Mechanical Properties of Large Diameter Pipe with Increased Deformation Capacity (For Active Tectonic Fracture Zones)

Abstract

Results are summarized for testing the mechanical properties of pipe of strength class K60 (corresponds approximately to strength category X70) with increased deformation capacity 1420 mm in diameter with wall thickness of 25.8 and 32.0 mm of industrial batches. The change of tensile test properties of basic pipe metal of the pipes after simulating application of an anticorrosive coating (200–250 °C, 5 min) and strain ageing is shown. After heating the pipe base metal retains low values of σ_y(R_t0.5)/σ_f ratio (along the rolling direction 0.75–0.84) and good ductility (along the rolling direction δ₅ ≈ 22–23% and δ_t ≈ 8–12 %; across the rolling direction δ₅ ≈ 21–22 % and δ_t ≈ 8–12 %). Relationships are determined for properties whose values depend on the specific nature of the steel microstructure of these pipes σ_y(R_t0.5)/σ_f, δ_t, KCV^–40, CTOD^–20). An increase in strength (σ_f) of the basic metal up to the upper standard limit does not lead to a reduction in ductility. However, with high strength pipe base metal there is a tendency towards a reduction in CTOD^–20 values of base metal and fusion zone metal.