What is ASME B31.4?
Developed and maintained by ASME, ASME B 31.4 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 B 31.8 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 B 31.4 and ASME B 31.8 are pipeline design codes that cover the design, fabrication, installation, inspection, and testing of pipeline facilities. But, ASME B 31.4 deals with pipelines transporting liquids and slurries whereas ASME B 31.8 deals with gas transmission and distribution. Now the question is whether both can be used interchangeably and if not then what are the differences.
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 down the expansion stress range results for the same stress system with the same parameters analyzed in Caesar II-2018.
Results show that expansion stress ratio for the system is around double (26.5%) for code ASME B 31.8 as compared to ASME 31.4 (13.7%) which means code ASME B 31.8 is more stringent from stress analysis consideration.
In this article, we will list down a few of the major differences in a tabular format. There may be more that we have missed. Kind request to readers to list those in the comments section and We will add them to the table in due course.
|Parameter||ASME B 31.4||ASME B 31.8|
|Scope||This code governs the design requirements for pipeline systems that transports liquid or aqueous slurries of non-hazardous materials||This code governs the design requirements for pipeline facilities used for the transportation of gas|
|Exclusions||building service piping, such as water, air, or steam pressure vessels, heat exchangers, pumps, meters, and other such equipment, including internal piping and connections for piping casing, tubing, or pipe used in oil wells and wellhead assemblies||cryogenic piping systemsvent piping to operate at substantially atmospheric pressures for waste gases of any kindpiping in oil refineries or natural gasoline extraction plants|
|Minimum Temperature Range||ASME B 31.4 covers pipelines with temperature above -30 Deg C||Minimum design temperature as per ASME B 31.8 can be reduced further subject to inclusion of a proper fracture control program for that material.|
|Maximum Temperature Range||Maximum metal temperature limit for B 31.4 is 120 Deg C||ASME B 31.8 covers piping with metal temperatures upto 232°C.|
|Allowable Stress||Allwable stress is dependent only on specified minimum yield strength of pipe material||Allowable stress is dependent on specified minimum yield strength and temperature derating factor which reduces the allowable values when temperature is more than 120 Deg C.|
|Design Factor F||Maximum Value of Design Factor F in thickness calculation is 0.72. Lower values can be used as service and location may dictate.||Depending on location class, value of F varies from 0.4 to 0.8|
|Toughness Requirement||Less Stringent||More Stringent|
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