ASME B31.12

Covers — piping and pipelines transporting gaseous hydrogen, gaseous hydrogen mixtures, and hydrogen in liquid service. The code is organized into three parts:

• Part GR — General Requirements — common requirements (materials, welding, examination, quality) referenced by all other parts.
• Part IP — Industrial Piping — hydrogen piping in plants, fueling stations, and process facilities (the B31.3-analogue).
• Part PL — Pipelines — hydrogen transmission and distribution pipelines, including distribution systems (the B31.8-analogue).

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

• Hydrogen storage vessels and containers → ASME BPVC Section VIII.
• Hydrogen generation equipment, reformers, and electrolyzers themselves (piping connecting them is in scope).
• Bulk cryogenic storage tanks and vehicle onboard fuel systems covered by other standards (e.g., CSA/SAE hydrogen vehicle codes).
• Facilities and services expressly assigned to other B31 sections where hydrogen is incidental.

Because Part IP mirrors B31.3 and Part PL mirrors B31.8, confirm which part governs your battery-limit boundary before applying design factors.

B31.12 sets minimum requirements across the full lifecycle of a hydrogen system:

• Materials — selection qualified specifically for hydrogen service, with hardness and fracture-toughness limits to resist hydrogen embrittlement; Option B invokes additional fracture-control testing (Part GR).
• Design — pressure design of pipe wall, branches, and components using either the prescriptive Option A or the performance-based Option B (which permits a material performance factor for higher-strength steels).
• Fabrication & Erection — welding procedures/welders qualified to BPVC Section IX with hydrogen-specific controls; bending and forming to limit residual stress and hardness.
• Examination, Inspection & Testing — expanded NDE of welds (Chapter IP-10 required-examination table) and pressure testing (hydrostatic preferred; pneumatic with added precautions).
• Operation & Maintenance — leak detection and integrity management appropriate to a small, flammable, embrittling gas.

The technical evaluations below determine whether a hydrogen system is safe for its design pressure and against hydrogen-specific damage.

Pressure Design

Minimum wall thickness follows the standard B31 pressure-design approach, but B31.12 applies a material performance factor that de-rates higher-strength steels unless the additional fracture-control testing of Option B is satisfied — so simply choosing a stronger pipe does not always buy thinner walls.

Hydrogen Embrittlement & Fracture Control

The defining technical concern: hydrogen ingress reduces ductility and fracture toughness. The code controls this through material selection, hardness caps, and (Option B) fracture-mechanics testing to prevent crack initiation and propagation under sustained hydrogen exposure.

Examination & Testing

Weld examination is expanded relative to B31.3, and testing preferences favor hydrostatic over pneumatic to limit stored energy in a leak-prone service.

Where to find it in the code: general/material rules → Part GR · industrial piping design → Part IP · pipelines → Part PL · required NDE → Chapter IP-10.

Engineering Note: B31.12 is not optional overlay on B31.3/B31.8 for hydrogen — it is the governing code; component standards such as ASME B16.5 and B16.9 still define the parts used within it.