API 6D - Specified Level for Hydrogen (SLH)

[Bazinga]

API 6D Appendix M states the 'Specification Level for Hydrogen (SLH) for valves in hydrogen service shall be specified'. In determining the SLH, App M.2 states:

"The following can influence the determination of the desired SLH:
1) location of valve (confined space, buried, open air, rural/remote);
2) percentage H2 in gas;
3) chemical elements in gas that could impact materials;
4) design pressure;
5) cyclic pressure service."

However, it doesn't say exactly how the SLH level should be determined. I.e. - how do you weight each of those factors? There doesn't appear to be consistent methodology for determining the SLH level where two people could arrive at the same specification given the same design parameters. The SLH level has quite a large impact on the testing and verification thats required so I need to be able to justify the selection to management from a cost perspective. Has anyone else come across this issue or come across a reasonable method for determining the SLH?

 

[jmec87]

This was an intentional choice by the 6D committee. They wanted to leave it up to the end users to figure out what SLH is appropriate for their application and risks, rather than specifying it for everybody.

The end user / customer needs to figure it out using their own process (considering any applicable jurisdictional requirements/regulations) and they can consider those factors if they want (it is not mandatory to consider those factors, but it's probably a good idea in most cases).

 

[Bazinga]

A somewhat idealistic and potentially misguided approach in my view... after all, what is to stop management pressure to classify everything as SLH1 if there is no consistent approach? In idealised cases where this does not happen, any corporation with strong governance would expect to see a methodlogy for consistently classifying SLH levels throughout the organisation. So why shouldnt we have one for the industry as a whole? In Australia, the obvious comparison is pressure vessel hazard levels, where there is clear, standardised method for determining the level, and easy for any engineer to defend. Interested to hear how others have dealt with determining SLH levels on their projects or facilities?