Predictive Model for Corrosion Rate of Oil Tubes in CO_2/H_2S Coexistent Environment Part Ⅰ: Building of Model

Introduction　　Sincethecorrosionofoiltubesinbrinesolutionscontainingcarbondioxide (CO2 )andhydrogensulfide(H2 S)gasesisasevereprobleminengineering ,itisveryurgenttobuildapredictivemodelofthecorrosionrate(rcorr)foroiltubesinCO2 /H2 Scoexistentenvironment …     

基于IMO标准的船用耐蚀钢应用技术研究综述

2010年5月国际海事组织(IMO)通过的《原油船货油舱保护涂层性能标准》和《原油船货油舱替代防腐措施性能标准》于2014年1月1日强制执行,鉴于日本在这方面有一定的技术优势,其正在中国设置专利障碍,船用耐蚀钢的国产化成为极为紧迫的一项任务。船用耐蚀钢的研发不仅关系我国船舶行业的发展问题,而且对我国船舶行业提升产业水平和国际竞争力有很大的影响。国产船用耐蚀钢的研制将有效打破国外耐蚀钢技术对我国钢铁、船舶行业造成的技术壁垒。本文基于IMO相关标准,以油船货油舱为研究对象,就国内外船用耐蚀钢耐蚀性、焊接性能等研究方面进行归类总结。探索船用耐蚀钢的应用技术的推广发展与前景。     

Remaining fatigue life assessment of corroded mooring chains using crack growth modelling

Failures caused by the combined actions of fatigue, corrosion and wear are important safety concerns for mooring chains used on floating structures in the oil and gas industry. Prediction of remaining corrosion fatigue life based on surface condition could therefore be a useful tool for the continued safe operation of corroded chains. This paper investigates the use of crack growth modelling for estimating the remaining corrosion fatigue life of mooring chains that exhibit significant pitting corrosion damage. A crack growth modelling approach is used to produce remaining fatigue life estimates for a selection of severely pitted mooring chains. Using fatigue crack growth rate test results for grade R4 high strength mooring chain steel, empirical crack growth laws are presented for free corrosion and cathodic protection conditions at load ratio R = 0.1. Two different methods for establishing equivalent cracks from surface scans of corrosion damage are presented. The mooring chains are proof loaded as part of their manufacturing process. Residual stresses introduced during this process have therefore been determined by finite element analysis and accounted for in the fatigue crack growth predictions. One of the equivalent crack models, accounting for the single dominant corrosion pit, provided quite accurate fatigue life predictions when compared with full scale test results.     

Analysis of S–N data for new and corroded mooring chains at varying mean load levels using a hierarchical linear model

Results from full scale fatigue tests of offshore mooring chains are analyzed. The data set includes new and used chains, tested at a variety of mean load levels. The used chains have been retrieved after operation offshore and include samples with varying surface conditions, ranging from as-new to heavily corroded. Based on a parameterized S–N curve intercept parameter, the effects of mean load and chain condition are estimated empirically by regression analysis. A hierarchical linear model is used, to account for and quantify correlations within subsets of the data. The choice of grouping criterion for the hierarchical model is discussed, and assessed based on the current data. Results show that the mean load and corrosion effects are both significant. Differences in the fatigue performance of new versus used chains are quantified and discussed.