Damage Analysis of Wire Rope from a 34-Month Ocean Mooring

摘要

Damage analysis of samples from a 304 stainless steel rope was conducted to determine the extent and origin of damage mechanism defects and to measure their accumulated effect upon mooring line break strength. The rope was located in the upper portion of the NOMAD buoy mooring line and had been subjected to 34 months of continuous immersion in the Gulf of Mexico. The primary objective of this initial study was to supply corrective information leading towards an extension of service life. Damage defects of mechanical and electrochemical origin were identified and located in the 1250-foot length of wire rope mooring. A study of these defects revealed a specific pattern of degradation. Dominant centers of damage were associated with a wire rope deformation-bend and with a 'protective' neoprene jacket cover. In each case the initiating damage mechanism was identified as an abnormal mechanical motion which removed the protective coatings afforded by lubricant and cathodic protection. Subsequent corrosion of the stainless steel generated an abrasive sediment in the lubricant to promote a self-supporting degradation process. The wire rope retained 88% of its initial break strength. Elimination of the causes that initiated abnormal mechanical motion would increase this retained strength to 96%. (Author)