Case story: German oil refinery reduces heat exchanger shutdowns
By installing heat exchanger tubes in Sandvik SAF 2707 HD hyper-duplex steel in the overhead condensation unit, a German oil refinery managed to reduce the number of shutdowns from eight to one over a 4-year period.
A German oil refinery experienced corrosion problems in the overhead condensation unit of its crude oil distillation column. Heat exchanger lifetime was short. Twice every year, the process had to be shut down to replace the carbon steel tube bundle. The oil refinery's goal was to increase the lifetime of the tube material in order to meet a standard 4-year inspection interval for the distillation column. They, therefore, called on Sandvik's metallurgical and materials processing expertise.
The Sandvik solution
As pitting and under deposit corrosion were the reasons for the short heat exchanger life, Sandvik recommended that the refinery should replace the carbon steel tubes with next generation duplex stainless steel grade, Sandvik SAF 2707 HD. This hyper duplex steel has good resistance to chloride induced stress corrosion cracking and its minimal thermal expansion makes it easy to install into a carbon steel construction. Due to the increased corrosion properties the wall thickness of the tubes could be reduced from 2.77 mm to 1.65 mm.
Sandvik SAF 2707 HD tubes were installed in 2006. The new tube bundle was inspected after 6 months and showed slight erosion corrosion. Shutdown after 4 years showed no further erosion corrosion. After cleaning, eddy current testing and hydro testing, the bundle was reinstalled to run for another 4 years.
Reducing the number of shutdowns from 8 to1 over a 4 year period has resulted in fewer steel bundle replacements, which has contributed to increased working safety. Operationally, it has meant large savings in terms of material replacement, manpower and lost production.
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