WINTER 2016

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