This document provides guidelines and establishes recommended procedures for inspection, maintenance, and repair of items for drilling and well servicing structures, in order to maintain the serviceability of this equipment. The information in this document should be considered as supplemental to, and not as a substitute for, the manufacturer's instructions and the recommendations in API 54. Items of drilling and well servicing structures covered by this document include - masts/derricks and accessories; - substructures and accessories. NOTE 1: Crown block sheaves and bearings are covered under API 8B. NOTE 2: Offshore masts, derricks, substructures and accessories are not under the scope of this document relative to 6.2.4, Category IV inspection requirements.