Hydrogen is stored at 400C in a long cylindrical steel vessel with an inner diameter of 0.1 m. Calculate the wall thickness of the vessel at which the hydrogen leaks from the vessel by diffusion through the wall at the rate of 0.1 cm (STP) per second per meter length of the vessel. The hydrogen pressure inside the vessel is maintained at 101.3 kPa, and the (hydrogen) pressure outside the vessel is negligibly small. At 400C, the diffusion coefficient for hydrogen in iron is 10-8 m/s, and according to Sievert's law, "CH(kg/m)=7.29x10-5p1/2 (Pa)."