The Ultimate Guide to Grade of Stainless Steel Pipe

When choosing the grade of stainless steel pipe, 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  grade of stainless steel pipe categorized into four metallurgical classes need consideration.

This article will provide an overview of the different grade of stainless steel pipe, including 300 Series Austenitic, 400 Series Martensitic, 400 Series Ferritic, and Precipitation Hardening Stainless Steel.The most widely used grade 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 of stainless steel pipe  for an application.


grade of stainless steel pipe

What are the various grading systems?

 

The grade of stainless steel pipe is governed by several established systems.

The Society of Automotive Engineers (SAE) employs a three-digit nomenclature that highlights the primary alloying elements and carbon content.

Alternatively, the American Society for Testing and Materials (ASTM) utilizes a six-digit system, which begins with 'A' to denote ferrous materials and incorporates additional specifications for various grades.

Understanding these grading systems is crucial for ensuring compliance and selecting appropriate stainless steel for specific applications.

 

The Society of Automotive Engineers 3-Digit System

 

Established by the Society of Automotive Engineers (SAE), the three-digit grading system classifies stainless steel based on its primary alloying elements and carbon content, facilitating standardized identification and specification across various applications. The SAE standards overview provides a clear framework for understanding the composition and performance characteristics of various  grape of stainless steel pipe , particularly relevant in the automotive industry usage.

Each grade number begins with a digit representing the primary alloying element—typically chromium or nickel—followed by two digits indicating the carbon percentage. This system allows for precise grade selection criteria, ensuring that engineers choose materials that meet specific corrosion resistance factors and mechanical performance requirements for their applications.

For instance, austenitic grade of stainless steel pipe like 304 and 316 are favored for their excellent corrosion resistance, making them suitable for parts exposed to harsh environments. Conversely, martensitic grade of stainless steel pipe may be selected for applications requiring higher strength and wear resistance.

Understanding the SAE three-digit system is essential for professionals in the field, enabling informed decisions about stainless steel applications across diverse sectors, including automotive, aerospace, and medical industries.

 

The American Society for Testing and Materials (ASTM) 6-Digit System

 

Utilizing a six-digit grading system developed by the American Society for Testing and Materials (ASTM) facilitates a comprehensive classification of stainless steel, beginning with an 'A' to denote ferrous materials and followed by specific numerical codes that indicate the stainless steel tube material's composition and properties.

This ASTM standards overview is vital for ensuring consistency across various applications in the industry.

The first two digits of the grade signify the primary alloying elements, while the subsequent digits detail additional elements and specific characteristics, aligning with robust stainless steel specifications.

Adhering to material compliance guidelines, stainles steel pipe manufacturers can ensure their products meet industry requirements, ultimately enhancing safety and performance.

Testing procedures explained in ASTM standards include mechanical, chemical, and corrosion resistance tests, which are critical for validating the integrity of stainless steel grades.

Furthermore, grade selection criteria are essential for engineers and designers to make informed decisions based on environmental conditions and mechanical demands.

This systematic approach fosters a sense of belonging within the engineering community, as professionals can rely on standardized classifications to communicate effectively and achieve optimal outcomes in their projects.

 

The American Society for Testing and Materials (ASTM) 6-Digit System

Adopting a six-digit grading system, the American Society for Testing and Materials (ASTM) provides a standardized method for classifying stainless steel, beginning with an 'A' to denote ferrous materials. This ASTM standards overview is crucial, as it defines compliance guidelines that ensure materials meet specific performance criteria.

The six-digit system enhances the grading system's importance by allowing for precise identification of alloy compositions and properties, essential for stainless steel applications across various industries, including construction, automotive, and medical.

Each grade within this system is formulated based on rigorous testing methodologies explained in ASTM documents, which outline how materials are evaluated for strength, corrosion resistance, and other critical properties. This systematic approach fosters consistency and reliability in material selection, ensuring that engineers and manufacturers can make informed choices aligned with industry standards.

Moreover, the six-digit classification aids in maintaining regulatory compliance, which is increasingly vital in a global market driven by quality assurance. Thus, the ASTM 6-digit system serves as a cornerstone for the effective utilization and application of stainless steel, reinforcing the need for standardized practices within the industry.

