Mooring chains replacement and life extension campaigns is trending in offshore West Africa and the rest of the world is not left out. Mooring chains being a critical component of floating production, storage and offloading (FPSO) and single point mooring (SPM) calm buoy for the purpose of station keeping. However, considering the extremely harsh environmental conditions the mooring chain is subjected to, the mooring chains will definitely undergo corrosion wastages over time. Although, general/uniform and pitting corrosion has been implicated by several researchers as major cause of mooring chain degradation and deterioration among other new discoveries. For example, the activities of microbial organisms referred to as microbial induced corrosion (MIC) has been identified and implicated in most cases as the key cause of pitting corrosion on mooring chains and its mechanism is highlighted on this paper together with other mooring chains challenges and mitigation strategies which are beneficial to mooring and marine engineers. Ageing and age related challenges such as wear and corrosion wastages across the mooring chains intergrip, side and straight bars were key considerations for life extension evaluations. It was remarked that marine corrosion wastage on mooring chains do not alter their chemical and mechanical properties but only changes their geometry. Thus, the remaining thickness is a measure of the remaining strength. It was observed that most design codes for mooring chains in temperate or tropical regions like Gulf of Guinea (GoG) are based on the code for North Sea. It was also noticed that temperature, dissolved nitrogen, and current velocity effects mooring chains corrosion wastage. Thus, the higher the temperature especially in GoG the higher the rate of corrosion wastage in the splash zone. Thus, usually higher than the immersed zones. It was also observed that the scarcity of real marine environment data made most researchers to adopt data from corrosion coupon in laboratory for the purpose of studies. However, there are still limited information as regards the type of data to measure, their collation, analysis and interpretations. While class society guidance notes appeared large to manage, this paper presents in a nutshell the relevant information that will serve as a guide to mooring, marine and subsea engineers involved in asset integrity management of FPSO and SPM calm buoy mooring chains/lines to have a first-hand knowledge of the data required for mooring performance evaluation and ultimately mooring chains life extension studies. The paper also, presents some new generations issues and mitigation strategy towards mooring chains longevity.
Ebunuoha et al. (Sat,) studied this question.