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Corrosion Resistant Metals

Understand the materials available to help control the many types of corrosion.

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316 Stainless Steel

Stainless Steel

In all stainless steels, chromium and nickel are critical for corrosion resistance and ductility. The addition of >10% chromium transforms steel into stainless steel, creating an adherent and invisible oxide layer that is chromium-rich. This oxide layer forms when chromium in the alloy reacts with oxygen in ambient air. This layer gives steel its stainless character. The addition of nickel provides good ductility and ease of forming and welding.

But not all bar stock is the same. Swagelok materials contain more than minimum requirements, and in some cases, more than industry trends, of both chromium and nickel.

Note that although stainless steels will not suffer from general corrosion, they can be affected by localized corrosion.

For Fighting:

General Corrosion; Localized Corrosion; Stress Corrosion Cracking; Hydrogen Embrittlement

Material Matters

The risk of stress corrosion cracking (SCC) increases when chloride concentrations, temperatures, and tensile stress are high. No stainless steel is completely immune to SCC. We have performed SCC testing on pressurized tube fittings with exceptional results.

316 stainless steel composition chart
Swagelok 316 stainless steel exceeds minimum ASTM specifications

6-Moly Alloys

Stainless Steel

With 6-Moly (6Mo) alloys such as 6HN and 254, the addition of enhanced levels of chromium, molybdenum, and nitrogen results in greatly improved resistance to pitting and crevice corrosion in chloride-rich environments. 6HN has a higher nickel (Ni) content than 254, increasing corrosion resistance. These alloys are termed superaustenitic stainless steels because they contain at least 6% molybdenum.

  • Resistance to chloride pitting and crevice corrosion
  • Resistance to chloride stress corrosion cracking (CSCC)
  • Material strength 50% greater than 300-series austenitic stainless steels
  • Impact toughness, workability, and weldability
  • Suitability for sour gas applications (NACE MR0175/ISO 15156)
  • Availability with NORSOK-approved supply chain qualification standard M-650
6 moly composition chart

For Fighting:

General Corrosion; Localized Corrosion; Stress Corrosion Cracking; Sour Gas Corrosion; Intergranular Corrosion; Hydrogen Embrittlement


Alloy 2507 Super Duplex Stainless Steel

Stainless Steel

Duplex stainless steels have a two-phase microstructure of austenite and ferrite grains. This structure gives these materials a combination of attractive properties, including strength, ductility, and corrosion resistance.

Alloy 2507 Super Duplex, ferritic-austenitic stainless steel is well-suited for service in highly corrosive conditions. Its composition includes nickel, molybdenum, chromium, nitrogen, and manganese, offering excellent resistance to general corrosion, pitting, and crevice corrosion, and stress corrosion cracking (SCC), while maintaining weldability.

  • Mechanical strength for higher tube pressure ratings
  • Thinner-wall, higher-flow tube required to maintain pressure rating
  • Weldability
  • Applications up to 482°F (250°C)
  • Higher thermal conductivity/lower coefficient of thermal expansion than 316SS
  • Suitability for sour gas applications (NACE MR0175/ISO 15156)
  • Availability with NORSOK-approved supply chain qualification standard M-650
2507 super duplex stainless steel composition chart
Mechanical strength makes alloy 2507 ideal for high-pressure offshore applications and subsea systems where corrosion, fluid flow, and weight are of concern

For Fighting:

General Corrosion; Localized Corrosion; Stress Corrosion Cracking; Sour Gas Corrosion; Intergranular Corrosion


Alloy 825

Nickel Alloys

Alloy 825 (Incoloy® 825) is a nickel-iron-chromium-molybdenum alloy designed to resist general corrosion, pitting, and crevice corrosion, as well as stress corrosion cracking (SCC), in a wide range of media.

  • Resistance to intergranular corrosion due to being stabilized with titanium
  • Suitability for sour gas applications (NACE MR0175/ISO 15156)
  • Resistance in reducing environments (i.e., sulfuric or phosphoric acid)
alloy 825 composition chart

For Fighting:

Stress Corrosion Cracking; Sour Gas Corrosion; Intergranular Corrosion 


Alloy 625

Nickel Alloys

Alloy 625 (Inconel® 625) is a nickel-chromium-molybdenum alloy with a small quantity of niobium to reduce the risk of intergranular corrosion in a wide variety of severely corrosive environments.

