The mathematical relationship for the pitting equivalent value (PRE), also known as the pitting index:
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The mathematical formula for the pitting equivalence value (PRE), also known as the pitting index, is: PRE(PREN) = %Cr + 3.3×%Mo + X×%N (where X = 10–30, and typically X = 16). When only the effects of Cr, Mo, and N are considered, it can be expressed as PREN. When considering the effect of W, it is expressed as PREW ； When considering the effect of Mn, it is expressed as PRE Mn ； When considering the effect of S P, it is denoted as PRE(S+P). PREW=%Cr+3.3x(%Mo+0.5%w)+16x%N PRE Mn=%Cr+3.3x%Mo+30x%N-%Mn PRE(S+P)=%Cr+3.3x%Mo+30x%N-123 x%(S+P)
The pitting equivalent value (PRE) or pitting index is used to assess a material’s resistance to pitting or pitting corrosion, with the basic formula being: PRE(PREN) = %Cr + 3.3x%Mo + 16x%N. When tungsten (W) is added, the formula becomes: PREW = %Cr + 3.3x(%Mo + 0.5%W) + 16x%N. When manganese (Mn) is added, the formula is: PRE Mn = %Cr + 3.3x%Mo + 30x%N - %Mn. When considering the effects of sulfur (S) and phosphorus (P), the formula is: PRE(S+P) = %Cr + 3.3x%Mo + 30x%N - 123x%(S+P). .