Ark. Code Ann. § 26-53-139

There is specifically exempted from any tax imposed by this subchapter including, but not limited to, §§ 26-53-106 — 26-53-108, parts and other tangible personal property incorporated into or which ultimately become a part of railroad parts, railroad cars, and equipment brought into the State of Arkansas solely and exclusively for the purpose of being repaired, refurbished, modified, or converted within this state.