I don't believe there is a specific maximum pressure written in the code.
However, you need to be cognisant of the scope of the code in section 802.1 and diagrams in Appendix Q.
B 31.8 is clearly intended for transmission of dry single phase gas used for fuel. It is difficult to envisage a pressure higher than ASME class 2500, which is a referenced standard.
What sort of pressure are you thinking of? and for what purpose?
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