Alloy 20 vs 28,what’s the difference?While both materials belong to the high-performance stainless steel family,they serve different chemical “battles.”
If you choose incorrectly,you risk premature stress corrosion cracking or localized pitting.This guide breaks down the chemical,mechanical,and practical differences between these two powerhouses.
If you choose incorrectly,you risk premature stress corrosion cracking or localized pitting.This guide breaks down the chemical,mechanical,and practical differences between these two powerhouses.
Understanding Alloy 20
Alloy 20 (UNS N08020) earned the nickname “The Sulfuric Acid Alloy” for a good reason.Scientists specifically developed this niobium-stabilized material to resist boiling sulfuric acid.It sits on the border between stainless steel and nickel alloys.
In a typical piping network,Alloy 20 is the go-to choice for chemical processing and food production.Its high nickel content prevents chloride-induced stress corrosion cracking.Furthermore,the addition of copper provides a unique defense against aggressive acids.For designers of stainless steel pipe fittings,Alloy 20 offers a reliable solution for mid-to-high concentration acid transport.
Understanding Alloy 28
Alloy 28 (UNS N08028) is a cold-worked,high-alloy austenitic stainless steel.While Alloy 20 focuses on acids,Alloy 28 thrives in deep,”sour” oil and gas wells.It contains higher levels of chromium and molybdenum compared to many standard grades.
This chemistry makes it exceptionally resistant to pitting and crevice corrosion.In the world of stainless steel pipe,Alloy 28 often appears in downhole tubing and heat exchangers.It handles high-pressure environments where hydrogen sulfide (H2S) and chlorides are present simultaneously.If your system faces deep-sea conditions or complex phosphoric acid production,Alloy 28 is the stronger candidate.
O que fazemos
- Placa
- Folha
- Forjados
- Barra redonda
- Mesa
- Tubos
- Conexões
- Personalizado
Entre em contato conosco para obter mais informações
When to Choose Alloy 20
- Sulfuric Acid Processing
- Food and Pharmaceutical Lines
- Complex Fabrication
- Niobium Stabilization Requirement
When to Choose Alloy 28
- Sour Gas Environments
- Phosphoric Acid Production
- Seawater Heat Exchangers
- High-Pressure Tubing
Alloy 20 VS 28:Chemical Composition Comparison
| Element (%) | Alloy 20 (UNS N08020) | Alloy 28 (UNS N08028) |
|---|---|---|
| Ni | 32.5 – 35 | 30 – 32 |
| Cr | 19 – 21 | 26 – 28 |
| Fe | Balance (~ 33) | Balance (~ 35) |
| Mo | 2 – 3 | 3 – 4 |
| Cu | 3 – 4 | 0.6 – 1.4 |
Alloy 20 VS 28:Pressure and Mechanical
Alloy 28 often undergoes cold-working to increase its mechanical properties.This makes it ideal for high-pressure tubing where wall thickness must be minimized.On the other hand,Alloy 20 maintains a more standard austenitic strength profile.It is easier to form into complex stainless steel pipe fittings like tees and reducers.
Additionally,the thermal expansion rates differ slightly.When you design a flange joint,you must ensure your gaskets and bolts can handle the thermal cycling of these alloys.Because both have high nickel content,they expand more than carbon steel.Therefore,using the correct assembly standards, such as ASME PCC-1,is vital for a leak-free connection.
Alloy 20 VS 28:Corrosion Resistance Comparison
| Mídia Corrosiva | Preferred Alloy | Reason for Selection |
|---|---|---|
| Sulfuric Acid (H2SO4) | Liga 20 | Higher Copper and Nickel content |
| Nitric Acid (HNO3) | Stable performance in oxidizing acids | |
| Pharmaceutical Fluids | Excellent purity and ease of cleaning | |
| Phosphoric Acid (H3PO4) | Liga 28 | Superior Chromium content (27%) |
| Sour Gas (H2S + Cl–) | Better resistance to Pitting/SSC |
Alloy 20 VS 28:Fabrication and Welding Challenges
Welding stainless steel of these grades requires professional expertise.Tubo de liga 20 is niobium-stabilized to prevent “Sensitization” during welding.This means you can weld it without losing corrosion resistance in the heat-affected zone.
Alloy 28 requires careful heat control to avoid the formation of intermetallic phases.If the weld pool stays too hot for too long,the material can become brittle.
Kaysuns professionals often use TIG welding with high-purity Argon gas for the root pass of an Alloy 28 pipe.This ensures the internal passive layer remains intact,preventing future localized corrosion at the joint.
Kaysuns professionals often use TIG welding with high-purity Argon gas for the root pass of an Alloy 28 pipe.This ensures the internal passive layer remains intact,preventing future localized corrosion at the joint.
Alloy 20 vs 28: Comparing PREN
When engineers evaluate Alloy 20 vs 28 for sea-water or chloride-rich environments,they look at the Pitting Resistance Equivalent Number (PREN).This formula gauges how well an alloy resists localized “pitting” holes.
PREN = Cr + 3.3 · Mo + 16 · N
Alloy 28 typically boasts a PREN of approximately 38 to 40,while Alloy 20 sits around 24 to 26.
Consequently,Alloy 28 is significantly better equipped for environments where salt deposits or stagnant fluids might cause localized breaches in the passive layer.If your piping system handles seawater cooled heat exchangers,the higher PREN of Alloy 28 is essential for long-term safety.
Consequently,Alloy 28 is significantly better equipped for environments where salt deposits or stagnant fluids might cause localized breaches in the passive layer.If your piping system handles seawater cooled heat exchangers,the higher PREN of Alloy 28 is essential for long-term safety.
Contate-nos
Entre em contato
- RM901 No.22 Tangjiaqiao Road Wenzhou China
- +86 577 8551 1171
- [email protected]
- https://www.kaysuns.com/
Encontre-nos
