270 barg... This appears to be serious.
RO is the cheapest solution when it can be used.
I am not an expert and I never did or saw something like that.
Why don't you reduce the pressure in stages using pressure regulators?
Are you taking into account that at 270 barg NG is liquid and at 1 bar NG is gas?
I don't know what you want to do exactly, but if you want to vent the vessel, be careful with the temperature (anti-freeze systems), the noise and the ATEX zone that you are going to generate.