GB/T 20801.5-2025Pressure piping code - Part 5: Hydrogen piping and pipelines (English PDF)

3.1 Piping

A system assembled from piping components, used for transporting, distributing, mixing, separating, discharging, metering, or shutting off fluid flow.

NOTE: In addition to piping components, this includes piping supports, but excludes supporting structures such as building frames, pipe racks, pipe galleries, and bases (pipe piers or foundations).

3.2 Gaseous Hydrogen Piping and Pipelines

Piping used for transporting gaseous hydrogen and hydrogen mixtures.

NOTE: The gaseous hydrogen piping and pipelines mentioned in this document include. gaseous hydrogen industrial piping, gaseous hydrogen transmission pipelines, and gaseous hydrogen utility pipelines.

3.3 Gaseous Hydrogen Industrial Piping

Piping used for transporting industrial gaseous hydrogen in various process units, hydrogen stations, hydrogen supply stations, and other facilities.

NOTE: Industrial hydrogen refers to gaseous hydrogen that meets the requirements of Table 1 in GB/T 3634.1-2006.

3.4 Gaseous Hydrogen Transmission Pipelines

Gas transmission pipelines used to transport gaseous hydrogen or hydrogen-blended gas among production sites, storage facilities, and users.

3.18 Cryogenic Hydrogen

Cold gaseous hydrogen formed by the evaporation of liquid hydrogen, with a pressure not lower than standard atmospheric pressure and a temperature of -196°C to -253°C.

3.19 Vacuum Jacket Insulated Pipe

Piping that reduces heat loss by employing a vacuum insulation layer.

NOTE: Typically, it consists of an inner pipe and an outer pipe, with a vacuum layer between them.

The insulation effect is achieved by wrapping the inner pipe with multiple layers of insulation material and creating a vacuum between the layers.

3.20 Stability Austenitic Steel

Stainless steel that does not readily form martensite after cold working and maintains a stable austenitic state.

NOTE: Based on the stability of austenite, austenitic stainless steel is divided into stability and metastability austenitic steel. The more austenitizing elements such as Ni, N, C, and Mn present in austenitic stainless steel, the more stable the austenite becomes.

4.1 General Provisions

4.1.1 The materials, design, calculations, fabrication and installation, inspection and testing of gaseous hydrogen industrial piping shall comply with the relevant provisions of this document and GB/T 20801.1-2025. In case of any inconsistency between GB/T 20801.1-2025 and this document, the provisions of this document shall prevail.

4.1.2 The materials, design, calculations, construction and installation, inspection and testing, safety protection, trial operation and commissioning, use and maintenance, and emergency repair of gaseous hydrogen transmission pipelines shall comply with the provisions of this document and GB/T 34275-2024 concerning gas transmission pipelines. In case of any inconsistency between GB/T 34275-2024 and this document, the provisions of this document shall prevail.

4.1.3 The materials, design, calculations, construction and installation, inspection and testing, safety protection, trial operation and commissioning, use and maintenance, and emergency repair of gaseous hydrogen utility pipelines shall comply with the provisions of this document and GB/T 38942-2020 concerning gas pipelines. In case of any inconsistency between GB/T 38942-2020 and this document, the provisions of this document shall prevail.

4.1.4 Unless otherwise specified, all pressures mentioned in this document refer to internal pressure (gauge pressure).

4.2 Gaseous Hydrogen Pressure Piping Classification

The gaseous hydrogen piping and pipelines conforming to the scope of the Special Equipment Catalogue shall be classified as follows.

a) The gaseous hydrogen industrial piping is classified into two levels. GC1 and GC2.

The gaseous hydrogen piping and pipelines with design pressures greater than or equal to 4.0 MPa are classified as GC1, and the rest as GC2.

b) The gaseous hydrogen transmission pipelines are classified into two levels. GA1 and GA2.The gaseous hydrogen piping and pipelines with design pressures greater than 4.0 MPa are classified as GA1, and the rest as GA2.

c) The gaseous hydrogen utility pipelines are classified as GB1. […]

5.1 General Provisions

5.1.1 The materials used in gaseous hydrogen industrial piping, gaseous hydrogen transmission pipelines, and gaseous hydrogen utility pipelines shall meet strength requirements and possess good plasticity, toughness, machinability, and economy. Material selection shall meet the relevant requirements of GB/T 20801.1-2025, GB/T 34275-2024, and GB/T 38942-2020, respectively.

5.1.2 The materials selected for gaseous hydrogen piping and pipelines shall meet the hydrogen compatibility requirements.

5.1.3 The gaseous hydrogen piping and pipelines shall use verified or mature metallic materials with good hydrogen compatibility. When using unverified or new materials, hydrogen compatibility testing shall be conducted.

5.1.4 Piping materials may be used for gaseous hydrogen piping and pipelines if the hydrogen compatibility test results meet the following requirements.

a) The slow strain rate tensile test shall comply with the relevant provisions of GB/T 34542.2, and the hydrogen embrittlement sensitivity coefficient of the base material should not exceed 40%.

