Sep-2024

Optimising refinery operations through innovative corrosion-resistant materials

A high alloyed austenitic stainless steel is supporting advances in the chemical and refinery industries.

Angela Philipp and Jonas Höwing
Alleima

Article Summary

Alleima’s proprietary Sanicro 35 (UNS N08935) has been installed globally in a variety of applications, including shell-and-tube heat exchangers and has shown excellent results. Based on long-term end-user partnerships, Alleima develops applications through unique materials that are lightweight, durable, corrosion-resistant, and able to withstand extremely high temperatures and pressures. A complete range of materials and products in austenitic, duplex, high-alloy austenitic stainless steels, nickel, titanium, zirconium, and bi-metallic tubing are available.

Bridging the gap
Sanicro 35 bridges the properties gap between super austenitic steel grades and more expensive high nickel alloys. Containing 35% nickel, it provides a high-performance alternative to conventional high nickel alloys and super austenitic alloys to support more cost-effective and efficient operations. This formulation was developed for highly corrosive environments in demanding industries like chemicals and refining, and to support ‘green’ technologies such as bio-refineries for renewable fuel production, biomass, waste gasification, the circular economy, and chemical recycling.

It’s pitting and crevice corrosion properties make it suitable for applications where seawater is used for cooling or heating. It has a high resistance to general corrosion in acid environments and can be used in heat exchanger applications such as overhead condensers and seawater coolers, hydraulic and instrumentation tubing, chlorinated hydrocarbon applications, and purified terephthalic acid (PTA) environments. In the chemicals industry, it can be used with organic acids (such as formic and acetic acid) and inorganic acids (such as phosphoric acid and sulfuric acid). It’s available in round bar, seamless pipe, and plates or sheets.

From R&D, to melt, to extrusion of hollows and manufacture of the final tube, high quality and full traceability are guaranteed. Like all Alleima materials, control of the supply chain ensures independence and security in product delivery.

Standards and approvals
Sanicro 35 complies with NACE MR0175/ISO 15156-3:2015, (Petroleum, Petrochemical, and Natural Gas Industries – Materials for Use in H₂S-Containing Environments in Oil and Gas Production – Part 3: Cracking-Resistant CRAs (Corrosion-Resistant Alloys) and Other Alloys) for Type 4a type 4c materials.

It complies with ANSI/NACE MR0103/ISO 17495-1:2016, (Petroleum, Petrochemical, and Natural Gas Industries - Metallic Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments) for highly alloyed austenitic stainless steels and nickel alloys.

Sanicro 35 has an ASME code case, no. 2982, for Boiler and Pressure Vessel Code, section VIII, Division I & II, covering ASTM B163 (tubes), B649 (bars), B677 (pipes), and B625 (plate and sheet). Maximum temperature is currently 450°C, which will be updated in future revisions to 550°C (842°F).

For the EU Pressure Equipment Directive (PED), a Particular Material Appraisal (PMA) is available as TÜV file 1326W043219, covering tube, pipe, bar and sheet  and plate products. Maximum temperature is 550°C (842°F).

Summary of properties
Several trials and tests were conducted to arrive at the optimum range of alloying elements. (Table 1).

Its balanced chemistry gives the Sanicro 35 a very high structural stability, not being prone to formation of intermetallic phases, and excellent pitting corrosion resistance with a PREN*   52. With its excellent pitting and crevice corrosion properties, it is particularly suitable for applications where chlorides are present. It also has a high resistance to general corrosion in acid environments, making it suitable for a variety of applications.

*PREN = %Cr + 3.3×(%Mo+0.5×%W) + 16×%N

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

The high mechanical strength together with the excellent ductility also allows for the use of thinner tube walls in pressurised systems. In heat exchangers, this gives weight savings, gives better heat transfer and efficiency of the equipment, and can lower the overall material cost.

Welding
Weldability is good and has been verified in ASME IX testing, using Alloy 59 as filler metal. A suitable method for fusion welding is TIG welding (GTAW), although Alleima can offer additional welding recommendations and pitting corrosion test results on welds.

Sanicro 35 can be welded to dissimilar materials such as Alloy 625, Alloy 825, super duplex or super austenitic alloys using different filler metals. For example, this makes it possible to retain existing tube sheets and only replace the tubes in a failing heat exchanger.

General corrosion
Sanicro 35 has better resistance to hydrochloric and sulphuric acid compared to stainless steels with a lower chromium and molybdenum content. With its high chromium content, it also exhibits good resistance towards nitric acid.

In organic acids it is beneficial with high chromium and molybdenum content, making Sanicro 35 an excellent material for many chemical and petrochemical applications. With its resistance towards pitting corrosion, it is also suitable for environments with organic acids contaminated by halides such as chlorides and bromides.