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.
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.
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 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 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.|
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