stainless steel pipes

ASTM A312 / A790 / A928 Stainless Steel, Duplex, and Super Duplex Pipes for Corrosive Service

stainless steel pipes

ASTM A312 / A790 / A928 Stainless Steel, Duplex, and Super Duplex Pipes for Corrosive Service

The ASTM A312 specification covers seamless and welded austenitic stainless steel pipes used for high-temperature and/or corrosive service (the most common grades are 304/304L and 316/316L). The A790 specification covers seamless duplex and super duplex pipes UNS S32205/31803 and UNS S32750/32760 (special SS grade with a mixed ferritic/austenitic microstructure). In this article, we illustrate the chemical and mechanical properties of the A312/A790 specifications.



ASTM A312 is a specification for seamless, welded, and heavily cold-worked austenitic stainless steel pipes intended for high-temperature and general corrosive service.

Stainless steel pipes ASTM A312 TP304 TP316
Stainless steel pipes ASTM A312 TP304 TP316

Stainless steel pipes manufactured according to ASTM A312 are widely used in various industries such as oil and gas, chemical processing, food processing, pharmaceuticals, and construction. 

Here are some key features of ASTM A312 stainless steel pipes:


ASTM A312 specification covers both seamless and welded austenitic stainless steel pipes. Seamless pipes are produced by extruding a billet through a mandrel or piercing a solid bar to form a hollow tube, while welded pipes are manufactured by welding together stainless steel plates or coils.


ASTM A312 stainless steel pipes are available in several grades, including:

  • Grade TP304/304L: The most commonly used grade of stainless steel for general corrosive service and low-temperature applications.
  • Grade TP316/316L: Known for its higher corrosion resistance and strength, particularly in high-temperature and aggressive chemical environments.
  • Other grades such as TP321, TP347, TP310, and TP904L are also available for specific applications requiring enhanced properties.


Chemical Composition

  • The chemical composition of ASTM A312 stainless steel pipes varies depending on the grade. However, common alloying elements include chromium, nickel, and molybdenum, which impart corrosion resistance, strength, and toughness to the steel.
  • The composition may also include elements such as carbon, manganese, silicon, and nitrogen in controlled amounts to achieve desired properties.


Mechanical Properties

  • ASTM A312 stainless steel pipes undergo various mechanical tests to ensure compliance with specified requirements. These tests may include tensile testing, hardness testing, and non-destructive testing (NDT) such as ultrasonic testing.
  • Mechanical properties such as tensile strength, yield strength, elongation, and hardness vary depending on the grade and heat treatment condition.


Dimensions and Sizes

  • ASTM A312 stainless steel pipes are available in a wide range of sizes and dimensions, ranging from 1/8 inch to 24 inches in nominal diameter. The wall thickness can vary depending on the nominal pipe size and grade.
  • Standard pipe schedules such as SCH 5, SCH 10, SCH 40, and SCH 80 are commonly available for ASTM A312 pipes.



ASTM A312 stainless steel pipes find applications in various industries, including:

  • Oil and gas: Pipelines, refineries, and petrochemical plants.
  • Chemical processing: Chemical reactors, storage tanks, and process piping.
  • Food processing: Dairy equipment, food processing machinery, and beverage production.
  • Pharmaceuticals: Pharmaceutical processing equipment and sterile piping systems.
  • Construction: Architectural structures, handrails, and decorative elements.



  • ASTM A312 stainless steel pipes are readily weldable using conventional welding methods such as TIG (tungsten inert gas) welding, MIG (metal inert gas) welding, and manual arc welding.
  • Preheating and post-weld heat treatment may be necessary to prevent sensitization and ensure corrosion resistance in welded joints.


Overall, ASTM A312 stainless steel pipes are widely preferred for their excellent corrosion resistance, high-temperature performance, and versatility in various industrial applications. When selecting ASTM A312 pipes for a specific application, it is essential to consider factors such as grade, size, wall thickness, surface finish, and end connections to ensure they meet the specific requirements and performance criteria.




The history of stainless steel is a fascinating journey that spans several centuries and involves numerous technological advancements and innovations. Here’s a brief overview of the key milestones in the history of stainless steel:

1. Discovery of Chromium Effects:
The story of stainless steel began in the early 20th century when metallurgists were experimenting with different alloy compositions to improve the corrosion resistance of steel. In 1912, Harry Brearley, a British metallurgist, discovered that adding chromium to steel significantly improved its resistance to rust and corrosion. This discovery laid the foundation for the development of stainless steel.

