The Ultimate Guide to Grade of Stainless Steel Pipe

When choosing the grade of stainless steel tubing, numerous factors come into play. The primary criterion for stainless steel is its corrosion resistance, specifically tailored for a particular application or environment. Additionally, factors like strength, fabrication qualities, and the extensive range of over 60 grades categorized into four metallurgical classes need consideration.

This article will provide an overview of the different grades of stainless steel pipe, including 300 Series Austenitic, 400 Series Martensitic, 400 Series Ferritic, and Precipitation Hardening Stainless Steel.The most widely used grades of stainless steel pipes are 304 and 316, which contain chromium and nickel in varying amounts.

It will also discuss the different chemical compositions of these grades and provide guidance on how to choose the right grade for an application.


grade of stainless steel pipe

Austenitic Stainless Steel

Austenitic stainless steel exhibits non-magnetic properties and boasts exceptional resistance against corrosion. It excels in weldability, formability, fabricability, and ductility. This stainless steel variant upholds its corrosion resistance even in extreme temperatures, reaching as high as 1500°F. Its versatility makes it invaluable for applications requiring both low and high-temperature service. The following content are several type grade of stainless steel pipe and the chemical component and application of all kind of austentic stainless steel

Austenitic Grade of Stainless Steel Pipe

 

Type 301: Offers high ductility for shaped products and quick hardening during mechanical work, boasting good weldability. Exhibits superior wear resistance and fatigue strength compared to 304.

Type 302: Shares the corrosion resistance of 304 but holds slightly higher strength due to added carbon content.

Type 303: Recognized as an easier-to-machine version of 304 by incorporating sulfur and phosphorus. Referred to as "A1" as per ISO 3506 standards.

Type 304/304L :The most common grade; the classic 18/8 stainless steel. Also referred to as "A2" in accordance with International Organization for Standardization ISO 3506.

Type 309: Demonstrates improved temperature resistance compared to 304.

Type 316/316L: The second most prevalent grade, particularly suitable for food and surgical stainless steel applications. The addition of molybdenum prevents specific types of corrosion. Known as "marine grade" due to heightened resistance to chloride corrosion in contrast to type 304. Commonly used in constructing nuclear reprocessing plants and prevalent in many stainless steel watches.

Type 321: Shares similarities with 304 but lowers the risk of weld decay by including titanium. Also, consider type 347, which incorporates niobium for desensitization during welding.

 

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Alloy Component  /Characteristics /  Application

 

Grade

Alloy Component

Characteristics & Application

303

18Cr-8Ni-S

Free cutting steel

304

18Cr-8Ni

Basic steel grade. Use for general purpose steel for many applications in many fields

304L

18Cr-8Ni-Low C

309

22Cr-12Ni

Oxidation resistance. Use in Chemical plant pipes and tubes, Radiant tubes, Thermocouple protection tubes

309S

22Cr-12Ni

310

25Cr-20Ni

310S

25Cr-20Ni

312L

20Cr-18Ni-6Mo-0.2N

Seawater resistance. Use in Seawater desalination plant pipes

316

18Cr-12Ni-2Mo

Corrosion resistance. Use in LNG plant pipes, Boilers, nuclear power and chemical industry pipes and tubes

316H

18Cr-12Ni-2Mo-High C

316L

18Cr-12Ni-2Mo-Low C

316Ti

18Cr-12Ni-Mo-Ti

lntergranular corrosion resistance

317

18Cr-12Ni-3Mo

Pitting corrosion resistance. Use in Chemical tanker pipes

317L

18Cr-12Ni-3Mo-Low C

321

18Cr-9Ni-Ti

Intergranular corrosion resistance. Use in Chemical plant pipes

321H

18Cr-9Ni-Ti-High C

High-temperature strength. Use in Boiler heater tubes and reheater tubes

347

18Cr-9Ni-Nb

lntergranular corrosion resistance. Use in Chemical plant pipes and tubes

347H

18Cr-9Ni-Nb-Low C

High-temperature strength. Use in Boiler heater tubes and reheater tubes

310MoLN

25Cr-22Ni-2Mo-N

lntergranular corrosion resistance. Use in Urea reactor tubes

 

Ferritic Stainless Steel

 

Ferritic stainless steel, being magnetic and high in carbon content, tends to be brittle and exhibits relatively lower corrosion resistance when compared to austenitic stainless steel. It remains non-hardenable through heat treatment but showcases robust resistance against chloride stress corrosion cracking.

