Material Comparison

Written By Jaimee Walsh

OVERVIEW

Selecting the right material for a highly corrosive and high-vibration environment is critical to ensuring long-term performance and durability. While 316 stainless steel is a commonly used material in corrosive settings, Duplex and Super Duplex stainless steels offer superior mechanical properties and corrosion resistance. This document compares these materials and provides a recommendation for the best option based on the given conditions.

MATERIAL COMPARISON:

MILD STEEL VS. 316 STAINLESS STEEL VS. SUPER DUPLEX 2507

MATERIAL COMPARISON

1. 316 Stainless Steel

Corrosion Resistance: Good resistance to general corrosion but susceptible to pitting and crevice corrosion in chloride-rich environments.

  • Strength: Lower mechanical strength compared to Duplex and Super Duplex steels.

  • Fatigue & Vibration Resistance: Moderate resistance to fatigue, but prolonged exposure to vibration can lead to stress cracking.

  • Cost: Lower initial cost but higher long-term maintenance costs due to possible corrosion related failures.

  • Typical Applications: Food processing, marine applications, and moderate chemical environments.

2. Duplex Stainless Steel (2205 - UNS S32205/S31803)

  • Resistance: Significantly better than 316 stainless steel, with improved resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC).

  • Strength: About twice the strength of 316 stainless steel.

  • Fatigue & Vibration Resistance: Higher resistance to fatigue cracking, making it a better choice for vibrating environments.

  • Cost: Slightly more expensive than 316 SS but offers a longer lifespan and lower maintenance costs.

  • Typical Applications: Oil & gas, marine structures, chemical processing, and industrial piping.

3. Super Duplex Stainless Steel (2507 - UNS S32750/S32760)

  • Corrosion Resistance: Exceptional resistance to highly corrosive environments, including seawater, aggressive chemicals, and acidic conditions.

  • Strength: Higher tensile and yield strength than 2205 Duplex stainless steel.

  • Fatigue and Vibration Resistance: Excellent resistance to fatigue and stress cracking, making it ideal for environments with continuous vibration.

  • Cost: Higher upfront cost but significantly lower lifecycle cost due to increased durability and minimal maintenance.

  • Typical Applications: Offshore oil & gas, desalination plants, high-pressure pipelines, and chemical processing.

BENDING CONSIDERATIONS

Duplex and Super Duplex stainless steels can be bent using a mandrel bender, but special precautions must be taken due to their high strength and lower ductility compared to 316 stainless steel:

  • Higher Force Required: These materials have nearly twice the strength of 316 SS, requiring greater bending force.

  • Controlled Bending Radius: A larger bend radius (typically 3-5 times the pipe diameter) is recommended to prevent cracking.

  • Mandrel Type: A ball mandrel or plug mandrel helps prevent ovalization and ensures uniform bending.

  • Heat Assistance (if necessary): While cold bending is possible, localized heating may be needed for tighter bends to minimize cracking.

  • Springback Compensation: Due to the high strength of Duplex and Super Duplex steels, more spring back occurs compared to 316 SS, requiring adjustments in the bending process.

COST COMPARISON

The cost of Duplex and Super Duplex stainless steels is generally higher than 316 stainless steel, but the long-term benefits outweigh the initial investment:

  • 316 Stainless Steel: Lower upfront cost but higher long-term maintenance due to corrosion and fatigue issues.

  • Duplex 2205: Typically 1.5 to 2 times the cost of 316 SS per kilogram, but with greater durability and reduced maintenance.

  • Super Duplex 2507: 2 to 3 times more expensive than 316 SS, but offers significantly better corrosion resistance, strength, and fatigue resistance, reducing long-term costs.

While the initial cost is higher for Duplex and Super Duplex, their extended lifespan, reduced downtime, and lower maintenance costs make them more cost-effective over time.

RECOMMENDATION

Given the extreme conditions of high corrosion and high vibration, Super Duplex 2507 (UNS S32750/S32760) is the best-suited material. It offers:

  • Superior resistance to pitting and crevice corrosion, especially in chloride-rich and acidic environments.

  • Exceptional mechanical strength, reducing the risk of fatigue failure.

  • Excellent vibration resistance, minimizing the risk of stress corrosion cracking.

  • Longer service life and reduced maintenance, making it cost-effective over time.

  • If cost is a concern and the environment is moderately corrosive, Duplex 2205 can be a viable alternative, providing a balance between performance and cost.

For applications where cost is a major constraint and corrosion is not extreme, 316 stainless steel may be acceptable, but it is not recommended for long-term durability in highly corrosive and high-vibration environments.

CONCLUSION

For optimal performance in highly corrosive and high-vibration conditions, Super Duplex 2507 is the most suitable material. It provides outstanding corrosion resistance, high strength, and excellent fatigue resistance, making it the best long-term investment for demanding industrial applications.

Jaimee Walsh
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