Xi'an Dongmeng Group Co., Ltd. is one of the most reliable manufacturers and suppliers of duplex / super duplex seamless stainless steel pipe in China, also supports customized service. With abundant experience, we warmly welcome you to wholesale cheap products in stock here and get free sample from our factory. For price consultation, contact us.
Duplex and Super Duplex Seamless Stainless Steel Pipe
Dongmeng Group supplies duplex and super duplex seamless stainless steel pipe and tube for offshore, oil and gas, chemical processing, desalination, seawater handling and heat-transfer systems.
Our products are available in lean duplex, standard duplex and super duplex grades. Each order can be supplied with material traceability, dimensional inspection, mechanical testing, nondestructive examination and project-specific documentation.
What Is Duplex Stainless Steel Seamless Pipe?
Duplex stainless steel contains both ferritic and austenitic phases in its microstructure.
This two-phase structure provides higher mechanical strength than conventional austenitic stainless steels and improved resistance to chloride stress corrosion cracking. Molybdenum- and nitrogen-alloyed grades also provide strong resistance to pitting and crevice corrosion.
Duplex 2205 offers approximately twice the proof strength of standard austenitic stainless steel, while super duplex 2507 provides higher resistance for more aggressive chloride-containing environments.
Seamless pipe is manufactured without a longitudinal weld. It is commonly selected for critical pressure systems, small and medium diameters, heavy walls or projects with strict weld-seam restrictions.
The final material grade must be selected according to the actual process fluid, pressure, temperature, chloride content, pH, oxygen level, H₂S exposure and applicable design code.
Duplex and Super Duplex Grade Comparison
| Grade | Type | Common Designation | Typical PREN Level | Recommended Applications |
| UNS S32304 | Lean Duplex | 2304 / EN 1.4362 | Mid-20s | Water systems, structural piping and moderately corrosive service |
| UNS S31803 | Duplex | 2205 composition range | Above 30 | General chemical, process and chloride-containing service |
| UNS S32205 | Duplex | 2205 / EN 1.4462 | Typically above 35 | Offshore piping, heat exchangers, brackish water and process systems |
| UNS S32750 | Super Duplex | 2507 / EN 1.4410 | Typically 40 or higher | Seawater, desalination, subsea and highly corrosive process systems |
| UNS S32760 | Super Duplex | EN 1.4501 | Typically 40 or higher | Offshore, seawater, chemical and sour-service project components |
Representative Chemical Composition
| Grade | C Max. | Cr | Ni | Mo | N | Other Principal Elements |
| S32304 | 0.03% | Approx. 22.5% | Approx. 4.5% | Approx. 0.3% | Approx. 0.10% | Cu approximately 0.3% |
| S32205 | 0.03% | Approx. 22% | Approx. 5% | Approx. 3.2% | Approx. 0.18% | - |
| S32750 | 0.03% | Approx. 25% | Approx. 7% | Approx. 4% | Approx. 0.30% | - |
| S32760 | 0.03% | Approx. 25.5% | Approx. 7% | Approx. 3.8% | Approx. 0.26% | Cu and W additions |
These are representative nominal compositions for grade comparison. Material acceptance must be based on the chemical limits in the applicable ASTM, EN or project specification and the supplied Mill Test Certificate.
Product Standards
| Product Requirement | Applicable Standard |
| Seamless Duplex Stainless Steel Pipe | ASTM A790/A790M |
| Seamless Duplex Stainless Steel Tube | ASTM A789/A789M |
| European Seamless Stainless Steel Tube | EN 10216-5 |
| General Requirements for ASTM Pipe | ASTM A999/A999M |
| General Requirements for ASTM Tube | ASTM A1016/A1016M |
| Standard Stainless Steel Pipe Dimensions | ASME B36.19 |
| Detection of Detrimental Intermetallic Phases | ASTM A923 |
| Pitting and Crevice Corrosion Testing | ASTM G48, when specified |
| Inspection Certificate | EN 10204 3.1 or 3.2 |
| Offshore Material Data Sheets | NORSOK M-630, when specified |
| Manufacturer Qualification | NORSOK M-650, when specified |
| Sour-Service Requirements | NACE MR0175 / ISO 15156, subject to service conditions |
ASTM A790 covers seamless and straight-seam welded ferritic-austenitic stainless steel pipe. ASTM A789 covers seamless and welded duplex tubing for general corrosion-resistant service. ASTM A928 should not be listed as a seamless-pipe standard because it specifically covers electric-fusion-welded pipe made with filler metal.