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.

 

You may also like:

Differences Between 316 and 316L Welded Stainless Steel Pipe

 

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

 

What is the difference between 316 and 304?

 

Cost

The cost of stainless steel largely depends on the alloys present in its composition. All stainless steels require a minimum of 10.5% chromium and are primarily alloyed with iron, which constitutes a significant portion of their final makeup. However, the other elements present affect the properties and characteristics, ultimately influencing the cost.

316 stainless steel contains at least 2.0% molybdenum, making it much more corrosion-resistant than 304. Due to molybdenum being a more expensive element, 316 is generally a more expensive grade of metal.

You may also like: 

Deciphering the Dynamics: Unraveling Stainless Steel Round Tube Prices

 

 

Chemical composition

 

GradeCSiMnPSNCrNiMo
3040.071.002.000.0450.0150.1017.5 - 19.58.0 - 10.5-
3160.071.002.000.0450.0150.1016.5 - 18.510.0 - 13.02.0 - 2.5

 

Magnetism

 

Both grades are austenitic, meaning they do not possess magnetic properties. However, cold working can affect this. When stainless steel is formed or cut, there is a slight increase in its magnetic properties, although this increase is minor.

 

Corrosion Resistance

 

Stainless steel, as a family of metals, is highly corrosion-resistant. The addition of molybdenum in 316 increases its ability to withstand harsh environments, often earning it the designation of marine grade. 316 is suitable for use in more aggressive environments than ambient ones, though regular cleaning is still recommended to prolong its service life.

 

Applications for 304 Stainless Steel

 

The high concentration of chromium in stainless steel 304 gives it excellent corrosion resistance, making it suitable for various applications, including:

  • Kitchen appliances like refrigerators and dishwashers
  • Heat exchangers
  • Commercial food processing equipment and kitchen fittings like sinks and splashbacks
  • Saucepans, cutlery, and flatware
  • Architectural paneling
  • Nuts, bolts, screws, and nuts
  • Brewery, food, and pharmaceutical production equipment

Generally, stainless steel is used in applications where standard carbon steel would corrode.

You may also like :

Can 304 stainless steel rust?

The Life Expectancy of 304 Stainless Steel

Is 304 Stainless Steel Surgical Grade?

 

Applications for 316 Stainless Steel

 

Originally developed for use in paper mills, stainless steel 316 is now commonly used in various applications, including:

  • Food, chemical, and petrol production and processing equipment
  • Laboratory benches and equipment
  • Architectural paneling in coastal regions
  • Boat fittings
  • Mining screens
  • Kitchenware, sanitaryware, and troughs
  • Tubing
  • Medical implants

316 stainless steel offers better corrosion resistance than 304 and often exhibits greater strength at high temperatures.

Discover More:

What Is the Difference Between 201 and 304 Stainless Steel?

316 Stainless Steel Rectangular Tube

The Life Expectancy of 316 Stainless Steel

 

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

Type 309- Better temperature resistance than 304

Type 309 - Exhibits better temperature resistance compared to Type 304.

Type 316 - This grade  of stainless steel pipe ranks as the second most common after Type 304. It is widely used in food processing  and surgical stainless steel applications. The addition of molybdenum enhances its resistance to specific types of corrosion, making it ideal for marine environments and earning it the nickname "marine grade stainless steel." Type 316 is also commonly used in the construction of nuclear reprocessing plants. Most stainless steel watches are made with this grade, except for Rolex, which uses a different quality.

Type 904L - Known as 18/10 stainless steel, this grade is also referred to as “A4” according to the International Organization for Standardization ISO 3506.

Type 321 - Similar to Type 304, but with a lower risk of weld decay due to the addition of titanium.

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  grade of stainless steel pipe  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 grade pf stainless steel pipe  is their corrosion resistance. Type 316, fortified with molybdenum, even combats chloride ions commonly found in marine and chemical processing settings. Irrespective of the grade of stainless steel pipe , 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.

