The super-austenitic grade Alloy 35Mo (UNS N08935) has excellent corrosion resistance and mechanical properties for harsh corrosion environments within refinery and petrochemical industry, e.g. shell-and-tube heat exchangers in sour water services and seawater cooling. The process fluids in the heat exchangers can be highly corrosive and correct material selection is critical for reducing corrosion failures, maintenance, and repair costs.
In this paper, different corrosion testing methods and results of Alloy 35Mo will be presented and compared with common existing corrosion resistance alloys (CRA) in refinery and petrochemical industry. The corrosion test methods cover pitting and crevice corrosion resistance, and setups approximating the corrosive condition in a hydroprocessing reactor effluent air cooler (REAC) in a refinery. The latter test will be carried out in hydrogen sulfide (H2S) dominated environments with different ammonium bisulfide (NH4HS) concentrations. The results show that Alloy 35Mo is an excellent alternative to the established corrosion resistance alloys in refinery and petrochemical industry.
The super-austenitic grade Alloy 35Mo has recently been developed and already been installed in shell-and-tube heat exchangers globally. The grade has shown excellent results in different laboratory tests. However, the grade must also be tested in industrial environments, which will take some time until results can been obtained.
It has been a universal choice to go for nickel base alloys when stainless steels have not been able to withstand certain harsh corrosive environment conditions, for example shell-and-tube heat exchanger using seawater as cooling media or solid salt deposits of ammonium bisulfide (NH4HS) forming in reactor effluent air cooler (REAC). Alloy 35Mo can be an option to nickel base alloys.
When developing new alloys, it is key to investigate the weldability and the properties of the material. This is especially of importance for the fabricator since welding is the common way of joining high pressure equipment, such as heat exchangers. The paper will present pitting corrosion resistance results after tube-to-tubesheet welding.
The purpose of this paper is to present the corrosion properties of the super-austenitic grade Alloy 35Mo (UNS N08935) and compare it with nickel base alloys, such as Alloy 625 (UNS N06625).
