Oil casing pipes are used to support the walls of oil and gas wells, ensuring the proper functioning of the well during drilling and after completion. There are two primary types of steel pipes used for petroleum casing: Seamless Casing and ERW Casing. Here’s a detailed comparison between them.
Seamless Casing
Manufacturing Method: Seamless pipes (SMLS) are made using methods such as hot rolling, cold rolling, hot drawing, or cold drawing. These pipes do not have any welds.
ERW Casing
Manufacturing Method: ERW pipes are straight seam welded pipes made through high-frequency resistance welding. The raw material is low-carbon micro-alloy steel rolled through the TMCP (Thermo-Mechanical Control Process).
Detailed Differences Between Seamless and ERW Casing Pipes
- Outer Diameter Tolerance
Seamless Steel Pipe: Uses a hot rolling process with sizing completed at around 800°C. The outer diameter is influenced by the raw material composition, cooling conditions, and roll cooling states, resulting in a larger fluctuation range.
ERW Steel Pipe: Formed by cold bending with a 0.6% diameter reduction at room temperature, allowing for precise control of the outer diameter with minimal fluctuation.
- Wall Thickness Tolerance
Seamless Steel Pipe: Produced through round steel perforation, leading to significant wall thickness deviation. Hot rolling can reduce unevenness, but the best control achievable is within ±5-10%t.
ERW Steel Pipe: Uses hot-rolled coils with modern thickness tolerance controlled within 0.05mm.
- Appearance
Seamless Steel Pipe: Surface defects from the raw material cannot be entirely removed during hot rolling and can only be polished off post-production. Spiral marks from perforation remain partially.
ERW Steel Pipe: Made from hot-rolled coils, ensuring high-quality surface finishes, as the surface quality of the coils translates directly to the pipes.
- Ovality
Seamless Steel Pipe: Difficult to control the outer diameter precisely due to the hot rolling process and varying conditions.
ERW Steel Pipe: Cold bending allows for precise outer diameter control with minimal fluctuation.
- Tensile Test
Seamless Steel Pipe: Meets API standards but often at the upper strength limit and lower plasticity limit.
ERW Steel Pipe: Exceeds API standards, with strength and plasticity achieved through microalloying, refining, and controlled cooling and rolling.
- Hardness
ERW Steel Pipe: Ensures uniform performance due to precise control during the rolling process.
- Grain Size
ERW Steel Pipe: Made from wide, thick continuous casting billets with fine-grain surfaces and dense structures, further refined through controlled cooling and rolling.
- Anti-Collapse Test
ERW Steel Pipe: Superior wall thickness uniformity and ovality enhance anti-collapse performance compared to seamless pipes.
- Impact Test
ERW Steel Pipe: Higher base material impact toughness, with weld impact energy ensured to meet high standards through meticulous control of welding parameters.
- Burst Test
ERW Steel Pipe: Exceeds standard burst test performance due to consistent wall thickness and diameter.
- Straightness
Seamless Steel Pipe: More challenging to control straightness due to hot state formation.
ERW Steel Pipe: Better straightness due to cold processing and online straightening.
- Material Usage in 120,000 Meters of Footage
ERW Steel Pipe: Uniform wall thickness allows for longer casing lengths with less material, reducing steel usage by 5-10% compared to seamless pipes, effectively lowering purchase costs by the same percentage.
Conclusion
The market price of welded steel pipes is influenced by numerous factors, including raw material costs, specifications, production techniques, and market conditions. Understanding these factors is crucial for making informed purchasing decisions and obtaining the best value for money. Changes in supply chains, market demand, technological advancements, and production costs all play significant roles in determining the price of welded pipes.