Typical Supply Range
| Parameter | Typical Available Range |
| Product Form | Seamless pipe, seamless tube and heat-exchanger tube |
| Outside Diameter | 6–273 mm standard commercial range |
| Special Outside Diameter | Subject to grade, wall and production-route review |
| Wall Thickness | 0.8–30 mm typical |
| Heavy Wall | Available after mill feasibility review |
| Standard Pipe Sizes | NPS 1/2 to NPS 12, subject to grade and schedule |
| Schedules | 5S / 10S / 40S / 80S and project-specific walls |
| Standard Length | 5.8 / 6 / 11.8 / 12 m |
| Custom Length | Cut according to project requirements |
| Ends | Plain / Beveled / Threaded by special request |
| Surface | Pickled and passivated / Bright annealed / Cold drawn |
| Dimensional Basis | ASME B36.19 or specified OD × WT |
Commercial size availability varies substantially between S32304, S32205, S32750 and S32760. For reference, established seamless-tube producers list maximum standard outside diameters of approximately 260 mm for several duplex and super duplex grades. Larger diameters should therefore be confirmed against the actual mill route before quotation.
Do not publish a maximum OD of 610 mm as a standard seamless range unless the production mill and manufacturing route have been verified.
Reference Mechanical Properties
The following values are representative of solution-annealed seamless tube and pipe with wall thicknesses generally not exceeding 20 mm. Final acceptance must follow the specified product standard and MTC.
| Grade | 0.2% Proof Strength | Tensile Strength | Elongation | Maximum Hardness |
| S32304 | ≥400 MPa | 630–820 MPa | ≥25% | 30 HRC |
| S32205 | ≥485 MPa | 680–880 MPa | ≥25% | 28 HRC |
| S32750 | ≥550 MPa | 800–1000 MPa | ≥25%* | 32 HRC |
Duplex 2205 vs Super Duplex 2507
| Selection Factor | Duplex 2205 / S32205 | Super Duplex 2507 / S32750 |
| Alloying Level | Approximately 22Cr-5Ni-3Mo-N | Approximately 25Cr-7Ni-4Mo-N |
| PREN | Typically above 35 | Typically 40 or higher |
| Mechanical Strength | High | Very high |
| Chloride Resistance | Strong | Higher |
| Typical Environment | Brackish water and many process fluids | Seawater and more aggressive chloride service |
| Material Cost | Lower | Higher |
| Welding Control | Important | More restrictive heat-input control |
| Typical Use | Process piping and heat exchangers | Desalination, offshore and subsea systems |
Super duplex is not automatically required for every marine or chemical application. Duplex 2205 may provide the better lifecycle cost where the operating conditions fall within its corrosion and mechanical limits.
The material-selection decision should be made by the project corrosion or piping engineer using actual operating and upset conditions.
Seamless Manufacturing Process
A typical production route includes:
Raw-material and billet identification
Billet heating
Rotary piercing or extrusion
Hot rolling or pilger processing
Cold drawing or cold pilgering when required
Solution annealing
Rapid water or air quenching
Straightening and dimensional calibration
Pickling and passivation or bright annealing
Hydrostatic or nondestructive electric testing
Final dimensional, surface and marking inspection
Correct solution annealing and rapid cooling are especially important for duplex stainless steel because inappropriate thermal history can create detrimental intermetallic phases and reduce toughness and corrosion resistance. ASTM A923 provides test methods for detecting such phases.
