The standards that rate the iron
API Spec 4F covers drilling and well servicing structures, setting design, manufacturing, and testing requirements for the derricks, masts, and substructures that carry drilling loads. API Spec 7K covers drilling and well servicing equipment, the components that do the work under those loads. Both are written because the failure of a mast or a piece of drilling equipment is not a maintenance event, it is a life event. The rating on the iron is only valid if the iron was built to the spec and has been maintained inside it, which is what an inspection program verifies.
The inspection record is the proof
Rig inspection practice centers on documented, scheduled verification: visual checks, dimensional checks, non-destructive testing where the service demands it, and review of the manufacturer's recommendations for the specific unit. The record matters because the iron does not tell you it is tired; the crack, the worn pin, and the stretched bolt are found by inspection or by failure. Rental and contractor agreements reference the standards because both sides need the same baseline: the equipment was rated, inspected, and maintained to a known envelope.
Who checks, and what they check
Operators, rental houses, and insurers increasingly ask for the inspection paper, not the assurances: the last inspection date, the inspector's findings, the repairs made, and the load history of the unit. Third-party inspection firms and qualified internal programs both work, as long as the record is real and current. A rig that cannot produce its inspection history is a liability that happens to have a mast on top. The pre-job verification, the document review, and the site walk-down are the same habit, and the gap is the same everywhere: the record stops being maintained.
Rig inspection sits next to the other equipment disciplines: critical lifts, rig move planning, and downtime cost. If inspection dates and repair history live in a file that travels with the rig, an operations audit will show which iron is verified and which is running on reputation.