Corrugated Stainless Steel Tubing or CSST for short is a newer type of gas pipe first used around 1988. It's a flexible pipe covered with a plastic sheathing and is very common to see in newer homes. To make the pipe flexible a continuous ridge was designed into the pipe. Which is how the "corrugated" made it's way into the name.
CSST is a great advancement in gas piping. Because it is flexible and available on large spools long continuous pipe runs are possible without the need for connections. Fewer connections mean less potential for leaks.
However a problem with the pipe began to show up some years after the first installations.
Because the pipe is metal it is electrically conductive. What was discovered after some years was that a lightning strike entering the home can disperse through the CSST resulting in holes in the pipe (see picture). The ridges are thought to create electrical arcs and at some point along the path burn a hole through the tubing.
A hole in a homes gas supply piping, as you can imagine, is not a good thing.
Because of this problem a class action suit was brought against 4 of the 6 manufactures of CSST alleging; "that CSST poses an unreasonable risk of fire due to lightning strikes."
The solution has been to electrical bond the CSST to ground. Or more accurately more thoroughly bond the system. Bonding of gas piping was in existence in the National Fuel Gas Code (NFGC) in 1988 (diagram).
The manufactures have now written electrically bonding the CSST into their design and installation manuals. Never the less I do not see CSST electrically bonded during an inspection.
The second to last picture is from a home built in 2005. The picture is of the main gas supply pipe entering the home. There should be a ground wire on this pipe. Additionally in some jurisdictions there should also be a bonding jumper wire at connections which are missing in the last photo.
There is still debate on the requirements of bonding CSST. As an inspector knowing the potential for a fire due to a lack of bonding on a CSST system there is no debate for me. When I find CSST in a home without bonding it is called out as defect with a recommendation to correct.
James Quarello
NRSB #8SS0022
JRV Home Inspection Services, LLC
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