Hydrogen is a non-toxic, odorless gas that is highly flammable and around 14 times lighter than air. It has been used as a fuel in pipelines for more than 50 years, with hundreds of miles of pipelines laid to transport it. Despite its flammability, there have been no reports of injury due to hydrogen pipelines. This article will explore more about hydrogen piping and pipeline systems.
ASME B31.3 vs ASME B31.12
Due to the flammability of hydrogen, special care must be taken when designing mechanical joints for hydrogen piping and pipelines. Additionally, the flame of hydrogen is invisible in daylight, making it difficult to detect and extinguish hydrogen fires. As a result, two codes of practice have been developed to ensure the safe installation of hydrogen piping and pipeline systems. These codes of practice are ASME B31.3 and ASME B31.12.
Codes and Standards for Hydrogen Piping and Pipeline System
ASME B31.12: The Definitive Code and Standard for Hydrogen Piping and Pipeline System ASME B31.12 is the leading code and standard for hydrogen piping and pipeline systems. The code has four parts, beginning with the General Requirements (Part GR), which provides a broad overview of the code’s content. The code then goes on to provide information on Industrial Hydrogen Piping Systems, detailing the design criteria, pressure design requirements, and guidelines for piping components, flexibility, support, service requirements, fabrication, erection, inspection, testing, and assembly.
Hydrogen Pipeline Design and Installation Guidelines The ASME B31.12 code’s third part contains detailed guidelines for hydrogen pipelines, outlining the components required, fabrication details, design, installation, and testing requirements. This section provides valuable insights into best practices for designing and constructing a safe and reliable hydrogen pipeline system.
Mandatory and Non-Mandatory Appendices for Hydrogen Piping and Pipeline Systems The fourth and final part of the ASME B31.12 code contains a series of mandatory and non-mandatory appendices that provide further information on the code’s content. These appendices cover critical information on topics such as hydrogen stress cracking, hydrogen embrittlement, and hydrogen diffusion, as well as useful design tables and figures.
Evolution of Hydrogen Piping and Pipeline Codes and Standards ASME B31.12 is a relatively recent development in hydrogen piping and pipeline codes and standards. Prior to its introduction, ASME B31.3 and ASME B31.8 were the relevant codes for hydrogen piping and pipeline transportation systems, respectively. The first edition of the ASME B31.12 code was published in 2008, with the latest edition released in 2019. As hydrogen technology continues to advance, codes and standards like ASME B31.12 will continue to evolve to ensure the safe and efficient use of this important energy source.
ASME B31.3 vs ASME B31.12: Key Differences in Hydrogen Piping Standards
ASME B31.3 and ASME B31.12 are both piping codes but with some notable differences, particularly in the context of hydrogen piping systems. Here are some of the key differences between the two:
Pressure Design Thickness Calculation: While both codes have similar equations for pressure design thickness calculation, ASME B31.12 introduces a performance factor, Mf, to account for the loss of material ductility in hydrogen services. This can result in thicker pipes compared to ASME B31.3.
Allowable Displacement Stress Range: ASME B31.12 has a higher allowable displacement stress range, particularly for low alloy steels designed below 150ºC (300ºF), due to the risk of hydrogen embrittlement.
Branch Connection Requirements: ASME B31.12 requires full weld joint penetration for stub-on and stub-in branches and prohibits the use of certain piping joints not allowed by the code, such as caulked, soldered, bell and gland, and plastic joints.
Materials: ASME B31.12 has stricter requirements on materials used in hydrogen piping systems, particularly with regard to nickel-based alloys. Additionally, duplex stainless steel (DSS) is an unlisted material in ASME B31.12.
NDE Requirement: The non-destructive examination (NDE) requirement in ASME B31.12 is more stringent than ASME B31.3, particularly regarding radiography (RT) or ultrasonic testing (UT) after post-weld heat treatment (PWHT) for low alloy steels.
Welding Requirements: ASME B31.12 mandates an 80ºC (175ºF) preheat for carbon steel of any thickness, which is not required by ASME B31.3.
Overall, the differences in code requirements between ASME B31.3 and ASME B31.12 mainly result in increased costs for hydrogen piping systems, particularly with regard to material selection, NDE, and welding.
Materials Used for Hydrogen Piping and Pipelines Hydrogen piping systems require materials that can withstand the unique properties of hydrogen. The common materials used for hydrogen piping systems include high-purity stainless steel, composite pipes, austenitic stainless steels, and carbon steel. The selection of materials is dependent on factors such as temperature and pressure limits, potential for leaks, and fire safety acceptability. Seamless pipes and tubes are preferred for hydrogen piping systems.
Guidelines for Hydrogen Piping System Design Hydrogen piping systems require proper design to minimize the potential for leaks and easy detection. Single wall piping is used for gaseous hydrogen service, and vacuum-insulated piping is used for liquid hydrogen service. During the design process, the system isolation during maintenance, depressurization for maintenance, and purging of the system with an inert gas before maintenance should be considered. The piping system should be labeled to indicate content and flow direction. All electrical equipment and electrical grounding apparatus shall comply with NFPA 70.
Cleaning and Installation of Hydrogen Piping Systems Before being placed in hydrogen service, the hydrogen piping systems should be thoroughly cleaned with a procedure suitable for the type of contaminant and providing the required level of cleanliness. Hydrogen pipe installation must be done in accordance with ASME B31.12 and local, state, and national codes. Access to joints and fittings must be provided for leak checking, and cold surfaces, head impact, tripping hazards, etc., should be minimized.
Hydrogen Pipelines Hydrogen pipeline transport is used to transport the hydrogen from the production point to the delivery point. High Strength Line pipes and FRP pipes are preferred for transporting hydrogen through pipelines. The selection of the pipeline material is dependent on factors such as pressure, temperature, soil condition, and potential for external damage. Properly sized pressure relief devices and properly labeled shutoff valves must be provided at safe locations for pipeline safety.