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The difference between erw steel pipe and seamless steel pipe

1, diameter tolerance 

ERW pipe: The roll forming, reducing by 0.6% complete sizing, its process at room temperature is almost constant, and thus control the exact outer diameter, a small fluctuation range, help eliminate black buckle; 
Seamless steel tube: hot rolled molding process, which is at around 8000C sizing is complete, has a greater impact on its outside diameter steel pipe material composition, cooling conditions and the cooling roll status, and thus difficult to accurately control the outer diameter, and the fluctuation large range. 

2, wall thickness tolerance 
ERW pipe: Using hot-rolled coils for raw materials, modern hot strip rolling thickness tolerances can be controlled within 0.05mm of, and seamless steel pipe produced using round perforation, thickness deviation is large, then rolled partially eliminate wall thick uneven, but the most advanced unit can only be controlled within ± 5 ~ 10% t, corresponding to the pipe 8.94mm thickness. 
Seamless steel pipe: Extreme wall thickness control accuracy is 0.9mm. 

3, ovality 
ERW pipe: The roll forming, and thus control the exact outer diameter, a small fluctuation range. 
Seamless steel: The outer diameter has a greater impact on its molding process hot-rolled, steel raw ingredients, cooling conditions and the cooling roll status, and thus difficult to accurately control the outer diameter and greater volatility range. 

4, the tensile test 
Seamless steel pipe and ERW steel pipe stretching performance indicators are in line with API standards, but generally in the upper limit of seamless steel strength, plasticity is the lower limit, comparatively speaking, ERW steel pipe strength index at its best, the plasticity index higher than the standard 33.3% reasons for ERW steel pipe materials - hot-rolled coil performance is to rely on micro-alloying smelting, refining and controlled rolling and controlled cooling and other means to ensure; seamless steel tubes mainly rely on means of increasing the carbon content, it is difficult to ensure the strength, ductility reasonable match. 

5, the hardness 
ERW steel pipe materials - hot-rolled coils controlled rolling and controlled high precision cold rolling process, to ensure uniformity with the volume of each part of the performance. 

6, grain body 
ERW steel pipe materials - hot-rolled coil is used in generous slab, there is a thick layer of fine-grained surface solidified, columnar grain zone and no shrinkage and loose, composition deviation is small, compact; during subsequent rolling process , the application of controlled rolling and controlled cooling technology to further ensure the grain size of raw materials. 

7, collapsing test 
ERW steel pipe for its raw materials, pipe and process characteristics. Its uniform thickness, ovality far superior seamless performance is higher than the seamless steel pipe collapsing the main reason. 

8, the impact test 
ERW steel pipe due to the impact toughness of the base material several times in the seamless steel pipe, weld toughness is the key ERW steel pipe, by controlling the impurity content of raw materials, slitting burr height and direction, forming the edge shape, fillet welding speed , heating power and frequency welding extrusion amount, iF withdraws temperature and depth, air-cooled length to ensure that the weld process parameters such as impact energy to achieve more than 60% of the base material, such as further optimized to achieve weld impact energy close to mother timber, enabling seamless performance. 

9, burst test 
ERW pipe burst test performance is much higher than the standard requirements, mainly due to high ERW steel pipe wall thickness, uniform diameter size. 

10, straightness 
ERW steel pipes are cold, and with a line straightening in reducing state-foot plus unlimited times, so straightness better; 
Seamless steel molding in plastic state, with a single fold-foot (3 to 4 times rolling feet) straight pipe end is relatively difficult to control. 

11, the appearance of 
ERW steel pipe using hot-rolled coil as raw material, the surface quality is the surface quality coil ERW steel pipe, hot-rolled coil and surface quality and high quality easy to control, and therefore the surface of far superior quality ERW steel pipe seamless steel pipe . 
Seamless steel billet outer surface defects can not be used in hot rolling process by eliminating only after the completion of the finished, polished off defects; perforation after leaving for spiral Road, in the process of reducing the wall, only partially eliminated.