COOLING WATER SIDE CORROSION-RESISTANCE OF HIGH ALLOYED MATERIALS FORHANDLING OF PROCESS SIDE SULFURIC-ACID

The approved materials for use in sulfuric acid alloy 825 (German mate rial No. 2.4858) and alloy 20 (German mater. No. 2.4660) have only a l ow resistance against localized corrosion in chloride containing water and are unsuitable for handling of sulfuric acid. The newly developed austenitic Cr-base alloy, alloy 33, (X1CrNiMoCuN 33-32-1, German mate r. No. 1.4591) with 33% Cr, 31% Ni, 0,6% Mo and 0.4% N should have an excellent resistance against pitting and crevice corrosion additional to its high sulfuric acid resistance, too, because its Fitting Resista nce Equivalent No. calculated according to PREN = %Cr + 3,3 . %Mo + 30 %N runs to 50. Fitting and crevice corrosion properties of the alloy 3 3 are tested in comparison to those of reference materials in high chl oride containing solutions (1M NaCl, artificial and modified sea water , 10% FeCl3 . 6H(2)O, 500 g/l CaCl2). Fitting potentials and potential s of repassivation of pitting, critical temperatures of localized corr osion (FeCl3-test, CaCl2-test, artificial sea water), potentials of re passivation of crevice corrosion as well as depassivation pH values of crevice corrosion following Crolet have been determined. The results confirm that the localized corrosion behaviour of the alloy 33 corresp onds to its PREN. With regard to pitting corrosion alloy 33 is compara ble with the special stainless steel alloy 31 (mater. No. 1.4562), wit h regard to crevice corrosion it is comparable with alloy 926 (German mater. No. 1.4529).