Seamless casing pipe vs ERW casing pipe

Posted by zora li on August 25th, 2022

Seamless steel casing pipes-casing made of seamless steel pipe as raw material

Seamless pipe refers to a steel pipe manufactured by four methods: hot rolling, cold rolling, hot drawing, and cold drawing. There is no weld seam on the pipe body itself.

ERW casing pipe-casing made of electric welded pipe as raw material

ERW pipe refers to a straight seam welded pipe manufactured through a high-frequency resistance welding process. The raw material steel plate (coil) of ERW welded pipe is made of low-carbon microalloy steel rolled by TMCP (Thermo-Mechanical Control Process).

Outer diameter tolerance

Seamless steel pipe: hot-rolled forming process is adopted, and the sizing is completed at about 8000C. The raw material composition, cooling condition and cooling state of the roll of the steel pipe have a great influence on its outer diameter, so the outer diameter control is difficult to be accurate and fluctuates The range is larger.

ERW steel pipe: adopts cold-formed forming, and sizing is completed by 0.6% reduction. The process temperature is basically constant at room temperature, so the outer diameter control is accurate and the fluctuation range is small, which is helpful to eliminate black leather buckles;

Wall thickness tolerance

 Seamless steel pipe: It is produced by round steel perforation, and the wall thickness deviation is large. The subsequent hot rolling can partially eliminate the unevenness of the wall thickness, but the most advanced unit can only be controlled within ±5-10%t.

ERW steel pipe: using hot-rolled coil as raw material, the thickness tolerance of modern hot-rolling can be controlled within 0.05mm.

Exterior

 The outer surface defects of the blanks used in seamless steel pipes cannot be eliminated by the hot rolling process, and the defects can only be polished after the finished product is completed; the spiral path left after piercing can only be partially eliminated in the process of reducing the wall.

ERW steel pipe uses hot-rolled coils as raw materials. The surface quality of the coils is the surface quality of ERW steel pipes. The surface quality of hot-rolled coils is easy to control and high in quality. Therefore, the surface quality of ERW steel pipes is much better than seamless steel pipes. .

Ovality

 Seamless steel pipe: hot-rolled forming process is adopted. The raw material composition of the steel pipe, the cooling condition and the cooling state of the roll have a great influence on its outer diameter, so it is difficult to accurately control the outer diameter and has a large fluctuation range.

ERW steel pipe: adopts cold bending forming, so the outer diameter control is accurate and the fluctuation range is small.

Stretching test

 The tensile performance indexes of seamless steel pipes and ERW steel pipes are in line with API standards, but the strength of seamless steel pipes is generally at the upper limit and the plasticity is at the lower limit. In comparison, the strength index of ERW steel pipes is in the best state, and the plasticity index is 33.3% higher than the standard. The reason is that the performance of hot-rolled coils, the raw material of ERW steel pipes, is guaranteed by means of microalloying smelting, out-of-furnace refining, and controlled cold and controlled rolling; seamless steel pipes mainly rely on means of increasing carbon content, which makes it difficult to ensure strength and plasticity. Reasonable match.

hardness

 The raw material of ERW steel pipe, hot-rolled coil, has extremely high precision of controlled cold and controlled rolling during the rolling process, which can ensure the uniform performance of all parts of the coil.

Grain size

 The raw material of ERW steel pipe-hot-rolled coil is made of wide and thick continuous casting billet, with thicker fine-grained surface solidification layer, no columnar crystal area, shrinkage cavity and porosity, small composition deviation, compact structure; in the subsequent rolling process In the middle, the application of controlled cold and controlled rolling technology further ensures the grain size of raw materials.

Anti-collapse test

 ERW steel pipe is due to the characteristics of its raw material and pipe making process. Its wall thickness uniformity and ellipticity are far better than seamless steel pipes, which is the main reason why the collapse resistance performance is higher than that of seamless steel pipes.

Impact test

 Since the impact toughness of the base material of ERW steel pipe is several times that of seamless steel pipe, the impact toughness of the weld is the key of ERW steel pipe. By controlling the impurity content of raw materials, the height and direction of slitting burr, the shape of forming edge, the welding angle, and the welding speed , Heating power and frequency, welding extrusion volume, intermediate frequency withdrawal temperature and depth, air-cooling section length and other process parameters ensure that the impact energy of the weld reaches more than 60% of the base metal. If further optimized, the impact energy of the weld can be close to that of the base metal. Material, so as to achieve seamless performance.

Blasting test

 The blasting test performance of ERW steel pipe is much higher than the standard requirement, mainly due to the high uniformity of wall thickness and uniform outer diameter of ERW steel pipe.

Straightness

 The seamless steel pipe is formed in a plastic state, and the straightness of the pipe end is relatively difficult to control with single ruler (3 to 4 times ruler for continuous rolling);

 The ERW steel pipe is cold-worked, and it has online straightening in the reduced diameter state, plus infinite times the ruler, so the straightness is better.

 Steel consumption of casing for ten thousand meters of footage.

The wall thickness of ERW steel pipe is uniform, and its wall thickness tolerance can be neglected. The control accuracy limit of seamless steel pipe wall thickness difference is ±5%t, and it is generally controlled at ±5-10%t. In order to ensure that the minimum wall thickness can meet the standard requirements and performance, the solution can only be solved by appropriately increasing the wall thickness. Therefore, in the casing of the same specification and the same weight, the ERW steel pipe is 5-10% longer than the seamless steel pipe, or even more, which reduces the steel consumption of the casing for 10,000 meters by 5-10%. Even at the same price, ERW casing pipe virtually saves users 5-10% of purchasing costs.