The Difference Between Seamless Casing And ERW Casing

Seamless casing and ERW (Electric Resistance Welded) casing are two common types of petroleum casing. Seamless casing is a casing made of seamless steel pipe. Seamless steel pipe refers to steel pipes made by four methods: hot rolling, cold rolling, hot drawing, and cold drawing. The pipe body itself has no welds. ERW casing is a casing made of electric welded pipe as raw material. ERW (steel pipe) refers to a straight seam welded pipe manufactured by high-frequency resistance welding process. The raw material steel plate (coil) of ERW welded pipe is low carbon micro-alloy steel rolled by TMCP (thermomechanical control process). Today we will mainly explain belowthe difference between seam casing and ERW casing.

1. Outer diameter tolerance

Seamless steel pipe: using hot rolling forming process, sizing is completed at around 8000C. The raw material composition, cooling conditions and cooling state of the roll have a great influence on its outer diameter, so it is difficult to control the outer diameter accurately and the fluctuation range is large.

ERW steel pipe: cold-formed, with a sizing reduction of 0.6%. The process temperature is basically constant at normal temperature, so the outer diameter is accurately controlled and the fluctuation range is small, which is beneficial to eliminating black leather buckles;

2. Wall thickness tolerance

Seamless steel pipe: produced by perforated round steel, with large wall thickness deviations. Subsequent hot rolling can partially eliminate uneven wall thickness, but the most advanced units can only control it within±5~10%t.

ERW steel pipe: hot-rolled coil is used as raw material, and the modern hot-rolled thickness tolerance can be controlled within 0.05mm.

3. Appearance

The outer surface defects of the blank used for seamless steel pipes cannot be eliminated through the hot rolling process, and the defects can only be ground away after the finished product is completed; the spiral path left after perforation can only be partially eliminated during the wall reduction process.

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

4. Ovality

Seamless steel pipe: using hot rolling forming process. The raw material composition, cooling conditions and cooling state of the rolls of the steel pipe have a great influence on its outer diameter. Therefore, precise control of the outer diameter is difficult and the fluctuation range is large.

ERW steel pipe: It is formed by cold bending, so the outer diameter is accurately controlled and the fluctuation range is small.

5. Tensile test

The tensile performance indicators of seamless steel pipes and ERW steel pipes both 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 contrast, the strength index of ERW steel pipe 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 through micro-alloying smelting, out-of-furnace refining, controlled cooling and controlled rolling; seamless steel pipes mainly rely on increasing carbon content, which makes it difficult to ensure strength and Plasticity. Reasonable combination.

6. Hardness

The raw material of ERW steel pipe, hot-rolled coil, has extremely high precision during the rolling process, which can ensure the uniform performance of each part of the coil.

7. Grain size

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

8. Anti-collapse test

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

9. Impact test

Since the impact toughness of the base material of ERW steel pipes is several times that of seamless steel pipes, the impact toughness of the weld is the key to ERW steel pipes. By controlling the impurity content of raw materials, the height and direction of slitting burrs, the shape of the forming edge, welding angle, welding speed, heating power and frequency, welding extrusion amount, medium frequency retraction 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 welding impact energy can be close to that of the base material, achieving seamless performance.

10. Explosion test

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

11. Straightness

Seamless steel pipes are formed in a plastic state, and it is difficult to control the straightness of the pipe end with a single ruler (continuous rolling requires 3 to 4 rulers);

ERW steel pipes are cold-worked steel pipes that are straightened online in a reduced diameter state. In addition, it is infinite times, so the straightness is better.

12. Steel consumption for 10,000 meters of casing

ERW steel pipes have uniform wall thickness and negligible wall thickness tolerances. The control accuracy limit of seamless steel pipe wall thickness difference is±5%t, which is generally controlled at±5-10%t. In order to ensure that the minimum wall thickness can meet the standard requirements and performance, the only solution is to increase the wall thickness appropriately. Therefore, among casings of the same specifications and weight, ERW steel pipes are 5-10% longer than seamless steel pipes, or even more, reducing the steel consumption for 10,000-meter casings by 5-10%. Even at the same price, ERW casing virtually saves users 5-10% of purchasing costs.

Summarize:

Judging from the current situation at home and abroad, seamless casing is generally more popular in high-strength and high-pressure environments, while ERW casing is more suitable for general purposes. We need to choose which type of steel pipe to use based on specific application needs and budget. If you have more questions, please contact: sales@union-steels.com