Rig 47 sits forty-three nautical miles southeast of Ras Tanura, its triple-cone derrick rising two hundred and ten feet above the Arabian Gulf. The structure was erected in 1983 by a crew of sixty-three welders working twelve-hour shifts through the monsoon season. Every inch of its A-36 structural steel has spent four decades absorbing salt spray, hydrogen sulfide, and the relentless thermal cycling of Gulf summers that push surface temperatures past sixty degrees Celsius. When I first climbed its ladder in the winter of 2007, the steel felt cold and certain under my gloves. I was twenty-two years old and believed, with the unearned confidence of a newly certified mechanical engineer, that I understood corrosion.
I did not. Corrosion on a derrick is not a single failure mode but a library of them, each one written in a dialect of rust. Pitting corrosion bores millimeter-wide craters into an I-beam where a paint blister went unnoticed. Crevice corrosion colonizes the hidden gap between a bolted gusset plate and the column flange, spreading where no coating crew can see it.