Inspection and Quality Assurance
Inspection can be arranged according to the applicable standard, purchase order and inspection and test plan.
Available inspection items include:
Heat-number and material traceability
Chemical composition verification
Positive Material Identification
Tensile and hardness testing
Hydrostatic testing
Ultrasonic testing
Eddy-current or electromagnetic testing
Outside diameter and wall-thickness measurement
Straightness and length inspection
Visual and surface inspection
Ferrite or phase-balance examination when specified
Charpy impact testing at the specified temperature
ASTM A923 testing for detrimental phases
ASTM G48 corrosion testing when required
Pickling and passivation verification
Third-party inspection
ASTM A923 should be described as a detrimental-intermetallic-phase test, not as a ferrite-content standard. Its methods include an etch examination, Charpy impact testing and ferric-chloride corrosion testing.
Available Documentation
EN 10204 3.1 Mill Test Certificate
EN 10204 3.2 certificate when contractually arranged
Heat-treatment record
Hydrostatic test report
NDT report
PMI report
Dimensional inspection report
Ferrite or metallographic report
Impact-test report
Corrosion-test report
Certificate of Conformity
Packing list and heat-number list
Third-party inspection release note
The required inspection level and documentation package should be agreed before production.
Welding Recommendations
Duplex and super duplex materials can be welded successfully, but the welding procedure must maintain an acceptable phase balance and avoid the formation of detrimental phases.
General considerations include:
Preheating is normally not used.
Interpass temperature is commonly controlled below 150°C.
Heat input must follow the qualified welding procedure.
ER2209-type filler is commonly used for 2205.
ER2594-type filler is commonly used for 2507 and S32760.
Post-weld heat treatment is not normally applied to conventional field welds.
Heat tint, oxide and contamination should be removed where corrosion performance is critical.
Welding procedures and operators must meet the project construction code.
Published manufacturer guidance for S32750 and S32760 recommends controlled heat input, an interpass temperature below 150°C and no routine preheating or post-weld heat treatment.
Final welding requirements must be established through a qualified WPS/PQR for the exact grade, thickness, joint design and service.
Corrosion and Service-Temperature Considerations
Duplex stainless steels provide strong resistance to chloride stress corrosion cracking and localized corrosion, but they are not immune to corrosion.
Material suitability depends on:
Chloride concentration
Operating and cleaning temperature
pH
Oxygen and oxidizing conditions
H₂S and CO₂ partial pressure
Flow velocity
Crevice geometry
Deposits and fouling
Galvanic contact
Surface condition
Welding quality
Cathodic-protection conditions
Avoid publishing a universal maximum chloride concentration or a single maximum service temperature for every application.
Prolonged exposure at elevated temperatures can change the duplex microstructure and reduce impact toughness. Design limits must follow the selected grade, product form, pressure-design code and actual environment.
Typical Applications
Duplex and super duplex seamless pipes are used for:
Offshore production platforms
FPSO process piping
Subsea flowlines and equipment
Seawater injection systems
Seawater cooling systems
Reverse-osmosis desalination plants
High-pressure desalination piping
Oil and gas production systems
Sour-service piping subject to project qualification
Chemical and petrochemical processing
Heat exchangers and condensers
Pulp and paper processing
Brine and salt-production systems
Flue-gas cleaning equipment
Geothermal systems
Pressure equipment and instrumentation lines
S32750 is widely used in aggressive chloride-containing services including seawater handling, desalination and heat-exchanger systems. S32205 is commonly applied in chloride-bearing process systems, refineries and heat exchangers using brackish or chloride-containing cooling water.
Custom Processing Services
Dongmeng Group can provide raw pipe or processed components according to project requirements.
Available services include:
Fixed-length cutting
End facing
Bevel preparation
CNC turning
Drilling and machining
Pipe bending
U-bend heat-exchanger tubes
Surface pickling and passivation
Internal and external polishing
Custom marking
End caps and corrosion protection
Seaworthy wooden-case packing
Drawings should identify the material grade, standard, dimensions, tolerance, bending radius, end preparation and inspection requirements.
