Stainless steel for seawater desalination
The problem: crevice corrosion
The Ras Tanura oil refinery in Saudi Arabia, operated by the Arabian-American oil company, Aramco, is located in one of the world’s most arid climates. To get fresh water for drinking and for cooling operations at the plant, Aramco works with the engineering firm, AquaTech International, to build desalination units and design the condensation process to remove salt from seawater.
However, Aramco was experiencing corrosion problems in the condenser channels, particularly between tubes and tubesheets (where the tubes protrude from the sheets) and at gasket crevices. The corrosion problem was caused by a high chloride content, enhanced by high levels of chlorine.
The seawater off the East coast of Saudi Arabia, in the Persian Gulf, is unusually high in chlorides. To complicate matters, the Ras Tanura facility was also using a chlorine bacteria-killer additive in their water to prevent any potential problems from untreated sewage and wastewater. This chlorine additive only enhanced the aggressiveness of the natural chlorides in the seawater around Ras Tanura. Aramco engineers suggested 904L stainless steel to alleviate this problem.
The solution: Outokumpu 254 SMO and 654 SMO plate
Outokumpu’s metallurgists examined the problem and determined not only that 904L would not solve Aramco’s particular crevice corrosion problem but that neither duplex nor super duplex stainless steels would be the answer either.
Armed with test results and scientific papers from Outokumpu’s metallurgists, AquaTech convinced Aramco that their best approach would be a combination of Outokumpu 254 SMO plate for areas of the plant where the risk of stress corrosion cracking was highest, and 654 SMO plate for critical crevice situations.
What are 254 SMO and 654 SMO?
Outokumpu 254 SMO is an austenitic stainless steel designed for maximum resistance to pitting and crevice corrosion. Outokumpu 254 SMO offers very high resistance to chloride stress corrosion cracking—50% stronger than 300-series austenitic stainless steels. And 254 SMO combines excellent impact toughness, workability, and weldability.
The superaustenitic 654 SMO from Outokumpu contains unusually high levels of chromium, molybdenum, and nitrogen, to achieve levels of chloride pitting and crevice corrosion resistance not previously possible with an austenitic stainless steel. 654 SMO combines very high strength with good formability.
Superior performance with Outokumpu special grades
Outokumpu’s stainless steel special grades—in a wide range of product forms—are designed for exceptional performance in the most technically and environmentally chllenging conditions across virtually all industries. Outokumpu has provided stainless steel for desalination plants in more than 16 countries. The successful experience of using 254 SMO and 654 SMO stainless steels for desalination is proving relevant to other technology needs, as well, such as for use in industrial waste water treatment plants.