Hydrogen energy is a clean, efficient, and sustainable zero-carbon energy source, playing a crucial role in the global transition to carbon neutrality. As hydrogen technology progresses, large-scale centralized hydrogen production and long-distance transport are emerging as key trends. Cost-effective and efficient pipeline transport is essential for the widespread commercialization of hydrogen energy, and several countries have already implemented operational hydrogen pipelines. Steel pipes are essential components of hydrogen pipelines, with their quality and performance directly impacting the operational safety of the system.
ISO/TC 197 (Technical Committee on Hydrogen Energy) develops international standards for hydrogen production, storage, transport, testing, and applications. Since June 2008, China has established the National Hydrogen Energy Standardization Technical Committee (SAC/TC 309), tasked with formulating and revising national hydrogen energy standards in alignment with ISO/TC 197. The committee is managed by the China National Institute of Standardization.
European and American countries have been at the forefront of research and development in hydrogen pipeline infrastructure development. Through extensive research and engineering experience over the years, they have established a comprehensive standard system for hydrogen pipelines. Key standards include ASME B31.12 Hydrogen Pipelines, published by the American Society of Mechanical Engineers, and CGA G-5.6-2005 (R2013) Hydrogen Pipeline Systems, published by the Compressed Gas Association. These standards govern the design, construction, operation, and maintenance of hydrogen pipelines.
This standard, published by the American Society of Mechanical Engineers, applies to long-distance, distribution, and service pipelines transporting hydrogen from production facilities to end users. It consists of three main sections:
General Requirements (GR Section): Defines the specifications for materials, forming, welding, heat treatment, testing, inspection, operation, and maintenance of pipelines and components.
Process Pipelines (IP Section): Covers hydrogen production and its use in refineries, chemical plants, power plants, hydrogen refueling stations, and fuel cells. This section specifies requirements for materials, components, design, manufacturing, assembly, installation, inspection, testing, operation, and maintenance.
Transmission and Distribution Pipelines (PL Section): Addresses pipelines transporting hydrogen from production facilities to final usage points, detailing requirements for materials, components, design, manufacturing, inspection, testing, operation, and maintenance.
Additionally, the appendix outlines design requirements for hydrogen facilities, including compressors, explosion protection, leak detection, and construction. It also references standards, definitions, safety measures, gas leakage criteria, allowable stress levels, and quality coefficients for designing metal pipelines.
ASME B31.12 specifies the requirements for the chemical composition, microstructure, mechanical properties, and weldability of steel pipes used in hydrogen pipelines. Carbon steel has been commonly used in hydrogen pipeline transportation for decades, with over 1,600 km of pipelines operated by industrial gas companies in the United States and Europe. Approved steel grades include ASTM A106 B, ASTM A53 B, and API SPEC 5L X42 and X52 (PSL2), with preference given to the latter two. These grades impose stricter limits on carbon (C) and sulfur (S) content, refine the grain structure, and reduce inclusions and segregation to improve overall performance.
To enhance weldability and minimize hydrogen embrittlement, the carbon equivalent limits are tightened, and weld seam hardness must not exceed 248 HV. The recommended strength grade is X52 (360 MPa) or lower, with acceptable pipe types including electric resistance welded, seamless, or double-sided submerged arc welded pipes.
Two fracture control methods, Method A and Method B, are defined, with corresponding tests and requirements provided in Tables 1 and 2. Method A specifies toughness requirements sufficient to control brittle fracture, which are slightly less stringent than the API SPEC 5L standards. Pipes that meet the API SPEC 5L standards generally satisfy the Method A requirements. Method B introduces stricter criteria, including resistance to hydrogen, for use in hydrogen environments.
To achieve superior fracture toughness in hydrogen environments, ASME B31.12 recommends a microstructure consisting of uniformly distributed polygonal and acicular ferrite with a grain size of ASTM grade 9 or finer. Low-carbon microalloy steel is required, with a Pcm below 0.17%, produced using the thermomechanical controlled rolling (TMCP) process.
