Conduit metal stuff

One, of conduit metal stuff choose
1.The characteristic of stuff of pressure conduit metal
Pressure conduit involves all trades and professions, it is to its main demand " safety and use " , safe to use, use must safe, use still involve economic issue, invest province, use fixed number of year to grow namely, this is concerned with a lot of elements of course. And the foundation that material is a project, want to meet the special requirement of stuff of pressure conduit metal above all. Pressure conduit is divided bear outside load, because lie below different environment, temperature and medium,work, still bearing special test.
(1) the change that metallic stuff leaves property in high temperature
① creep rolled steel suffers below high temperature when outside force action, as the extension of time, phenomenon of metabolic of plasticity of slow and successive generation, call creep. Feature of rolled steel creep and temperature and stress have very big concern. Temperature lifts or stress increases, creep speed is accelerated. For example, temperature of carbon steel job exceeds 300 ～ 350 ℃ , temperature of alloy steel job exceeds 400 ℃ of 300 ～ to be able to have creep. The stress that generation creep place needs under experiment temperature rolled steel succumb intensity. Accordingly, place of conduit of the boiler that makes to the permanent worker below high temperature, vapour, pressure vessel uses rolled steel to should have the good denaturation that fight squirm can, reach with preventing to produce a large number of is out of shape because of creep to cause structural rupture cause the malign accident such as explosion.
② ball is changed and graphitization falls in high temperature action, because the cementite in carbolic steel obtains energy to will happen migratory and gather, form the cementite with bulky grain and be mingled with in ferrite, its cementite is met from piece shape transforms gradually glomerate, call a ball to change. Because black lead intensity is extremely low, and with piece shape appears, make data strength is reduced greatly, brittleness increases, call the graphitization of material. Long-term job is in carbolic steel environment of 425 ℃ above is the ground, can produce graphitization, in be more than 475 ℃ more apparent. Highest use temperature is steel of SH3059 regulation carbon 425 ℃ , GB150 stipulates carbolic steel is highest use temperature is 450 ℃ .
If rolled steel of function of ③ hot exhaustion is long-term cold heat works alternately, so below the thermal stress effect that material interior causes in change of difference in temperature, can produce tiny flaw and expand ceaselessly, cause rupture finally. Accordingly, rise and fall in temperature the hot fatigue property of rolled steel of Lv of take an examination of the structure below metabolic work requirement, conduit.
The stuff of metal of high temperature oxidation of ④ material is in environment of medium of high temperature oxidisability (like flue) can be oxidized and produce oxidation skin, easy fragile fall. In the high temperature gas that carbolic steel is in 570 ℃ produce oxidation skin and make the metal is decreased easily thin. Reason lights the steel tube such as gas, flue to should be restricted work below 560 ℃ .
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