Technical requirements for high temperature and high pressure valve castings

When casting high temperature and high pressure valve castings, relevant personnel need to understand the relevant requirements of the service environment of valve castings, which is the reference basis for the selection of valve materials, structural design, manufacturing conditions and manufacturing process. Before and after the production of valve castings, relevant personnel should also do a good job in valve experimental inspection to ensure the quality of valve castings and reduce various casting defects. The following mainly analyzes the manufacturing process of high temperature and high pressure valve castings.

1. Chemical composition of CF8C

This paper mainly studies the manufacturing process of CF8C valve casting. First, we should understand the chemical composition and mechanical properties of the valve casting, and then select the materials according to the requirements. In the valve casting, its chemical components include C, Si, Cr, Ni, Nb, etc. the contents of these chemical components are different, among which the contents of Nb and Ni are higher. In terms of mechanical properties, the tensile strength of the valve casting should far exceed 485 MPa, and the yield strength should not be less than 205 MPa.

2. Metallographic examination

Because valve castings should be applied in complex high temperature and high pressure environment, when selecting metal materials, we should not only consider the quality and performance of the materials themselves, but also consider their coping ability in various harsh environments to see whether they meet the requirements of processing or heat treatment and other processes, and whether they can maintain their original performance and function under the action of these processes. Based on this, relevant personnel shall conduct metallographic inspection on valve casting materials. The inspection standard mainly refers to ASTM E381 of American Society for testing and materials. The composition of metal materials is complex, and these inclusions will affect the purity of effective components in valve castings. Therefore, in metallographic testing, the content of these inclusions should be specified so that they will not exceed the standard. These inclusions include sulfide, aluminum chloride, etc., and their grades shall not exceed 1.0. The bands in the metal structure shall be kept uniform, and the segregation size shall not exceed the standard range.

3. Intergranular corrosion detection

Make the valve casting in the sensitized state, and then implement the intergranular corrosion detection technology to detect the corrosion resistance of the valve casting in the application environment. In the test and detection, ASTM a262 standard is mainly used as a reference. If the test results are not within the scope of the standard, relevant personnel have to re select materials or improve the process.

4. Nondestructive testing

Nondestructive testing can check the quality and performance of its internal structure without damaging the valve casting, so as to expose its defects. There are two main detection technologies. First, radiographic testing. In this detection method, the detection scope and reference standards of the detection method are different. The main detection contents are the porosity of the valve casting. Generally, the shrinkage defect of the valve casting cannot be greater than grade 2. If the detection results are inconsistent with it, it is proved that the valve casting has defects. The second is liquid penetrant testing. This method is mainly used to detect various defects to see whether their size, area and other parameters meet the requirements. The inspection objects include linear display casting defects, circular casting defects and dense casting defects. The scope of these defects is specified in relevant documents. For the first two, their length shall be less than 2 mm and 4 mm; For centralized casting defects, relevant personnel need to check the defect size within the fixed distribution range. Within the area range of 0.01 m2, the defect length should be consistent with the requirements of linear display defect length.

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