EFFECT OF CONDENSER DESIGN ON STRESS-CORROSION CRACKING OF STAINLESS ALLOYS IN BOILING CHLORIDE SOLUTIONS

The design of condensers used to reflux boiling chloride solutions for stress corrosion tests on stainless alloys was shown to have a signif icant effect on time to cracking. This effect resulted from the differ ent steady-state concentrations of oxygen produced by various types of condensers. The condenser that provided the least amount of preheatin g before returning the condensate to the solution established the larg est concentrations of air (oxygen) in the boiling solution and the sho rtest times to failure by stress corrosion cracking (SCC). This was de monstrated with magnesium chloride (MgCl2) and sodium chloride (NaCl) solutions on type 304 stainless steel (UNS S30400), Carpenter 20 Cb-3( dagger) (UNS N08020), and Incoloy 825(dagger) (UNS N08825). In MgCl2, the effect of oxygen on stress corrosion depended upon the concentrati on oft he solution. The effect was maximum in the range from 24% to 32 % and decreased or disappeared at higher concentrations depending upon the alloy. These findings can be used to assess previously published data, for the design of new experiments, and for the development of ne w evaluation tests. Using a solution of 26% NaCL with phosphoric acid (H3PO4) to reduce the pH to 1.0 provides a more realistic method for e valuating alloys for service on plants than testing in MgCl2 solutions .