04-10-2012, 01:43 PM
B31.3 PROCESS PIPING
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BACKGROUND AND GENERAL
INFORMATION
ASME B31.3 covers process piping. It has the broadest scope
of application of any of the ASME B31 Codes for Pressure
Piping. This chapter covers essentially the entire Code, including
design, materials, fabrication, assembly, erection, examination,
and testing. Also included are special topics such as piping for
Category M and High Pressure Fluid Services, as well as nonmetallic
piping.
This chapter is based on the 2006 edition of ASME B31.3,
Process Piping Code. As changes, some very significant, are
made to the Code every year, the reader should refer to the Code
for any specific requirements. This chapter should be considered
to provide background information, and not specific, current Code
rules.
The equations that are numbered in this chapter use the same
numbers as are used in ASME B31.3. Equations that are not numbered
are either not in ASME B31.3 or are not numbered therein
also.
References herein to Sections I, II, III, V, VIII, and IX are references
to sections of the ASME Boiler and Pressure Vessel
Code. References to a para. are references to a paragraph in
ASME B31.3, except when otherwise specified.
References are listed at the end of each major section of this
chapter. Reference documents other than codes, standards, and
similar publications are numbered. Codes and standards that are
mentioned in each major section, such as those provided by
ASME, API, AWWA, and ASTM, are simply listed at the end of
each reference section.
History of B31.3
In 1926, the American Standards Institute initiated Project
B31 to develop a piping code. ASME was the sole administrative
sponsor. The first publication of this document, American
Tentative Standard Code for Pressure Piping, occurred in 1935.
From 1942 through 1955, the Code was published as the
American Standard Code for Pressure Piping, ASA B31.1. It was
composed of separate sections for different industries.
These sections were split off, starting in 1955 with the Gas
Transmission and Distribution Piping Systems, ASA B31.8. ASA
B31.3, Petroleum Refinery Piping Code Section was first published
in 1959. A number of separate sections have been prepared,
most of which have been published.
What is Piping?
ASME B31.3 covers process piping, but what is within the
scope of piping? This is defined in the Code in the definitions part
of Chapter I.
A piping system is defined as follows.
Interconnected piping subject to the same set or sets of design
conditions.
Piping is defined as follows.
Assemblies of piping components used to convey, distribute,
mix, separate, discharge, meter, control, or snub fluid flows. Piping
also includes pipe-supporting elements, but does not include support
structures, such as building frames, bents, foundations, or any
equipment excluded from this Code (see para. 300.1.3).
Piping includes piping components, which are defined as follows.
Mechanical elements suitable for joining or assembly into
pressure-tight fluid-containing piping systems. Components
include pipe, tubing, fitting, flanges, gaskets, bolting, valves, and
devices such as expansion joints, flexible joints, pressure hoses,
traps, strainers, in-line portions of instruments, and separators.
Piping also contains pipe, which is defined as follows.
A pressure-tight cylinder used to convey a fluid or to transmit a
fluid pressure, ordinarily designated pipe in applicable material
specifications. Materials designated tube or tubing in the specifications
are treated as pipe when intended for pressure service.
These definitions should be reviewed when determining whether
something is within the scope of the Code. Some examples follow.
There is often some confusion as to whether instrumentation is
covered by the Code. However, the definition of piping components
makes it clear that in-line portions of instruments are
included in the scope and must comply with ASME B31.3 rules.
Often, they are qualified as unlisted components.
Intent
The ASME B31.3 Code provides minimum requirements for
safety. It is not a design handbook. Further, it is for design of new
piping. While the intent of ASME B31.3 may be considered for
evaluating existing piping, piping that has been in service is not
within the scope of the Code. Other codes such as API 570,
Piping Inspection Code, should be considered for use with piping
after it has been placed in service. The ASME B31.3 Code does
not address operation or maintenance of piping systems.
The scope of the Code is new piping; it does not include repair.
However, the issue of replacement is less clear. While an earlier
interpretation indicated that replacement was covered by ASME
B31.3, a recent interpretation stated that the subject of replacement
was not addressed. The wording of the Code scope had been
changed between those two interpretations, and the committee is
perhaps more rigorous now in issuing interpretations that are
clearly supported by specific requirements in the Code.