Flowserve Nordstrom Dynamic Balance Plug Valve and Double DB Plug Valve - Manual (Page 4)

Flow Control
Nordstrom Valves
4 Dynamic Balance ® Plug Valve and Double DB ® Double Isolation Plug Valve FCD NVENIM2005-01
1 Valve Selection
1.1 Introduction
It is beyond the scope of this manual to make recommendations
for specific applications. This manual is intended to call attention to
important considerations in the selection of valves. Keep in mind that
misapplication of a valve type could result in operating problems that
adversely affect system safety and efficiency. The manual addresses
the important subjects of Shipping and Storage, Installation, and
Operation and Maintenance. Observance of the recommendations
and practices offered provides increased assurance of satisfactory
valve performance.
The valve industry offers a wide variety of valve types and materials
for use in industrial piping applications. There are usually several
possible choices for any given requirement and any one valve may
offer significant advantages and/or limitations when compared
with another valve. It is good practice to consult the manufacturer
regarding specific requirements. When purchasing valves, low cost
is certainly a major consideration, but also important is ensuring
that the valves purchased are satisfactory for the intended service.
The lowest total user (life cycle) cost criteria should be used only in
choosing between alternatives that are known to satisfy the service
requirement.
1.2 Pressure-Temperature Rating
The pressure-temperature rating of the valve must be properly
selected for the service requirement. If the service involves a tem-
perature above 100ºF (38ºC), the valve pressure rating at the service
temperature must be verified as meeting the requirements of the
application.
If system testing will subject the valve to a pressure in excess of
its working pressure rating, then the intended testing pressure and
a statement explaining whether the test pressure is through the
opened valve or a differential across the closed valve should be
included in the purchase specification.
Sample Source References for Pressure-Temperature Ratings:
ASME B16.34 Valves, Flanged, Threaded, and Welding End
API 6D Specification for Pipeline Valves
MSS SP-84 Steel Valves – Socket Welding and Threaded Ends
API 6A Specification for Wellhead and Christmas Tree Equipment
1.3 Bending Strength
Piping systems are subject to mechanical constraints at fixed
support points such as rigid nozzles, anchors, etc. Cold springing
at assembly, system temperature changes, together with gravity,
possible inertia loads, landslides, nonuniform subsidence in buried
lines, etc., all potentially affect the bending moment at various points
in the piping.
Valves are subjected to the bending moment occurring in the
adjacent pipe in addition to the normal pressure loading. Bending
loads can cause deformation in valve bodies that can be detrimental
to a valve’s functional performance. It is therefore a recommended
design practice to avoid locating valves at points of large bending
loads.
In many cases, normal valve design practice results in a body
strength greater than the strength of the adjoining pipe, thereby
providing inherent protection against valve damage. In other cases,
piping conditions or systems designs may increase the possibility of
harmful valve body deformation.
The following are examples of possible problems:
a. Basic “standard” valves that are made into “venturi” type valves
by providing enlarged end connections on the smaller standard
basic valves.
b. Any “standard” valve installed in heavy wall “overweight” piping
where the extra thickness may cause the pipe to be stiffer and
stronger than the valve.
Valve designs having a high body-bending strength should be used if
there is reason for concern regarding possible high bending loads.
1.4 Fire Safety
The terms “fire safe” and “fire tested” are not definitive and should
not be used without an accompanying specification of what is
required. Such a specification may be provided in the form of a
requirement for a defined test or for limitations on the valve failure
mode. Examples of such limitations are:
a. Destruction of elastomeric or polymeric materials in the valve
shall not result in gross valve pressure boundary leakage.
b. Destruction of elastomeric or polymeric materials in the valve
shall not result in leakage greater than a specified rate when the
valve is closed.
c. External heating of the valve shall not cause uncontrolled buildup
of pressure in the body cavity of a double-seated valve.
Requirements related to after-fire operability and seat tightness are
difficult to define other than by testing using standardized proce-
dures. Valve post-fire operability simulation fire testing is covered by