Duplex Stainless Steel – Learning From Field Experience in Oil & Gas and Petrochemical Services

Duplex stainless steels are a family of stainless steels. Named duplex (or austenitic-ferritic) grades because their metallurgical structure consists of two phases, austenite, and ferrite in approximately equal proportions. They are expected to provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion, and higher strength than standard austenitic stainless steels such as Type 304 or 316. They are therefore used extensively in the offshore oil and gas and in the petrochemical industry in the form of piping and pressure vessels. This paper describes some applications that ended up in failures and the importance to adhere to tight fabrications fabrication controls and consider the effect of common manufacturing and fabrication deviations in the expected material performance. The first one is a shell and tube heat exchanger. On the shell side the material choice was 2205 duplex stainless steel. The shell side fluid is fed from debutanizer which feeds from upstream high pressure and low-pressure low temperature separators. Overhead stream contains H2S, NH3, HCl. The duplex was selected for this exchanger to mitigate potential dew point NH4Cl corrosion. The shell ended up leaking in less than two years after being placed in service. The second case is a super duplex 2507 seawater filter which failed after few weeks in service. Qualified welding procedures were not properly followed during fabrication leading to impaired corrosion resistant weldments. The third case describes one more failure of a hydrocracker reactor effluent air cooler. Tube to tubesheet and partition plates to tubesheet welds failed after ∼ 20 years in service.