Answer
A- i) Pitting Corrosion – is defined as scattered corrosion spots/ areas with local material reductions which are
greater than the general corrosion in the surrounding area.
ii) Edge Corrosion – is defined as local material loss at the free edges of plates, stiffeners, primary support members & around openings
iii) Grooving Corrosion – is typically local material loss adjacent to weld joints along abutting stiffeners and at stiffener or plate butts or seams.
iv) Substantial Corrosion – is an extent of corrosion such that assessment of corrosion pattern indicates wastage in excess of 75% of allowable margins, but within acceptable limits. For the ships built under IACS Common Structural Rules, Substnl Corrsn is an extent of corrsn such that the assessment of the corrsn pattern indicates a measured thickness b/w Tren + 0.5 mm & Tren. Renewal thickness(Tren) is the minimum allowable thickness in mm, below which renewal of structural members shall be carried out.