A gas main should normally be laid with a minimum depth of cover of 750 mm in a road or verge and 600 mm in a footpath. A gas service pipe should normally be laid with a minimum depth of cover of 375 mm in private ground and 450 mm in footpaths and highways. However, these depths are only a guide and should not be relied on when carrying out. Piping materials. Steel, copper, brass: The most common gas piping is black steel. Galvanized steel, copper, brass or CSST (Corrugated Stainless Steel Tubing) also can be used in some areas, but some utilities specifically prohibit the use of copper. In other areas, the use of copper is widespread. You should know what is acceptable in your area. Country. 21 Mar 2013. #1. Hi, I'm in the process of fitting a new bathroom suite and I’ve discovered that our cast iron soil pipe is corroded and leaking so needs replacing. I've read through a few threads on here and I intend replacing the soil stack with black plastic or imitation cast iron. Here is a photo showing the middle section and. April, 2005. When it was first introduced, this method was used only in replacing cast iron gas distribution lines; it was later employed to replace water and sewer lines. By 1985, the process was further developed to install up to 16-inch outer diameter (OD) medium-density polyethylene (MDPE) sewer pipe. Replacement of sewers in the UK. Open manhole, find correct branch. Put smoke pellets in branch I typically put them on something heat resistant. Light them up and bung the branch with a bung. You may also need to bung the vent pipe. Go inside and inspect for traces of smoke. Reply to Soil pipe replacement cost and advice in the Plumbing Forum | Plumbing Advice area at.