ERW or Seamless

Im Inspecting on a Pipeline in a new area. The old area had Higher amonts of H2s and some co2 with some liquids, and methane gas being 90% of the volume. Or standard for this area is x52 seamless and and always sch 40 below ground and all y grade fittings or xh above ground The new area has a very low H2s content but a higher level of co2. above 5%. with lots of liquid hydrates. There using ERW pipe No ygrade fitttings above or below ground and all std weght pipe above and below ground. Even in the pig barrells. Line pressure for both average 900psi. Icould use some advice. or at least help findinng a place to get the inf. My resident eng is not helping. Your help would be greatly app.