The performance of the newly developed hyper duplex grade Sandvik SAF 2707 HDTM (UNS S32707) in natural sea water as well as in neutral chloride solutions has been investigated. The nominal composition of SAF 2707 HD is 27%Cr, 6.5%Ni, 5%Mo, 0.4%N resulting in a nominal Pitting Resistance Equivalent number (PRE) of approximately 49. This results in a significant increase in corrosion resistance over conventional super duplex grades such as Sandvik SAF 2507 (UNS S32750) and 6Mo austenitic grades in chloride containing environments. Results from three months of continuous testing of crevice and pitting corrosion in natural sea water are presented. Tube and weld specimen were tested at constant temperature at three different potentials: at the free corroding potential, at +300mV(sce) and at +600mV(sce), respectively. In addition, short term crevice corrosion testing in 3%NaCl is also reported. No pitting was observed at the open circuit potential at 50 deg C, 65 deg C or 80 deg C for SAF 2707 HD for both welded and non welded tube specimens. Further, no pit-ting was observed for tubes in grade SAF 2707 HD at +600 mV(sce) at 50 deg C and 65 deg C and at +300mV (sce) at 80 deg C. Welded SAF 2707 HD tube specimens experienced no significant pitting at +600 mV(sce) at 50 deg C. The formation of calcareous deposits at 65 deg C and 80 deg C and no observed pitting indicates that the maximum operation temperature for tubular heat exchangers of SAF 2707 HD may be set higher than for SAF 2507. In both laboratory testing and exposure in natural seawater SAF 2707 HD experienced better results than SAF 2507.
Performance of Sandvik SAF 2707 HD (UNS S32707) in severe chloride containing environments
Leistungsfähigkeit des Sandvik-Stahls SAF 2707 HD (UNS S3207) in einigen chloridhaltigen Umgebungen
2007
13 Seiten, 13 Bilder, 6 Tabellen, 8 Quellen
Conference paper
English
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