Corrosion resistance performance of super alloys while heat exchange
In the recent times more emphasis is put on safe disposal of chlorinated solvents. Combustion specifically on-site incineration is a suitable way to safety dispose of these materials rather hauling of solvents on public sites. Additionally it is very economical to combust on the site. Considering these factors, a combustion system was selected by an industrial waste incinerator operator for dealing with chlorinated solvents produced from a coating operation. The system comprises of a blower that attracts the methanol and methylene chloride fumes, comprising of 97% air, from the coater in the U-bend of the preheater or exchanger. The gas stream is isolated into distinct, fully isolated alternating passages developed by the fixed plates. Excellent performance of Inconel 625 Wire is suitable in this media.

The gas releasing from the heat exchanger is heated to 427oC or 800oF. The preheated gas enters a natural gas fired combustor where the temperature is maintained between 927oC to 982oC. The combustion gases then travel through a fire tube boiler. The gases leave the boiler at 760oC or 1400oF and travel through the hot region of the pre-heater or exchanger that reduces the gas temperature to 316C. The gases then travel through a scrubber and in the atmosphere. The actual heat exchanger was made from stainless steel 309. Initial evaluation of heat exchanger after around six months of service shown wide scalling of thin plates. Almost all of the original thickness 0.48mm of the plate has been oxidized and the remainder had received internal corrosion.

Due to time factors, a decision was made to install another steel made heat exchanger and simultaneously, include a test rack of samples of different alloys in the gas stream ahead of the exchanger for evaluation of other materials. The samples included SS 309, SS 316, Inconel 600, Inconel 625 and Incoloy 800, 825 and Hastelloy C276. The samples were served to service conditions for 300 hours. The studies showed higher corrosion and internal attack for these alloys. Inconel alloy 600, 625 and Hastelloy C276 offered nominal corrosion. It was similar to the outcomes received from the lab corrosion study.
Considering the test rack data Inconel alloys 600, 625 and Hastelloy C276 were judged to be suitable materials. Alloy Inconel 718 Wire was ruled out due to its cost and limited presence. Inconel alloys 600 and 625 could be counted equivalent as alloy 600 was attacked only little more than Inconel 625 and the disadvantage of having a slightly higher corrosion rate could at least slightly be offset by its economical price. The ultimate decision was made to use Inconel 625 considering a slighter longer life could be anticipated that would amortize buy and installation costs over a longer duration of time. Besides, Inconel Bar alloy 625 offers higher resisting to pitting and crevice corrosion in acid condensate exposure during down time. After the configuration of Inconel alloy 625 heat exchanger, first inspection was conducted around five months of service. The whole hear transfer surfaces described a uniform gray oxide without spalling. Depending on this corrosion functionality, the exchanger is anticipated to around 5–8 years, as compared to one year service life for stainless steel 309.
Another system is designed for similar application and Hastelloy Bar is specified as the heat exchanger material for excellent performance.
With high nickel, chromium, niobium and molybdenum concentration, Inconel alloy 625 has excellent aqueous corrosion resistance in a variety of highly aggressive media. IN various conditions, the resistance of Inconel alloy 625 to aqueous corrosion is similar to Hastelloy G3, C276, and Hastelloy C22. It prevents general corrosion and intergranular corrosion in various conditions discovered in the chemical processing conditions. It prevents pitting and crevice corrosion in applications of flue gas desulfurization. It prevents corrosion and fatigue damages in sea water where it is usually used in naval applications.
Corrosion prevention by Monel Bar is also found suitable for use in diverse environments.
