Discussions on the question of ERW steel pipe to adapt to the temperature range

1, about the ERW steel pipe to adapt to the high temperature range: abroad is also used under high temperature and high pressure tube. Straight seam steel pipe and seamless tube are metal products, such as Japanese standard ISO standard only, regardless of seam and seamless.

: the influence of temperature on the metal deformation at high temperature, metal plastic deformation resistance, are generally smaller than at low temperature, therefore, the higher the temperature, the lower the strength and hardness of the metal is, the higher the plasticity and toughness.

From the point of metallography, the temperature of the metal hot working or cold working line, is to distinguish the recrystallization temperature. All above the recrystallization temperature of pressure processing is called hot working, below the recrystallization temperature for processing called cold working pressure. Steel in the 600-600  when processing, in order to be hot working, 400  when processing, or cold.

The influence of temperature on the strength of metal:

(1) the domestic some literature points out: "allowable stress value of the pipes under 400  is based on the material yield limit, the proportional limit. At above 400  high temperature for a long time (such as: 35 kg/cm2) of steam pipe, due to generate significant creep, allowable stress is based on the creep strength. Various specifications of the allowable stress values are based on." [2]

General knowledge of metal heat treatment from known:

(2) when the temperature is 200 , the yield limit of carbon steel instead of reduced, instead a slight increase, so the carbon steel body under 250  high temperature at work, you don't have to consider the effect of temperature on the static strength.

(3) temperature effect on the fatigue strength

Carbon steel at 350 , 400  high temperature, fatigue strength rather than reduce, instead of rising.

From the above analysis shows that under the condition of high temperature and high pressure abroad is still use tube has a scientific basis.

The provisions of the relevant national standards:

(1) of the People's Republic of China national standards GB150-1998 "steel pressure vessel" holdings "provisions of the applicable scope of the carbon steel composed plate" is as follows:

Q235 - A steel plate: P 1.0 Mpa or less container design pressure, steel plate temperature of 0-350 , when used in the shell, the thickness of the steel plate is not greater than 16 mm.

(2) of the People's Republic of China power industry standard DL/T 5054-5054 technical regulations for design of thermal power plant steaming-water pipe

20 g steel pipe, if you want to use for life is no more than 20 years, using the temperature to 450  can be improved, but the metal supervision should be strengthened during use.

ERW steel pipe of pipeline steel material can refer to the scope of temperature of the alloy steel pipe.

2, about the ERW welded pipe to adapt to the low temperature range:

From national ERW pipe production, in addition to high productivity, low cost, high dimensional accuracy, its weld tensile strength, elongation, reduction of area, bending test and room temperature impact toughness values, etc all can satisfy the requirement of relevant specification. But there are many manufacturers of ERW steel pipe weld toughness at low temperature is poorer, limiting the use under low temperature condition.

Our country has a factory is introduced by material for X46 Φ 355.6 ERW steel pipe was tested.

ERW steel pipe weld lower toughness at low temperature for the solution:

Japan NKK X65 steel pipe weld pipe factory FATT value, SA = 50%, FATT - 65 ; SA = 80%, FATT da 45 . Can meet the delivery propylene (- 48 ) and propane (- 42 ) requirements.

Optimizing parent metal FATT value: their way is: the raw material for production of ERW steel pipe, special S and Ca processing refined, pure with good low temperature toughness of material is obtained.