An autogenous duplex weld, made without filler, cools with too much ferrite and too little austenite unless it is annealed afterwards, which is why welded duplex pipe made with an over-alloyed filler to ASTM A928 is often preferred for demanding service. The filler puts the austenite back. Our duplex welded pipes and tubes cover UNS S31803 and S32205 in the sizes seamless production cannot reach economically. Welded construction is what makes large-bore duplex affordable. It serves chloride-bearing systems at plants across Oman. Seamless options and super duplex grades sit on the duplex and super duplex hub.
Where Welded Duplex Is Used
- Large-diameter process and water lines in chloride service
- Seawater, brine and produced water headers
- Desalination plant piping above seamless sizes
- Structural and tank connection piping in marine environments
- Projects where the cost difference against seamless is decisive
For small bores and services that exclude seams, duplex seamless pipes and tubes are the alternative.
A790 Welded or A928: Two Routes to a Welded Duplex Pipe
Route | How the seam is made | Consequence |
|---|---|---|
Welded pipe to ASTM A790 | Usually welded without filler metal, then solution annealed | Annealing restores phase balance; no filler chemistry to consider |
Welded pipe to ASTM A928 | Welded with filler metal, in classes that define heat treatment and radiography | Nickel-rich filler helps austenite form; class sets NDE and joint efficiency |
Where a project specification names A928 and a class, that choice affects both the design wall thickness, through weld joint efficiency, and the amount of radiography performed. Where the specification simply says "welded duplex", ask which standard and class the design assumed before ordering.
Sour Service
Under NACE MR0175 / ISO 15156-3, duplex grades are accepted within defined limits, and the hardness limit applies to the weld and heat-affected zone as well as the pipe body. For welded duplex, that makes weld procedure qualification and hardness surveys part of the acceptance, not an optional extra. State your service conditions in the RFQ; requirements are confirmed at quotation.
Price Factors
- Grade and UNS number
- Standard and class, particularly A928
- Diameter, wall and length
- Radiography, ferrite and corrosion testing
- Quantity and stock availability versus a mill order
- Certification (EN 10204 3.1 or 3.2) and third-party inspection
- Incoterm and destination port
Quotations are available in USD, OMR, AED, SAR, QAR, KWD and BHD, on EXW, FOB, CFR or CIF terms.
What to send for a quotation:
grade and UNS number, standard and class, NPS or OD, schedule or wall, length, quantity, testing, certification, inspection, destination port and required date.
Certificates and Inspection
Welded duplex is supplied with EN 10204 3.1 certificates as standard, and EN 10204 3.2 certificates on request. Inspection by the buyer's nominated third-party agency can be arranged; state your requirement in the RFQ. The package should cover chemistry with nitrogen, welding and filler details where applicable, heat treatment, tensile and hardness results, radiography and any ferrite or corrosion testing. See the MTC and EN 10204 certification guide.
Storage and Handling
Lead time is confirmed at quotation. Pipe ships capped and, where specified, wrapped. Segregate duplex from carbon steel and austenitic stainless, use dedicated tools, and protect the surface from iron contamination during storage and fabrication.
Fittings and Related Products
Welded duplex is used across desalination and water treatment, marine and offshore and fertilizer plants.
Duplex Welded Pipe FAQ
What is the difference between A790 welded and A928 pipe?
A790 welded duplex is usually made without filler metal and then solution annealed. A928 pipe is welded with filler metal and supplied in classes that define heat treatment and radiography.
Why does filler metal matter in duplex welding?
Duplex weld metal needs enough austenite. Nickel-rich filler promotes austenite formation, which an autogenous weld cannot do on its own.
Is welded duplex acceptable for sour service?
Yes, within ISO 15156-3 limits, with hardness limits applying to the weld and heat-affected zone and procedure qualification required.
Why is S32205 preferred over S31803 for welded work?
Its higher nitrogen minimum helps austenite re-form as the weld cools, so corrosion resistance is more reliably retained.
What testing is usual?
Ferrite measurement, impact testing, ASTM G48 corrosion testing and radiography per the class.
What should I send for a quotation?
Send the grade and UNS number, standard and class, size, wall, length, quantity, testing, certification, inspection and destination port.
Request a Quote for Duplex Welded Pipes and Tubes
Send the UNS number, standard and class, size and quantity, with any testing requirements. Every enquiry is checked against ASTM A790 or A928 before the offer is prepared, so the class that governs your design wall thickness is confirmed at the start.