2. Introduction of Martensitic Stainless Steel:
In 1913, Brearley produced the first stainless steel, known as martensitic stainless steel, by adding around 12% chromium to steel. This alloy exhibited remarkable corrosion resistance and was initially used in cutlery and surgical instruments.

3. Development of Austenitic Stainless Steel:
In the 1920s, researchers at Krupp in Germany and researchers in the United States independently developed austenitic stainless steel, which contained higher levels of chromium and nickel. Austenitic stainless steel offered superior corrosion resistance and became the most widely used type of stainless steel.

4. World War II and Stainless Steel Demand:
During World War II, the demand for stainless steel soared as it proved invaluable for military applications such as aircraft, naval vessels, and weaponry. Stainless steel’s corrosion resistance, strength, and durability made it indispensable for critical wartime infrastructure.

5. Post-War Industrial Boom:
After World War II, stainless steel experienced a surge in demand as industries around the world expanded rapidly. Its versatility, hygiene properties, and aesthetic appeal led to its widespread adoption in various sectors, including automotive, construction, chemical processing, and food processing.

6. Advancements in Stainless Steel Manufacturing:
Over the decades, advancements in metallurgy, manufacturing processes, and alloy compositions have led to the development of a wide range of stainless steel grades tailored for specific applications. These advancements include the development of duplex stainless steel, precipitation-hardening stainless steel, and high-temperature alloys.

7. Modern Applications and Innovations:
Today, stainless steel is ubiquitous in everyday life and is used in a myriad of applications, including kitchen appliances, architectural structures, medical devices, transportation infrastructure, and renewable energy systems. Innovations continue to drive the evolution of stainless steel, with ongoing research focused on improving its properties, sustainability, and recyclability.


The history of stainless steel pipes is closely intertwined with the broader history of stainless steel itself. Stainless steel pipes have played a crucial role in various industries due to their exceptional corrosion resistance, durability, and versatility. Here’s a brief overview of the history of stainless steel pipes:

1. Early Developments in Stainless Steel:
The discovery of stainless steel in the early 20th century paved the way for the development of stainless steel pipes. In 1912, Harry Brearley, a British metallurgist, discovered that adding chromium to steel significantly improved its corrosion resistance. This led to the creation of the first stainless steel alloys, which were initially used in cutlery and surgical instruments.

2. Introduction of Stainless Steel Pipes:
As the demand for corrosion-resistant materials grew, stainless steel pipes emerged as a vital solution for various industries. In the 1920s and 1930s, austenitic stainless steel, containing higher levels of chromium and nickel, became the preferred material for pipe manufacturing due to its superior corrosion resistance and durability.

3. World War II and Industrial Expansion:
During World War II, stainless steel pipes played a crucial role in military applications such as shipbuilding, aircraft construction, and weapon manufacturing. The war effort led to increased production of stainless steel pipes and spurred technological advancements in pipe manufacturing processes.

4. Post-War Boom and Diversification:
After World War II, the industrial boom led to a surge in demand for stainless steel pipes across various sectors, including oil and gas, chemical processing, food processing, and construction. Stainless steel pipes found widespread use in pipelines, refineries, petrochemical plants, and architectural structures.

5. Advancements in Manufacturing Processes:
Over the years, advancements in metallurgy and manufacturing processes have further enhanced the quality and performance of stainless steel pipes. Innovations such as seamless pipe manufacturing techniques, improved welding technologies, and advanced surface finishing methods have made stainless steel pipes more reliable and cost-effective.

6. Specialized Applications and Grades:
As industries evolved, the demand for specialized stainless steel pipes grew. Manufacturers began producing pipes in a wide range of grades and sizes to meet the specific requirements of different applications. Specialized grades such as duplex stainless steel, high-temperature alloys, and corrosion-resistant alloys have been developed to address the unique challenges of various industries.

7. Modern Innovations and Sustainability:
Today, stainless steel pipes continue to be at the forefront of innovation, with ongoing research focused on improving their performance, sustainability, and lifecycle characteristics. Innovations in alloy design, manufacturing processes, and surface coatings have made stainless steel pipes more durable, environmentally friendly, and cost-effective.

