Pickling or pre-odorization is a process used to prep new gas pipe before commissioning for use. In new gas lines, it is very common to experience odor fade or have the natural gas odorant scrubbed or removed from the gas stream, therefore making it odorless, a significant safety hazard.
In a new pipe, odorant molecules attach to the pipe wall. Therefore, the odorant no longer remains in the gas stream, and it becomes odorless. The pipeline continues to adsorb the odorant until the line becomes saturated, then the odorant begins to stay in the gas. It is unclear, however, how long this process can take which is why it is common to “pickle” the line to speed up the progression.