Technical Characteristics, Production, and Applications of X90M Straight Seam Steel Pipe

First, Material Characteristics and Standard System of X90M Straight Seam Steel Pipe

X90M belongs to microalloyed high-strength pipeline steel. Its naming follows the American Petroleum Institute (API) 5L standard: "X" represents high-strength pipeline steel, "90" indicates a minimum yield strength of 90 ksi (approximately 621 MPa), and "M" indicates thermomechanical controlled process (TMCP). Compared to traditional X70 and X80 steel grades, X90M maintains good weldability while achieving an optimal balance between strength and toughness through precise chemical composition design and controlled rolling and cooling processes. Typical chemical composition includes C≤0.12%, Mn≤2.0%, and the addition of microalloying elements such as Nb, V, and Ti, combined with an ultra-low sulfur and phosphorus content of ≤0.0025%, enabling the Charpy impact energy to remain ≥190 J even at -20℃.

Second, Analysis of Key Production Processes for X90M Straight Seam Steel Pipes

1. Plate and Coil Preparation Stage: Continuously cast slabs smelted using ladle refining + vacuum degassing processes are subjected to multi-stage controlled rolling on a 3500mm or thicker plate mill. In the roughing stage, austenite grain refinement is achieved in the recrystallization zone. In the finishing stage, dislocation strengthening is achieved through cumulative deformation in the non-recrystallization zone. After final rolling, the slab is immediately water-cooled at a rate of 15-30℃/s to the bainite transformation temperature range, ultimately obtaining a uniform acicular ferrite microstructure. Actual test data from a large steel mill shows that this process can stabilize the yield strength of 18.4mm thick steel plates at 625-690MPa, with a yield strength ratio ≤0.93.

2. Forming and Welding Technology: Mainstream manufacturers adopt the JCOE forming process, which avoids edge stress concentration through up to 20 progressive pressing steps. High-frequency welding (HFW) requires a high-frequency current of 400kHz or higher, coupled with milling equipment with a precision of 0.1mm, to ensure the V-groove angle is controlled within 65±5°. Post-weld, online medium-frequency heat treatment (850-900℃) is necessary to refine the grain size in the weld zone to 5-8μm. A project acceptance report shows that the weld coefficient of the treated pipe can reach 0.96, significantly higher than the lower limit of 0.85 specified in API 5L.

3. Testing and Certification System: In addition to routine 100% ultrasonic testing and X-ray inspection, X90M straight seam steel pipes must pass a full-size burst test (verification pressure ≥ 1.25 times the design pressure) and a HIC hydrogen-induced cracking resistance test (CLR ≤ 15%).

Third, Analysis of the Engineering Application Advantages of X90M Straight Seam Steel Pipes

During the construction of a mountainous section of the "West-East Gas Pipeline III," X90M straight seam steel pipes demonstrated significant advantages:

- Economic Efficiency: X90M straight seam steel pipes with a diameter of 1219mm and a wall thickness of 18.2mm are 10% thinner than the X80 scheme, saving 82 tons of steel per kilometer and reducing overall costs by approximately 15%.

- Construction Efficiency: When using automatic welding technology, the welding heat input is controlled within the range of 25-35kJ/cm, achieving high-quality welding at -15℃ without preheating, shortening the construction period by 20%.

- Safety Reserve: Based on strain-based design verification, X90M straight seam steel pipes maintain a deformation capacity coefficient of 0.85 under 1.5% axial strain conditions, making them particularly suitable for seismically active areas.

Fourth, the technological development trend of X90M straight seam welded steel pipes.

With the increasing demand for deep-sea pipelines and polar projects, X90M technology is making breakthroughs in two directions:

1. Thicker wall thickness: An international company has developed X90M UOE welded pipes with a wall thickness of up to 32mm, solving the problem of uniform performance in the thickness direction through gradient composition design.

2. Improved low-temperature toughness: A modified X90M with added 1.5% Ni can maintain a DWTT shear area of ≥85% at -60℃, and has been applied to the Arctic LNG2 project.

The domestic industrial chain is also accelerating its improvement. According to the China Steel Pipe Association, by 2026, the proportion of X90M straight seam welded steel pipes in domestic high-pressure trunk pipelines will increase from the current 18% to 35%.

Fifth, Key Points for Procurement and Quality Control of X90M Straight Seam Steel Pipes

When selecting steel pipes for engineering projects, the following should be emphasized:

- The manufacturer must possess a complete TMCP process chain and online testing system;

- Each batch of pipes should be accompanied by a third-party SSCC test report (NACE TM0177 standard);

- On-site acceptance requires a 3% pilot bending test with a bending radius ≤38t (t is wall thickness);

- During storage, the relative humidity inside the steel pipes must be maintained at ≤40% to prevent stress corrosion.

Currently, the main challenge facing the industry is cost control. X90M straight seam steel pipes are approximately 8-12% more expensive than X80, but with the explosive growth in demand for hydrogen pipeline construction and the large-scale production of steel enterprises, the price difference is expected to narrow to less than 5% after 2025. For trunk line projects with design pressures exceeding 12MPa, X90M straight seam steel pipes have become the most cost-effective solution.