Overall, the history of stainless steel pipes reflects the remarkable evolution of stainless steel as a material and its pivotal role in shaping modern industrial infrastructure and everyday life.


Before delving into the various grades, let’s take a moment to examine the types of stainless steel available in the market and how they are classified.

As a general rule, any steel alloy containing at least 10.5% chromium may be considered stainless steel. However, the market offers a multitude of grades based on the combination of alloying elements such as nickel, chromium, molybdenum, titanium, copper, nitrogen, and others. Each alloy possesses a distinct structure and specific chemical and mechanical properties.

The primary characteristic of stainless steel is its corrosion resistance, attributed to an outer layer of chromium oxide. This oxide layer serves as a microscopic protective barrier, reacting with oxygen to inhibit corrosion. Additionally, stainless steel alloys exhibit superior toughness in cryogenic applications compared to carbon steel, along with enhanced strength, hardness, ductility, and low maintenance costs.

Stainless steels may be grouped into a few families, designated as “series”. Let’s take a closer look.

Austenitic Stainless Steel (Series 300)

These are the most common grades of stainless steel. The microstructure of austenitic stainless steels is obtained with the addition of nickel, manganese, and nitrogen which give weldability and formability properties to the alloy. The corrosion resistance can be further improved by augmenting the percentage of chrome, moly, and nitrogen in the base alloy.

Nevertheless, the basic austenitic grades are vulnerable to stress corrosion cracking (higher percentages of nickel are necessary to enhance the stress corrosion cracking). Austenitic stainless steel cannot be hardened by heat treatment but can work hardened to high strength levels while retaining a reasonable level of strength and ductility.

Even if austenitic steels are generally non-magnetic, they can show some magnetic properties based on the actual alloy composition and the work hardening given during production. Austenitic stainless steels are divided into the series 200 (chromium-manganese-nickel alloys) and 300 (chromium-nickel alloys like 304, 309, 316, 321, 347, etc). Grade 304/304L is the most common austenitic stainless steel that suits most corrosive applications. Any other grade in the 300 series enhances the basic features of SS304.

Martensitic Stainless Steel (Series 400)

Martensitic stainless steels are similar to ferritic steels as they both have remarkable chromium content, however, martensitic steels have higher carbon content up to 1%. The high carbon content allows martensitic steels to be hardened and tempered as standard carbon and chrome alloy steels (but show generally low weldability and ductility).

This type of stainless steel is specified in case of high strength and moderate corrosion resistance requirements. Different from standard austenitic stainless steels, martensitic grades are magnetic. Common martensitic grades are 410, 420, and 440C.

Ferritic Stainless Steel (SS430)

Ferritic stainless steels have significant chrome content but low additions of carbon (generally below 0.1%). The name of this family of stainless steels comes from the fact that their microstructure is quite similar to carbon and low alloy steels.

These steels have a wide range of applications, except for thin surfaces as they have low resistance to welding or applications requiring formability (ferritic steels show low formability and ductility). Ferritic stainless steel cannot be hardened by heat treatment. By adding moly to a ferritic grade, the steel can be used in highly aggressive applications such as desalination plants and seawater.

These steel show also remarkable resistance to stress corrosion cracking. Likewise, martensitic steels and ferritic SS are magnetic. The most common ferritic grades are the 430 (17% chromium), and the 409 (11% chromium), largely used in the automotive sector.

Duplex and Super Duplex Stainless Steel (UNS S32205, S31803, S32750/760)

Duplex stainless steel contains a balanced mixture of austenite and ferrite phases, typically with higher chromium (19% to 32%) and molybdenum (up to 5%) content. It offers a combination of high strength, corrosion resistance, and resistance to stress corrosion cracking. Duplex stainless steel is commonly used in applications requiring excellent resistance to pitting and crevice corrosion, such as marine environments and chemical processing. Common grades include 2205 (S32205) and 2507 (S32750).

Precipitation hardening (PH 17-4)

PH steels can feature remarkable strength due to the addition, in the alloy, of elements such as copper, niobium, and aluminum.

These steels can be machined to very specific shapes with high tolerance requirements before the final aging treatment. This is different from conventional hardening and tempering of martensitic steels that are subject to distortion during the treatment.

