper than other steel alloys.
Chrome-molybdenum steel is a good material, and its performance is located between carbon steel and stainless steel. Compared to carbon steel to resist high pressure and temperature, is that she will make the operation of high pressure steam and condensate. He's mildly better than carbon steel and is almost the same, and stainless steel, chromium molybdenum steel corrosion resistance than stainless steel.
The special alloy is specified for the valve of the special conditions or serious conditions. For example, selection of the Hastelloy B and C or titanium to avoid and fluid lack of coordination, such as highly acidic fluid. Other cases, the choice of Mengna Er or bronze for pure oxygen conditions here due to security reasons for choice of playing the material of the spark is dangerous.
Table 2.9 lists a number of commonly used valve material and its temperature limit. The valve body is made by casting, forging or bar stock, or by pipeline tees and flanges manufacturing. As manufacturers adopt the technology and mass production, the manufacturing cost is the lowest. You need to short-sighted, special materials and / or a higher rated pressure the entry ANSI1500 level (PN250), the 2500 level (from the pivotal PN400) or 4500 (PN700). Manufacturing body for conveying the risk of circulation can not use the valve body casting or forging, or structural integrity, then use the bar. Large angle valve body manufacturing. As a general rule, the valve cover or valve cap (used to seal body parts at the top part) to use the same body of material. Although most of the use of bar instead of casting to produce. The one exception to the general rule is the offset voltage chromium molybdenum valves, valve size 6in (DN150) or more hours, regular use of stainless steel valve cover.
Second, the material selection criteria
Several parts of the body is under stress, the process fluid. Corrosion and other operations under the influence of the provisions of these parts is the body. The valve cover. The valve cover bolts. Cocks, balls, valve plate, wedge / or water joints. Although the natural pressure vessel out of the plug valve rod or shaft, but they do not have the relevant organizations to consider the quality and safety for pressure parts.
American National Standards Institute has published a specific pressure and temperature limits of specified materials (standard B 16.34). Before being selected to ensure that he can fit the correct temperature and pressure limits should be carried out with these standards in the review. Materials for pressure parts structure is specified by the American Society for Testing and Materials (ASTM) specifications. ASTM standard test procedures and acceptance criteria for materials, ASTM material technical specifications. ASTM specifications are demanding, they guarantee that the material is repeated in the correct technical specifications, or again, regardless of the manufacturer views. If the material is again repeated by the technical specifications or, regardless of the manufacturer and that. Such as over material according to the technical specifications of production, his performance should be able to withstand the Note and a way out of design conditions, such as corrosive fluid, drama hot temperature and high pressure.
ASTM specifications do not want to include all known materials, but includes all common materials used in known conditions. Because every year a number of new materials, ASTM regulations to allow new material delivery acceptance, sometimes even prior to the ASTM formal acceptance, as long as strict compliance with the program is allowed to use. Table 2.10 provides the appropriate body and bonnet material standards (ANSI standard B16.34 and, 900,), it includes castings, forgings and bar stock.
Another one involving the pressure is not necessarily manufacture and performance of the organization is the American Society of Mechanical Engineers (the ASEM), the management and publishing of the Boiler and Pressure Vessel Code. The specification of two materials and ASTM materials showed that almost all materials are standard included. 2 cheat materials and ASTM materials have the same number Oh of, but as ASTM add a prefix "S" before the number. ASEM limit the welding process, heat treatment and lead warm-up. Another organization, the American Welding Society (AWS) welding rod and wire to make the supervision and control methods |