NOTE: Hydrogen embrittlement sensitivity coefficient = (Reduction of area of specimen in inert gas atmosphere - Reduction of area of specimen in hydrogen atmosphere) / Reduction of area of specimen in inert gas atmosphere.

6.1 General Provisions

This clause specifies the general requirements for the fabrication and installation of gaseous hydrogen piping and pipelines, mainly including welding, preheating, and heat treatment. Other aspects related to material acceptance, fabrication, assembly and installation, and piping cleaning shall comply with the following provisions.

a) The gaseous hydrogen industrial piping shall comply with the provisions of Clause 9;

b) The gaseous hydrogen transmission pipelines shall comply with the provisions of Clause 10;

c) The gaseous hydrogen utility pipelines shall comply with the provisions of Clause 11.

6.2 Welding

6.2.1 General requirements

6.2.1.1 Welding between pressure-bearing components and between pressure-bearing components and non-pressure-bearing components in piping shall employ qualified welding procedures. Welding procedure qualification shall comply with the relevant requirements of Clauses 9 to 11.

6.2.1.2 Welding consumables (including electrodes, welding wires, fluxes, and shielding gases) shall comply with the provisions of design documents and relevant standards for welding consumables, and shall be verified through welding procedure qualification. When not specified in the design, the selection of welding consumables shall be determined comprehensively based on factors such as the chemical composition, mechanical properties, weldability, pre-weld preheating, post-weld heat treatment, service conditions, and on-site construction conditions of the base metal, and shall meet the following requirements.

a) The tensile strength of the weld metal shall not be less than the lower limit of the specified tensile strength of the base metal. For welding two base metals of different strengths, the tensile strength of the weld metal shall not be lower than the specified lower limit of the tensile strength of the base metal with the lower tensile strength.

b) The chemical composition of the weld metal shall be similar to that of the base metal.

For welding two base materials with different chemical compositions, except for welding austenitic steel and ferritic steel together, the chemical composition of the weld metal shall be consistent with or between either of the base materials.

c) When austenitic steel and ferritic steel are welded together, the weld metal shall have a significant austenitic crystal structure. 25Cr-13Ni type welding consumables or welding consumables with higher nickel content can be selected.

d) The welding process performance of the welding consumables shall be good.

e) When using untested or new welding consumables, hydrogen compatibility testing shall be conducted.

f) The welding consumables for gaseous hydrogen industrial piping, gaseous hydrogen transmission pipelines, and gaseous hydrogen utility pipelines shall also meet the requirements of Clauses 9 to 11, respectively.

6.2.1.3 The welding environment shall comply with the relevant provisions of GB/T 20801.1-2025.

6.2.1.4 The welding requirements for gaseous hydrogen industrial piping, gaseous hydrogen transmission pipelines, and gaseous hydrogen utility pipelines shall also comply with the provisions of GB/T 20801.1-2025, GB/T 34275-2024, and GB/T 38942-2020, respectively.

6.2.2 Weld placement

The placement of circumferential welds on piping (excluding jacketed pipes) shall avoid stress concentration areas, facilitate welding, heat treatment, and inspection, and comply with the following provisions.

a) Except for standard fittings, the distance between two pairs of welds on a straight pipe section shall not be less than three times the pipe thickness. When post-weld heat treatment is required, it shall not be less than six times the weldment thickness, and shall meet the following requirements.

1) For piping with a nominal diameter less than DN150, the distance shall not be less than the outer diameter and not be less than 50 mm;

2) For piping with a nominal diameter greater than or equal to DN150, the distance shall not be less than 150 mm.

b) The distance from the center of the piping circumferential weld to the bend point of the bend (excluding the elbow) shall not be less than the outer diameter of the pipe, and shall not be less than 100 mm.

c) The net distance between the piping circumferential weld and the support/hanger shall not be less than 50 mm. The distance between welds requiring heat treatment and supports/hangers shall not be less than 5 times the weld width, and shall not be less than 100 mm; pipe supports shall be installed away from welds.

d) It is not advisable to make openings in welds or along their edges. When making an opening in a weld - or reinforcing such an opening - cannot be avoided, the weld within a radius of 1.5 times the opening diameter (or the diameter of the reinforcing plate) centered on the opening must undergo nondestructive testing. This nondestructive testing shall consist of radiographic testing or ultrasonic testing; the opening may be made only after the testing results have been deemed acceptable. The weld covered by the reinforcing plate shall be ground smooth. There shall be no welding defects at the edge of the pipe opening.

e) The distance between the piping circumferential weld and the edge of an opening for a branch pipe or pipe fitting shall be no less than 50 mm, nor less than the diameter of the opening itself.

f) When fitting up welded pipes and fittings, cross welds should be avoided. When cross welds or longitudinal welds cannot be avoided, and the staggered distance is less than or equal to 100 mm, the welds in these areas shall pass radiographic or ultrasonic testing.

6.2.3 Fillet welds

The forms and sizes of fillet welds are shown in Figure 1. Fillet welds (including socket welds) can be concave or convex, and their sizes shall comply with the following provisions.

a) For equal-leg fillet welds, the weld leg size shall be the leg length of the inscribed isosceles right triangle with the maximum weld, and the weld thickness shall be 0.7 […]