Corrosion properties of high silicon iron-based alloys in nitric acid

The effect of copper and rare-earth elements on corrosion behavior of high silicon iron-based alloys in nitric acid was studied by means of static and loading current corrosion experiments.The anodic polarization curve was also made to discuss the corrosion mechanism.The examination on alloy microstructure and SEM corrosion pattern showed that when silicon content reached 14.5%,the Fe3Si phase appeared and the primary structure of the iron-base alloy was ferrite.When adding 4.57% copper in the iron alloy,its corrosion resistance in static diluted sulfuric acid was improved while its corrosion resistance and electrochemical corrosion properties in the nitric acid were decreased.In contrast,the addition of rare earth elements could improve the corrosion properties in all above conditions including in static diluted sulfuric acid and in nitric acid.

Progressive Collapse Analysis of an FPSO Vessel Hull Girder Under Vertical Bending Considering Different Corrosion Models

Nowadays,with the increasing operational life of ships,the aging effects on their structural behavior need to be investigated precisely.With the corrosive marine environment taken into consideration,one of the important effects of aging that must be studied is thickness degradation.In this paper,with the use of previously proposed equivalent thickness formulations for corroded plates,the progressive collapse analysis software HULLST is enhanced,and then,the effects of different corrosion models of uniform,random,pitting,and tanker pattern types on the ultimate and residual strengths of a floating production,storage,and offloading vessel hull girder are evaluated for the ages of 0 to 25 years.Results reveal that the uniform corrosion and random corrosion models have close outcomes.The value of relative reduction in the ultimate strength of ship hull girder(compared with the intact condition)ranges roughly from 6%for the age of 5 years to 17%for the age of 25 years in the hogging mode.The relative reduction in the ultimate strength ranges from 4%to 16%in the sagging mode.Pitting corrosion and tanker pattern(random)corrosion models lead to higher relative reductions in ultimate strength.The pitting corrosion model leads to a 16%–32%relative reduction in the ultimate strength for the ages of 5–25 years of the ship in either hogging or sagging.The tanker pattern(random)corrosion model leads to a 6%–37%relative reduction in the ultimate strength in the hogging mode and 3%–31%in the sagging mode at ship ages of 5 to 25 years.