13) What is the formation deposited on pipes due to hardness of water?

14) What is the defect of slow and continuous degradation of metallic surface by chemical reaction?

15) What is the wear of metal pipe surface caused by impact of particles suspended in liquid?

16) What is the localised formation as cavities or pores on stainless steel due to salty water condition?

17) What is the defect on metal plate with discontinuity or flat and thin subsurface separation on its thickness?