Figure 1: Reels of CSST on site, with pipework routed up external ventilated risers
is that far fewer joints are needed than with rigid steel or copper gas piping, so there are less potential leak sources. It also makes CSST much faster to install than rigid materials. CSST is also very light compared to rigid materials, so is easier to transport and store on site. As an example, a 45 m reel of DN 50 CSST will weigh approximately 55 kg, compared to more than 200 kg for the equivalent length and size of rigid steel pipe. CSST assembly only requires the use of standard hand tools, eliminating the need for threading machinery/ tools and the associated need for on-site electric power. Joint assembly is simple, and the CSST fittings can be reused several times if repair or re-routing is required.
Installation of CSST Each manufacturer of CSST will provide a range of fittings allowing its CSST to be joined to rigid materials or, if required, to join CSST to CSST – manufacturers’ fittings are not interchangeable. Most CSST fittings form a metal-to-metal
Figure 2: Reel of CSST with assorted fittings and standard hand tools
This should be considered when specifying CSST and the environment through which it will be routed. Where a product is not annealed during the manufacturing process, the product will be more resistant to mechanical damage. Following the formation and corrugation of
the CSST, a yellow polyethylene outer jacket is extruded over the bare stainless steel. This is primarily to provide corrosion protection. If the product is manufactured to BS 7838, the outer jacket must contain protection against attack from ozone and ultraviolet light and be suitable for continuous use at an ambient temperature of 95°C. Other provisions that may be designed in to the outer jacket include chemicals that prevent flame spread and reduce smoke density when exposed to a fire. Manufacturers also need to follow robust
quality and testing procedures to ensure the product they supply is gas-tight when it leaves the manufacturing facility. The gas-tightness test involves a pressure test at 2 bar (26 times the maximum operating pressure of a BS 7838-compliant product). CSST is typically supplied on wooden
reels (similar to electrical cable) of various lengths up to 90 m, rather than in the shorter straight lengths of rigid pipe. Some CSST manufacturers also supply shorter lengths in a ‘kit’ format, typically in lengths under 15 m. Being semi-rigid and available in long lengths, a significant benefit of using CSST
62 CIBSE Journal September 2013
seal between the brass fitting and stainless steel pipe. Where this form of seal is achieved, no jointing compound or PTFE tape may be used on the metal-to-metal sealing faces or internal thread section. Some fittings, however, will need a washer (or similar gasket) between the sealing faces to form a gas-tight seal. If this seal is required, it must only be a washer/gasket as specified and supplied by the manufacturer. There will also be differing methods
to form the sealing face on the CSST. Some manufacturers will use a fitting that automatically forms a flare on the end of the CSST when the fitting is tightened; in this case, no specialist tools are required. Other manufacturers require specialist tools for their product. In all cases, assembly of the CSST fittings
must be carried out in accordance with the manufacturer’s instructions. Once the fitting has been assembled and
Installation standards
BS 6891:2005 +A2:2008 Installation of low pressure gas pipework of up to 35 mm (R1¼) in domestic premises (2nd family gas) – specification
BS 5482-1:2005
Code of practice for domestic butane- and propane-gas-burning installations – part 1: installations at permanent dwellings, residential park homes and commercial premises, with installation pipework sizes not exceeding DN 25 for steel and DN 28 for corrugated stainless steel or copper
IGEM/UP/2 Edition 2 IGE/UP/7 Edition 2 IGEM/UP/11
IGEM/G/5 Edition 2 UKLPG COP22
Installation pipework on industrial and commercial premises Gas installations in timber-framed and light steel-framed buildings Gas installations for educational establishments Gas in multi-occupancy buildings
Code of practice 22 – design, installation and testing of LPG piping systems: 2011
This list of standards should not be considered as exhaustive, as other standards may apply. Table 1: A selection of relevant installation standards for CSST
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Figure 3: Section through typical CSST fitting (CSST to male BSP) showing flare for sealing face
a gas tightness test completed, any exposed stainless steel needs to be wrapped with the manufacturer’s approved tape. This is typically a self-amalgamating silicone tape that forms a water tight seal between the fitting and the outer jacket of the CSST. If this seal is not achieved, corrosion of the stainless steel may occur.
Installation standards All of the standards below (see table 1) include guidance on how CSST should be installed, but the most important consideration is the CSST manufacturer’s specific installation requirements. Both BS 7838 and BS EN 15266 place a requirement on the manufacturer to provide guidance on the installation requirements of its product. In many cases these will follow the same principles as the normative documents listed above. However, in some cases, the manufacturer’s specific guidance will take precedence. It is for this reason that the Gas Safe Register considers manufacturers’ instructions to be ‘appropriate standards’ for compliance with legislation such as the Gas Safety (Installation and Use) Regulations.
General installation practices CSST is installed following the same general principles as rigid pipework. Sleeving – Although CSST has a yellow polyethylene outer jacket, it must still be sleeved where it passes through any wall or solid floor.
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