The resistance to corrosion of. precipitation hardening steels are comparable to standard austenitic steels like SS304.
The most common precipitation-hardening stainless steel is the 17-4PH, which features 17% chromium and 4% nickel.



The table shows the chemical composition of the most common grades of stainless steel pipes under the ASTM A312-ASME SA312 specification:

TP304NS304510.082.00.0450.0301.018.0-20.08.0-18.0   0.10-0.16
TP304LNS304530.0352.00.0450.0301.018.0-20.08.0-12.0   0.10-0.16
TP309CbS309400.082.00.0450.0301.022.0-24.012.0-16.00.75 10xC min
1.10 max
TP309HCbS309410.04- 10xC min
1.10 max
TP310CbS310400.082.00.0450.0301.024.0-26.019.0-22.00.75 10xC min
1.10 max
TP310HCbS310410.04- 10xC min
1.10 max
TP316NS316510.082.00.0450.0301.016.0-18.010.0-14.02.0-3.0  0.10-0.16
TP316LNS316530.0352.00.0450.0301.016.0-18.011.0-14.02.0-3.0  0.10-0.16
TP321S32100.082.00.0450.0301.017.0-19.09.0-12.0   0.10
TP321HS321090.04-   0.10
TP347LNS347510.05-  0.20-


SS Pipes Grade
Tensile Strength
N/mm2 (min)
Yield Strength
N/mm2 (min)
% (min)
TP321OD < 17,1 mm – 515;OD < 17,1 mm – 205;35
OD > 17,1 mm – 485OD > 17,1 mm – 170


Stainless Steel Pipe Grades
Werkstoff/DINEN gradesASTM grades
1.4541X6CrNiTi18-10A 312 Grade TP321
1.4571X6CrNiMoTi17-12-2A 312 Grade TP316Ti
1.4301X5CrNi18-10A 312 Grade TP304
1.4306X2CrNi19-11A 312 Grade TP304L
1.4307X2CrNi18-9A 312 Grade TP304L
1.4401X5CrNiMo17-12-2A 312 Grade TP316
1.4404X2CrNiMo17-13-2A 312 Grade TP316L
1.4462X2CrNiMoN22-5-3UNS S 31803 (Duplex)
1.4529X1NiCrMoCuN25-20-7UNS N 08926
1.4539X1NiCrMoCu25-20-5UNS N 08904 (904L)
1.4547X1CrNiMoCuN20-18-7UNS S 31254


The standard stainless steel pipe dimensions are set by the ANSI ASME B36.19 specification.

Seamless SS pipes are available in the size range 1/8″ thru 24″, and welded stainless pipes are manufactured in the range 2″ thru 36″ (ASTM A312, ASTM A358, i.e. electric-fusion-welded austenitic chromium-nickel stainless steel pipe, or as rolled).


Nominal Pipe SizeOutside DiameterStainless Steel Pipes Dimensions
Schedule 5SSchedule 10SSchedule 40SSchedule 80S
(mm)(inch)WT / WEIGHT
mm (in)kg/mmm (in)kg/mmm (in)kg/mmm (in)kg/m
1/810.30.4051.25 (0.049)0.281.73 (0.068)0.372.42 (0.095)0.47
1/413.70.5401.66 (0.065)0.492.24 (0.088)0.633.03 (0.119)0.80
3/817.20.6751.66 (0.065)0.632.32 (0.091)0.853.20 (0.126)1.10
1/221.30.8401.65 (0.065)0.812.11 (0.083)1.002.77 (0.109)1.273.74 (0.147)1.62
3/426.71.0501.65 (0.065)1.022.11 (0.083)1.282.87 (0.113)1.683.92 (0.154)2.20
133.41.3151.65 (0.065)1.302.77 (0.109)2.093.38 (0.133)2.504.55(0.179)3.24
1 1/442.21.6601.65 (0.065)1.662.77 (0.109)2.693.56 (0.140)3.394.86 (0.191)4.47
1 1/248.31.9001.65 (0.065)1.912.77 (0.109)3.113.69 (0.145)4.065.08 (0.200)5.41
260.32.3751.65 (0.065)2.402.77 (0.109)3.933.92 (0.154)5.455.54 (0.218)7.49
2 1/273.02.8752.11 (0.083)3.693.05 (0.120)5.265.16 (0.203)8.647.01 (0.276)11.4
388.93.5002.11 (0.083)4.523.05 (0.120)6.465.49 (0.216)11.37.62 (0.300)15.3
3 1/2101.64.0002.11 (0.083)5.183.05 (0.120)7.415.74 (0.226)13.68.08 (0.318)18.6
4114.34.5002.11 (0.083)5.843.05 (0.120)8.376.02 (0.237)16.18.56 (0.337)22.3
5141.35.5632.77 (0.109)9.463.41 (0.134)11.66.56 (0.258)21.89.53 (0.375)31.0
6168.36.6252.77 (0.109)11.33.41 (0.134)13.97.12 (0.280)28.310.9 (0.432)42.6
8219.18.6252.77 (0.109)14.83.76 (0.148)20.08.18 (0.322)42.512.7 (0.500)64.6
10273.110.7503.41 (0.134)22.74.20 (0.165)27.89.28 (0.365)60.412.7 (0.500)81.5
12323.912.7503.97 (0.156)31.34.58 (0.180)36.19.53 (0.375)73.912.7 (0.500)97.4


