hydrogen diffused from inner pipe 12 into space 20 fills the free space the void space in the insulation 16 and the free space between the outer surface of insulation 16 and the inner surface of outer pipe 18 the settle out pressure in the space 20 can be limited in the design process by choosing the hydrogen content of the steel of the inner pipe 12 and to a lesser extent outer pipe 18 the wall thickness of the inner pipe 12 the dimensions of space 20 the thickness of insulation 16 and estimating the average temperature in space 20 in one example of system 10 inner pipe 12 has a nominal diameter of 6 inches schedule 40 and is formed from steel with a hydrogen content of about 1 part per million by weight outer pipe 18 has a nominal diameter of 10 inches schedule 10 and 4 layers of spaceloft u2122 ar5103 aerogel blanket are wrapped around inner pipe 12 making insulation 16 one inch thick a calculation of the rate of pressure rise in space 20 over the operating life of this example shows the time taken to asymptotically approach the settle out pressure is about 10 years while half this pressure is reached in one year provided that no leaks are developed into space 20 the settle out pressure should not be exceeded over the extended operating life of system 10 the design parameters of system 10 can thus be manipulated to result in a low settle out pressure under which conditions aerogel insulation 16 develops and maintains its high resistance to heat loss to the surroundings from the warm flowing fluid 14 for the purposes of this application we define u201c low settle out pressure u201d as preferably less than.