Abstract: A method of reducing metallic impurities in an ozone gas piping means, which entails producing ozone gas in an ozone-generating means and piping the produced ozone gas to stainless steel piping means, wherein the ozone gas is produced from a raw material oxygen gas containing at least one additional gas selected from the group consisting of nitrogen, helium, carbon dioxide, carbon monoxide and ozone; the additional gas being used in an amount of 0.025% by volume or more in total, with the proviso that nitrogen is not used as or in said additional gas in an amount of more than 1.0% by volume.

Abstract: A precipitation-hardening-type Ni-base alloy exhibiting improved resistance to stress corrosion cracking in a sour gas atmosphere containing elemental sulfur at high temperatures is disclosed. The alloy consists essentially of, by weight %;______________________________________ Cr: 12-25%, Mo: over 9.0 and up to 15%, Nb: 4.0-6.0%, Fe: 5.0-25%, Ni: 45-60%, C: 0.050% or less, Si: 0.50% or less, Mn: 1.0% or less, P: 0.025% or less, S: 0.0050% or less, N: 0.050% or less, Ti: 0.46-1.0%, Al: 0-2.0%.

Abstract: A precipitation-hardening-type Ni-base alloy exhibiting improved resistance to stress corrosion cracking in a sour gas atmosphere containing elemental sulfur at high temperatures is disclosed. The alloy comprises essentially, by weight %;______________________________________ Cr: 12-25%, Mo: 5.5-15%, Nb: 4.0-6.0%, Fe: 5.0-25%, Ni: 45-60%, C: 0.050% or less, Si: 0.50% or less, Mn: 1.0% or less, P: 0.025% or less, S: 0.0050% or less, N: 0.050% or less, Ti: 0-1.0%, Al: 0-2.0%.