The scorch was the oldest unreplaced piece of hull plating on the USS Enterprise. In 2259, it was located on the forward dorsal section on the primary hull.
Lower ranking crewmembers often tried sneaking out onto the hull to sign their names on the plating, as part of the game Enterprise bingo. It was considered good luck to do so. (SNW: "Spock Amok")
This section of hull was destroyed when the Enterprise was engaged with the Section 31 fleet at the Battle near Xahea in 2258, creating a slight continuity error. However the Enterprise likely was refitted and the "Scorch" was last piece of original hull plating not removed or recycled.