Fe-Ni alloy base pipe and manufacturing method thereof

C ≦ 0.04%, Si ≦ 0.50%, Mn: 0.01~6.0%, P ≦ 0.03%, S ≦ 0.01%, Cr: 20~30%, Ni: 30~45%, Mo: 0~10%, W: 0-20%, however, Mo (%) + 0.5W (%): 1.5% greater than 10%, Cu: 0.01~1.5%, Al ≦ 0.01%, N: comprises 0.0005 to 0.20%, the balance being substantially of Fe in, 1440-6000P-100S-2000C ≧ 1300, Ni + 10 (Mo + 0.5W) + 100N ≦ 120, (Ni-35) +10 (N-0.1) -2 (Cr-25) -5 (Mo + 0.5W- Fe-Ni alloy base pipe having a chemical composition of 3) + 8 ≧ 0 is excellent in inner surface properties, it can be finished in seamless tube by the Mannesmann rolling piercing mill. Since the seamless pipe is excellent in corrosion resistance under sour gas environment and having excellent mechanical properties, above Fe-Ni alloy base pipe is blank tube of OCTG and line pipe, further, a nuclear power plant and chemical it can be used as a base pipe of various structural members in an industrial plant.