Material selection for a certain project
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There are numerous projects involving this client; let’s take a representative one and break it down: this client is a foreign-funded company, and the project involves a heat exchanger with sulfuric acid as the medium. The concentration ranges from 0.1% to 98%, the design temperature is 160°C, and the operating pressure is 0.5 MPa. Having worked in the field of anti-corrosion equipment for many years, I have some knowledge of various such devices and solutions. I recommend the silicon carbide heat exchanger solution. At such a concentration range of sulfuric acid, it is very difficult to find metal materials that can withstand it. The corrosion resistance of a material against a medium is a temperature-concentration dependent curve. In this case, only PTFE offers reliable corrosion resistance, but its heat exchange capacity is too poor, making it unsuitable for the customer’s application requirements. Silicon carbide is not a guarantee either, but its wide range of applications does prove its corrosion resistance to a certain extent. Then the client asked me to provide various supporting documents... I’m exhausted from dealing with the client’s requests.
For heat exchangers under such concentration and temperature and pressure conditions, tantalum is generally used.
For tantalum, a concentration of 75% or less is more reliable; higher concentrations pose risks. Lead, platinum, gold, and enamel are all good choices, but their cost-performance ratio is not high.
For 98% sulfuric acid at 160 degrees, a silicon carbide heat exchanger is a reliable choice.
The range is from 0.1 to 98, which is a very wide range rather than a single concentration value; if it’s concentrated sulfuric acid at 98%, then carbon steel material will suffice
Don’t overlook 160 degrees! At 160 degrees, carbon steel cannot be used at any concentration ranging from 0.1% to 98%; otherwise, no rust will be visible at all.
Currently, equipment for the leaching of nickel-cobalt materials is being developed, using sulfuric acid as the medium
Within this sulfuric acid concentration range, there is a risk regardless of the metal used; experiments are required
This requires a thorough understanding of and communication regarding the manufacturing process; if the process permits it, or if it can be adapted to do so, a dual-loop or two-stage heat exchange design with different concentration levels should be adopted to meet the operational requirements. For the division points of concentration ranges, ordinary carbon steel should be used as much as possible in high-concentration areas, while materials with high corrosion resistance should be selected for low-concentration areas
Heat exchange tubes with a stainless steel lining and PFA coating can be used. Of course, the tube sheet also needs to be lined with PFA.