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Distributor's Link Magazine Winter Issue 2016 / Vol 39 No1

28 THE DISTRIBUTOR’S

28 THE DISTRIBUTOR’S LINK Guy Avellon Guy Avellon has been in MRO and Fastener Distribution for over 30 years, in such positions Sales Engineer, Chief Engineer, Manager of Product Marketing, Product Engineering & Quality and Director of Quality & Engineering. He founded GT Technical Consultants where he performs failure analysis, lectures on fastener safety, works for law firms and designs/audits Quality systems. He is a member of SAE, is Vice Chairman of the ASTM F16 Fastener Committee, Chairman of the F16.01 Test Methods Committee and received the ASTM Award of Merit in 2005. Guy can be contacted at 847-477-5057, Email: ExpertBoltGuy@gmail.com or visit www.BoltFailure.com. WHAT FASTENER DISTRIBUTORS NEED TO KNOW ABOUT PIPE FITTINGS I have heard several concerns expressed by veteran people in the industry regarding the quality of the products they have been receiving. We usually espouse about nuts and bolts, but how about other threaded products: pipe fittings? There are pipe fittings made from brass, stainless steel and carbon steel. The latter two are primarily used for pneumatic and hydraulic hose end fittings. Brass is a very common material used for a variety of low pressure applications. Brass Fittings Brass fittings are primarily produced by three different methods; cast, forged and extruded. Since there is a huge difference in performance and safety between these methods, it is necessary to be able to not only identify the method of manufacture, but to use them in their proper applications. A casting is made by pouring molten metal into a mold, letting it cool, and then finishing it by drilling pathways and tapping threads. This is an extremely inexpensive process and does not provide for accurate wrench pads for proper tightening. Valve bodies, for example, are made from cast iron, cast steel or cast brass. The grain structure of any cast part is very coarse. Subsequently, this will produce a part that has such a natural porosity that under low pressures will actually permit highly volatile fluids to ‘bleed’ through the walls of the fitting. If transmitting gasoline under pressure, the bodies of the fittings will ‘sweat’ from the liquid and CONTRIBUTOR ARTICLE vapors forcing their way through the fitting. Therefore, these fittings are never used in fuel delivery applications. The brass used in castings is an SAE C85400. The ‘as cast’ tensile strength is 30,000 PSI and has a yield strength of only 11,000 PSI. Cast fittings have the lowest strength of the three types of production methods and the poorest dimensional consistency. Forged fittings are formed from oversized blanks of metal that are pounded, or hammered into shape from repeated blows from a heavy press and shaping dies. This hammering process forces the metal grain structure into a tighter and more compact structure, especially on the outer surface. The forging process increases the tensile strength of the SAE C37700 brass to 50,000 PSI and an increased yield strength of 23,000 PSI. The fittings produced have more accurate body dimensions and wrench pads. The compacted grain structure offers better thermal expansion properties, thus providing for a longer life in air conditioning and refrigeration systems. The SAE recommends forged fittings for these applications. The final method is that of extrusion. Similar to extruding wire in preparation for making a bolt, this process is more forceful as the dies are more complex in size and shape. Here, intense pressure forces the metal through a die to form a ‘bar stock’. This blank bar stock has an extremely dense and compressed molecular structure. Subsequently, the possibility of porosity and fluid leakage is practically eliminated. Extruded fittings only are recommended for fuel delivery applications. CONTINUED ON PAGE 120

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