Feb-2025

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Sanicro 35 from Alleima bridges the gap between stainless steels and nickel alloys.

Jonas Howing
Alleima

Article Summary

Sanicro 35 has been developed for highly corrosive environments in demanding industries like chemicals and refining. It also supports ‘green’ technologies such as chemical recycling and renewable fuel production. It bridges the corrosion resistance gap between super austenitic stainless steel grades and more expensive high nickel alloys, making it an attractive upgrade material. Its chemical composition is shown below:

Sanicro 35 chemical composition (nominal) %
    C      Mn    P           S          Si      Cr    Ni
0.030    1.2    0.030    0.020    0.5    27    35

Mo     Cu    N             Fe
6.5     0.4    0.3     Remainder

Sanicro 35 has very high mechanical strength compared to other super austenitic and nickel base alloys. The yield strength for heat exchanger and hydraulic and instrumentation (H&I) tubing is 425 MPa (62 ksi). In addition, it has high ductility, resulting in good cold forming properties.

Localised corrosion
Sanicro 35 has excellent pitting corrosion resistance with a PREN1 » 52, making it suitable for applications where chlorides are present. Its pitting corrosion resistance compared to other Alleima grades, using a modified ASTM G150 test, is shown in Figure 1. A comparison of Sanicro 35 and Alloy 625 using another slightly modified ASTM G150 test method is shown in Figure 2. The grade also exhibits good crevice corrosion resistance, and in ASTM G48 testing, it performs better than Alloy 625 and is at least on par with Alloy C-276 (see Figure 3).

Environmental-induced cracking
Chloride stress corrosion cracking (Cl-SCC) can easily lead to catastrophic failures if a pressurised shell or pipe cracks and releases process fluids into the environment. Several Cl-SCC tests have shown that Sanicro 35 has a very high resistance towards this corrosion mechanism.

General corrosion
Sanicro 35 has shown high corrosion resistance in caustic environments and high resistance towards sulphuric acid, making it suitable for a number of applications within the chemical process industry. In organic acids, it is beneficial with high chromium and molybdenum content, making Sanicro 35 an excellent material for many petrochemical applications. Combined with excellent pitting corrosion resistance, it is also suitable for environments with organic acids contaminated by halides such as chlorides and bromides.

For refineries and renewable fuels
Sanicro 35 has great resistance to ammonium chloride corrosion, and in laboratory testing, it has shown similar performance to Alloy 625. This makes it a good option for overhead condensers in refineries.

In hydrotreater plant heat exchangers, stabilised 304 grades TP321 and TP347 can suffer corrosion and cracking due to long-term build-up of ammonium chloride deposits. The standard solution has been to upgrade the tubes to Alloy 625, but Sanicro 35 can offer a cost-effective alternative to the nickel base alloy.

Hydrotreater plants processing renewable feedstock use Alloy 625 extensively due to ammonium chloride deposits or high-temperature, acidic water phases containing chlorides. Advanced laboratory tests have shown that Sanicro 35 is resistant to these kinds of environments and, therefore, offers a cost-efficient alternative to Alloy 625.

For hydrotreater reactor effluent air coolers (REACs), ammonium bisulphide corrosion is commonly the main concern. However, in some cases, the process stream can also contain high amounts of chlorides. In such cases, Sanicro 35 offers a cost-effective alternative to the standard solution of using Alloy 625.
The grade’s high chromium and molybdenum content makes it resistant to high TAN feedstocks. It is, therefore, also suitable for several waste-to-hydrocarbon processes, and has, in several pilot and demo plants, outperformed Alloy 625 and other nickel base alloys.

Offshore, marine, and seawater applications
Sanicro 35 has excellent resistance towards offshore marine environments and sour service. It is, therefore, considered a good alternative to Alloy 625 when sour service resistance is required in H&I systems.

Thanks to its fully austenitic microstructure, it is not susceptible to hydrogen-induced stress cracking (HISC). The grade is, therefore, considered a good alternative to precipitation hardened nickel base fasteners in offshore environments.

In service and advanced laboratory testing, it has shown excellent resistance towards chlorinated seawater. The grade is, therefore, a good material for seawater-cooled heat exchangers.

Moving industry forward
Sanicro 35 bridges the properties gap between super austenitic steel grades and more expensive high nickel alloys for the chemical, petrochemical, and refinery industries sectors. Its excellent corrosion resistance and mechanical properties make it an interesting and cost-saving alternative for many applications where nickel base alloys are the traditional material solutions.