Measurement and Ranking of Permeation Specimen Thickness Profiles: High-Density Polyethylene Swatches

As part of the Explosive Destruction System for the Non-Stockpile Chemical Materiel Program, the Universal Munitions Storage Container was evaluated as a candidate for over-packing munitions (leaking and non-leaking) that contain chemical warfare agents for storage until destruction. A 12 year storage period was the program goal. Permeation experiments were performed with a series of material thicknesses over a 13 month period, and thickness versus breakthrough time was extrapolated to the 1-2 year target. Accurate measurement of permeation specimen thickness is important for the extrapolation of short-term permeation breakthrough times with thinner specimens to longer storage times for the munitions containers at full thickness. To meet this objective regarding thickness accuracy, about 3000 thickness measurements on 128 swatches were completed, statistically analyzed, and ranked. The most uniform specimens were selected for use in permeation testing. An exploratory study revealed that machining with an end mill produced adequate permeation specimens. The rather wide distribution of thickness values for any given set demonstrated that it was important to rank and select the specimens with the lowest variability for use in the test matrix. Overall, it is recommended that the swatches be accepted for use in the permeation experimentation.