 

You may also like

Essential Tips for Purchasing Stainless Steel Welded Pipe
Type of Different Stainless Steel Tube Material

 

American (ASTM) standards for stainless steels for general applications

The table displays only the most up-to-date standards, as ASTM standards undergo annual review and status updates, regardless of whether changes have been made. Therefore, the original and current years of issue are not included in the table. To locate a specific standard, use the ‘Ctrl’ and ‘F’ keys.

 

 

Table

 

Std NumberTitle
General
ASTM A450Specification for General Requirements for Carbon, Ferritic Alloy, and Austenitic Alloy Steel Tubes
ASTM A480Specification for General Requirements for Flat-Rolled Stainless And Heat-Resisting Steel Plate, Sheet and Strip
ASTM A484Specification for General Requirements for Stainless Steel Bars, Billets, and Forgings
ASTM A555Specification for General Requirements for Stainless Steel Wire and Wire Rods
ASTM A999Specification for General Requirements for Alloy and Stainless Steel Pipe
ASTM A1016Specification for General Requirements for Ferritic Alloy Steel, Austenitic Alloy Steel and Stainless Steel Tubes
Flat Products
ASTM A167Specification for Stainless and Heat-Resisting Chromium-Nickel Steel Plate, Sheet and Strip
ASTM A176Specification for Stainless and Heat-Resisting Chromium Steel Plate, Sheet, and Strip
ASTM A666Specification For Annealed or Cold-Worked Austenitic Stainless Steel Sheet, Strip, Plate and Flat Bar
ASTM A693Specification for Precipitation-Hardening Stainless And Heat-Resisting Steel Plate, Sheet and Strip
 
Long Products
ASTM A276Specification for Stainless Steel Bars and Shapes
ASTM A314Specification for Stainless Steel Billets and Bars for Forging
ASTM A493Specification for Stainless Steel Wire and Wire Rods for Cold Heading and Cold Forging
ASTM A564Specification for Hot-Rolled And Cold-Finished Age-Hardening Stainless Steel Bars and Shapes
ASTM A565Specification for Martensitic Stainless Steel Bars, Forgings, and Forging Stock for High Temperature Service
ASTM A582Specification for Free Machining Stainless Steel Bars
Tubes & Pipes
ASTM A182Specification for Forged or Rolled Alloy-Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service
ASTM A268Specification for Seamless and Welded Ferritic Stainless Steel Tubing for General Service
ASTM A269Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service
ASTM A312Seamless and Welded Austenitic Stainless Steel Pipe
ASTM A358Electric Fusion Welded Austenitic Chromium Nickel Alloy Steel Pipe for High Temperature Service
ASTM A403Specification for Wrought Austenitic Stainless Steel Piping Fittings
ASTM A409Specification for Welded Large Diameter Austenitic Steel Pipe for Corrosive or High Temperature Service
ASTM A511Specification for Seamless Stainless Steel Mechanical Tubing
ASTM A554Specification for Welded Stainless Steel Mechanical Tubing
ASTM A632Specification for Seamless and Welded Austenitic Stainless Steel Tubing (Small-Diameter) for General Service
ASTM A731Specification for Seamless and Welded Ferritic Stainless Steel Pipe
ASTM A789Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service
ASTM A790Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Pipe
 
ASTM A813Specification for Single or Double Welded Austenitic Stainless Steel Pipe
ASTM A814Specification for Cold Worked Welded Austenitic Stainless Steel Pipe
Forgings
ASTM A473Specification for Stainless Steel Forgings
ASTM A705Specification for Age Hardening Stainless and Heat Resisting Steel Forgings
Castings
ASTM A297Specification for Steel Castings, Iron-Chromium and Iron-Chromium-Nickel, Heat-Resistant for General Application
ASTM A743Standard Specification for Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant, for General Application
ASTM A744Standard Specification for Castings, Iron-Chromium-Nickel, Corrosion Resistant, for Severe Service
ASTM A890

Standard Specification for castings, iron-chromium-nickel-molybdenum corrosion-resistant, duplex (austenitic/ferritic) for general application

The above table originating from :

https://bssa.org.uk/bssa_articles/american-astm-standards-for-stainless-steels-for-general-applications/

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.

Leave a Reply

Your email address will not be published. Required fields are marked *

Get in Touch

    Brochure Catalog