I. Classification and Grading of Piping (Core Definitions in TSG)

Pressure piping is divided into 4 major categories by application. Category GC is further graded to match regulatory intensity. Category GA: Long-Distance PipingDefinition: Oil or gas pipelines crossing provincial or municipal boundaries.Standard: GB/T 34275-2024 Code for Pressure Piping — Long-Distance Piping. Category GB: Public Utility PipingSubcategories:

• GB1: Urban gas piping
• GB2: urban heating pipingStandard: GB/T 38942-2020 Code for Pressure Piping — Public Utility Piping.

Category GC: Industrial Piping (Core Grading)Grading basis: medium hazard, design pressure (P), design temperature (T).Grading determines regulatory and inspection requirements.

• GC1: Piping for highly toxic or extremely hazardous substances; P ≥ 10.0 MPa; P ≥ 4.0 MPa and T ≥ 400℃; Class A/B flammable gases or liquefied hydrocarbons per fire hazard classification.
• GC2: Industrial piping other than GC1/GC3, e.g., flammable medium piping with P ≥ 1.6 MPa.
• GC3: Low-hazard liquid or small-bore low-hazard gas piping with P ≤ 1.0 MPa and T ≤ 185℃ (technical grading only, not subject to mandatory regulation).

Category GD: Power PipingDefinition: Main steam, reheat steam and similar piping in thermal power plants.Standard: Supporting specifications to GB/T 16270 Steels for Boilers.

II. Detailed Core National Standards

Industrial Piping: GB/T 20801.1-2025(replaces 2020 edition, effective 2026-05-01)Applicable scope:Maximum working pressure ≥ 0.1 MPa (gauge), medium being gas, liquefied gas, steam, flammable, explosive, toxic, corrosive or high-temperature liquid, nominal diameter ≥ 50 mm.Excludes small-bore low-risk gas piping. Core contents:material selection (allowable stress, compatibility), design calculation (wall thickness, stress analysis), fabrication and installation (welding, heat treatment), inspection and testing (NDT, pressure / tightness test), safety protection (static electricity, corrosion prevention). Public Utility Piping: GB/T 38942-2020Applicable to:Urban gas piping (mainly PE pipes, pressure 0.4–0.8 MPa) and heating piping (steel insulated pipes for hot water / steam above 130℃). Key requirements:Leak detection for gas piping every 3 years; comprehensive inspection for heating piping every 2 years; safe clearance from buildings and structures. Long-Distance Piping: GB/T 34275-2024Applicable to:Trunk oil and gas pipelines, covering full life cycle: design, construction, inspection, commissioning, trial operation, maintenance and emergency repair.

III. Core Technical Boundaries and Exemptions

Regulatory Boundary (TSG D0001)Industrial piping subject to regulation must meet all of the following:

• Maximum working pressure ≥ 0.1 MPa
• Medium is gas, liquefied gas, steam, flammable, explosive, toxic, corrosive or high-temperature liquid
• Nominal diameter ≥ 50 mm

Exempted Cases

• Piping with nominal diameter ＜ 150 mm and maximum working pressure ＜ 1.6 MPa, conveying non-toxic, non-flammable, non-corrosive gases (excluding liquefied gas, steam, oxygen).
• Piping integral to equipment (e.g., vessel nozzles).
• Category GC3 low-risk piping (technical grading only, no administrative licensing required).

IV. Key Compliance Points

Grading FirstDetermine GC1/GC2/GC3 based on medium hazard, P and T, then match corresponding design, welding and inspection standards. Priority of Standard SelectionTSG codes (mandatory) → GB/T 20801/38942/34275 (basic) → industry standards (e.g., SY/T, SH/T, detailed specifications). Critical Inspection and Testing Items

• Pressure test: hydrostatic (1.5 × design pressure) or pneumatic (1.15 × design pressure), held until acceptance.
• Pneumatic tightness test: held at design pressure with qualified leakage rate.
• Non-destructive testing: 100% RT/UT for critical welds in GC1 piping; random sampling for GC2 piping.

V. Common International Equivalent References

ASME B31 Series (USA)

• B31.1: Power piping
• B31.3: Process piping
• B31.4: Liquid petroleum transportation piping
• B31.8: Gas transmission and distribution piping

EN 13480 (EU)Design and installation of industrial metallic piping.

Summary

Domestic pressure piping codes take TSG safety supervision as the baseline and GB/T series standards as the technical core. Piping is classified into GA/GB/GC/GD, with Category GC under graded regulation, covering the full life cycle.In practice, grading shall be performed first, followed by standard selection and strict inspection and testing to ensure compliance and safety.