Table 5-1.—Wall Thickness Schedule Designations for Pipe160 pipe has a 0.815 ID. In each case the OD is1.315 (table 5-1) and the wall thicknesses are0.133 0.179 and 0.250 respectively. Notethat the difference between the OD and IDincludes two wall thicknesses and must be dividedby 2 to obtain the wall thickness.Tubing differs from pipe in its size classi-fication. Tubing is designated by its actual OD.(See table 5-2.) Thus, 5/8-inch tubing has an ODof 5/8 inch. As indicated in the table, tubing isavailable in a variety of wall thicknesses. Thediameter of tubing is often measured andindicated in 16ths. Thus, No. 6 tubing is 6/16 or3/8 inch, No. 8 tubing is 8/16 or 1/2 inch, andso forth.The wall thickness, material used, and IDdetermine the bursting pressure of a line or fitting.The greater the wall thickness in relation to theID and the stronger the metal, the higher thebursting pressure. However, the greater the ID fora given wall thickness, the lower the burstingpressure, because force is the product of area andpressure.MaterialsThe pipe and tubing used in fluid powersystems are commonly made from steel, copper,brass, aluminum, and stainless steel. Each of thesemetals has its own distinct advantages ordisadvantages in certain applications.Steel pipe and tubing are relatively inexpensiveand are used in many hydraulic and pneumaticsystems. Steel is used because of its strength,suitability for bending and flanging, andadaptability to high pressures and temperatures.Its chief disadvantage is its comparatively lowresistance to corrosion.Copper pipe and tubing are sometimes usedfor fluid power lines. Copper has high resistanceto corrosion and is easily drawn or bent. However,it is unsatisfactory for high temperatures and hasa tendency to harden and break due to stress andvibration.Aluminum has many of the characteristics andqualities required for fluid power lines. It has highresistance to corrosion and is easily drawn or bent.In addition, it has the outstanding characteristicof light weight. Since weight elimination is a vitalfactor in the design of aircraft, aluminum alloytubing is used in the majority of aircraft fluidpower systems.Stainless-steel tubing is used in certain areasof many aircraft fluid power systems. As a generalrule, exposed lines and lines subject to abrasionor intense heat are made of stainless steel.An improperly piped system can lead toserious power loss and possible harmful fluid5-2
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