The face to face expansion of the graphite packing of the pile reduces the gun barrel sum-clearance and if continued will strain the aluminum tubes with ultimate rupture of the Van Stone joints. The graphite expansion may be determined while an aluminum process tube is out of the unit. The distance from the graphite at the inner end of one gun barrel to the corresponding point at the opposite face is measured and compared to a similar measurement that was made during construction of the pile. The replacement of the two scored aluminum tubes at F Pile provided an opportunity to make these measurements. A corresponding measurements made during construction indicates an expansion of 28/32in. at Tube 2174-F and 23/32in. at 2284-F on November 5, 1946, after a total pile exposure of 132,896 MWD. Measurements of gun barrel sum-clearance and aluminum tube length before replacement indicated a graphite expansion of 25/32in. at Tube 2174-F and 24/32in. at 2284-F, which is in reasonable agreement with the above graphite measurements.