  • Resistance to hydrochloric and nitric acids
  • Strength and ductility
  • Resistance to crevice and pitting corrosion in high-temperature use
  • Suitability for sour gas applications (NACE MR0175/
    ISO 15156)
alloy 625 composition chart

For Fighting:

General Corrosion; Localized Corrosion; Stress Corrosion Cracking; Sour Gas Corrosion; Intergranular Corrosion 


Alloy C-276

Nickel Alloys

Alloy C-276 (Hastelloy® C-276) contains nickel, molybdenum, and chromium. Its high molybdenum content makes it exceptionally resistant to pitting and crevice corrosion, and it is one of only a few materials that can withstand the corrosive effects of wet chlorine gas, hypochlorite, and chlorine dioxide.

  • Resistance to oxidizing and reducing media
  • Ductility, toughness, and strength at high temperatures
  • Resistance to crevice and pitting corrosion, sulfide stress cracking, and intergranular corrosion
  • Suitability for sour gas applications (NACE MR0175/ISO 15156)

Note that this alloy is NOT recommended with highly oxidizing environments, such as hot and concentrated nitric acid.

alloy C-276 composition chart

For Fighting:

Stress Corrosion Cracking; Sour Gas Corrosion; Intergranular Corrosion


Alloy 400

Nickel Alloys

Alloy 400 (Monel® 400) is a nickel-copper alloy known for its exceptional resistance to hydrofluoric acid, as well as resistance to stress corrosion cracking and pitting in most fresh and industrial waters.

  • Strength and corrosion resistance in a wide range of temperatures and media
  • Mechanical properties retained at subzero temperatures

Note that stagnant seawater has been shown to induce crevice and pitting corrosion in this alloy.

alloy 400 composition chart

For Fighting:

Localized Corrosion; Stress Corrosion Cracking 


Titanium Alloys

Other Alloys

Titanium alloys have excellent resistance to corrosion in a wide variety of environments, including seawater, salt brines, inorganic salts, bleaches, wet chlorine, alkaline solutions, oxidizing acids, and organic acids, where they generally outperform stainless steels.

Titanium is especially resistant to the following:

  • Crevice corrosion
  • Fatigue and cracking at moderate heat
  • Creep (the tendency of a solid material to move slowly or deform permanently under the influence of mechanical stresses)

Note that unalloyed titanium (Grades 1, 2, 3, and 4) typically is not resistant to crevice corrosion at temperatures below 175° F (80° C).

Due to its combustibility, titanium is NOT suitable for oxygen service. It is also incompatible with fluorides, strong reducing acids, very strong caustic solutions, and anhydrous chlorine.

For Fighting:

Crevice Corrosion


Engineered Combinations

Engineered combinations use Swagelok standard 316 stainless steel tube fittings with a variety of alloy tubing options. Elevated chromium and nickel levels in Swagelok fittings, plus the unique low temperature carburization process used to make our ferrules, mean we can offer engineered combinations as a rated alternative to full exotic alloy solutions in certain applications.  This can be a cost-efficient, corrosion-resistant solution for installations exposed to seawater that provides these advantages:

  • Swagelok standard 316 stainless steel fittings with nickel and chromium content higher than required for ASTM A479 result in a higher PREN number
  • Use of alloy tubing results in pitting and crevice corrosion resistance
  • Unique SAT 12 low-temperature carburization process provides superior tube grip, for use on alloys
  • Low risk of galvanic corrosion based on Anodic Index
how corrosion resistance is calculated chart

As with any mixed-material assembly, pressure ratings for tubing and fittings from different alloys will be governed by the lower material rating.

For Fighting:

General Corrosion; Pitting and Crevice Corrosion; Stress Corrosion Cracking; Intergranular Corrosion 

Talk to a trusted advisor Access Expert-Level Services


For more information, check out these additional helpful reference materials from Swagelok.



> View and download a print-friendly version of the Material Selection Guide