NPSASTM A312/ASME SA312 OD Tolerance
1/8 to 1 1 /2
> 1 1 /2 to 4
> 4 to 8
> 8 to 18
> 18 to 26
> 26 to 34
> 34 to 48


The nominal wall thickness tolerance is +/- 12.5%.

NPSASTM A312/ASME SA312 WT Tolerance, %
1/8-2 1 /220.012.5
3~18, t/D≤ 5%22.512.5
3~18, t/D> 5%15.012.5
≥ 20, welded17.512.5
≥ 20, seamless, t/D≤ 5%22.512.5
≥ 20, seamless, t/D> 5%15.012.5


PolishingManufacturers can polish any stainless steel pipe item to a #4 polish, #6 Polish, #7 polish or a #8 mirror finish.
CuttingsStainless steel pipes can be produced in standard lengths or cut to size (standard lengths are 20′ and 40′ depending on the nominal pipe size).
BevelingManufacturers can bevel the edges of stainless steel pipes to prepare them for welding.
ThreadingStainless steel pipes can be supplied, besides plain and beveled ends, also with threaded ends (generally for NPS below 2 inches)
Pipe Honing & TurningManufacturers can hone SS pipe and tube, using precision abrasion tools and obtain any desired finish or dimensional tolerance.
Heat treating & AnnealingMost stainless steel pipe grades can be heat treated to modify their mechanical properties.
Positive Material Identification (PMI)Manufacturers can perform PMI testing to ascertain the actual content of Nickel, Chrome, and Moly in the pipe.
UT TestingIn some cases, UT testing of the stainless steel plates may be required.

We recommend purchasing the ASTM A312 specification from the ASTM website or the IHS store to get a complete understanding of this topic.


A duplex pipe features, at the same time, the qualities of a ferritic SS pipe (high resistance to corrosion cracking and tensile strength) and of an austenitic SS pipe (easy manufacturing and good resistance to corrosion and erosion). Duplex pipes 2205 (UNS S31803/UNS S32205) are used for applications below 600 degrees (F).

Duplex and super duplex pipes ASTM A790
Duplex and super duplex pipes ASTM A790

Duplex and super duplex stainless steels are weldable and have moderate formability. These types of stainless steels are magnetic but to a lower extent than ferritic, martensitic, and precipitation hardening grades due to the 50% austenitic content.

The common grades in this family are:

  • Lean duplex: UNS S32101, S32202 (UR2202), S32304, and S32003.
  • Standard duplex: UNS S31803/S32205
  • Super duplex: UNS S32760 (Zeron 100), S32750 (2507), and S32550 (Ferralium 255)
  • Hyper duplex: UNS S32707 and S33207

The ASTM A790 specification covers seamless duplex and super duplex pipes for demanding applications, with high corrosion, temperature, and pressure.

Electro-fusion welded duplex and super duplex welded pipes are covered, instead, by the ASTM A928 specification.

Duplex and super duplex can be considered as ‘higher grade’ stainless steel pipes, and are available on the market in the same dimensional range of conventional A312 stainless steel pipes (size range covered by the ASME B36.19 specification).

There are a few differences between duplex/super duplex pipes and conventional stainless steel pipes, which are explained below.


