Black steel gas pipe
Entry in Metal pipe · Updated · Written by the Know Your Pipes editors from the sources listed under References
Black steel gas pipe, usually called black iron pipe, is threaded steel pipe with a dark surface finish used to carry natural gas and propane inside buildings. Gas piping makers specify Schedule 40 steel pipe to ASTM A53 with a black oxide coating for their rigid stub-outs, for example[1]. Unlike galvanized steel pipe, it has no zinc coating. This entry explains how the pipe is used; installing, extending or altering gas piping is work for a licensed installer under a permit.
1 How rigid gas systems are laid out
Rigid steel gas piping is usually arranged as a series system: a main run, or header, with tees branching off to each appliance[1]. In a traditional series system the gas pressure downstream of the meter is typically under 1/2 psi[1]. Some homes use an elevated-pressure system instead, often at 2 psi, with a regulator that drops the pressure before the appliances[1].
Building a rigid system means measuring, cutting and threading each length and assembling the joints by hand, which is the work that flexible CSST gas tubing was designed to reduce[1]. Steel pipe, CSST and copper can appear in one system, joined at threaded fittings; threaded pipe joints explains how tapered pipe threads seal.
| Material | Form | Joining | Notes |
|---|---|---|---|
| Black steel | Rigid lengths | Threaded fittings | Series layout is typical[1] |
| CSST | Flexible coils | Maker's brass fittings | Bonding or arc-resistant jacket required[3] |
| Copper types K and L | Rigid or soft | Per code and maker | Listed for natural gas and LP by a tube maker[4] |
Galvanized pipe is not used as a substitute for black pipe on gas where the code or the gas utility prohibits it; check the local code.
2 Codes and bonding
The National Fuel Gas Code is published jointly as ANSI Z223.1/NFPA 54; its 2024 edition was approved by ANSI on November 1, 2023[2]. Many jurisdictions use the International Fuel Gas Code (IFGC) or the fuel gas provisions of the International Residential Code instead[3], and the state or city decides which applies.
Gas piping is part of the building's electrical bonding: the IFGC and IRC require gas piping to be bonded for ground-fault protection, and a bonding clamp for CSST may be fixed to a length of rigid pipe or a malleable iron fitting[3]. A gas piping system must pass inspection before the utility turns on the gas, according to one piping maker's installation guide[1]. See plumbing codes for how model codes are adopted.
See also
- CSST gas tubingFlexible jacketed stainless steel gas tubing; yellow CSST must be bonded to the electrical grounding system against lightning damage.
- Which pipe for which jobA job-by-job guide to the pipe materials used for water supply, service lines, drains, vents and gas, with their main limits.
- Galvanized steel pipeZinc-coated steel water pipe found in older homes; it corrodes from the inside and can hold lead from upstream sources.
- Threaded pipe jointsHow NPT tapered pipe threads seal, common sizes and pitches, thread sealants, and why plastic female threads crack.
- Copper pipe types K, L and MThe three wall grades of copper water tube under ASTM B88, how to tell them apart and where each is normally used.
- Copper DWV pipeHard copper drainage tube made to ASTM B306 for drain, waste and vent lines, identified by a yellow print line.
References
- Gastite Division, Titeflex Corporation, "Flexible Gas Piping Design and Installation Guide" (2020) — gastite.com
- American Gas Association, "2024 National Fuel Gas Code" — aga.org
- International Code Council, "CodeNotes: Bonding of Corrugated Stainless Steel Tubing (CSST) Gas Piping Systems" (2020) — iccsafe.org
- Cerro Flow Products, "Copper Tubing" — cerro.com