Comparison of ERW Welded Pipe and Seamless Steel Pipe (tested by PetroChina Pipe Institute)

1. Outer diameter tolerance
ERW steel pipe: It is cold-formed and sizing is completed by reducing the diameter by 0.6%. The process temperature is basically constant at room temperature. Therefore, the outer diameter is controlled accurately and the fluctuation range is small, which is helpful to eliminate black leather buckles.

Seamless steel tube: The hot-rolling forming process is used, and its sizing is completed at about 8000C. The raw material composition, cooling conditions, and cooling conditions of the rolls of the steel pipe have a large impact on its outer diameter, so it is difficult to accurately control the outer diameter and fluctuate Larger range.

2. Wall thickness tolerance

ERW steel pipe: using hot-rolled strip as the raw material, the thickness tolerance of modern hot-rolled strips can be controlled within 0.05mm, and seamless steel pipes are produced by round steel perforation, with large wall thickness deviations. The subsequent hot rolling can partially eliminate the wall thickness. Thickness non-uniformity, but currently the most advanced units can only be controlled within + 5 ~ 10% t, corresponding to steel tubes with a thickness of 8.94mm.

Seamless steel pipe: The limit of wall thickness control accuracy is 0.9mm.

3. Ovality
ERW steel pipe: cold-formed, so the outer diameter is controlled accurately and the fluctuation range is small.
Seamless steel pipe: The hot-rolled forming process is used. The raw material composition, cooling conditions, and cooling conditions of the rolls have a large impact on the outer diameter of the steel pipe. Therefore, it is difficult to control the outer diameter accurately and the fluctuation range is large.

4. Tensile test
The tensile properties of seamless steel pipes and ERW steel pipes meet 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 of ERW steel pipes is at its best and the plasticity index is 33.3% higher than the standard. The reason is that the performance of the raw material and hot-rolled strip of ERW steel pipe is guaranteed by means of micro-alloying smelting, refining outside the furnace, and controlled cold and controlled rolling; seamless steel pipes mainly rely on means of increasing carbon content, which is difficult to ensure strength and plastic Reasonable match.

5. Hardness
The raw material of the ERW steel pipe, the hot-rolled strip coil, has a high precision of controlled cooling and rolling during the rolling process, which can ensure the uniform performance of each part of the strip coil.

6. Grain body

The raw material of ERW steel pipe, a hot-rolled strip coil, uses a wide continuous casting slab with a thick solidified surface of fine crystals, no columnar crystal regions, shrinkage and looseness, small composition deviation, and dense structure; in the subsequent rolling process The application of medium and cold controlled rolling technology further ensures the grain size of the raw materials.

7. Anti-collapse test
ERW steel pipe is characterized by its raw materials and pipe manufacturing process. Its wall thickness uniformity and ellipticity are far superior to seamless steel tubes, which are the main reasons why the crush resistance is higher than seamless steel pipes.

8. Impact test
Because the impact toughness of ERW steel pipe base material is several times that of seamless steel pipe, the impact toughness at the weld is the key to ERW steel pipe. By controlling the impurity content of raw materials, the height and direction of longitudinal burrs, the shape of the forming edge, the welding angle, and the welding speed , Heating power and frequency, welding extrusion amount, 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, it can achieve the impact energy of the weld close to the mother Material
Achieve seamless performance.

9. Burst test
The burst test performance of ERW steel pipe is far higher than the standard requirements, mainly due to the high uniformity of wall thickness and uniform outer diameter of ERW steel pipe.

10. Straightness
ERW steel pipe is cold-worked, and has on-line straightening in the state of reduced diameter, plus an infinite multiple rule, so the straightness is better; seamless steel pipe is formed in a plastic state, plus a single rule (continuous rolling is 3 ~ 4 times rule) Tube straightness is relatively difficult to control.

11. Appearance
The defects on the outer surface of the billet used in the seamless steel tube cannot be eliminated by the hot rolling process, and the defects can only be polished after the finished product is completed; the spiral channel left after the perforation can only be partially eliminated during the wall reduction process. ERW steel pipe uses hot rolled coil as the raw material. The surface quality of the coil is the surface quality of the ERW steel pipe. The surface quality of the hot rolled coil is easy to control and the quality is high. Therefore, the surface quality of the ERW steel pipe is far better than that of the seamless steel pipe. 

12. Steel consumption of 10,000 meters footage
The wall thickness of the ERW steel pipe is uniform, and its wall thickness tolerance is negligible. The control accuracy limit of the difference in wall thickness of the seamless steel pipe is + 5% t, which is generally controlled at + 5 ~ 10% t.

In order to ensure that its minimum wall thickness can meet the standard requirements and use performance, it can only be solved by appropriately increasing the wall thickness. Therefore, in the same specifications and the same weight of the casing, ERW steel pipe is 5-10% longer or even more than the seamless steel pipe, which reduces the steel consumption of 10,000 meters footage 5-10%. Even at the same price, ERW bushings virtually save users 5 to 10% of procurement costs.

Taking 9-5 / 8 * 8.94mm casing as an example, it can save 26.8 ~ 53.6 tons per 10,000 meters, and save an average cost of 300,000 yuan. In 2007, the main foreign users of our company were mainly Russian National Petroleum Corporation, and the oil production areas were distributed in Russia's Siberia. J55 steel grade oil, casing down to a depth of about 2400m. The depth of N80 steel-grade oil and casing pipe running is about 4800m. Part of this oil production area belongs to sulphur-bearing, low-temperature wells and high anti-crushing geological conditions. So far, no quality problems have occurred in the use of the product.

In 2008, foreign users were mainly based in Texas oil fields and Russian oil fields. The domestic oilfields are mainly North China oilfields and Daqing oilfields. The products are mainly used in J55, N80 steel grade φ73.02mm, φ139.7mm series oil and casing. The P110 steel graded ladder buckle type φ139.7x7.72mm casing was also used in the Texas oil field in the United States, and the same effect was obtained. The P110 steel graded ladder buckle type casing went down to a depth of 5400m.