The term “duplex” refers to a family of stainless steels that have double structure – i.e. they are neither a fully austenitic SS structure, like 304 stainless, nor a standard ferritic, such as the 430 series.

Duplex stainless steel (UNS S31803/UNS S32205) has been developed to overcome the issues of the 300 series stainless steels as 316L and 317L (chloride stress corrosion cracking, under tensile stress in cases where the metal is exposed to fluids containing chlorides or by steel exposure to high temperatures).

The microstructure of duplex steels consists of austenite pools surrounded by a continuous ferrite phase (approx 40-50% ferrite).

Therefore, duplex pipes combine the qualities of ferritic and austenitic stainless steel materials.

UNS 2205 duplex steel finds application in marine projects, oil & gas exploration, closed loops water systems, desalinization plants, hydrocarbon storage and transportation, downstream refining, pulp, and paper.

Duplex are resistant to stress corrosion cracking. While standard duplex steels have corrosion resistance comparable to standard austenitic steels (but show better strength and resistance to stress-corrosion-cracking), the so-called super duplex steels feature enhanced strength and resistance to any type of corrosion compared to standard austenitic steels.


Duplex stainless steel shows a superior corrosion resistance to grade 316 for most applications (excellent resistance to localized corrosion including intergranular, pitting, and crevice corrosion; the CPT of 2205 is generally at least 35ºC). Duplex is also resistant to chloride corrosion cracking (SCC) at temperatures up to about 150ºC.

Grade 2205 duplex will often perform well in environments that cause premature failure of the standard austenitic grades of series 300 stainless steel. It has also stronger resistance to seawater corrosion, compared to stainless steel 316.

Note that, despite Duplex stainless steel showing good high-temperature oxidation resistance, 2205 suffers from embrittlement if kept at temperatures above 300ºC for some time. (a situation that can be rectified only by a full solution annealing treatment).

For this reason, Duplex stainless steels are never used for temperatures over 300ºC. Duplex pipes match the following fittings materials: ASTM A815 (butt weld fittings) and ASTM A182 F51 / F53 / F55 (flanges / forged socket weld – threaded fittings).



The main difference between duplex pipes and traditional stainless steel pipes lies in their microstructure and composition, which result in distinct properties and performance characteristics. Here’s a comparison between duplex pipes and conventional stainless steel pipes:

1. Microstructure:

  • Duplex Pipe: Duplex stainless steel pipes have a two-phase microstructure consisting of roughly equal proportions of austenite and ferrite phases. This unique microstructure provides a balance of high strength and excellent corrosion resistance.
  • Stainless Steel Pipe: Traditional stainless steel pipes, such as austenitic or ferritic stainless steels, typically have a single-phase microstructure predominantly composed of either austenite or ferrite.

2. Corrosion Resistance:

  • Duplex Pipe: Duplex stainless steel pipes offer superior corrosion resistance compared to conventional stainless steel pipes, particularly in chloride-rich and acidic environments. They demonstrate excellent resistance to pitting and crevice corrosion.
  • Stainless Steel Pipe: While conventional stainless steel pipes also provide corrosion resistance, duplex pipes generally offer enhanced resistance to certain types of corrosion, making them suitable for more demanding applications.

3. Strength:

  • Duplex Pipe: Duplex stainless steel pipes are known for their high strength, which exceeds that of austenitic and ferritic stainless steel. This makes duplex pipes suitable for applications requiring structural integrity and load-bearing capacity.
  • Stainless Steel Pipe: Traditional stainless steel pipes exhibit varying levels of strength depending on the grade and microstructure. While some grades offer adequate strength for general applications, duplex pipes provide higher strength levels.

4. Toughness and Ductility:

  • Duplex Pipe: Duplex stainless steel pipes maintain good toughness and ductility despite their high strength, allowing them to withstand impact and deformation without fracturing.
  • Stainless Steel Pipe: Conventional stainless steel pipes also exhibit toughness and ductility, but the specific properties may vary depending on the grade and microstructure.

5. Weldability:

  • Duplex Pipe: Duplex stainless steel pipes are generally weldable using standard welding techniques, although precautions may be necessary to avoid the formation of harmful phases during welding.
  • Stainless Steel Pipe: Traditional stainless steel pipes are typically weldable using conventional welding methods, with varying degrees of susceptibility to welding-related issues such as sensitization and distortion.

