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Standard yellow CSST Gas piping hazards (C) InspectPedia & Carson Dunlop Associates TorontoCorrugated Stainless Steel Tubing (CSST) Gas Piping
What is CSST, where is it used, how do manufacturers want it to be installed?

  • GAS PIPING, FLEXIBLE CSST - CONTENTS: corrugated stainless steel tubing used for gas piping: manufacturers, sources, installation specifications & building codes. Field report of CSST gas leak. CSST gas piping protection measures.
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Flexible gas piping CSST:

This article describes CSST: corrugated stainless steel tubing used for gas piping in buildings. Since 1990 CSST has been used within many buildings in both exposed and enclosed areas to install new gas system piping. The article discusses CSST uses, sources, installation specifications, and safety measures to protect the gas piping from damage by abrasion, puncture, lightning strikes or other hazards. Gas piping codes and industry sources of CSST are included.

Our page top photo, provided courtesy of Carson Dunlop Associates, a Toronto home inspection & education firm, illustrates an improper installation of standard yellow CSST gas piping - routed in ground contact in a wet area. Yellow "Standard" CSST gas pipin galso requires special electrical ground bonding to reduce risk of damage & leaks in areas of high lightning strike activity.



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CSST Gas Piping: Corrugated Stainless Steel Tubing

Article Contents

What is CSST Gas Piping & How is it Identified in Buildings

CSST or Corrugated Stainless Steel Tubing is a flexible gas piping system that has been in use in the U.S. since 1990. In Japan the system has a decade more experience. "Standard Yellow CSST" such as shown below (adapted from csstafety.com) may appear in homes where gas piping was installed or modified since 1990. Through csstsafety.com the National Association of State Fire Marshals and the CSST industry recommend that homes where gas piping has been installed or modified since 1990 be inspected for the presence of yellow CSST and that the electrical ground bonding in those homes be inspected.

[Click to enlarge any image]

Standard yellow CSST gas piping needs special electgrical ground bonding - see www.cssafety.org

Newer black or dark-jacketed CSST gas piping (shown below, adapted from GasTite's FlashShield CSST sales literature) currently sold by most manufacturers may not require special bonding.

Black CSST gas piping, adapted from GasTite's FlashShield sales literature cited in this article.

Watch out: Let's avoid a point of confusion: CSST used as gas piping runs in buildings is not the same product as the flexible gas connector tubing (shown below) used to actually connect gas appliances to the gas supply system, and different installation and product protection measures are required. CSST gas piping is used to route natural gas or LP gas supply through a building while the flexible gas tubing shown below is specifically designed for the connection of gas appliances to the gas piping system.

Gas appliance connector tubing (C) Daniel Friedman

Where is CSST Gas Piping Being Installed?

Look for corrugated stainless steel tubing (CSST) used as gas piping in buildings constructed in the U.S. or Canada after 1990 and also look for it in older buildings where gas piping was newly installed or modified since 1990. CSST is also installed in other countries.

Collapsing building © Daniel FriedmanStandard "yellow" or newer black CSST can be recognized in (usually) long runs between the building gas source and its point of use at gas appliances. The gas appliance connector itself (shown in the photo just above) may be connected directly between the end of the CSST and the appliance, or the CSST may terminate or be mixed with black iron gas piping in the same building.

CSST gas piping is run both in exposed locations and through building cavities such as walls, ceilings or floors.

How many homes have CSST installed? We had trouble relating industry estimates with US Census data and U.S. Energy Information Agency data, but there is no doubt that the piping has been installed in many homes in Canada, the United States, and Japan.

According to the CSST Safety Website (below), corrugated stainless steel tubing is installed in about 500,000 new homes each year. As the U.S. Census Bureau and U.S. HUD February 2015 New Construction Data news release reports a seasonally adjusted annual rate of new construction in the U.S. of about one million homes, that suggests that half of all new homes are being built with CSST gas piping.

Or if we look at the February housing start data that means that almost 100% of new homes are using CSST gas piping - which sounds a bit dubious. In 2014 the U.S. EIA reported that 27% of all U.S. homes were supplied with natural gas and less than 1% with other gases.

Still, the system is in active use in the U.S. and Canada and continues in use in Japan.or fires.

Fire & Safety Measures to Protect CSST Gas Piping from Damage &Leaks

Standard yellow CSST Gas piping hazards (C) InspectPedia & Carson Dunlop Associates Toronto

Reader Question: report of gas leak from punctured CSST Gas Piping

[At left, a new CSST gas piping installation, incomplete, is illustrated, courtesy of Carson Dunlop Associates.]

I'm a dwelling contractor in Wisconsin, I would like more information on Corrugated Stainless Steel Tubing (CSST) used for gas piping in buildings. It seems like manufacturers don't require it to be secured or strapped very much at all. 'm not sure what the codes say about that. I've seen it snaked all over the place without support -- and here is a story of one consequence (quoting from an email to a manufacturer):

Email sent to ProFlex Technical Assistance

I wonder if you could give me an idea about support and protection requirements for CSST. I just came back from helping my Brother-in-Law with a few issues in his Condo in Boston -- he had a sprinkler pop over the winter, so a lot of the drywall had to be removed to dry things out. When the restoration contractor removed one section of drywall, the smell of gas poured out. CSST had been snaked through floor trusses and had looped up in one location, where a pneumatic nail from the wood flooring installation had punctured it.

Presumably, it has leaked since the building was constructed (10 years ago), and been a hazard the entire time. Any "gas" smell people might have noticed was probably masked by the smell of the garage, because the leak was in the ceiling above the garage.

