Hydrogen Valves
Figure 3 : Crack in O-ring following RGD testing in 100 % hydrogen .
the main requirements of API 6D other than the need to show suitability of sealant or lubricant used in lubricated plug valves and requirements related to body penetrations . Of note is the ability to block body penetrations to avoid the applicable leak path in hydrogen service . However , if the blocking of that body penetration prevents future venting of the body cavity , then the valve cannot be marked as a double block and bleed ( DBB ) or double isolation and bleed ( DIB-1 or DIB-2 ) valve , even if this capability normally exists .
Material design considerations
Of particular interest to many are the requirements covering both metallic and nonmetallic materials for valves in hydrogen gas service . The metallic material requirements outlined in Annex M are limited to temperatures below 175 ° C , above which the guidance of API Recommended Practice 941 is suggested . This is due to a shift in the primary damage mechanism from hydrogen embrittlement – related damage at lower temperatures to hightemperature hydrogen attack ( HTHA ) at higher temperatures . Requirements for metallic materials are split into two sections , one for permitted materials and the other for materials that are permitted with additional testing . Permitted materials are further divided into two categories , the first of which can be used essentially anywhere in the valve and includes carbon steels , low-alloy carbon steels , and austenitic stainless steels that comply with NACE MR0175 / ISO 15156 . Of these permitted materials , carbon steel has an additional restriction that the chemical composition and carbon equivalent are limited for all pressure-containing parts , primarily to avoid the risk of cracking at pressure-containing welds . The second permitted material category allows use only in pressure-controlling and drive train
components and requires compliance with NACE MR0175 / ISO 15156 . This includes solution annealed or annealed nickel-based alloys or precipitation-hardened nickel-based alloys in conformance with API Standard 6ACRA . These requirements are based on extensive evidence in the literature that although hydrogen-related damage in H 2
S- containing environments is different than in hydrogen environments , it is more severe for these materials in most cases . Annex M also allows the use of other materials or nickel-based alloys for other components , provided that additional testing is performed that satisfies both the manufacturer and the purchaser . No specific testing protocol is provided because the specifics will depend on the operating conditions of the application in question , but several test standards are listed for reference . These standards include ASME BPVC VIII Division 3 Section KD-10 for the design of high-pressure hydrogen vessels utilizing a fracture mechanics – based approach . Nonmetallic material requirements include rapid gas decompression ( RGD ) testing of elastomer materials and aging testing of both elastomer and thermoplastic materials used in valves for hydrogen gas service . In several instances , elastomers previously qualified to NORSOK M710 / ISO 23936-2 for RGD resistance have failed RGD testing in 100 % hydrogen . For this reason , elastomers used in valves for high-pressure hydrogen gas service must be RGD tested in 100 % hydrogen or 100 % carbon dioxide , which is seen as the most challenging fluid for RGD . Also , to prove the stability of nonmetallic materials in hydrogen , short-term aging testing at a specified temperature and pressure must be performed roughly in alignment with ISO 23936-1 .
Welding and documentation
Section M . 5 covers welding and includes general requirements as well as requirements for overlays , cladding , and nondestructive examination ( NDE ). The use of nickel-based alloys in pressure-containing welds is prohibited . The section also establishes that the hardness requirements for weld metal and heat-affected zones ( HAZs ) must be in compliance with NACE MR0175 / ISO 15156 . Overlays and cladding are permitted provided that , as with surface treatments such as plating and coating , the overlay cannot be used to prevent degradation of the base material due to exposure to hydrogen . For NDE , all pressurecontaining welds require both surface NDE and volumetric NDE , which is also the requirement for pup welds in the main body of API 6D . The final sections of Annex M are related to marking and documentation . The nameplate of the valve is required to identify the applicable SLH in addition to the QSL and other marking required by the main body of API 6D . The documentation section includes the requirement to retain documents on the design validation , materials conformance , and supplemental testing results as specified for the applicable SLH . With the availability of Annex M in the release of the second addendum to API 6D , end users now have an international reference standard to derive requirements for valves for use in upcoming hydrogen projects . In parallel , valve manufacturers have a framework for fully qualifying valves for hydrogen service in preparation of the demand to come . API 6D Annex M will help ensure that as hydrogen infrastructure projects continue to be proposed and evaluated — and eventually built — industry will have valves available that are capable of overcoming the unique challenges of hydrogen gas service .
About the authors Matthew Doherty is currently a senior Transition Technologies™ engineer for the SLB Valves business line . In this role , Matthew researches the technical challenges for valves in hydrogen , CCUS , and renewable fuels service to enable the selection and development of the ideal valve configurations for these trending and challenging applications . Prior to this role , he spent more than 10 years in various shop , field , and office-based engineering roles supporting the repair and remanufacture of valves . Matthew is a licensed professional engineer in the state of Texas and holds bachelor ’ s degrees in mathematics and mechanical engineering from the University of Houston and a master ’ s in engineering from the University of Arkansas .
Jonathan Geleijns has more than 30 years of valve experience , gained in engineering , sales , aftermarket and field services , and technical support in multiple geographical locations . His current position is Energy Transition Technologies™ manager for the Valves business line at SLB . In this role , he focuses on developing markets for hydrogen , CCUS , biofuels , geothermal , emissions control , and other associated applications by investigating and influencing market trends , market needs , product gaps , and industry standards and regulations . Jonathan is also cochair of the API Specification 6D Annex M Valves in Hydrogen Service Task Group and is involved with other committees , such as for Hydrogen Europe and ASME B31.12 .
Note : Orbit Low-E and Transition Technologies are marks of SLB .
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