Black gas pipe in unconditioned crawlspace?
Sewer pipe is typically cast iron ( or plastic). Gas pipe should be steel, ( may be called "black iron") many jurisdictions do not permit galvanized steel in gas service. In my opinion , a very misguided concern over corrosion by sulfur. Steel corrosion is often caused by water, especially with salts. If no water sprays in your crawl space you are very unlikely to have corrosion with the gas pipe. Good ventilation should prevent any condensation caused corrosion. In a similar situation , I had some corrosion of the galvanized electric conduit but not the gas pipe.