Pipe wall thickness as per B31.3, B31.4, and B31.8

Differences in Pipe Wall Thickness Calculations for ASME B31.3, B31.4 and B31.8. ASME B31.3, ASME B31.4 and ASME B31.8 are different standards published by the American Society of Mechanical Engineers (ASME) that pertain to various aspects of piping systems. Let’s explore the key differences between these three standards:

ASME B31.3

ASME B31.3 is the Code for Process Piping. It specifically addresses requirements for designing, constructing, and inspecting piping systems used in chemical, petroleum, pharmaceutical, and other related industries where fluids
or gases are processed at high temperatures and pressures. This standard covers a wide range of materials and applications, including both metallic and non-metallic piping systems.

Key points of ASME B31.3

  • Applicable to process piping systems.
  • Includes a wide range of applications and industries.
  • Addresses high-temperature and high-pressure services.
  • Includesguidelines for design, materials, fabrication, installation, and testing.
  • Focuses on the safety and integrity of the piping system during its entire lifecycle.
  • Requirements for examination, inspection, and quality control are detailed.

ASME B31.4

ASME B31.4 is the Code for Pipeline Transportation Systems for Liquids and Slurries. This standard specifically deals with transportation pipelines that carry liquids and slurries, such as crude oil, natural gas liquids, and water. It is mainly applied in the oil and gas industry, especially for pipelines that operate at relatively moderate temperatures and pressures.

Key points of ASME B31.4

  • Applicable to liquid and slurry transportation pipelines.
  • Primarily used in the oil and gas industry.
  • Focuses on pipelines operating at moderate temperatures and pressures.
  • Covers design, construction, inspection, and maintenance of liquid and slurry pipelines.
  •  Emphasizes safety and reliability in the transportation of hazardous liquids.

ASME B31.8

ASME B31.8 is the Code for Gas Transmission and Distribution Piping Systems. This standard specifically addresses the design, construction, operation, and maintenance of pipelines that transport natural gas, from the point of production or import to distribution and ultimately to the consumers.

Key points of ASME B31.8

  • Applicable to natural gas transmission and distribution pipelines.
  • Focuses on the transportation of natural gas.
  • Covers a wide range of pipeline sizes and pressures.
  • Includes requirements for design, materials, construction, inspection, and integrity management.
  • Prioritizes safety and environmental protection.

Differences in Pipe Wall Thickness Calculations for ASME B31.3, B31.4 and B31.8

Parameter ASME B31.3 ASME B31.4 ASME B31.8
Hoop Stress Basic formula is a variation of Basic formula is a variation Basic formula is a variation of Barlow’s Hoop
Barlow’s Hoop Stress Formula of Barlow’s Hoop Stress Stress Formula
Weld Joint Factor included Yes Yes Yes
Quality Factor Defined based on type of pipe No such separate factor The Weld Joint Factor in ASME B31.8 is based
fabrication such as Seamless, defined. However, the on the pipe ASTM designation and the pipe
Electric Resistance Welded (ERW), understanding is that in fabrication method i.e., seamless, ERW, EFW,
Electric Fusion Welded (EFW) and majority applications for FBW, Submerged Arc Welding (SMAW). No
Furnace Butt Welded (FBW) pipeline transportation of separate quality factor is defined like ASME
Generally following values used: liquids and slurries, B31.3
Seamless: 1 seamless pipe is adopted
ERW: 0.85 where the value is 1 for the
EFW 100% Radiographed: 1 quality of the pipe based on
EFW Double Butt seam: 0.85 fabrication method.
EFW Single Butt seam: 0.8
FBW: 0.6
EFW spot radiography: 0.9
Coefficient for effective Incorporated in the wall thickness No such factor defined. No such factor defined.
stressed diameter, Y (for (WT) formula. Value depends on
t < D/6) where D is OD of the type of steel and the
pipe and t is wall temperature the pipe is subjected
thickness to. For temperatures ≤4820C the
following values are used:
Ferritic Steels (including CS): 0.4
Austenitic Steels: 0.4
Nickel Alloys: 0.4
Gray Iron (Cast Iron): 0
Basic Allowable+30:45 Stress, S Directly values given in tabular form Basic allowable stress The SMYS is directly used in the formula for
for wall thickness for various steel types and the calculated based on a WT calculation without any design factor as in
calculations corresponding ASTM designations maximum design factor (DF) ASME B31.4
of 0.72 multiplied by the
Specified Minimum Yield
Strength (SMYS) dependent
on the ASTM designation
and fabrication method.
Temp. limits are -30 to
Design Factor based on Not Applicable Not applicable. The DF of A DF based on the location of the gas pipeline
Location 0.72 as above to be used for / piping is used in the WT calculations as
all WT calculations follows:
Location Class 1, Division 1: 0.8; Location
Class 1, Division 2: 0.72; Location Class 2: 0.6
Location Class 3: 0.5; Location Class 4: 0.4


In summary, ASME B31.3, ASME B31.4, and ASME B31.8 are different ASME standards that apply to specific types of piping systems. ASME B31.3 is for process piping in various industries, ASME B31.4 is for liquid and slurry transportation pipelines, and ASME B31.8 is for natural gas transmission and distribution pipelines. Each standard caters to different applications, materials, and operational conditions, ensuring the safe and reliable functioning of the specific type of piping system it covers.


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