The SABS has approved and is legislating the adoption of ISO 14520 as the clean agent gas extinguishing standard in South Africa. In Part 3 we continue to look at the standard in great detail.
Storage containers
Containers shall be designed to hold the specific extinguisher. Containers shall not be charged to a fill density greater than specified in that part of ISO 14520 relating to the specific extinguishant. These specific gases and fill densities are shown in Part 2-15 of ISO 14520. Where required, the container and valve assembly should be fitted with a pressure relief device. Furthermore, means shall be provided to indicate that each container is correctly charged by means of a gauge.
Marking
Each halocarbon container shall have a permanent nameplate or other permanent marking specifying the extinguishant, tare and gross mass and the super-pressurisation level (where applicable) of the container. Each inert gas container shall have a permanent marking specifying the extinguishant, pressurisation level of container and nominal volume.
Manifolded containers
When two or more containers are connected into the same manifold, automatic means (such as check valves) shall be provided to prevent extinguishant loss from the manifold if the system is operated when any containers are removed for maintenance.
Containers connected to a common manifold in a system shall be of the same nominal form and capacity; filled with the same nominal mass of extinguishant; and pressurised to the same nominal working pressure.
Different sized storage containers connected to a common manifold may be used for nonliquefied gas containers provided they are all pressurised to the same nominal working pressure.
Unless otherwise approved, in-servicing container operating temperatures for total flooding systems shall not exceed 50°C and not be less than -20°C. External heating or cooling should be used to keep the temperature of the storage container within the specified range unless the system is designed for proper operation with operating temperatures outside this range.
Distribution
Pipework and fittings are the continued point of argument of many gas installers as to what is applicable in South Africa. The following is an attempt to clarify the situation: pipework and fittings shall comply with the appropriate national standards, shall be noncombustible and able to withstand the expected pressures and temperatures without damage. Before final assembly, pipe and fittings shall be inspected visually to ensure they are clean and free of burrs, spelter and rust, and that no foreign matter is inside and the full bore is clear. After assembly, the system shall be thoroughly blown through with dry air or other compressed gas.
A dirt trap consisting of a tee with a capped nipple, at least 50 mm long should be installed at the end of each pipe run. Drain traps protected against interference by unauthorised personnel should be fitted at the lowest points in the pipework system if there is any possibility of a build up of water.
In systems where valve arrangements introduce sections of closed piping, such sections shall be equipped with:
* An indication of extinguishant trapped in piping.
* A means for safe manual venting.
* An automatic relief of over-pressures, where required.
Over-pressure relief devices shall be designed to operate at a pressure not greater than the test pressure of the pipework. Pressure relief devices, which can include the selector valve, should be fitted so that the discharge, in the event of operation, will not injure or endanger personnel and, if necessary, so that the discharge is piped to an area where it will not become a hazard to personnel.
In systems using pressure-operated container valves, automatic means shall be provided to vent any container leakage that could build up pressure in the pilot system and cause unwanted opening of the container valve. The means of pressure venting shall not prevent operation of the container valve.
The manifolds to the container and valve assembly shall be hydraulically tested by the manufacturer to a minimum pressure of 1,5 times maximum working pressure. Adequate protection shall be given to pipes, fittings or support brackets and steelwork that are likely to be affected by corrosion. Special corrosion-resistant materials or coatings shall be used in highly corrosive atmospheres.
Piping
Piping shall be of noncombustible material having physical and chemical characteristics such that its integrity under stress can be predicted with reliability. The thickness of the pipe wall shall be calculated in accordance with the relevant national standard. The pressure for this calculation shall be the developed pressure at a maximum storage temperature of not less than 50°C. If higher operating temperatures are approved for a given system, the design pressure shall be adjusted to the developed pressure at maximum temperature. In performing this calculation, all joint factors and threading, grooving or welding allowances shall be taken into account.
Where a static pressure-reducing device is used in a nonliquefied gas system, the maximum working pressure in the distribution pipework downstream of the device shall be used in the calculation of the downstream pipe wall thickness. Cast iron and nonmetallic pipes shall not be used.
Flexible tubing or hoses (including connections) shall be of approved materials and shall be suitable for service at the anticipated extinguishant pressure and maximum and minimum temperatures.
Fittings
Fittings shall have a minimum rated working pressure equal to or greater than the maximum pressure in the container at 50°C, or the temperature specified in the national standard, when filled to the maximum allowable fill density for the extinguishant being used. For systems that use a pressure-reducing device in the distribution piping, the fittings downstream of the device shall have a minimum rated working pressure equal to or greater than the maximum anticipated pressure in the downstream piping.
All pipe fittings for installation of gas extinguishing systems in South Africa are imported so limited selection is available. The two types commonly available are 300 lb fittings and steam fittings to BS 1740.
3000 lb fittings provide a 300 bar working pressure whereas BS 1740 steam fittings only provide a test pressure of 48,5 bar, therefore a recommended working pressure of 32 bar. In general, most 200 bar systems at their 'highest' pressure point are in excess of 32 bar downstream. The FDIA's recommendation is 'be safe' and use 3000 lb fittings on all inert agent extinguishant systems.
Welding and brazing shall have a melting point above 500°C. Welding shall be performed in accordance with relevant national standards. Where copper, stainless steel or other suitable tubing is joined with compression fittings, the manufacturer's pressure/temperature ratings of the fitting shall not be exceeded and care shall be taken to ensure the integrity of the assembly.
In the next issue we will look at other aspects of ISO 14520, including pipe and valve supports, nozzles and filters.
For further details contact the FDIA on tel: (011) 397 1618, e-mail: [email protected]
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