1.4563 Stainless Steel: Material Selection for Seawater Systems

Mar 18, 2026

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1.4563 stainless steel, commonly known as Alloy 28 or UNS N08028, is a high-performance, molybdenum-enhanced austenitic stainless steel designed for extreme corrosion resistance, particularly in sulfuric acid and phosphoric acid environments. With its high chromium, nickel, and molybdenum content, combined with copper addition, it offers outstanding resistance to both oxidizing and reducing acids. It is widely used in chemical processing, acid production, and offshore applications where standard grades like 316L or even 904L are insufficient.

Standard	Equivalent Grade
EN (Europe)	1.4563
ASTM/AISI (USA)	Alloy 28, UNS N08028
Common Name	Alloy 28, Sanicro 28

Element	C	Si	Mn	P	S	Cr	Ni	Mo	Cu
Content (%)	≤ 0.02	≤ 0.7	≤ 2.5	≤ 0.03	≤ 0.01	26.0 - 28.0	29.0 - 32.0	3.0 - 4.0	0.6 - 1.4

Property	Yield Strength (Rp0.2)	Tensile Strength (Rm)	Elongation (A)	Hardness (HB)
Typical Value	≥ 220 MPa	500 - 700 MPa	≥ 35%	≤ 220

Excellent Acid Resistance: Particularly resistant to sulfuric acid across a wide range of concentrations and temperatures, as well as phosphoric, nitric, and organic acids. It is the preferred material for phosphoric acid evaporators and sulfuric acid handling equipment.

High Chloride Resistance: Offers good resistance to pitting and crevice corrosion in chloride-containing environments, including seawater and brine, with PREN typically 32-35.

Good Stress Corrosion Cracking Resistance: The high nickel content provides excellent resistance to chloride stress corrosion cracking.

Good Weldability and Formability: Can be welded using common techniques and exhibits good ductility for forming operations.

Chemical Processing: Reactors, heat exchangers, and piping for sulfuric acid, phosphoric acid, and other aggressive media.

Fertilizer Industry: Phosphoric acid evaporators, concentrators, and handling systems.

Pollution Control: Scrubbers, ducts, and chimney liners in flue gas desulfurization (FGD) systems.

Oil & Gas: Downhole tubing, wellhead components, and offshore platforms in sour service.

Pharmaceutical: Equipment requiring high purity and resistance to corrosive cleaning agents.

Pulp & Paper: Bleaching equipment and digesters.

Both are high-alloy austenitic grades, but Alloy 28 contains higher levels of chromium (27% vs. 21%) and nickel (30% vs. 25%), with similar molybdenum and copper content. This gives Alloy 28 superior resistance to sulfuric acid and better overall corrosion performance in mixed acid environments. Alloy 28 is particularly preferred for phosphoric acid service, where its higher chromium content provides excellent resistance to the aggressive conditions in wet-process phosphoric acid production. While 904L is an excellent general-purpose high-alloy stainless steel, Alloy 28 is often selected for more severe conditions, especially in sulfuric and phosphoric acid service where higher reliability is required.

Welding Alloy 28 requires matching or over-alloyed filler metals, such as Alloy 625 or Alloy 59 type fillers, to maintain corrosion resistance in the weld zone. The material has good weldability using common techniques including TIG, MIG, and SMAW. Controlled heat input (typically 0.5-1.5 kJ/mm) and proper shielding gas (argon-based) are important to avoid excessive grain growth and precipitation of detrimental phases. Interpass temperature should be kept below 100°C. Post-weld cleaning and pickling/passivation are recommended to restore corrosion resistance and ensure optimum performance.

Alloy 28 is suitable for a wide temperature range, from cryogenic conditions up to about 400°C (752°F) for continuous service. Its high nickel content ensures excellent toughness at low temperatures. For corrosion resistance, it performs exceptionally well in sulfuric acid up to about 120°C, and in phosphoric acid up to boiling temperatures. Above 400°C, long-term exposure may lead to microstructural changes that could affect properties, so higher temperatures should be evaluated based on specific application requirements.

GNEE Steel supplies premium Alloy 28 (1.4563/UNS N08028) stainless steel in plate, pipe, fitting, and bar forms for the most demanding corrosive applications. We provide full material traceability and certification (EN 10204 3.1) to ensure optimal performance. If you have any requirements, please feel free to contact us.