Overall, while both duplex pipes and traditional stainless steel pipes offer corrosion resistance and durability, duplex pipes stand out for their superior strength, corrosion resistance, and balance of mechanical properties, making them ideal for demanding applications in industries such as oil and gas, chemical processing, and marine engineering.


UNSChemical CompositionMin. Tensile (KSI)Min. Yield
UNS S31803C 0.30 max
Cr 21.0-23.0
Mn 2.00 max
Mo 2.50-3.50
N 0.08-0.20
Ni 4.50-6.50
P 0.030 max
S 0.020 max
Si 1.00 max
UNS S32205C 0.30 max
Cr 22.0-23.0
Mn 2.00 max
Mo 3.00-3.50
N 0.14-0.20
Ni 4.50-6.50
P 0.030 max
S 0.020 max
Si1.00 max

Duplex pipes are manufactured according to the ASME B36.19 standard.



Super duplex stainless steel is a variation of the duplex steel alloy which is used in the oil & gas, chemical, power generation, mechanical, and desalination industries:

  • oil & gas production equipment
  • Offshore platforms
  • heat exchangers
  • process and service water systems
  • fire-fighting systems
  • injection and ballast water systems
  • piping
  • high-pressure RO plants and seawater piping
  • High-strength and corrosion-resistant parts in mechanical applications
  • FGD systems (power generation)
  • Utility and industrial scrubber systems
  • Absorber towers

The higher chromium and molybdenum content of Super Duplex vs. Duplex makes it extremely resistant to uniform corrosion by organic acids like formic and acetic acid.

Super Duplex also provides excellent resistance to inorganic acids, especially those containing chlorides.

The pitting Resistance equivalent of Super Duplex, calculated by PREN = Cr + 3.3Mo + 16N, will exceed 40 in most material forms.


UNSChemical CompositionMin. Tensile
Min. Yield
UNS S32750C 0.030 max 
Cu 0.5 max
Mn 1.20 max
Mo 3.0-5.0
N 0.24-0.32
Ni 6.0-8.0
P 0.035 max
S 0.020 max
Si 0.8 max
UNS S32760 (“Sandvik”)C 0.03 max 
Cu 0.5-1.0
Mn 1.0 max
Mo 3.0-4.0
N 0.2-0.3
Ni 6.0-8.0
P 0.03 max
S 0.01 max
Si 1.0 max
W 0.5-1.0


Duplex and super duplex pipes are both types of stainless steel pipes with a two-phase microstructure, but they differ in their composition and performance characteristics. Here are the key differences between duplex and super duplex pipes:

1. Composition:

  • Duplex Pipe: Duplex stainless steel pipes typically contain a balanced combination of austenite and ferrite phases, with chromium content ranging from 22% to 26% and nickel content between 4.5% to 6.5%. Common grades include Duplex 2205 (UNS S32205/S31803) and Duplex 2304 (UNS S32304).
  • Super Duplex Pipe: Super duplex stainless steel pipes have a higher chromium content (typically around 24% to 27%) and increased levels of other alloying elements such as molybdenum (up to 6%) and nitrogen (up to 0.3%). This results in superior corrosion resistance and mechanical properties compared to standard duplex grades. Common grades include Super Duplex 2507 (UNS S32750) and Super Duplex Zeron 100 (UNS S32760).

2. Corrosion Resistance:

  • Duplex Pipe: Duplex stainless steel pipes offer excellent corrosion resistance, particularly in chloride-containing environments. They are suitable for applications where moderate to high corrosion resistance is required, such as chemical processing plants and offshore oil and gas platforms.
  • Super Duplex Pipe: Super duplex stainless steel pipes provide even greater corrosion resistance than standard duplex grades, especially in highly corrosive environments such as seawater and acidic solutions. They are preferred for applications subjected to severe corrosion, such as marine engineering, desalination plants, and chemical processing.

3. Strength:

  • Duplex Pipe: Duplex stainless steel pipes exhibit high strength and toughness, making them suitable for structural applications requiring load-bearing capacity and durability.
  • Super Duplex Pipe: Super duplex stainless steel pipes offer higher strength and superior mechanical properties compared to standard duplex grades. They provide enhanced resistance to stress corrosion cracking and fatigue, making them ideal for demanding applications in harsh environments.

