When visually inspecting a hydraulic cylinder, what specific type of surface corrosion is cause for immediate removal from service?

When visually inspecting a hydraulic cylinder, any surface corrosion that exhibits pitting is cause for immediate removal from service. Pitting corrosion is a localized form of corrosion that creates small holes or cavities in the metal surface. Unlike uniform surface rust, which may be superficial, pitting indicates that the corrosion has penetrated the material and weakened its structural integrity. These pits act as stress concentrators, meaning they significantly reduce the cylinder's ability to withstand pressure and can lead to catastrophic failure, especially under high loads. The depth and density of the pits are critical factors. Even relatively shallow but numerous pits can be more dangerous than a few deep pits. If pitting corrosion is observed on the cylinder rod, cylinder body, or any welded areas, the cylinder should be removed from service immediately and either repaired by a qualified technician or replaced. Repair often involves grinding out the pitted areas and re-welding, followed by machining to restore the original dimensions and surface finish. Simply painting over the pits is not an acceptable repair, as the underlying corrosion will continue to weaken the material. The presence of pitting corrosion indicates that the cylinder's protective coating (such as paint or plating) has been compromised, allowing moisture and corrosive agents to attack the underlying metal.