ASME B31.4

Covers — pipeline systems transporting aqueous slurries and liquids such as crude oil, condensate, natural gasoline, natural gas liquids, liquefied petroleum gas, carbon dioxide, liquid alcohol, liquid anhydrous ammonia, and liquid petroleum products. The scope includes:

• Piping between facilities, pump stations, terminals, and tank farms.
• Offshore pipeline systems.
• Storage and working tanks, pipe-type storage facilities, and all associated piping.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Gas transmission and distribution systems → ASME B31.8.
• Cross-country pipelines transporting gases and refrigerants → ASME B31.8 or ASME B31.5.
• Plant process piping (refineries, chemical plants) → ASME B31.3.
• Boiler external piping → ASME B31.1.
• Water and sewage systems covered by AWWA or other standards.
• Piping designed for internal pressure less than 15 psi (105 kPa).

The boundary between B31.4 (transportation) and B31.3 (plant piping) is usually set at the first or last valve within the plant boundary (battery limit).

B31.4 sets minimum requirements across the full lifecycle of a liquid pipeline system:

• Materials — allows use of API 5L line pipe and various ASTM materials; requires specific material toughness for certain applications to prevent brittle fracture.
• Design — dictates pipeline pressure design considering internal pressure, external pressure, and other loadings (thermal, seismic, wave/current for offshore); defines design factors based on location or fluid.
• Fabrication & Erection — requirements for welding (usually qualified to API 1104 or ASME BPVC Section IX), bending, and handling.
• Examination, Inspection & Testing — visual and NDE requirements for welds; hydrostatic testing of constructed pipelines before operation.
• Operation & Maintenance — mandates corrosion control (cathodic protection, coating), pipeline integrity management, and procedures for operation, maintenance, and emergency response.

The technical evaluations below determine whether a pipeline is safe for its design pressure and temperature.

Pressure Design

Calculation of minimum wall thickness uses Barlow's formula modified by a design factor (F), longitudinal joint factor (E), and temperature derating factor (T). Unlike plant piping codes, B31.4 relies heavily on the specified minimum yield strength (SMYS) rather than allowable stress tables.

Stress Analysis

• Sustained & Thermal loads — pipeline stress analysis evaluates restrained and unrestrained pipelines differently. Restrained pipelines (e.g., buried) must manage axial compressive stresses and soil interactions.
• Offshore considerations — Chapter IX adds requirements for wave, current, and installation loads (e.g., laying tensions).

Corrosion Control

Stringent requirements for internal and external corrosion mitigation, including coatings and cathodic protection systems.

Where to find it in the code: design equations → Chapter II · allowable stresses (SMYS) → Table 403.3.1-1 · offshore → Chapter IX.