In the late 80s and early 90s, XDSS (super duplex stainless steel) UNS S32760 in wrought form was chosen for two of Australia's largest oil and gas facilities to be the material of choice for seawater handling. The choice was based on laboratory and suppliers data. Little in-service corrosion design data was avaliable at the time. The first facility, a large gas/condensate fixed leg platform, about 140 km offshore in the North West of Australia, was pre-commissioned in 1993 and came into production in 1995. Failures of the firewater system began to occur in 1994. The other facility in the same geographical location, also experienced failures within 12 months of comissioning the firewater system. Failures with this material were originally due to localized corrosion in the LTHAZ (low-temperature heat-affected zone). As time progressed, severe galvanic problems were encountered, followed by crevice attack, material faults and weld decay. The mechanisms and root causes are well understood and are discussed briefly in this paper. Correction of the problems, non of which threatened integrity in operation facilities, has proven to be a very expensive and lengthy process. The process actually involves a combination of approaches, to result in the cost-effective fix. RCP (resistor-controlled cathodic protection) is being evaluated to combat LTHAZ, material faults and weld decay in some areas and non-metallic composite design in others. Inappropriate galvanic couplings are being removed by replacing materials, e.g., nickel aluminium bronze valves have been replaced in XDSS. The crevice attack is fixed in some areas by replacing the seawater with fresh water and RCP in others. The lesson that the wrought alloy UNS S32760 has severe limitations when used in warm (20 - 30 deg C) seawater has been clearly demonstrated. The correction of the deficiencies is underway and will take considerable time.
Service experience of super duplex stainless steel in seawater
Betriebserfahrung mit nichtrostendem Superduplexstahl in Seewasser
Stainless Steel World ; 9 , 10 ; 61-65
1997
4 Seiten, 4 Bilder, 3 Tabellen
Article (Journal)
English
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