carbon steel pipe

Carbon steel pipe is used as the base pipe of bimetallic combination tubing, which has an internal liner made of stainless steel, titanium alloy steel, copper or aluminum, and so on. This type of tubing has high mechanical performance, high corrosion resistance, high weldability, high operational convenience, and high safety. It combines a surface coating technique that has low cost and wide usable range with a corrosion-resisting alloying technique that has complete structure and high tightness (no blowhole) of material; thus, it has high applicability.

• 1.

• Application of bimetallic combination tubing

  Bimetallic combination tubing has higher resistance to corrosion in comparison with carbon steel pipe and has cost superiority in comparison with diphase stainless steel and nickel-based alloy steel. Thus it is widely applied in the oil and gas industry and has very high cost performance especially under high chloride corrosion environment conditions. In the light of different corrosion environments, there are SSC-resistant tubing and casing, CO2-resistant tubing and casing, and tubing and casing that can resist SSC, chloride, and carbon dioxide.

  The studies and experience indicate that the application of nickel-based alloy steel in high sour environments is greatly restricted due to its cost, which is 20 to 25 times the cost of corrosion-resistant steel, despite the fact that it has high resistance to corrosion in high sour environments. The bimetallic combination pipe that has been developed combines the high corrosion resistance of corrosion-resistant alloy with the high mechanical performance of carbon steel or low-alloy pipe:

  • a.

  • In comparison with nickel-based alloy steel, its strength is increased, its weight is reduced, and its cost is reduced by about 100%.

  • b.

  • In comparison with carbon steel, its corrosion resistance is obviously increased, thus solving the puzzle of the corrosion problem.

  • c.

  • It has very high cost performance and involves the outstanding performances of both carbon steel and corrosion-resistant alloy steel. Its corrosion resistance is the same as that of corrosion-resistant alloy steel. Its cost is reduced by 70% to 80%. Its service life is 10 to 15 times the service life of corrosion-resistant steel.

  
  

  Super diphase stainless steel has been applied in oil and gas field development. For instance, UR52N plus S32520 has been used for gathering lines and pipelines in North Sea fields, and SAF2507 steel has been used for oil and gas well production and offshore production platform facilities and oil and gas pipelines in Alaska, the North Sea, and the Gulf of Mexico, and so on. It is generally used under harsh sour environment conditions with no corrosion inhibitor used.

  The application of the diphase combination pipe technique and steel selection technique greatly reduces the application cost of the corrosion-resistant alloy technique and makes its use more convenient, thus promoting the application of the corrosion-resistant alloy technique in the oil and gas industry and enabling corrosion-resistant alloy to be widely applied.

• 2.

• Basic structure

  Base pipe is seamless or welded carbon steel pipe or seamless alloy steel, while liner pipe is common or special stainless steel pipe, titanium-aluminum-copper alloy steel pipe, or other corrosion-resistant alloy steel pipe (Figure 11-32).

  

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  Figure 11-32. The basic structure of bimetallic combination tubing.

  Base pipe and liner, which is a thin-wall corrosion-resistant alloy steel pipe, are coaxially assembled at first, and then a hydraulic power pipe is assembled in the liner. The instantaneous chemical energy generated by the hydraulic power pipe is transmitted to the liner through media in the form of detonation waves, so that the liner generates plastic deformation and the base pipe generates elastic deformation. In the moment of deformation, the resilience of base pipe due to deformation is much greater than that of the liner, which makes base pipe and liner nestle together closely and attain an overlapping state.

• 3.

• Main performance indices

  • a.

  • Steel

    • (1)

    • Steel for base pipe (mechanical performance). Carbon steel and alloy steel (seamless or welded steel pipe).

    • (2)

    • Steel for liner (corrosion resistance). Stainless steel, titanium alloy, aluminum alloy, or copper alloy.

    • (3)

    • Environmental temperature −35 to 300°C.

    
    

  • b.

  • Size indices

    • (1)

    • Total wall thickness of combination pipe ≥ 3 mm

    • (2)

    • Base pipe wall thickness ≥ 2.5 mm

    • (3)

    • Liner wall thickness 0.5–2 mm

    • (4)

    • Combination-pipe OD Φ20–1200 mm

    • (5)

    • Combination-pipe length ≤ 10 m

    • (6)

    • Combination-pipe OD, wall thickness, and allowable deviations (in accordance with international allowable deviations for base pipe)

    
    

  • c.

  • Mechanical performance indices

    • (1)

    • Combination-interface shearing strength ≥ 0.5 MPa

    • (2)

    • Combination-pipe tensile strength slightly higher than the tensile strength of base pipe

    • (3)

    • Combination-pipe internal pressure resistance slightly higher than the internal pressure resistance of base pipe

    • (4)

    • Combination-pipe external pressure resistance equal to the external pressure resistance of base pipe

    
    

  • d.

  • Combination-layer surface performance indices

    • (1)

    • Corrosion resistance equal to the corrosion resistance of the liner

    • (2)

    • Combination-layer surface roughness Ra ≤ 0.07 μm

    • (3)

    • Combination-layer surface hardness ≥ liner hardness

    
    

  • e.

  • Connecting form

    The connections are the weak links of tubing string; thus, it is required that the connections have strengths and seals that are equal to those of the pipe body. Under poor sealing in the J position of combination tubing collar thread, having an external thread cross-sectional area smaller than that of the internal thread may speed up thread corrosion and boring.

    On the basis of the J value range of tubing and the tightening torque range, a special collar seal structure appropriate for different hole conditions has been developed. This structure includes a special adaptive Teflon seal ring and internal corrosion-resistant alloy steel liner (Figure 11-33). The special adaptive Teflon seal ring has high abrasion resistance, tear resistance, oilproofness, leakproofness, and corrosion resistance and is suitable for the matching sealing of combination tubing under different end face treatments. The internal corrosion-resistant alloy steel liner that seals the exposed part of the collar thread can prevent galvanic corrosion in the J position of combination tubing collar thread in combination with the sealing of a special adaptive Teflon seal ring.