In the fields of Oil drilling and oil wells, high-frequency resistance welding casing (referred to as ERW casing) has several advantages over seamless casing, including high dimensional accuracy, strong weld toughness, good anti-squeezing and anti-explosion performance, and low cost. Therefore, it has been widely used abroad and has achieved good results.

Characteristics of ERW casing (compared with seamless casing):

  • High dimensional accuracy: The ERW casing is formed by mechanical sizing and coating process, and its dimensions (outer diameter, wall thickness, roundness, etc.) are further improved compared with the seamless casing. The average deviation of the outer diameter is not more than ±0.5%. For example, the standard deviation of the wall thickness of 6244.5 n ‘un ERW casing produced by Nippon steel is 0.10 mm, while that of the corresponding seamless casing is 0.41 mm.
  • Good weld toughness: The manufacturing process of ERW casing can ensure the obtaining of low C, S, P content in the component structure and high-strength, high-toughness welds in the substrate, making the weld toughness of the casing seamless with the seamless casing.
  • Superior anti-squeezing and anti-explosion performance: Compared with the same  API seamless casing, the anti-squeezing and anti-explosion performance (internal pressure) of the ERW casing is increased by about 50%.
  • Advanced technology and strict product quality control: The ERW parent material adopts controlled rolling coils, which are isotropic, and 100% non-destructive testing is performed.
  • Low cost: Compared with the same type of seamless casing, the cost of the ERW casing is 5% to 10% lower, with high efficiency, high degree of mechanization and automation, and low production energy consumption; the finished product rate of the ERW casing is 93% to 98%, while that of the seamless casing is 85% to 90%; the investment in the entire ERW casing project is 40% lower than that of the seamless casing project.

technical characteristics of ERW casing:

  • The raw material of controlled rolling coils is selected for the ERW casing, and the content of S and P is strictly controlled. The carbon equivalent is usually W (S)≤0.015%, and the carbon equivalent≤0.25%. Trace alloy elements such as Nb, V, Ti, and Cu are used to improve the toughness, weldability, and corrosion resistance of the steel.
  • Thick coils are milled on the edge to reduce local overheating and oxidation caused by welding burrs.
  • Continuous production is widely adopted by spiral active loops to avoid welding stops caused by roll-to-roll batch production and product quality defects caused by restarting welding, as well as unstable current and voltage.
  • The most advanced hydraulic deburring process is often used to control the height of the inner burr of the casing to within 1.14 NLNL.
  • Welding parameters, including input power, welding V-angle, welding speed, and welding temperature, are strictly controlled. The welding temperature is controlled by a high-frequency welding speed closed-loop power supply, with a control fluctuation of less than ±5°C.
  • Attaching importance to post-weld heat treatment to improve the microstructure and internal stresses in the weld zone.
  • High-strength and glue-applying devices are used to reduce the accuracy of finished products.
  • Full-line or offline non-destructive testing is performed on welds and steels to detect defects in a timely and accurate manner, so as to adjust the production process in a timely manner and ensure product quality.

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