 

Ferritic Grade of Stainless Steel Pipe

 

Type 408:

Heat-resistant but exhibits poor corrosion resistance with 11% Chromium and 8% Nickel content.

Type 409:

Economical variant primarily used in automobile exhausts; ferritic in nature, composed of iron and chromium.

Type 416:

Notable for its ease of machining due to additional sulfur content.

Type 430:

Mainly used for decorative purposes such as automotive trim; a ferritic stainless steel featuring good formability but exhibiting reduced temperature and corrosion resistance.

 

Alloy Component  /Characteristics /  Application

Grade

Alloy Component

Characteristics & Application

409

10.5-11.7 Cr  0.5 Ni

Automotive Exhaust Systems

430

18Cr

Chloride corrosion resistance and stress corrosion crack resistance. Use in water heater pipes

444

19Cr-2Mo-Ti/Nb

446

25Cr-N

Duplex Stainless Steel

Duplex stainless steels are a combination of austenitic and ferritic stainless steels, and are composed of chromium, molybdenum, nickel and other elements. Typical grades of duplex stainless steel pipe include 1Cr18Mn10Ni5Mo3N, 2101 and 2205.

 

The duplex grade of stainless steel pipe

 

UNS S31803 (SAF 2205):

This is the most widely used duplex stainless steel grade. It contains approximately 22% chromium, 5-6% nickel, and 3% molybdenum. UNS S31803 offers excellent corrosion resistance, high strength, and good weldability.


UNS S32205 (SAF 2205):

 Similar to UNS S31803, UNS S32205 offers the same composition and properties. It provides high resistance to stress corrosion cracking, making it suitable for applications involving harsh environments and chloride-containing solutions.


UNS S32750 (SAF 2507): 

This grade, also known as super duplex stainless steel, contains approximately 25% chromium, 7% nickel, and 4% molybdenum. UNS S32750 offers exceptional corrosion resistance, high strength, and excellent resistance to pitting and crevice corrosion. It is commonly used in offshore and marine environments, chemical processing plants, and desalination systems.


UNS S32760 (Zeron 100): 

Another super duplex stainless steel grade, UNS S32760 contains higher amounts of chromium, nickel, and molybdenum compared to UNS S32750. It provides excellent corrosion resistance, high strength, and improved resistance to corrosion fatigue and erosion. UNS S32760 is often used in applications where superior corrosion resistance and mechanical properties are required.

 

Alloy Component  /Characteristics /  Application

 

  Grade

Alloy Component

Characteristics

Applications

UNS S31803 (SAF 2205)

22% chromium, 5-6% nickel, 3% molybdenum

Excellent corrosion resistance, high strength, good weldability

Chemical processing, oil and gas, pulp and paper, desalination

UNS S32205 (SAF 2205)

Similar to UNS S31803

High resistance to stress corrosion cracking, suitable for harsh environments and chloride-containing solutions

Similar applications as UNS S31803

UNS S32750 (SAF 2507)

25% chromium, 7% nickel, 4% molybdenum

Exceptional corrosion resistance, high strength, excellent resistance to pitting and crevice corrosion

Offshore, marine environments, chemical processing, desalination

UNS S32760 (Zeron 100)

Higher chromium, nickel, molybdenum than S32750

Excellent corrosion resistance, high strength, improved resistance to corrosion fatigue and erosion

Applications requiring superior corrosion resistance, better mechanical prop

Martensitic Stainless Steel

Martensitic stainless steel pipe is a type of stainless steel pipe which contains a high carbon content and is typically used for applications requiring high strength and hardness.

The martensitic grade of stainless steel pipe

 

 Grade

Alloy Component

Characteristics

Applications

Type 410

11.5-13.5% chromium

High strength, hardness, and wear resistance

Valve components, pump parts, shafts

Type 420

12-14% chromium

Good corrosion resistance, high hardness, moderate strength

Surgical instruments, cutlery, molds

Type 431

15-17% chromium, 1.25-2.5% nickel

Good corrosion resistance, high strength, hardness

Aircraft components, fasteners, pump shafts

Type 440C

16-18% chromium, 0.95-1.20% carbon

Excellent hardness, wear resistance, corrosion resistance

Bearings, surgical instruments, cutting tools

How to choose the right grade of stainless steel pipe?

