National Fuel Gas Code Practice Test

The maximum allowable hydrogen sulfide level in gas for using copper and brass pipes is indeed .3 grain. This standard is established to protect the integrity of the piping materials and to prevent corrosion, which can occur when these metals are exposed to higher concentrations of hydrogen sulfide.

Copper and brass are susceptible to stress corrosion cracking and other forms of degradation when exposed to hydrogen sulfide. Therefore, limiting the concentration in natural gas to .3 grain helps ensure that the material remains safe and functional during its use in gas distribution systems.

Lower thresholds, such as .1 grain, .5 grain, or 1 grain, while theoretically safer for the materials, do not align with the regulatory standards that specify .3 grain as the maximum, ensuring that utilities and facilities can confidently use copper and brass pipes without risking substantial damage or failure due to hydrogen sulfide exposure.