The Gas Research Institute (GRI) is funding research to investigate alternative gas piping technologies which can make gas service as easy to install as electric service. The semirigid tubing systems being evaluated are soft copper tubing and a Japanese product, corrugated stainless steel tubing (CSST). Both use mechanical fittings and are designed to operate using either traditional low pressure (8 in. of water column (WC)) or a special hybrid pressure (2 psi and 8 in. WC) approach. This research has been conducted at several different single family and multifamily buildings located throughout the United States.

Results from these sites indicate that regardless of the building type, semirigid tubing systems can be installed in less time and usually at lower cost than conventional steel pipe systems. The labor savings vary between 30 and 70 percent, while the cost savings vary between 10 and 50 percent. The use of these semirigid tubing systems also makes a decentralized gas distribution system more viable.


In 1983, GRI began its Residential/Commercial Interior Piping Research Program. The first activity completed by GRI's research contract, Foster-Miller, Inc., was to determine the state of the art of interior gas piping systems found both in the United States and abroad. Subsequently, Foster-Miller developed an. optimized gas distribution system for the United States housing market based on commercially available piping technology.

The most commonly used interior gas distribution system in the world is a series/branch arrangement using Schedule 40 steel pipe with threaded joints operated at low pressure (nominally 8 in. WC). Copper (either as semirigid tube or rigid pipe) is used in several countries for interior gas distribution, but far less frequently than steel pipe. The most innovative hardware discovered in the review is a CSST system with special mechanical fittings used exclusively in Japan. One innovative approach to the interior gas distribution was found in the United States, where copper tubing systems are operated at 2 psi pressure. Gas utilities using these semirigid (copper or CSST) tubing systems (both at low pressure and 2 psi) report cost reductions in the total installed cost when compared with the equivalent steel pipe system.

Both the copper and the CSST systems have several advantages. The flexible nature of the tubing allows the system to be installed with a significant reduction (over the traditional steel pipe) in labor; the tubing is supplied in coils allowing long, continuous runs to be installed; thus minimizing the number of joints. Since there are fewer system components to handle, the overall installation time is less. -The semirigid tubing is easily snaked through or around existing structural obstacles which are typically faced when field-run systems are installed. Since the tubing components are lightweight, fewer installers are needed, with less effort required of the installers during installation.

A series of initial field tests were completed at two single family sites. During these studies, the current installation practices and piping hardware were evaluated.

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