Perhaps 160k does not impress.But,that was 120 years ago. Even now it has not gone to 300k for bridge work. The boiler does not have to be dry.Even the most itty bitty bubble that occurs and does not take the heat away will allow ultra heat with the resulting damage to the tube.The big ones run at 1000F+ and up to 3500psi for the steam. BTY,since drawn wire was so strong,that is why there was serious consideration to wire bound big guns.