In the process industry, seawater is commonly used when available to cool process fluids. However chlorination of the seawater is widely used to limit any microbial activity; that makes the environment quite aggressive. Chlorination oxidizes and increases the corrosion potential to approximately +600mVSCE for stainless steels and leads to higher susceptibility to localized corrosion.

Super duplex stainless steels, PRENw >40, in seawater-cooled heat exchangers can be used at limited temperatures otherwise Ti Gr.2 shall be used for equipment integrity over the service life.

Recent results with combination of hyper duplex UNS S32707 tubes and super austenite UNS S31266 plate, with PRENw of 49 resp. 53, for seawater-cooled heat exchangers are presented. Testing is performed in seawater cooled scale model heat exchangers with 0.5 ppm residual chlorine during a period of 18 months. Thus, it shows a corrosion resistance of the materials at a heat flux representative to a tube skin temperature up to 95°C inside in the seawater.

These new results also show a good correlation with the field service and help to challenge the use of Titanium in seawater-cooled heat exchangers.

Subject
Materials, Fluxes, Oxides, Skin, Chlorinated seawater, Tubes, Welding, Seawater, Heat exchangers, Heat, Pitting, Chlorine, Corrosion resistance
Keywords:
Seawater, pitting corrosion, chlorination, heat exchanger, cooling, hyper duplex stainless steels, super austenitic stainless steels, UNS S32707, UNS S31266
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2017
Association for Materials Protection and Performance (AMPP)
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