Stainless Steel Grade Selection
Stainless Steel Grade Selection
Fundamental Properties for Selection
Selection for corrosion resistance
- Stainless steels corrode often through local corrosion. The presence of chloride in the operating environment controls the mechanisms of crevice and pitting corrosion.
- Pitting Resistance Equivalent: The pitting and crevice corrosion resistance of a particular stainless steel grade is denoted by a Pitting Resistance Equivalent number (PRE). PREs can be calculated using the following equation:
PRE = %Cr + 3.3 %Mo + 16 %N
- It was estimated that grades having high alloying elements such as molybdenum, nitrogen and chromium are more resistant to crevice and pitting corrosion. Due to this reason, grade 316, with 2% molybdenum, is used in marine fittings
- The PRE number for various stainless steel grades are tabulated below:
Selection for fabrication
- Grades are selected for corrosion resistance and then consideration is given to how the product can be fabricated.
- Fabrication should be considered as early as possible in the grade selection process, as it greatly influences the economics of the product.
- Fabrication affects the cost-effectiveness of the product; hence this factor must be considered very seriously.
The rate of comparisons in the below table is on arbitrary scales with 10 representing excellent fabrication using a specific method.
