Alloy 28, designated as UNS N08028, is a nickel-chromium-molybdenum alloy built for corrosive acidic and chloride-bearing environments. Engineers looking at Alloy 28 plate for pressure vessels or elevated-temperature piping need to look past general corrosion data. The full picture includes design pressure, service temperature, exposure medium, plate thickness, and the code the project falls under. A plate selected on corrosion resistance alone can still fail a fabrication or mechanical requirement later in the project.
Why Alloy 28 Plate Is Considered for Demanding Service
Corrosion resistance is the starting point, not the deciding factor. Alloy 28’s corrosion resistance in sulfuric and phosphoric acid service, along with its resistance to pitting and crevice attack in chloride environments, makes it a candidate material for process equipment exposed to aggressive media. Strength at the design temperature matters just as much. So does the chemical composition of the process stream itself, since concentration and contaminant levels shift how the alloy behaves in practice. None of this means Alloy 28 Plate fits every high-pressure or high-temperature job by default. Each application still needs to be checked against its own operating conditions and the governing specification.
Alloy 28 Plate and Temperature Considerations
Temperature does not act alone. It works together with the corrosive environment, the mechanical properties required at that temperature, and the condition the plate is supplied in. A solution-annealed plate behaves differently under thermal load than one in another condition, and the design code will call for specific property values at the intended operating temperature. Thickness plays into this too, since heavier sections respond differently during heat treatment and welding. Rather than quoting a blanket maximum service temperature for the alloy, the correct approach is to check the applicable specification and code tables against the actual project conditions.
Alloy 28 Plate for Pressure Service
Pressure-service suitability comes down to more than the alloy’s chemistry. Plate thickness has to match the design pressure and temperature combination worked out during vessel or piping design. Mechanical properties, yield strength, tensile strength, and elongation need to meet the values the code demands at the operating conditions, not just at room temperature. Fabrication adds another layer. Welding procedures, forming methods, and heat treatment after fabrication all affect whether the finished component holds up in service. Inspection and testing requirements, set by the project specification, confirm that the plate actually meets what the order called for. Corrosion resistance gets a material onto the shortlist. It does not decide pressure suitability on its own.
Alloy 28 vs SA 387 Grade 22
These two materials come from different families and are selected for different reasons. SA 387 Grade 22 is a chromium-molybdenum low-alloy steel used widely in pressure vessel and piping applications where elevated-temperature strength and cost are the main drivers. Alloy 28 is a nickel-based alloy chosen where the process stream is corrosive enough that a low-alloy steel would degrade too fast. Alloy 28 vs SA 387 Grade 22 is not a straightforward better-or-worse comparison. Grade 22 can outperform Alloy 28 on cost and on certain high-temperature strength applications where corrosion is not the governing concern. The right choice depends on the specific service conditions, not a general ranking between the two.
What Buyers Should Verify Before Ordering Alloy 28 Plate
Before placing an order, buyers should confirm the following points against project requirements and the applicable specification.
- The plate carries the correct UNS N08028 plate designation matching the purchase order.
- It is supplied to ASTM B709, which covers solution-annealed UNS N08028 plate, sheet, and strip.
- Plate thickness and dimensional tolerances match the design drawing requirements.
- The supply condition, typically solution-annealed, is confirmed in writing by the mill.
- Mechanical property requirements are specified and tied to the actual service temperature.
- Inspection and testing methods are agreed upon before manufacturing begins.
- Material test certificates accompany each shipment and match the heat of the material supplied.
- Heat and lot traceability is documented from melt through final delivery.
- Any project-specific requirements, such as additional NDE or third-party inspection, are confirmed with the supplier in advance.
Alloy 28 Plate: Quick Comparison
The two materials serve different purposes in a project, and the table below shows where each one is best used.
| Factor | Alloy 28 Plate | SA 387 Grade 22 |
| Material type | Super-austenitic stainless steel (UNS N08028 / 1.4563). | Chromium–molybdenum alloy steel plate for pressure vessels. |
| Main selection consideration | Chosen for extreme corrosion resistance in acids, chlorides, and sour service. | Chosen for high-temperature strength in boilers and pressure vessels. |
| Corrosion considerations | Excellent resistance to pitting, crevice corrosion, and SCC; strong in sulphuric/phosphoric acids and seawater. | Moderate corrosion resistance; relies on oxidation resistance and alloying, not for severe acids. |
| Pressure/temperature suitability | Good pressure capability; typically used up to ~350 °F (175 °C) in sour/corrosive service. | Designed for elevated temperatures; suitable up to ~600 °C (1110 °F) in pressure vessels. |
FAQs
Is Alloy 28 plate suitable for high-pressure service?
It can be, depending on plate thickness, mechanical properties at the design temperature, and the governing code. Suitability is confirmed through design calculations, not assumed from the alloy type alone.
How does temperature affect Alloy 28 plate selection?
Temperature affects required mechanical properties, plate condition, and the corrosive behaviour of the process medium at that temperature. All of these need to be checked together against the design code, not in isolation.
What is the difference between Alloy 28 and SA 387 Grade 22?
Alloy 28 is a nickel-based alloy chosen for corrosion resistance in aggressive media. SA 387 Grade 22 is a low-alloy steel used where elevated-temperature strength is the priority and corrosion resistance is not a major concern.
What should buyers verify when ordering UNS N08028 plate?
Buyers should confirm the ASTM B709 specification, supply condition, mechanical properties, thickness, and heat traceability before placing an order. Material test certificates should accompany every shipment.
