EN
AR
BG
HR
CS
DA
NL
FI
FR
DE
EL
HI
IT
JA
KO
NO
PL
PT
RO
RU
ES
SV
TL
VI
TH
TR
GA
CY
BE
IS
Hastelloy B-3 vs. Traditional Alloys: Performance Data for Sulfuric Acid Applications
Hastelloy B-3 vs. Traditional Alloys: Performance Data for Sulfuric Acid Applications
Selecting the right material for sulfuric acid (H₂SO₄) service is one of the most critical and challenging decisions in chemical processing. The wrong choice leads to catastrophic corrosion, unplanned shutdowns, safety incidents, and costly replacements.
This guide provides a performance-based comparison between the advanced nickel-molybdenum alloy Hastelloy B-3 and traditional materials, arming you with the data needed to make an informed, economic, and safe selection.
Why Sulfuric Acid is a Corrosion Nightmare
Sulfuric acid's corrosiveness is highly dependent on concentration and temperature. Materials that resist dilute acid may be destroyed by concentrated acid, and vice-versa. The presence of impurities (e.g., chlorides, oxidizing agents) further complicates material selection. The key is to match the alloy's strengths to the specific process conditions.
The Contenders: Alloy Overview
| Alloy | Family | Key Composition | Primary Strength | Primary Weakness |
|---|---|---|---|---|
| Hastelloy B-3 | Nickel-Molybdenum | Ni (~65%), Mo (~28.5%), Cr (~1.5%) | Excellent resistance to all concentrations of H₂SO₄, especially under reducing conditions. Superior to B-2 in fabricability and thermal stability. | Very poor resistance to oxidizing environments (e.g., Fe³⁺, Cu²⁺, HNO₃, O₂). Vulnerable to pitting in chlorides. |
| Alloy 20 (Carpenter 20) | Austenitic Stainless | Fe (~40%), Cr (~20%), Ni (~35%), Mo (~2.5%), Cu (~3.5%) | Good resistance to dilute sulfuric acid and excellent resistance to chloride stress corrosion cracking (SCC). | Limited by severe graphitization and corrosion in hot, concentrated H₂SO₄. |
| 316L Stainless Steel | Austenitic Stainless | Fe (balance), Cr (~17%), Ni (~13%), Mo (~2.2%) | Low-cost option for very cold, very dilute (<20%) acid services with no contaminants. | Highly susceptible to pitting, crevice corrosion, and SCC in chlorides. Useless for concentrated acid. |
| Hastelloy C-276 | Nickel-Chromium-Molybdenum | Ni (balance), Cr (~16%), Mo (~16%), W (~4%) | The "universal" alloy. Excellent for oxidizing and mixed acids. Resists pitting/SCC. | More expensive than B-3. Not as optimized for pure, hot sulfuric service. |
Performance Data Showdown: Corrosion Rates
Corrosion rates are typically measured in mils per year (mpy). <1 mpy is outstanding, 1-20 mpy is often acceptable for general corrosion (with corrosion allowance), and >20 mpy is usually unacceptable.
The following data, compiled from industry sources and manufacturer literature, illustrates the performance gap.
Scenario 1: Concentrated Sulfuric Acid (90-98%) at 50°C (122°F)
This is a common condition for acid handling, transfer, and storage.
| Material | Typical Corrosion Rate (mpy) | Assessment & Comments |
|---|---|---|
| Hastelloy B-3 | <1 - 5 | Excellent. The high Molybdenum content provides stellar resistance. The standard choice for concentrated acid service. |
| 316L Stainless Steel | >100 | Catastrophic. Rapid general corrosion and graphtization. Completely unsuitable. |
| Alloy 20 | 20 - 50 | Poor to Severe. High corrosion rates are expected. May be used with large corrosion allowances but risks contamination. |
| Hastelloy C-276 | 5 - 15 | Good to Fair. Performs acceptably but is not optimized for this service. B-3 is typically superior. |
Scenario 2: 50% Sulfuric Acid at 80°C (176°F)
A common intermediate concentration in processing.
| Material | Typical Corrosion Rate (mpy) | Assessment & Comments |
|---|---|---|
| Hastelloy B-3 | <5 - 10 | Excellent to Good. Remains the top performer for this hot, reducing environment. |
| 316L Stainless Steel | >500 | Catastrophic. Would fail in a very short time. |
| Alloy 20 | 50 - 100 | Severe. High and likely unpredictable corrosion. Not recommended. |
| Hastelloy C-276 | 10 - 20 | Good to Fair (Acceptable). A reliable choice, though B-3 often shows a lower rate. |
Scenario 3: 10% Sulfuric Acid at 50°C (122°F) - With 1000 ppm Chlorides
This "dirty" dilute acid scenario is where things get complex.
| Material | Typical Corrosion Rate (mpy) | Assessment & Comments |
|---|---|---|
| Hastelloy B-3 | <10 (General) but risk of Pitting | Good General Corrosion resistance. However, B-3 is not highly resistant to chloride-induced pitting/crevice corrosion. Risk of localized attack. |
| 316L Stainless Steel | >500 + Severe Pitting/SCC | Catastrophic. The worst possible material for this service. |
| Alloy 20 | 20 - 50 + Possible Pitting | Poor. General corrosion is high, but its higher Cr/Ni content gives it better pitting resistance than B-3. A complex trade-off. |
| Hastelloy C-276 | <1 - 5 | Excellent. This is where C-276 shines. Its Chromium content provides superb passivation against chlorides, making it the superior choice. |
Critical Consideration: The "Oxidizing Agent" Trap
This is the most important concept when considering Hastelloy B-3.
Hastelloy B-3 is designed for reducing environments. Its lack of Chromium makes it vulnerable to any oxidizing agent.
If your sulfuric acid stream contains even trace amounts of:
-
Dissolved oxygen (air)
-
Ferric ions (Fe³⁺)
-
Cupric ions (Cu²⁺)
-
Nitrates (NO³⁻)
...the corrosion rate of Hastelloy B-3 can increase exponentially, from <5 mpy to >100 mpy. In such environments, an alloy with Chromium (like Hastelloy C-276, Alloy 20, or 316L) is mandatory.
Conclusion: Performance vs. Economics
-
For pure, concentrated sulfuric acid service (especially >70%) without oxidizing impurities, Hastelloy B-3 is the performance-optimized champion. It offers the best corrosion resistance and is often the most economical choice when considering lifetime cost, despite its high initial price.
-
For dilute acid or acid contaminated with oxidizing ions or chlorides, Hastelloy B-3 is the wrong choice. In these environments, you must pay the premium for a Chromium-containing alloy like Hastelloy C-276.
-
Traditional stainless steels (316L, Alloy 20) have a place only in very specific, mild, and clean sulfuric acid conditions. Their lower initial cost is almost always offset by higher risk, shorter service life, and potential for catastrophic failure.
Final Recommendation: Never select an alloy for sulfuric acid based on price alone. Define your exact process conditions (concentration, temperature, contaminants) and then choose the alloy whose performance data proves it can survive. For critical applications, investing in the superior, data-backed performance of Hastelloy B-3 (for reducing acid) or C-276 (for mixed/oxidizing acid) is the most cost-effective decision over the total lifecycle of your equipment.
