MARTENSITE-BASED STAINLESS STEEL SEAMLESS PIPE

A martensitic stainless seamless steel pipe having excellent general corrosion resistance in an enhanced mild sour environment having an H2S partial pressure of more than 0.03 to 0.1 bar is provided. The seamless steel pipe according to the present disclosure includes a chemical composition consisting of, in mass%, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 3.00 to 6.50%, Cr: more than 10.00 to 13.40%, Mo: 0.50 to 4.00%, V: 0.01 to 1.00%, Ti: 0.010 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), and a microstructure containing, in volume ratio, 80.0% or more of martensite, wherein a depassivation pH of an inner surface is 3.50 or less. Cr+2.0Mo+0.5Ni+0.5Co≥16.0