Reading a few manufacturers' installation guides, there doesn't seem to be a requirement to SECURE the gas line at all -- it just has to be supported every 8' or so horizontally, right? In my Brother-in-Law's condo, the gas line was snaked all over and not really strapped anywhere, although it was protected by nail plates at stud and joist penetrations. Is this acceptable, according to your guidelines and any applicable codes?

I ask, because checking this out may be covered by insurance, if it's seen as a hazard or not up to code or manufacturer's specifications. Thanks, J.

The manufacturer's reply was essentially that the CSST needed to be kept 3" away from finished surfaces or protected by nail plates if also within 5" of some constraint (like a penetration through a framing member). Beyond that, it has an "escape" for nail penetrations. This did not prevent the leak I described, as the CSST looped up and was hit by a pneumatically-driven flooring nail... CSST seems like a great thing -- easy to install, etc. I wonder if you would do an article on it?
Thanks J.

Reply:

Our reply to reader J. begins immediately below

Lightning Strike Hazards and CSST Gas Piping Leaks

The history and field experience of CSST use in North America led to concerns about possible pitting, corrosion or perforation of the original yellow CSST gas piping in areas where lightning strikes were common. Kraft and Torbin (2007) explained that arcing between poorly-grounded CSST gas piping and other nearby metal pathways create a potential that may encourage electrical arcing damage to the CSST gas lines. Such lightning-related electrical arcing can weaken or even perforate the gas piping leading to dangerous gas leaks.

The risk of arcing damage to CSST is increased in areas where lightning activity is greatest and where the CSST is not well bonded to a grounding system.

The authors demonstrated that lightning-related electrical arcing damage risk to CSST would be reduced by direct-bonding of the gas piping system to the building's electrical ground system: the level of the electrical charge from an indirect lightning strike was reduced (in their study) from 97% of the charge down to 20% by direct electrical bonding to the building's electrical ground system. Their 2007 report concluded with a recommendation for direct ground bonding of CSST as a proposal to the National Fuel Gas Code. In 2009 the same authors reported that CSST could perform acceptably but made important and detailed recommendations for the ground bonding of CSST gas piping systems.

Goodson in a patent application (2009) also reported on the effectiveness of direct bonding of both yellow and black CSST gas piping to reduce the risk of damage from indirect lightning flashing. Goodson explained that CSST was generally not a good electrical ground, thus lending importance to the "direct bonding" discussion for this gas piping system. Stringfellow (2013) continued to report on electrically-induced gas distribution piping.

Currently (2015) the manufacturers have pretty much switched to an improved, more durable CSST gas piping whose design includes a protective outer jacket and for which extra manufacturer-specified ground bonding is not required. I think that only Ward continues to produce the yellow CSST for sale in the U.S.

According to Jim Narva, executive director of the National Association of State Fire Marshals, that association is focusing on informing homeowners of the need for retrofit ground bonding of older CSST installations.

... we are focused on a safety campaign to make homeowners aware of the need to bond yellow CSST. It is estimated to be in about 6-8 million homes where it was installed before bonding was a code requirement or manufacturer installation instruction. Between the early 1990’s when it was introduced in the US market and the mid 2000’s when the requirements came about is the target we are trying to reach and unfortunately no one knows where those 6-8 million homes are in the US. - private email, Narva to Friedman, 14 April 2015

Nail or Screw Puncture Risks with CSST Gas Piping

OPINION: I agree that CSST needs to be protected from damage, including or perhaps in particular when it is run through building cavities where, hidden from view, it's otherwise too easy for a future building occupant or worker to shoot a nail or screw through the material. One would think that excluding concerns for corrosion, similar worries apply to (and generally prohibit the use of) flexible copper tubing when used for gas piping: it is not routed within building cavities. Instead in those situations it's common to use steel piping for such gas lines.

In the CSST installation example specifications listed below you'll see that the manufacturers typically require a number of installation details to assure safe reliable operation of the gas piping system, including nail plates, flexible corrugated steel armor in some locations, support, and other measures. Some local jurisdictions further detail CSST gas piping installation specifications such as where and how it can be routed.

Below at left is an example of a traditional steel gas pipe routed through a wall cavity during building renovations of a New York Home. And at below right you can see the traditional change from flexible copper tubing to steel piping when the gas piping system had to penetrate the building wall.

Steel gas piping new installation (C) D Friedman E Galow Change from flexible copper to steel gas piping at wall penetration (C) Daniel Friedman

But CSST is indeed in widespread use as gas piping in both exposed and hidden locations. Here are some typical protective measures specified by CSST tubing manufacturers cited in the references above.

CSST Gas Piping Installation Code, Safety & Protection Features

Local CSST Gas Piping Specifications Extending the Model Codes for Improved Safety

The following example is excerpted from a local Oklahoma Building Code for Rogers County, Appendix H, , Subsection "Policy for installation of Corrugated Stainless Steel Tubing (CSST)", in Appendix H-17General Information and Responsibilities for One & Two Family Residential Construction, - retrieved 14 April 2015, original source: http://www.rogerscounty.org/planning/zoning%5CAH.pdf -

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CSST Gas Piping Bonding suggestion for Oklahoma's Rogers County CSST Gas Piping Bonding suggestion for Oklahoma's Rogers County

CSST Gas Piping Codes, Specifications, Industry Trade Associations

CSST Gas Piping Safety Research, Patents, Studies

Examples of CSST Patents Aiding in Finding the History of CSST Gas Piping Usage

Sources of CSST Corrugated Stainless Steel Tubing

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