Packaging and Traceability
Standard export protection may include:
Plastic end caps
Waterproof wrapping
Individual pipe sleeves
Bundled steel frames
Reinforced wooden cases
Desiccant for sea transport
Heat-number labels
Color-coded tags
Customized shipping marks
Heat numbers should remain traceable from the Mill Test Certificate to the pipe marking, packing list and individual bundle.
Why Choose Dongmeng Group?
Dongmeng Group provides metal-material supply, seamless pipe sourcing, custom processing, quality inspection and international project delivery.
The group website reports five manufacturing centers, 18 production lines, 10 warehouses and 588 employees. It also displays ISO 9001, SGS, CPR and RoHS-related certificates and reports.
Customers can receive:
Multiple duplex and super duplex grades
Standard and project-specific dimensions
Technical review before quotation
Material traceability and MTC verification
NDT and third-party inspection coordination
Cut-to-length and end processing
Project documentation packages
Export packaging
FOB, CFR, CIF and DDP shipping support
NORSOK, DNV, ABS, BV or Lloyd's requirements must be confirmed against the exact manufacturing mill, qualification record and inspection scope before the order is accepted.
Request a Technical Quote
For an accurate quotation, please provide:
Product type: pipe or tube
Material grade and UNS number
Applicable material standard
NPS or outside diameter
Schedule or wall thickness
Required length
Quantity
Surface condition
Design temperature
Process medium
Inspection and testing requirements
MTC type
NORSOK or sour-service requirements
Destination port or delivery address
Company: Dongmeng Group
Email: office@dongmjd.com
Phone / WhatsApp: +86 157 6921 4734
Website: www.cndmmetal.com
Recommended CTA: Request a Duplex Pipe Technical Quote
Frequently Asked Questions
What is the difference between ASTM A789 and ASTM A790?
ASTM A789 covers duplex stainless steel tubing, while ASTM A790 covers duplex stainless steel pipe. The correct standard depends on whether the product is ordered as tube by actual outside diameter and wall thickness or as pipe by NPS and schedule.
Does ASTM A928 apply to seamless duplex pipe?
No. ASTM A928 applies to electric-fusion-welded duplex stainless steel pipe manufactured with filler metal. It should not be used as the main standard on a seamless-pipe product page.
Is S31803 the same as S32205?
They are closely related 2205 duplex grades, but S32205 has tighter chemistry controls intended to provide more consistent corrosion performance. The purchase order should specify the exact UNS grade required.
When should S32750 be selected instead of S32205?
S32750 is generally considered where the environment presents more severe chloride, pitting or crevice-corrosion risk. Final selection must be based on the complete process conditions and engineering design.
Are duplex seamless pipes twice as strong as 316L?
Duplex grades commonly provide roughly twice the proof strength of conventional annealed austenitic stainless steels. The exact design advantage depends on the product standard, wall thickness, temperature and design code.
Is ASTM A923 a ferrite-content test?
No. ASTM A923 is used to detect detrimental intermetallic phases that can reduce toughness and corrosion resistance. Ferrite or phase balance must be evaluated using the method specified by the project.
Can you supply NORSOK-compliant pipe?
Project supply can be reviewed against the applicable NORSOK M-630 material data sheet. Compliance depends on the exact grade, product form, manufacturing route, size range, mill qualification and required testing.
Can duplex and super duplex pipe be welded?
Yes. Welding requires a qualified procedure with controlled heat input, interpass temperature, filler metal and surface restoration. ER2209 is commonly used for 2205 and ER2594 for super duplex grades.
What documents are required for offshore projects?
Typical packages may include an EN 10204 3.1 or 3.2 certificate, heat-treatment record, NDT reports, PMI, ferrite or microstructure report, impact testing, corrosion testing and third-party inspection release.
Can you provide custom sizes?
Yes. Dongmeng Group supports custom OD, wall thickness, length, beveling, bending and machining, subject to grade availability and production feasibility.
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