Aircraft fluid lines are usually made of metal flexible hose. Metal tubing (also called rigid ) is used in stationary applications and where long,.relatively straight runs are possible. They are in aircraft for fuel, oil, coolant, oxygen, instrument, and hydraulic lines. Flexible hose is with moving parts or where the hose is considerable vibrationOccasionally, it may be necessary to repair or aircraft fluid lines. Very often the repair made simply by replacing the tubing. However, are not available, the needed parts to be fabricated. Replacement tubing should the same size and material as the original tubingAll tubing is pressure tested prior to initial installation,.and is designed to withstand several times the pressure to which it will be subjected. tube bursts or cracks, it is generally the result vibration, improper installation, or by collision with an object. All tubing be carefully studied and the cause of the Fluid the early days of aviation, copper tubing was in aviation fluid applications. In , aluminum alloy, corrosion resistant steel or titanium tubing have generally replaced copper tubingAluminum Alloy made from 1100 H14 (1/2-hard) or 3003 H14.(1/2-hard) is used for general purpose lines of low fluid pressures, such as instrument ventilating conduits. Tubing made from 2024-T3,.5052-O, and 6061-T6 aluminum alloy materials in general purpose systems of low and , such as hydraulic and pneumatic 1,000 psi systems, and fuel and oil resistant steel tubing, either annealed , CRES 321 or CRES 304-1/8-hard, is used extensively in high pressure hydraulic systems (3,000 psi ) for the operation of landing gear, flaps, brakes,.and in fire zones. Its higher tensile strength permits of tubing with thinner walls; consequently, the weight is not much greater than that of wall aluminum alloy tubing. Steel lines are there is a risk of foreign object damage (FOD);.., the landing gear and wheel well areas. markings for steel tubing differ, includes the manufacturer’s name or trademark,.the Society of Automotive Engineers (SAE) number,.and the physical condition of the metalTitanium type of tubing and fitting is used transport category and high performance systems for pressures above 1,500 psi. Titanium is 30 percent stronger than steel and 50 than steel. Cryofit fittings or swaged used with titanium tubing. Do not use and fittings in any oxygen system assemblyTitanium and titanium alloys are oxygen reactive. If formed titanium surface is exposed in , spontaneous combustion could occur at making repairs to any aircraft tubing, it to make accurate identification of . Aluminum alloy, steel, or titanium be identified readily by sight where it is used basic tubing material. However, it is difficult whether a material is carbon steel or , or whether it is 1100, 3003, 5052-O, 6061-T6 aluminum alloy. To positively identify used in the original installation, compare of the replacement tubing with the on the tubing being of Band1100White3003Green2014Gray2024Red5052Purple6053Black6061Blue and Yellow7075Brown and YellowFigure 7-1. Painted color codes used to alloy large aluminum alloy tubing, the all
