Flowserve 50165 Nordstrom Figure - Manual (Page 12)

Nordstrom Figure 50165 and 50169 Dynamic Balance Iron Plug Valve FCD NVENIM2006-00 – 09/05
12
MSS SP-92 in part, reads as follows:
Section 3.4c Cast iron flanges are less “forgiving” of improper installation than flanges of
ductile materials. The use of lower strength bolting is recommended to reduce the possibility of
overstressing the flanges by excessive flange bolt preload. Full-face gaskets on flat flanges provide
desirable protection against flange breakage by over-torquing of flange bolts. A flat-face flange
should not be installed against a raised face flange.
Good preassembly alignment is especially important in cast iron flange joints in order to assure that
adequate gasket compression can be achieved without excessive bolting loads.
Section 3.4d Check gasket material. For flange joints using low-strength bolting, such as may be
provided for iron flanges (see Section 3.4c above) or Class 150 steel, metal gaskets (flat, grooved,
jacketed, corrugated, or spiral wound), should not be used. See ASME B16.5 for additional require-
ments.
in summary, all of this means that the following is to be considered:
1. Either full-face or flat ring gaskets may be used in conformance with recognized standards.
2. The use of flat ring gaskets requires the use of low-strength ASTM A307 Grade B bolting.
3. The use of full-face gaskets should minimize flange breakage.
4. Cast iron flange breakage is always a possibility if the mating flanges are not properly aligned.
c) Check the gaskets for freedom from injurious defects or damage.
d) Use care to provide good alignment of the flanges being assembled. Use suitable lubricants on the
bolt threads. Sequence the bolt tightening to make the initial contact of the flanges and gaskets as
flat and parallel as possible. Tighten the bolts gradually and uniformly to avoid the tendency to twist
one flange relative to the other. Use of a torque wrench is helpful to ensure correct and uniform final
tightening of the flange bolting. Parallel alignment of flanges is especially important when assem-
bling a valve into an existing system. It should be recognized that if the flanges are not parallel,
then it would be necessary to bend something to make the flange joint tight. Simply forcing the
flanges together with the bolting may bend the pipe or it may bend the valve. This is particularly true
in large diameter piping. Such conditions should always be brought to the attention of someone
capable of evaluating the bending condition and the corrective measures that need to be taken. The
assembly of certain “short pattern” valves between mating flanges requires that the installation be
checked for any possibility of interference between the moving parts of the valve and the adjacent
pipe, fitting, or valve.
a Caution: Torque wrenches should always be used to assure proper tightening of the flange
bolting. If, in the tightening process, the torque on a given bolt has been increasing with each
part turn and then is observed to remain unchanged or increase a much lesser amount with an
additional part turn, that bolt is yielding. That bolt should be replaced and discarded since it is
no longer capable of maintaining the proper preload.