ASME B31.1

Covers — piping typically found in electric power generating stations, industrial and institutional plants, geothermal heating systems, and central/district heating and cooling systems. The scope is divided into:

• Boiler External Piping (BEP) — piping from the boiler up to and including the applicable stop-valve boundary defined by BPVC Section I. Also covers BEP for power boilers and high-temperature water boilers where steam/vapor is generated above 15 psig [100 kPa], or high-temperature water above 160 psig [1,103 kPa] and/or above 250 °F [120 °C].
• Nonboiler External Piping (NBEP) — piping within the power cycle but outside the BEP boundary.
• Covered fluids — steam, water, oil, gas, and air.

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

• The boiler and pressure vessels themselves → ASME BPVC (Sections I / VIII).
• Process piping in chemical/refinery service → ASME B31.3.
• Liquid pipelines → B31.4; gas transmission/distribution → B31.8; refrigeration piping → B31.5; building-services piping → B31.9.
• Plumbing, sprinkler/fire-protection, and general building-service systems covered by other codes.

The boundary between B31.1 and its sibling B31 codes is the single most common source of code mis-application — always confirm which code has jurisdiction before design.

B31.1 sets minimum requirements across the full lifecycle of a piping system:

• Materials — selection of materials qualified for high pressure/temperature service (allowable stresses drawn from BPVC Section II).
• Design — pressure design of pipe wall thickness, branch connections, flanges, and other components.
• Fabrication & Erection — cutting, bending, forming, welding (procedures/welders qualified to BPVC Section IX), and installation.
• Examination, Inspection & Testing — nondestructive examination (NDE) of welds per BPVC Section V methods, and pressure testing (hydrostatic or pneumatic) before commissioning.
• Operation & Maintenance — requirements for in-service piping, including Covered Piping Systems (CPS) provisions.

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

Pressure Design

Calculation of the minimum required wall thickness to contain internal pressure, including corrosion/erosion allowance and mill (manufacturing) tolerance.

Stress Analysis

• Sustained loads — pressure plus the weight of pipe, fluid, insulation, and components.
• Thermal (displacement) loads — stresses from thermal expansion/contraction over the operating range.
• Occasional loads — wind, seismic, and dynamic events such as relief-valve discharge or water/steam hammer.

Flexibility & Supports

Stress intensification factors (SIF) and flexibility factors assess fittings and layout flexibility; supports and hangers are spaced to limit deflection and control stresses at connections and equipment nozzles.

Where to find it in the code: allowable stress tables → Mandatory Appendix A · SIF / flexibility factors → Appendix D.

Engineering Note: B31.1 governs the overall system; component standards such as ASME B16.5 (flanges), ASME B16.9 (fittings), and MSS SP-58 (supports) define the parts used within it.