Table 1 Specification-based design method (method A)
Properties |
Requirements |
Brittle Fracture
|
If the pipe diameter exceeds 114.3 mm, refer to Appendix G of API SPEC 5L for the impact and drop hammer tests. The average shear value of the Charpy impact specimen should be ≥80% (≥85% for smaller specimens), and the average fracture shear area of the drop hammer test should be ≥40%. No testing is required for pipe diameters less than 114.3 mm. The test temperature is either 0°C or the expected minimum metal temperature. |
Crack Arrest Toughness |
If the pipe diameter exceeds 114.3 mm, refer to Appendix G of API SPEC 5L for the impact and drop hammer tests. No testing is required for pipe diameters smaller than 114.3 mm. The test temperature is either 0°C or the expected minimum metal temperature. |
Strength |
The tensile strength of the pipe body and weld metal should not exceed 690 MPa, and the yield strength should not exceed 485 MPa. |
Impact Toughness |
For the Charpy impact energy of the weld seam and heat-affected zone: If the outer diameter is ≤ 1422 mm, the energy for full-size specimens should be ≥27 J, or for small-size specimens, ≥338 kJ/m². If the outer diameter is >1422 mm, the energy for full-size specimens should be ≥40.6 J, or for small-size specimens, ≥508 kJ/m². |
Table 2 Design method based on material hydrogen resistance (method B)
Properties |
Requirements |
Toughness |
The requirements for brittle fracture control, crack arrest toughness, weld seam, heat-affected zone strength, and impact toughness are aligned with Option A. |
Fracture Resistance |
The critical stress intensity factor, K, should be ≥KA and not less than 55 MPa·m¹/². |
Steel Pipes and Welding Materials |
The applicable rules in Section KD-10 of Part 3, Volume VI of the ASME BPVC Code must be followed. |
Composition and Inclusions |
The phosphorus content (w(P)) must not exceed 0.015%. Attention should be given to controlling the shape of inclusions. |
Strength |
The maximum tensile strength of the pipe body and weld metal should not exceed 758 MPa, and the minimum yield strength of the steel pipe should not be less than 552 MPa. |
This standard, developed jointly by the Compressed Gas Association (CGA) and the European Industrial Gases Association (EIGA), governs the transportation and distribution of pure hydrogen and hydrogen mixtures in gaseous form. It applies to temperature ranges from -40°C to 175°C and pressures from 1 MPa to 21 MPa.
CGA G-5.6 specifies that steel pipes for hydrogen pipelines must meet API SPEC 5L standards and be either HFW welded, seamless, or submerged arc welded. The hardness of the pipe, including the body, weld seam, and heat-affected zone, must not exceed 22 HRC. To prevent hydrogen embrittlement, the following material conditions must be met:
If these requirements are not met, the operating pressure should be reduced to below 30% of the minimum yield strength or 20% of the ultimate tensile strength. Additionally, steel pipe surfaces must be free of scratches, corrosion, or defects. During hydrostatic testing, pipes should be subjected to pressures ranging from 75% to 100% of the minimum yield strength, held for 5 to 10 seconds, depending on the pipe diameter.
Materials such as carbon steel, stainless steel, and nickel alloys are susceptible to hydrogen embrittlement, with carbon steel being the most commonly used material for hydrogen pipelines. CGA G-5.6 highlights that welded joints, which are typically harder than base materials, are particularly vulnerable to embrittlement, with the risk increasing as tensile and yield strengths rise. Therefore, pipeline design should specify both minimum and maximum yield strengths to mitigate embrittlement. Commonly used materials include API SPEC 5L X52 (and lower grades) and ASTM A106 Grade B.
Table 3 Material Property Requirements for Carbon Steel
Properties |
Requirements |
Heat Treatment |
Weld seams should undergo partial normalizing heat treatment. For pipelines subjected to high stress levels, carbon steel should be normalized. |
Chemical Analysis |
1. The carbon equivalent (CE) should not exceed 0.43%. All additional elements, including calcium and rare earth elements for sulfide shape control, aluminum for deoxidation, and any elements used for CE calculation, must be reported. |
Toughness |
Comply with references 2.1 and 16.3.1 in Appendix K. |
Microalloy steel pipes are widely used in hydrogen pipelines, particularly since the early 1990s, when X52-grade microalloy pipes became the standard for pipelines operating at pressures exceeding 7 MPa. These pipes include high-frequency welded (HFW), seamless, and submerged arc-welded pipes, with HFW being the primary manufacturing process for microalloy steel pipes. This section outlines the specific requirements for welded pipes.
Flattening test acceptance criteria for HFW welded pipes are stricter than those of API SPEC 5L standards, requiring reduction to half the pipe’s original outer diameter (D). Charpy impact energy requirements (Table 4) must be met at 0°C, with full-size specimens tested. The shear area of these specimens should be at least 75% of the Charpy V-notch impact energy values specified in Table 4. No single test value should fall below 60%. For small-diameter pipes, only longitudinal specimens are required.
Table 4 Requirements for Charpy V-notch impact energy specimens of different sizes
Specimen Size |
Transverse Impact Energy (J) |
Longitudinal Impact Energy (J) |
||
Single Value |
Mean Value |
Single Value |
Mean Value |
|
Full Size |
94 |
71 |
118 |
88 |
3/4 |
71 |
53 |
88 |
67 |
2/3 |
48 |
48 |
78 |
58 |
1/2 |
34 |
35 |
58 |
43 |
1/3 |
23 |
23 |
39 |
30 |
1/4 |
18 |
18 |
30 |
22 |