Flowserve PlugSeal - Manual (Page 6)

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SECTION II.
PRESSURE CONTAINING FASTENERS
MATERIAL SELECTION
Selecting the proper fastener material is the ultimate
responsibility of the customer because the supplier does
not typically know in what service the valves will be used
or what elements may be present in the environment.
Flowserve normally supplies B7 (carbon steel) for ductile
cast iron and carbon steel valves. For stainless steel and
high alloy valves, B8, Class 2B (stainless steel)
fasteners are supplied as standard. All fasteners used
must have minimum yield strength of 40,000 PSI, a
minimum elongation of 12% and be compatible with the
process fluid. Determining compatibility to the process
fluid goes beyond a material being resistant to general
corrosion because the more important consideration is a
material’s resistance to stress corrosion cracking.
Depending on the service, it may make sense to use B7
fasteners on high alloy valves. One such service would
be marine environments because of stainless steel’s
susceptibility to stress corrosion cracking in chloride
environments. Another key aspect of fasteners is
frequent visual inspection. Because of the common
practice of using steel fasteners rather than stainless
steel to avoid chloride stress corrosion cracking, visual
inspection is recommended to monitor the general
corrosion of these fasteners. If jacketing or insulation is
used on a valve, it must be periodically removed for
visual inspection of the fasteners. If you wish assistance
in determining the proper fasteners to use, please refer
to the attached chart.
DESIGN & TYPE
Flowserve’s valve design standards adopt ASME
B18.2.1 (latest reision) as the standard for fastener type
and design. This national standards requires that
finished hex ‘head’ cap screws be used when the head
of the fastener is turned. A finished hex ‘head’ cap screw
and a heavy hex cap screw have a bearing surface
under the head to minimize frictional resistance during
tightening. They also comply to qualified body diameters
and fully formed head dimensions. Cookeville Valve
Operation’s policy is to use finished hex ‘head’ and
heavy hex ‘head’ cap screws for all pressure retaining
fasteners. This includes top caps, packing adjusters,
plug adjusters, bottom caps, body halves or other
pressure retaining components. Compliance is made
with ANSI B18.2.2 (latest revision), Square and Hex
Nuts, when studs and heavy hex nuts are required.
Additional information on these items may be obtained
from the Flowserve Corporation, Cookeville Valve
Operation, Cookeville, Tennessee.