Heat lost from bare steam pipe

Heat lost from bare steam pipe or the title could be heating with bare steam pipe.
I am intending to heat an insulated box with steam. The steam pressure is 100psi gage (337 deg F steam). I have to heat the box to 300 F using bare steam piping as radiation so I only have a 37 deg. TD steam to air (once were up to temp). My heat loss will be in the neighborhood of 72,000btu/hr. I found several charts but none for steam pipes in this high an ambient.

How do I calculate the heat loss from bare steal pipe @ 337 deg surounded with 300 deg air if the surface area of the pipe is known?

Thanks for any help,
Ed