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CSST gas tubing

Entry in Metal pipe · Updated · Written by the Know Your Pipes editors from the sources listed under References

CSST gas tubing (corrugated stainless steel tubing) is flexible, jacketed stainless steel gas piping, and CSST bonding is the wire connection from a yellow CSST system to the building's grounding electrode system that limits lightning damage[1]. The code alternative is CSST with a listed arc-resistant black jacket[1]. This entry explains the requirements; installing CSST or its bonding is work for qualified, licensed installers and electricians, not a homeowner project.

The International Code Council's Building Safety Journal describes CSST as a widely used gas piping material in new homes[3].

1 Construction

One maker's tubing is type 304 stainless steel (ASTM A240), annealed for flexibility, inside an extruded polymer jacket that insulates the tube electrically[2]. The system is tested to ANSI LC1/CSA 6.26, which rates CSST for pressures up to 25 psi[2]. Lengths are joined with the maker's own brass mechanical fittings, which end in standard tapered pipe threads so they can connect to black steel gas pipe and other approved gas piping[2].

Because it is flexible, CSST is pulled through a building much like electrical cable, usually in long runs with few joints[2]. The same maker warns that the thin wall may be punctured by a nail more easily than steel pipe, so hardened steel striker plates are fitted wherever the tubing passes through studs, joists or plates[2].

2 Why bonding matters

A nearby lightning strike can energize metal systems in a house, and differences in voltage between them can cause an arc that burns holes in CSST[2]. Bonding the gas piping to the grounding electrode system lowers the voltage that builds up on the tubing and brings it to the same potential as other bonded metal, such as water pipe, structural steel and coaxial cable, which reduces the chance of arcing[1].

Yellow and black CSST under the 2021 IFGC and IRC
FeatureYellow (non-arc-resistant)Black (arc-resistant, marked "AR")
Code sectionIFGC 310.2 / IRC G2411.2IFGC 310.3 / IRC G2411.3
Extra bonding conductorRequiredNot required if conditions are met
Bond still needed whenAlwaysNo appliance has an equipment grounding conductor, or any yellow CSST is in the system
JacketStandard polymer jacketPasses arc-resistance tests in CSA/ANSI LC-1

Table source: ICC CodeNotes on the 2021 codes[1]. Jurisdictions on the 2015 or earlier codes may treat black CSST like yellow unless local rules or the maker's listing say otherwise[1].

3 The bonding requirement

For yellow CSST, the bonding conductor must be at least 6 AWG copper (or the aluminum equivalent) and no longer than 75 ft, and a shorter run works better[1]. It connects to a grounding electrode, the grounding electrode conductor or the electrical service enclosure, following NFPA 70[1]. At the gas end, a single clamp listed to UL 467 is enough for the whole system, but it must be fixed to rigid pipe, a malleable iron fitting, a manifold or a brass CSST fitting, never to the corrugated tubing itself[1].

The ICC places installation and inspection of grounding electrodes with the electrical contractor and electrical inspector[1]. One CSST maker requires installers to be licensed and trained on its system, and advises building owners to confirm that a qualified contractor has bonded the CSST to the grounding electrode system[2]. Owners who are unsure whether existing yellow CSST is bonded can have a licensed electrician check it.

Safety

If you smell gas, leave the house immediately and keep others out. Avoid using switches, phones or electrical devices inside. Call 911 or the gas utility from a safe spot outdoors.

Related entries: threaded pipe joints, plumbing codes and reading pipe markings.

See also

  • 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.
  • Black steel gas pipeThreaded Schedule 40 steel pipe with a dark finish, long used for natural gas and propane piping inside buildings.
  • 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.
  • Galvanized steel pipeZinc-coated steel water pipe found in older homes; it corrodes from the inside and can hold lead from upstream sources.
  • Cast iron drain pipeGray iron soil pipe for drain, waste, vent and sewer lines, made in hub-and-spigot and hubless (no-hub) forms.

References

  1. International Code Council, "CodeNotes: Bonding of Corrugated Stainless Steel Tubing (CSST) Gas Piping Systems, based on the 2021 IFGC and IRC" (2020) — iccsafe.org
  2. Gastite Division, Titeflex Corporation, "Flexible Gas Piping Design and Installation Guide" (2020) — gastite.com
  3. International Code Council, Building Safety Journal, "CodeNotes: Bonding of corrugated stainless steel tubing gas piping systems" (2020) — iccsafe.org