TX, B31.3 and B31.12 licensing requirements

[Slabguy]

Apologies if this is the wrong forum, I didn't see one that made sense for the question. Plumbing and mechanical work in the state of TX is pretty clear on licensing requirements but I can't find any info from the state on contractor licensing requirements to perform B31.3 and B31.12 piping work. Any suggestions on where to look or experience dealing with contractor licensing for this type of work? Thanks.