In my last job, R & D at a plastics compounder, we set or product in a xylene bath. Any polyethylene that had not crosslinked(cured) would dissove in the xylene and a very careful measurement (grams to 5 decimal places) would reveal the level of cure. If these epoxy liners have a hint of bad cure, a hint of the wrong mix ratio or some other system failure then it is only a matter of time. I know very little about these systems, about the epoxy used or about the chemical make up.