API 5L X70 seamless steel pipe, with its excellent corrosion resistance, has become a core material in the energy transportation fields such as oil and natural gas. X70 seamless steel pipe conforms to the American Petroleum Institute (API) 5L standard and has passed PSL2 certification. It has achieved internationally leading levels in chemical composition, mechanical properties, and non-destructive testing, especially demonstrating outstanding long-term stability in highly corrosive media environments.
The chemical composition of X70 seamless steel pipe is precisely controlled: carbon content ≤0.16%, manganese content ≤1.70%, phosphorus/sulfur content ≤0.015%, while adding microalloying elements such as niobium, vanadium, and titanium (total content ≤0.15%). This compositional design of X70 seamless steel pipe not only improves the material’s strength and toughness but also enhances its resistance to hydrogen-induced cracking (HIC) and sulfide stress corrosion (SSC) by refining the grain size (ASTM grain size ≥8). For example, in acidic environments containing hydrogen sulfide (H₂S), its HIC test pass rate is over 95%, and the corrosion rate can be controlled below 0.02 mm/a, far exceeding conventional steel pipe standards.
To cope with complex corrosive environments, X70 seamless steel pipes employ a multi-layer protection system:
- Inner wall corrosion protection: A dense isolation layer is formed through epoxy resin or polyethylene coating, effectively blocking corrosive substances such as chloride ions and carbon dioxide in the transported medium.
- Outer wall protection: An epoxy black paint or three-layer polyethylene (3PE) coating is applied. The epoxy black paint coating is 80-120 μm thick, exhibiting excellent resistance to acids, alkalis, and salts. In soils with a pH of 5-9, the weight loss rate is <0.5 g/m² over a 20-year service life. The 3PE coating combines the adhesion of epoxy powder, the flexibility of adhesives, and the weather resistance of polyethylene, making it suitable for marine or high-humidity environments.
X70 seamless steel pipes have been widely used in national strategic projects such as natural gas pipelines and the West-East Gas Pipeline III. For example, in the Tarim Oilfield’s gathering and transmission pipeline network renovation, X70 PSL2 steel pipes with a diameter of 219mm × 8mm, after being coated with epoxy black paint, successfully traversed the Gobi saline-alkali land. After 5 years of operation and testing, the coating integrity rate reached 98.7%. In addition, its low-temperature toughness (impact energy ≥40J at -20℃) and high-pressure resistance (yield strength ≥485MPa) also make it the preferred material for extreme scenarios such as Arctic LNG projects and deep-sea oil and gas development.
Post time: Nov-06-2025