Valve World Magazine December 2024 | Page 29

In September 2024 , the American Petroleum Institute ( API ) published the second addendum to API Specification 6D , which includes the much-anticipated Annex M covering valves for hydrogen gas service . The development of Annex M spanned over a year and a half , starting with initiation of its development by SLB in 2022 . This was a logical action in consideration of SLB ’ s extensive experience and internal testing of valves for hydrogen service and in recognition that the hydrogen economy will expose a much broader audience to the challenges hydrogen presents . With an effective date of March 5 , 2025 , Annex M could not have come at a better time . New hydrogen projects continue to be announced while companies continue working toward establishing requirements for valves in hydrogen systems that address hydrogen ’ s unique challenges , such as material degradation and sealing difficulty . This article provides an overview of the requirements in Annex M and context on how these requirements were derived .

Hydrogen Valves

API 6D Annex M — Setting the standard for hydrogen valves

This article explains the new Annex M of API Specification

6D , which establishes the first comprehensive standard for hydrogen valves , introducing four specification levels with increasingly stringent requirements to address the unique challenges of hydrogen service .

By Matthew Doherty , Senior Transition Technologies Engineer ,

SLB , and Jonathan Geleijns , Energy Transition

Technologies Manager , SLB

New specifications for hydrogen

Annex M begins with an introduction of the “ specification level for hydrogen ” ( SLH ) concept that drives the requirements for design validation as well as quality and supplemental testing requirements in production . As the SLH progresses from SLH1 through SLH4 , the requirements related to these levels in the Annex M sections increase to address the heightened criticality , or risk , of the application , as summarized in Table M . 1 in API 6D and reproduced here . The SLH level must be specified for valves conforming to Annex M .

Testing and quality controls

For SLH1 valves , the design validation requirements include extended-duration gas shell and seat testing and requirements for fire safe certification . The extended-duration pressure testing is done with nitrogen at twice the normal duration . Doubling the test duration enables using nitrogen as a test gas in place of hydrogen , which is dangerous to test with , or helium , which is becoming scarce . The extended duration is based on the theoretical difference in leak rate between hydrogen and nitrogen under laminar flow conditions . The doubled duration of high-pressure gas testing is found throughout all the design validation and supplemental testing in Annex M . For SLH2 valves , the requirements for SLH1 apply , as well as added requirements for dynamic gas pressure testing , antistatic testing , and fugitive emissions certification . The dynamic gas pressure

Figure 1 : Orbit Low-E™ certified low emissions valve undergoing fugitive emissions certification testing .

testing sequence is taken from API 6D Annex F and is followed by antistatic testing to validate that electrical continuity between components is retained after extensive cycling , thus addressing concerns related to the low ignition energy of hydrogen . SLH2 is also the first level for which fugitive emissions certification to ISO 15848-1 is required with a minimum tightness class of CH and endurance class of CO1 . SLH3 and SLH4 further increase in requirements from the previous levels by incorporating full API 6D Annex F design validation testing , again with pressure testing conducted with nitrogen and test durations doubled . As for SLH2 valves , SLH3 and SLH4 valves have an antistatic test done after Annex F testing is complete and they require fugitive emissions and fire safe certification . For SLH3 , fugitive emissions certification to ISO 15848-1 tightness class BH is required , and for SLH4 this escalates to tightness class AH , both with a CO1 endurance class at a minimum . Annex M does provide the option to apply scaling to design validation at the various SLH levels . For fire safe certification and fugitive emissions certification , scaling rules in the applicable standards are used . For the additional testing , scaling using the rules of API 6D Annex F is allowed . This provides the opportunity to qualify a few different sizes with each test valve , as well as additional pressure classes in some cases , provided there are no changes to the product as outlined in API 6D Section F . 2 . Annex M also requires revalidation of a design if there are changes to the material , design , or construction π www . valve-world . net Valve World December 2024

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