Application of alkali steel in regulating valve

Carbon steel is suitable for non corrosive medium. It can also be used in some corrosive media under certain conditions, such as under certain temperature and certain concentration. The applicable temperature is -29°-425 ° c.

1. Carbon cast steel

At present, the current domestic standard is GB/ "T12229--2005" general valve carbon steel component technical conditions ". The brands of the materials are WCA, WCB and WC. This standard is based on ASTM a216-200p

Standard specification for high temperature fusible carbon steel parts. This standard has been modified at least five times in the United States, and the newer version is ASTM A216/ a216m-2016, while GB/ t12229-2005 is still in use in China.

The following points should be noted:

1) qualified castings must have qualified chemical composition, qualified mechanical properties and fully meet the standard requirements, especially the control of impurity elements must be strict, otherwise the welding performance will be affected.

2) the maximum content of chemical elements is the mass fraction specified in the standard. In the manufacturing process, in order to obtain good welding performance and reach the mechanical properties stipulated in the standard, it is necessary to establish internal control standards for chemical element quality fraction, and conduct correct heat treatment for storage parts and test rods, otherwise qualified castings cannot be made. For example, the mass fraction of carbon in WCB steel is less than 0.30%. If the mass fraction of carbon in WCB steel is 0.10% or less, the mass fraction is qualified, but the mechanical properties do not meet the standard requirements. If the mass fraction of carbon is equal to 0.30%, it is also acceptable but has poor welding performance. Carbon mass fraction control at about 0.25% is the best. If "export" products are produced, some foreign companies will ask for carbon quality control requirements. 3) the temperature range of carbon steel regulating valve is as follows:

JB/ t5300-2008 "guide for selection of industrial valve materials", the applicable temperature range of carbon steel valve is -30 ~ 450℃.

(2) sh3064-2003 standard for selection, inspection and acceptance of universal valves made of petroleum and chemical industry steel stipulates that the applicable temperature of carbon steel valves is -20 ~ 425℃. The lower limit is -20℃, which is consistent with gb150-2010 steel force vessel.

3 ASME B16.34-2013 flange and welding end valve pressure ー temperature rating of the benchmark, WCB

The applicable temperature range of A105(carbon steel) is -29-425℃. Long-term use above 425℃ is not allowed. This is because carbon steel has graphitization tendency above 425℃.

Carbon steel forging

JB/ t7746-206 "compact steel valve", execute GB/ t1228-2006 "general valve carbon steel forging technical conditions". In JB/ t450-2008, JB/ t4726-2010, carbon steel and low-alloy steel forgings for pressure vessels, is implemented.

The most commonly used standard and brand is GB/T692015 "high quality carbon structural steel" 20, 25, 30, 35, 40 steel and 25M. Generally, the medium pressure forging steel regulating valve USES 25 steel to make pressure parts, and 35 and 40 steel are used to make pressure parts of PNI60 and PN320 forged high-pressure angular stop valve and throttle valve.

PN140 reducing diameter forging steel valve pressure pieces are commonly used 25 steel or 25 mn manufacturing.

Attention should be paid to heat treatment after forging. Below 25 steel (including 25 steel) shall be normalized; According to the mechanical properties of the products, 3035 and 40 steel adopt normalizing or tempering treatment.

After the introduction of equipment into China, the forged carbon steel regulating valve imported from abroad, such as Clas800 class forged steel valve, adopts ASTM a1055a1055-2013 "carbon steel forgings for pipe components". The mass fraction of its principal chemical elements

(%) is as follows :C≤0.35: Mn 0.6-1.05; P: 0.035 or less S 0.04 or less; Si is 0.10 ~ 0.35. Cu 0.4 or less MK4; Gr 0.3 or less; Mo 0.12 or less; V0.08; Nb い 0.0 or less. The mechanical properties are as follows :Rm.≥48SNPa:ReL≥250MPa; :A≥ 22% Z≥ 30%; Hardness 187 HBW or less.

Please note the following:

1.) below the specified maximum carbon content (0.35% 5), when the carbon content is reduced by 00.1%, 0.06% of the specified maximum manganese content (1.05% 0) is allowed until the maximum manganese content is 1.35%.

2) the total mass scores of C, N, Cr, Mo and V should not exceed 1.0%.

3) the total mass fraction of Cc and Mo should not exceed 0.32.

4) the quality scores of V and Nb or both may be increased to 0.10% and 0.05% respectively upon agreement between the buyer and the manufacturer. ,

5) the material specified in ASTM A105/A105M -- 2014 is not 25 steel or 25 mn steel of China. Although the mass fraction of its main chemical elements is equivalent to China's 25Mn, ASTM A105/ a105m-2014 has requirements for the control of its impurity elements Cu Ni, Cr, Mo, V, Nb, and the mass fraction of C and Mn.

6) whether the forging steel regulating valve needs to be tested for the mechanical properties of materials is determined according to the product design requirements. For low carbon steel, as long as the quality of chemical elements qualified, normalizing heat treatment process is correct, its mechanical properties are certain. Unlike medium carbon steel and high carbon steel, different tempering temperature after quenching can be used to obtain different mechanical properties. For forged high pressure net door, such as PN160, PN320 or higher pressure of the general steel regulating valve, the design determines the use of materials should achieve the mechanical properties. According to the required mechanical properties to determine the tempering temperature; To make the mechanical properties of the material meet the design requirements.