DIN 50 900, Part 1 (April 1982) gives this definition: "Selective attack on gray cast iron due to an imperfect protective surface layer, causing the ferrite and perlite to dissolve. Often the original appearance of the material is retained." Graphitic corrosion occurs in feed water pumps mainly at places of high turbulence. As a rule, the damage is first noticed in serious wear of the damage is first noticed in serious wear of the mechanical seal – due to the high proportion of magnetite (= a product of corrosion in the pumped medium – or in bearing failure, which is caused by uneven corrosive destruction in the pump's sealing and throttling gap and by the resultant irregular running of the shaft. Graphitic corrosion in feed water accelerates with rising pressure and increases (up to a certain point) with rising oxygen content. This can be countered by thoroughly degassing the feed water (O₂ content less than 0.02 mg/kg) and maintaining a pH-value greater than 9. The pertinent guidelines (feed water treatment) must be observed strictly and constantly. Should this not be possible, even temporarity, a material with a higher corrosion resistance must be used.