Page 12 of Tube Fabricating Equipment by Parker Hannifin Corporation Instrumentation Products Division

Tube Fabricating Equipment Parker Hannifin Corporation Instrumentation Connectors Division Huntsville, Alabama 12 Gas Service Special care must be taken when selecting tubing for gas service. In order to achieve a gas-tight seal, ferrules in instrument fittings must seal any surface imperfections. This is accomplished by the ferrules penetrating the surface of the tubing. Penetration can only be achieved if the tubing provides radial resistance and if the tubing material is softer than the ferrules. Thick walled tubing helps to provide resistance. Tables 2-7 indicate the minimum acceptable wall thickness for various materials in gas service. The ratings in white indicate combination of diameter and wall thickness which are suitable for gas service. Acceptable tubing hardness for general application is listed in Table 9. These values are the maximum allowed by ASTM. For gas service, better results can be obtained by using tubing well below this maximum hardness. For example, a desirable hardness of 80 Rb is suitable for stainless steel. The maximum allowed by ASTM is 90 Rb. System Pressure The system operating pressure is another important factor in determining the type, and more importantly, the size of tubing to be used. In general, high pressure installations require strong materials such as steel or stainless steel. Heavy walled softer tubing such as copper may be used if chemical compatibility exists with the media. However, the higher strength of steel or stainless steel permits the use of thinner tubes without reducing the ultimate rating of the system. In any event, tube fitting assemblies should never be pressurized beyond the recommended working pressure. The following tables (2-7) list by material the maximum suggested working pressure of various tubing sizes. Acceptable tubing diameters and wall thicknesses are those for which a rating is listed. Combinations which do not have a pressure rating are not recommended for use with instrument fittings. MAXIMUM ALLOWABLE WORKING PRESSURE TABLES Tube O.D. Size WALL THICKNESS Table 2 316 or 304 STAINLESS STEEL (Seamless) .010 .012 .014 .016 .020 .028 .035 .049 .065 .083 .095 .109 .120 .134 .156 .188 1/16 5600 6900 8200 9500 12100 16800 1/8 8600 10900 3/16 5500 7000 10300 1/4 4000 5100 7500 10300 5/16 4100 5900 8100 3/8 3300 4800 6600 1/2 2500 3500 4800 6300 5/8 3000 4000 5200 6100 3/4 2400 3300 4300 5000 5800 7/8 2100 2800 3600 4200 4900 1 2400 3200 3700 4200 4700 1-1/4 2500 2900 3300 3700 4100 4900 1-1/2 2400 2700 3000 3400 4000 4500 2 2000 2200 2500 2900 3200 (Technical Information contd)

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