4. Cost:

  • Duplex Pipe: Duplex stainless steel pipes are generally more cost-effective than super duplex grades, making them a preferred choice for applications where a balance between performance and cost is required.
  • Super Duplex Pipe: Super duplex stainless steel pipes are more expensive than standard duplex grades due to their higher alloy content and superior properties. They are typically selected for critical applications where superior corrosion resistance and mechanical performance are essential, regardless of cost.

In summary, while both duplex and super duplex stainless steel pipes offer corrosion resistance and durability, super duplex pipes provide enhanced properties such as superior corrosion resistance, higher strength, and better performance in harsh environments. The choice between duplex and super duplex pipes depends on the specific requirements of the application, including the level of corrosion resistance, mechanical strength, and budget considerations.

**DISCLAIMER: Accuracy and Reliability of Content**

The information provided in this blog post is intended for general informational purposes only and should not be construed as professional advice. While we strive to provide accurate and up-to-date information, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability, or availability of the content contained herein. Any reliance you place on the information presented in this blog post is strictly at your own risk. We disclaim any liability for any loss or damage, including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising from reliance on information contained in this blog post. We encourage readers to verify the accuracy and relevance of any information presented here with other sources and seek professional advice or guidance where appropriate. Links to third-party websites or resources provided in this blog post are for convenience only and do not imply endorsement or approval of the content, products, services, or opinions expressed on those websites. We have no control over the nature, content, and availability of those sites and assume no responsibility for their accuracy, legality, or decency. We reserve the right to modify, update, or remove any content in this blog post at any time without prior notice. By accessing and using this blog post, you acknowledge and agree to these terms and conditions. If you do not agree with these terms, please refrain from accessing or using the information provided herein.

About the Author

Picture of Fabrizio S.

Fabrizio S.

Fabrizio is a seasoned professional in the international trading of materials for projects, including piping, steel, and metal commodities with a distinguished career spanning over two decades. He has become a pivotal figure in the industry, renowned for his expertise in bridging the gap between EPC contractors, end users, manufacturers, and stockists to facilitate the seamless delivery of complex piping product packages across the globe. Starting his journey with a strong academic background in business administration and international trade, Fabrizio quickly distinguished himself in the field through his adept negotiation skills, strategic vision, and unparalleled knowledge of the project materials market. His career trajectory has seen him collaborate with leading names in the construction, oil & gas, and petrochemical industries, earning a reputation for excellence in executing large-scale projects (EPC Contractors, Oil & Gas End Users). At the core of Fabrizio's success is his ability to understand the intricate needs of EPC contractors and end users, aligning these with the capabilities of manufacturers and stockists. He excels in orchestrating the entire supply chain process, from product specification and procurement to logistics and on-time delivery, ensuring that each project phase is executed flawlessly. Fabrizio's role involves intense coordination and communication, leveraging his extensive network within the industry to negotiate competitive prices, manage complex logistical challenges, and navigate the regulatory landscape of international trade. His strategic approach to package assembly and delivery has resulted in cost efficiencies, timely project execution, and high satisfaction levels among stakeholders. Beyond his professional achievements, Fabrizio is an active participant in industry forums and conferences, such as Adipec, Tube, and similar, where he shares insights on market trends, supply chain optimization, and the future of project materials trading. His contributions to the field are not only limited to his operational excellence but also include mentoring young professionals entering the trade. Fabrizio is one of the co-founders of Projectmaterials, a B2B marketplace targeting the above markets.

Should you wish to reach out to the author of this article, we invite you to contact us via email

14 Responses

  1. This article serves as an excellent resource for engineers, project managers, and anyone involved in the selection and application of stainless steel pipes. The depth of information provided, along with the clarity of explanations, makes it a go-to reference for professionals navigating the complexities of stainless pipe standards.

  2. Thank you for mentioning that corrosion is a major problem in high-temperature situations when stainless steel pipes are employed. I recently moved into a new home and plan to add a steel structure to it. To assist me, I will speak with a structural steel expert.

  3. Hi,
    Very useful and up-to-date information. The accumulation of the sources and to describe it in such a well manner, I would say in one word “legendary”. Thanks for sharing and spreading the knowledge into the metal industry!
    All the very best.

Leave a Reply

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

This site uses Akismet to reduce spam. Learn how your comment data is processed.