There can be no such thing as material failure in the world of high stakes of industrial processing. In environments with aggressive acids and extreme temperatures, regular stainless steels are sometimes unsuitable. Here Alloy 28 material comes in super-austenitic stainless steel in order to resist the most severe conditions. This alloy is also referred to as Sanicro 28 and it is used in the oil and gas industry as well as in chemical production as a matter of fact.
At Solitaire Overseas, we understand that the key to how to choose the right material begins with how it is constructed. This guide disaggregates the Alloy 28 chemical composition and explains why Alloy 28 pipes and tubes are the best options in the critical infrastructure.
What is Alloy 28 (Sanicro 28)?
Alloy 28 (UNS N08028 / W.Nr. 1.4563) is a high alloy multi-purpose austenitic stainless steel. Initially it was created to address the issues of corrosion in the wet process phosphoric acid industry but it has since become a universal solution to a wide range of hostile environments.
The material fills the difference between inexpensive stainless steels and costly nickel alloys. It is unique in its chemistry making it resistant to attack by strong acids and highly mechanically resilient.
The Breakdown: Alloy 28 Chemical Composition
The effect of the Sanicro 28 is the direct result of the particular elemental balance. Alloy 28 chemical composition, unlike the common 316 or 304 stainless steel, contains a high amount of nickel and chromium, with molybdenum and copper fortification.
According to the industry standards, the standard composition is as follows:
- Nickel (Ni): 30.0 – 34.0%
- Chromium (Cr): 26.0 – 28.0%
- Iron (Fe): Balance (approx. 22% min)
- Molybdenum (Mo): 3.0 – 4.0%
- Copper (Cu): 0.6 – 1.4%
- Manganese (Mn): ≤ 2.0%
- Carbon (C): ≤ 0.02%
Why This Composition Matters for Industrial Use?
- High Nickel and Chromium: The large volume of nickel (above 30 percent) and chromium amounts to a high level of resistance to both aggressive oxidizing acids and stress corrosion cracking (SCC)- a frequent killer of low grade alloys.
- Molybdenum & Copper: Molybdenum increases the resistance to pitting and crevice corrosion, whereas copper increases the performance on the reduction of acids, including sulfuric acid.
Key Properties of Alloy 28 Material
It is clear that the Sanicro 28 chemical composition is the cause of its physical and mechanical superiority.
Excellent Corrosion Resistance: It has an excellent resistance to sulfuric acid, phosphoric acid and acetic acid. It is also resistant to pitting in the presence of chloride bearing solutions hence suitable in the sea waters.
Mechanical Strength: At tensile strength of about 500-750 Mpa and yield strength of ≥ 220 MPa,, Alloy 28 tubes are able to withstand high-pressure places without deformation.
Weldability: The material is very weldable even with its complicated chemistry. It does not normally undergo post-weld heat treatment and this makes the fabrication of Alloy 28 pipes simple.
Industrial Applications: Where is Alloy 28 Used?
Due to its versatility, Alloy 28 material is often used when specifying equipment that is required to survive a long time under exposure to corrosives.
- Chemical Processing: This is widely applied in making phosphoric and sulfuric acid. Sanicro 28 heat exchangers, evaporators, and piping systems have much longer lifespan compared to those constructed using the traditional steel.
- Oil & Gas: Deep sour gas wells subject downhole tubes to high pressure and temperature, and hydrogen sulfide (H2S). Alloy 28 tubes are used as production tubing and liners as they do not suffer sulfide stress cracking.
- Marine & Offshore: Seawater cooling systems use the Alloy 28 pipes courtesy of their resistance to crevice corrosion even in stagnant water.
- Nuclear Industry: Nuclear fuel reprocessing systems also make use of it, in which nitric acid resistance is of the essence.
Alloy 28 vs. 904L and Alloy 825
A common question we face is how Alloy 28 compares to other high-performance materials like 904L or Alloy 825.
- Vs. 904L: 904L is an aggressive alloy, but Sanicro 28 has superior levels of Chromium and Molybdenum. This means that it has better resistance to localized corrosion (pitting/crevice) and also higher resistance to high levels of acidity.
- Vs. Alloy 825: Alloy 28 tends to be more effective than Alloy 825 in the presence of phosphoric acid and chlorides. This also gives a slight advantage to the Alloy 28 in stress corrosion cracking resistance to some media due to the increased Nickel content.
Final Thoughts
The decision about the alloy will dictate the duration of your project. Alloy 28 provides the cost efficiency of a nickel alloy and the flexibility of a stainless steel. Alloy 28, which type of pipe, tube or custom fittings you need the knowledge of the chemistry, which holds the metal in high demand by the industrial engineers around the world.
At Solitaire Overseas, we are the providers of high-quality Sanicro 28 products that are adjusted to the requirements of your project. Get in touch with our team to talk about how we are going to help in your next industrial project.
