CPD PROGRAMME
Nominal Size Up to DN 15
DN 22 up to DN 50
Figure 4: CSST manufactured to BS 7838 being buried directly in the ground
The sleeve itself needs to be made of a material that is capable of containing gas, such as copper, steel or PVC. The sleeve needs to be secured to the fabric of the building (with an appropriate adhesive such as cement), and the annulus space between the CSST and the sleeve sealed at one end only with a non-setting fire-resistant compound. The seal should, where possible, be inside the property, so any potential gas escape within the sleeve will ventilate to the outside air. Support – CSST must be supported at regular intervals along its length. The maximum interval between supports will depend on the pipe diameter (see Table 2 for example intervals). CSST manufacturers may also specify different intervals, depending on whether or not the pipe is annealed. Pipework within fire escape routes/shafts – CSST can also be installed in one continuous length through protected shafts and fire escape routes. CSST used for this application will need to meet the requirements of Fire Test A, detailed in Annex A of BS EN 1775:2007 Gas supply – gas pipework for buildings – maximum operating pressure less than or equal to 5 bar – functional recommendations. If the CSST meets this
standard, it will be deemed to have a minimum 120-minute fire resistance, and will meet the requirements of the Building Regulations for such installations. Access to fittings – CSST fittings are deemed to be ‘mechanical fittings’ and, as such, should not be concealed within the fabric of the building, and must remain accessible. This does not prevent fittings from being concealed in such areas as risers or ceilings, providing an appropriately-sized access panel is also installed. Pipe sizing – When sizing a typical gas installation, the maximum pressure drop between the outlet of the meter and the inlet
to any connected appliance must not exceed 1 mbar when operating at maximum flow (all appliances in operation). As CSST is a corrugated pipe, there is a
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slightly higher pressure drop compared to smooth bore pipes of similar diameter. Sizing of CSST installations follows the same principles as smooth bore pipes but, rather than using the sizing data published in installation standards such as BS 6891, it is prudent to use the data published by the CSST manufacturer. This data will be more accurate than the generic data published in the standards and will, therefore, result in more efficient (and economical) installation design. Due to the longer lengths available, it is
more common to design a CSST installation as a radial system (fed from a manifold), rather than a series pipework installation (which is the traditional UK method). This often allows smaller pipes to be used, which also requires less space. Burial of CSST – CSST manufactured to BS 7838 can be buried directly in the ground or screed without the need for additional corrosion or mechanical protection. Products only manufactured to BS EN 15266 should not be used in this way. The burial depth will depend on the application. If a pipe is to be buried in the screed in domestic premises, a minimum of 25 mm depth of cover above the pipe would be needed; if buried externally – for example,
below a path – it would require a minimum of 450 mm cover above the pipe (Figure 4). Pipework passing through voids – It is a requirement of the Gas Safety (Installation and Use) Regulations 1998 that any void through which a gas pipe passes must be adequately ventilated. The requirements for ventilation of voids can be found in various installation standards, depending on the situation. Specific details for services in ducts and risers can be found in BS 8313:1997 Code of practice for accommodation of building services in ducts. If a void cannot be readily ventilated, it is
possible to pass a duct through that void (which is ventilated at each end to a safe space) and then pass the gas installation pipework through the duct. The benefit of using CSST for this application is that, as it is semi-rigid, it can be passed easily through a secondary containment such as a flexible polyethylene duct. This is often the method chosen by designers where pipework has to pass from a ventilated riser, through an unventilated ceiling void above a corridor, to individual apartments (see Figures 5 and 6). Flux and other contaminants – If soldering of copper pipework is being undertaken in the vicinity of CSST, it is important that no flux comes into contact with the CSST. Flux is
Interval for vertical run (m) 2
2.5
Interval for horizontal run (m) 1.5 2
Table 2: Recommended maximum interval between pipe supports (taken from BS 6891:2005)
highly corrosive and will cause pinholing in the CSST in a relatively short space of time. If flux does come into contact with CSST, it should be washed off immediately and the CSST thoroughly dried. Other contaminants – Chlorine-based products, such as cleaning fluids and some leak detection fluids (LDF), can affect the integrity of CSST. If LDF is used, it must be suitable for use with stainless steel, be non-corrosive and manufactured to BS EN 14291:2004 Foam producing solutions for leak detection on gas installations. After use, the CSST should be thoroughly flushed and dried. By employing CSST, the installation time
may be significantly reduced – manufacturers suggest that it can save 75% of installation time – by reducing the jointing needs and allowing the forming of bends by hand. Fewer joints will reduce the opportunity for leaks and will not require threading, welding or soldering. The relatively lightweight two-hour fire-rated material is designed to withstand normal shrinkage and movement in buildings, and when manufactured to BS 7838, can be buried directly in the ground or in concrete screed. © Jamie Cooper and Tim Dwyer, 2013.
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Figure 5: CSST inserted into polyethylene secondary containment
Figure 6: Secondary containment passing through unventilated ceiling void (with CSST inside)
September 2013 CIBSE Journal 63
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