how to adapt to the high temperature

About the welded steel pipe: how to adapt to the high temperature1.The influence of temperature on the metal deformation: at high temperature, the metal plastic deformation resistance is generally smaller than that at low temperature, therefore, the higher the temperature, the lower the strength and hardness of the metal, and the higher the plasticity and toughness. From the point of metallography, the temperature line, whether the metal hot working or cold working, is to be distinguished by the recrystallization temperature. All the pressure processing above the recrystallization temperature is called hot working, and below the recrystallization temperature for pressure processing called cold working. Steel processed in the 600-700  can be called hot working, and at 400  still belongs to cold working.2.The influence of temperature on the strength of metal:(1) Some domestic literature points out: "allowable stress value of the pipes under 400  is based on the material yield limit and the proportional limit. For the pipe at high temperature above 400  for a long time (such as: 35 kg/cm2 steam), due to significant creep phenomenon, its allowable stress is based on the creep strength. And the allowable stress values of various specifications are all based on it."(2) We can know from the general knowledge of metal heat treatment: when the temperature is 200 , the yield limit of carbon steel, instead of reduced, slightly increased, so when the carbon steel body works at high temperature under 250 , you don't have to consider the effect of temperature on the static strength.(3) The effect of effect of temperature on the fatigue strengthCarbon steel at the high temperature of 350 -400 , fatigue strength rises a lot rather than reduces. The above analysis shows that the use of seam tube has a scientific basis under the condition of high temperature and high pressure.3. The provisions of the relevant national standards:(1) The national standards GB150-1998 of the People's Republic of China: "steel pressure vessel" holdings "provisions of the applicable scope of the carbon steel composed plate" is as follows:Q235-A steel plate:when container design pressure Pd1.0 Mpa, the steel plate temperature is of 0-350 . When used in the shell, the thickness of the steel plate is not greater than 16 mm.(2) The power industry standard DL/T 5054-1996 of the People's Republic of China "technical regulations for design of thermal power plant steaming-water pipe"For 20G steel pipe, if require use for life is no more than 20 years, using the temperature can be up to 450 , but the metal supervision should be strengthened during use. And for the pipeline steel material of ERW steel pipe can refer to the temperature scope of the alloy steel pipe.