Technical points for field welding of straight seam steel pipes?
Use cellulose welding rods (such as E6010) for bottoming, and control the interlayer temperature at 100-150℃. The groove design is V-shaped 30°±5°, and the blunt edge is 1.6-2mm. A windbreak needs to be built when the wind speed is >8m/s. Perform 100% ultrasonic testing within 24 hours after welding.
How to prevent stress corrosion cracking of straight seam pipes?
Control the H2S partial pressure in the medium to <0.3kPa and the pH value to >9.5. Avoid cold bending during installation (radius of curvature ≥40D), and perform stress relief heat treatment after welding (580-620℃ insulation for 2 hours). Use guided wave detection (GWUT) regularly to check for hidden cracks.
Special measures for laying pipelines in frozen soil areas?
Use the "high overhead + hot rod" combination solution, and use low thermal conductivity materials (such as polyurethane) for pipe supports. The pipeline needs to be pre-cooled to below -5℃ for installation to prevent frost heave displacement. The monitoring system must include strain gauges (to measure displacement) and temperature optical fibers (accuracy ±0.5℃).
What are the repair technologies for old straight seam pipes?
CIPP lining (glass fiber reinforced resin) is commonly used for trenchless repair, and the pressure is restored to 80% of the original pipe. Local defects can be reinforced with carbon fiber composite materials (3 layers of circumferential winding). The severely corroded section adopts the technology of reducing the diameter and inserting HDPE pipe.
How to evaluate the remaining life of the straight seam steel pipe in use?
The maximum allowable defect size is calculated based on the ASME B31G standard, combined with eddy current detection data. Consider the corrosion rate (usually 0.1-0.3mm/year) and the number of cyclic loads (Miner cumulative damage theory). When the safety factor is 1.5, the remaining life = (measured minimum wall thickness-design wall thickness)/annual corrosion amount.
