What is gas pipingin construction?

Black steel (black iron) is rigid Schedule 40 pipe, threaded at small sizes and welded at larger ones; it is the default for commercial gas work, tough against physical damage, cheap as material but labor heavy. CSST is corrugated stainless steel tubing that routes like cable, cutting labor dramatically in framed construction, but it costs more per foot, requires manufacturer certification for installers, and must be bonded to the electrical grounding system to protect against lightning-induced damage.

The utility owns and sets the meter and everything upstream of it, including the service line and the service regulator. The contractor's scope starts at the meter outlet: the house line, line regulators on medium pressure systems, valves, and every run to the appliances. The estimator's trap is schedule, not dollars: the meter set requires a utility application and load letter, sometimes a service upgrade with long lead times, so the coordination belongs in the bid assumptions.

Because the sizing tables work on pressure drop. Gas flowing through pipe loses pressure to friction, and the longer the run, the more it loses, so the same BTU load needs a larger diameter to arrive at the appliance with usable pressure. Code sizing methods use the developed length to the farthest appliance for the whole system, which is why one distant rooftop unit can upsize pipe serving everything else, and why a 2 psi system can run smaller pipe than a low pressure one.