Uniform corrosion
Due to the combination of high contents of nickel, chromium and molybdenum, Sanicro® 35 has good resistance to many commonly found acids, such as sulfuric acid, nitric acid, phosphoric acid and organic acids.
Sanicro® 35 has better resistance in hydrochloric acid compared to stainless steels with a lower chromium and molybdenum content and can be useful in environments where moderate levels of hydrochloric acid is present.
In low to intermediate concentrations of sulfuric acid, the resistance of Sanicro® 35 is similar to or better than Ultra 904L.
In chloride contaminated sulfuric acid, Sanicro® 35 can be expected to offer better resistance than Ultra 904L and Ultra 254 SMO.
In addition, the active corrosion rates are typically lower than that for stainless steel alternatives, due to the high nickel content.
Pitting and crevice corrosion
Resistance to localized corrosion such as pitting, and crevice corrosion is determined mainly by the chromium, molybdenum and nitrogen content in the material.
This is often illustrated using the pitting resistance equivalent (PRE) for the material, which can be calculated using the formula: PRE = %Cr + 3.3 x %Mo + 16 x %N.
Although the PRE typically exhibits good agreement with practical performance, it is only a theoretical approximation.
A more reliable means to rank the alloys, based on laboratory testing, is by critical pitting temperatures (CPT) and critical crevice corrosion temperatures (CCT) of the material.
The CPT value for Sanicro® 35 indicates a pitting resistance significantly higher than Ultra 254 SMO, and on a similar level as Alloy 625.
Sanicro® 35 is resistant up to the maximum tested temperatures of 90°C in ASTM G150 and 85°C in ASTM G48 method E.
Stress corrosion cracking
Due to its high nickel content, Sanicro® 35 exhibits excellent resistance to chloride induced stress corrosion cracking (SCC).
Resistance to cracking can be expected in many environments where type 316L and similar grades would be susceptible to SCC.
Cracking may occur in the most extreme conditions, such as in the boiling 45% MgCl2 U-bend test.
Even then, Sanicro® 35 exhibits higher resistance than 6Mo grades such as Ultra 254 SMO.
The grade complies with NACE MR0175/ISO 15156-3 as a type 4a and 4c material, with significantly higher environmental limits than 6Mo grades like Ultra 254 SMO.