B31.4 vs B31.8-Differences between ASME B31.4 and
ASME B31.8 (With PDF)
whatispiping.com/differences-between-asme-b31-4-and-asme-b31-8/
Anup Kumar Dey
April 23, 2020
What is ASME B31.4?
Developed and maintained by ASME, ASME B31.4 is the design code for pipelines
transporting liquids and slurries between facilities, production, and storage fields,
plants, and terminals, and within terminals and pumping, regulating, and metering
stations associated with liquid pipeline systems.
What is ASME B31.8?
ASME B31.8 is the design code for pipelines for Gas Transmission and Distribution
Piping Systems. This means this code provides design guidelines for piping
transporting products that are predominately gas between sources and terminals,
including compressor, regulating, and metering stations, and gas gathering
pipelines.
Fig. 1: A Typical Pipeline
ASME B31.4 vs ASME B31.8
So, both the codes, ASME B31.4 and ASME B31.8 are pipeline design codes that
cover the design, fabrication, installation, inspection, and testing of pipeline
facilities. But, ASME B31.4 deals with pipelines transporting liquids and slurries
whereas ASME B31.8 deals with gas transmission and distribution. Now the
question is whether both can be used interchangeably and if not then what are the
differences between ASME B31.8 and ASME B31.4?
The liquid is incompressible while gas can be easily compressed, So the behavior of both
fluids is different under pressure and temperature conditions. Hence, the ASME B31
committee devised two different codes for liquid and gas pipelines.
Refer to the following image (Fig. 2) which lists the expansion stress range results for the
same stress system with the same parameters analyzed in Caesar II-2018.
Fig. 2: Expansion Stress output for the same system based on ASME B31.8 and ASME
B31.4
Results show that the expansion stress ratio for the system is around double (26.5%) for
code ASME B31.8 as compared to ASME 31.4 (13.7%) which means code ASME B31.8
is more stringent from stress analysis consideration.
In this article, we will list some of the major differences between B31.8 and B31.4 in a
tabular format. There may be more that we have missed. Kindly request the readers to
list those in the comments section and We will add them to the table in due course.
Parameter
ASME B31.4
ASME B31.8
Scope
The code ASME B31.4 governs the
design requirements for pipeline
systems that transport liquid or aqueous
slurries of non-hazardous materials
The ASME B31.8 code governs
the design requirements for
pipeline facilities used for the
transportation of gas
Exclusions
Building services piping, such as water,
air, or steam pressure vessels, heat
exchangers, pumps, meters, and other
such equipment, including internal
piping and connections for the piping
casing, tubing, or pipe used in oil wells
and wellhead assemblies are not part of
ASME B31.4
Cryogenic piping systems, vent
piping to operate at substantially
atmospheric pressures for waste
gases of any kind, piping in oil
refineries or natural gasoline
extraction plants, etc are excluded
from the scope of ASME B31.8.
Minimum
Temperature
Range
ASME B 31.4 covers pipelines with a
temperature above -30 Deg C.
The minimum design temperature
as per ASME B31.8 can be
reduced further subject to the
inclusion of a proper fracture
control program for that material.
Maximum
Temperature
Range
The maximum metal temperature limit
for ASME B31.4 is 120 Deg C.
ASME B31.8 covers piping with
metal temperatures up to 232°C.
Allowable
Stress
As per ASME B31.4, the allowable
stress is dependent only on the
specified minimum yield strength of pipe
material.
The allowable stress in ASME
B31.8 is dependent on the
specified minimum yield strength
and temperature derating factor
which reduces the allowable
values when the temperature is
more than 120 Deg C.
Design Factor
F
The Maximum Value of Design Factor F
in thickness calculation following ASME
B31.4 is 0.72. Lower values can be
used as service and location may
dictate.
Depending on the location class,
the value of F in code ASME
B31.8 varies from 0.4 to 0.8
Toughness
Requirement
The toughness requirement criteria in
B31.4 is comparatively less Stringent.
ASME B31.8 provides more
Stringent toughness requirements.
Table-1: ASME B31.8 vs ASME B31.4
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