1, Outside diameter tolerance
Seamless pipe: the use of hot-forming process, the sizing is about 8000C to complete the steel pipe raw material composition, cooling conditions and roll cooling state of its outer diameter have a greater impact, so the outer diameter control is difficult to be accurate and the fluctuation range is larger.
ERW pipe: the use of cold forming, through the 0.6% reduction of diameter to complete the sizing, the process temperature is basically constant at room temperature, so the outer diameter control is accurate, the fluctuation range is small, is conducive to eliminate black buckle;
2, Wall thickness tolerance
Seamless pipe: wall thickness control accuracy limit is 0.9mm.
ERW pipe: the use of hot-rolled coil as raw material, the thickness of the modern thermal connection can be controlled within 0.05mm tolerance, and seamless pipe with round steel perforation production, wall thickness deviation, followed by hot rolling can be part of the wall Thick nonuniformity, but the most advanced unit can only be controlled within ± 5 ~ 10% t, corresponding to the thickness of 8.94mm steel pipe.
3, Oval
Seamless pipe: the use of hot-rolled forming process, the composition of steel raw materials, cooling conditions and the cooling state of the roll and so on its outer diameter have a greater impact, so the outer diameter control is difficult to accurate, and a larger range of fluctuations.
ERW pipe: the use of cold forming, so the outer diameter control is accurate, the range of small fluctuations.
4, Tensile test
Seamless pipe and ERW pipe tensile performance indicators are in line with API standards, but the seamless pipe strength is generally in the upper limit, plastic at the lower limit, compared to ERW pipe strength index in the best condition, plastic index higher than the standard 33.3% , Because the raw material of ERW pipe - hot rolled coil performance is to rely on micro-alloy smelting, furnace refining and cold control rolling and other means to ensure that seamless steel pipe mainly rely on the means to increase carbon content, it is difficult to ensure strength, reasonable match.
5, Hardness
ERW pipe raw materials - hot rolled coil in the rolling process control cold rolling precision is extremely high, to ensure uniform performance of the various parts of the coil.
6, The crystal body
ERW pipe raw materials - hot rolled coil with a wide thickness of continuous casting billet, a thicker grain surface solidification layer, no columnar area and shrinkage and loose, the composition of small, dense organization; in the subsequent rolling process The application of medium and controlled cold rolling technology further ensures the grain size of raw materials.
7, Anti-crushing test
ERW pipe because of its raw materials, pipe technology characteristics. Its wall thickness uniformity, ellipticity is far superior to seamless pipe, anti-crushing performance is higher than the main reason for seamless pipe.
8, Impact test
As the impact toughness of ERW pipe base several times in the seamless pipe, the impact toughness of the weld is the key to ERW pipe, by controlling the raw material impurity content, slitting height and direction, forming edge shape, welding angle, welding speed, heating power and frequency, the amount of welding extrusion, the length of the air-cooled section of the process parameters to ensure that the impact of welding to achieve more than 60% of the base metal, such as further optimization, Material, in order to achieve seamless performance.
9, Blasting test
ERW pipe blasting test performance is much higher than the standard requirements, mainly from the ERW pipe wall thickness uniformity uniformity, uniform diameter.
10, Straightness
ERW pipe is cold working, and in the state with a reduced diameter with straightening, plus is an infinite scale, so the straightness is better; seamless pipe in the plastic state of molding, with a monometer (rolling for 3 ~ 4 times the scale) tube straightness is relatively difficult to control.
11, appearance
The blank surface defects used in the seamless tube can not be eliminated by hot rolling process, only the defects can be worn off after the finished product is finished; for the spiral hole, only partially eliminated in the process of reducing the wall surface. ERW steel tube is hot rolled steel coil as raw material, the surface quality of steel coil is ERW steel tube surface quality, hot rolled steel coil surface quality is easy to control, high quality, so the surface quality of ERW steel pipe is better than seamless tube.
12, 10 million meters into the foot of the steel pipe consumption
ERW tube wall thickness uniformity, wall thickness tolerance can be ignored, and seamless tube wall thickness control accuracy limit is + 5%t, generally controlled at + 5 ~ 10%t. To ensure that the minimum wall thickness meets the standard requirements and service performance, only proper wall thickness is increased. Therefore, in the same size, the same weight of the casing, ERW steel pipe is 5 to 10% more than seamless steel pipe, and even more, thus reducing the 5 to 10% meters of steel tube casing. Even at the same price, the ERW bushing can save users 5 to 10% of the purchase cost.