 

Opt for the Right Metal in Your Working Environment

To determine the most suitable steel grade for a specific environment, assess the conditions your final product will endure. Factors like extremely low pH, high stress, elevated temperatures, and crevice corrosion can detrimentally affect the performance of stainless steel. Austenitic  series steels, such as the commonly used 316 and 304 alloys, maintain their strength, toughness, and corrosion resistance across a wide temperature spectrum.

The primary consideration for selecting austenitic stainless grades is their corrosion resistance. Type 316, fortified with molybdenum, even combats chloride ions commonly found in marine and chemical processing settings. Irrespective of the steel grade, a well-designed structure is the best defense against corrosion.

 

Emphasize Strength, Ductility, and Toughness

 

  • Strength: A metal's ability to endure stress before deforming or fracturing.
  •  
  • Ductility: The material's capacity to change shape, like being drawn into a wire, without losing strength or breaking.
  •  
  • Toughness: The metal's ability to deform and absorb energy before fracturing.

Stainless steel, containing 10–30% chromium as an alloying element, resists corrosion. The inclusion of nickel in austenitic grades provides superior toughness and ductility among stainless grades. Alloys rich in chromium, molybdenum, and nickel exhibit the highest corrosion resistance.

Apart from alloy content, consider the material's processing, which impacts its mechanical properties. Cooling duration at various temperatures and the overall cooling rate during steel production affect its overall quality.

While heat treatment increases the hardness of carbon steels, cold working operations like rolling, bending, or drawing at lower temperatures harden austenitic stainless steel. However, note that increased hardness due to cold working may decrease properties like elongation and impact resistance.

 

Account for Form and Process

 

Austenitic stainless steel is available in various forms such as bar, wire, tube, pipe, sheet, and plate. Most products require additional shaping or machining for specific applications.

For instance, stainless steel tubing might need bending, coiling, machining, welding, or end forming. When machining processes like CNC machining are involved, select a machining rate that mitigates work hardening or opt for a "free-machining" grade containing sulfur.

During welding, embrittlement in the weld area is a concern. Opt for lower carbon grades like 304, 304L, or 316L to minimize carbide formation.

 

Consider Customer Preferences

Designers often select stainless steel for its aesthetic appeal—be it a shiny, electropolished "bright" finish, a dull "pickled" finish, a specific RMS polished matte surface, or a light-absorbing black oxide coating. Austenitic stainless steel grades can adopt these finishes and commonly undergo passivation.

Customers might also require certification for application-specific specifications, such as ASTM standards for different industrial uses. These standards ensure compliance with technical specifications for chemical composition, heat treatment, and other attributes.

 

Manage Material Costs and Availability

While high-performing austenitic stainless steels are initially more expensive, they prove worthwhile due to their corrosion resistance. Choosing a corrosion-resistant material suited to the application minimizes maintenance, downtime, and replacement expenses. Life-cycle costing methods enable a comprehensive comparison of different materials in terms of current and future costs.

 

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Conclusion

In essence, grade of stainless steel pipes epitomize the marriage of innovation and functionality. From the corrosion-resistant Austenitic to the robust Martensitic grades, each category offers a distinct set of attributes catering to diverse industries. The Duplex variety bridges the gap with a harmonious blend of strengths, while the Ferritic types excel in reliability.

What’s more, grade of stainless steel pipe is an important factor to consider when selecting a pipe for a particular application. The grade of stainless steel pipe should be chosen based on the chemical composition of the metal, the desired properties of the pipe, and the requirements of the application.

Contact the stainless steel pipe expert 

It is of utmost importance to seek the guidance of a professional expert when considering the selection of the appropriate grade of stainless steel pipe, particularly for new entrants in the stainless steel market. Foshan Vinmay Stainless Steel Co., Ltd. is your reliable source for expert advice and solutions regarding stainless steel pipes. Contact us today for your planing.

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