Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175 / ISO 15156-2
- NORSOK M-650 Qualified
- API 6A Certified
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Super Duplex 2507 Welding Filler, ER2594 and ER2553 (AWS A5.9)
Two welding fillers cover virtually all super duplex 2507 (UNS S32750, EN 1.4410) joining work: ER2594, an overmatching nitrogen-enhanced super duplex wire with PREN approximately 43 (slightly higher than the base material), and ER2553, a matching duplex wire with PREN approximately 38. Both are classified under AWS A5.9 / ASME SFA-5.9 for bare wire (GTAW, GMAW), with parallel SMAW classifications under AWS A5.4 (E2594-15, E2594-16, E2553-15, E2553-16) and FCAW classifications under AWS A5.22 (E2594T1, E2553T1). Selection between ER2594 and ER2553 is driven by service environment: ER2594 for chloride-aggressive or sour service, ER2553 for less aggressive applications. Both are compatible with the welding-procedure recommendations on the welding page.
ER2594 (Overmatching Super Duplex Filler)
ER2594 is the default first-choice filler for super duplex 2507 welding in chloride-bearing or sour service. The chemistry is designed to overmatch the base material in chromium, molybdenum, and nickel so that the weld metal PREN sits 1 to 3 points above the base PREN. The slight overmatch ensures that any pitting initiation occurs in the base metal rather than in the weld, where weld geometry would concentrate the corrosion.
| Element | ER2594, % | Function |
|---|---|---|
| Carbon (C) | 0.030 max | Carbide suppression |
| Chromium (Cr) | 24.0 to 27.0 | Pitting resistance, ferrite stabiliser |
| Nickel (Ni) | 8.0 to 10.5 | Austenite stabiliser, balanced for weld solidification |
| Molybdenum (Mo) | 3.5 to 4.5 | Pitting and crevice resistance |
| Nitrogen (N) | 0.20 to 0.30 | Austenite stabiliser, replaces nitrogen lost during welding |
| Manganese (Mn) | 2.5 max | Deoxidiser, sulfur control |
| Copper (Cu) | 1.5 max | Restricted residual |
| Tungsten (W) | 1.0 max | Restricted residual |
| PREN (calculated) | 43 to 45 | Overmatches UNS S32750 base material (PREN 41 to 43) |
ER2553 (Matching Super Duplex Filler)
ER2553 is a matching filler with PREN approximately 38, originally formulated for UNS S32550 (Ferralium 255) but routinely used on UNS S32750 in less aggressive service or where ER2594 is commercially unavailable. The lower PREN means the weld metal pitting resistance is below the base metal, so any pitting initiates preferentially in the weld; for that reason ER2553 is not the first choice in seawater or sour applications.
| Element | ER2553, % | Function |
|---|---|---|
| Carbon (C) | 0.040 max | Carbide suppression |
| Chromium (Cr) | 24.0 to 27.0 | Pitting resistance, ferrite stabiliser |
| Nickel (Ni) | 4.5 to 6.5 | Austenite stabiliser |
| Molybdenum (Mo) | 2.9 to 3.9 | Pitting and crevice resistance |
| Nitrogen (N) | 0.10 to 0.25 | Austenite stabiliser |
| Manganese (Mn) | 1.5 max | Deoxidiser |
| Copper (Cu) | 1.5 to 2.5 | Sulfuric-acid resistance (matches Ferralium 255 base) |
| PREN (calculated) | 37 to 39 | Slightly undermatches UNS S32750 base material |
Filler Metal Selection Matrix
| Service | Recommended Filler | Rationale |
|---|---|---|
| Seawater (chlorides up to 30,000 ppm) | ER2594 | PREN overmatch keeps pitting initiation in base metal |
| Sour service (NACE MR0175) | ER2594 | Overmatching chromium and nickel maintain SSC resistance |
| Subsea (API 17D) and topside oil and gas | ER2594 | NORSOK M-601 default for North Sea |
| FGD absorber, scrubber, ducting | ER2594 | Aggressive chloride plus reducing-acid environment |
| Pulp and paper (chlorine dioxide bleach) | ER2594 | Chloride plus oxidising acid; overmatch needed |
| Dilute sulfuric acid (below 50 percent) | ER2553 | Copper content of ER2553 raises sulfuric-acid resistance |
| Non-corrosive structural application | ER2553 or ER2594 | Either acceptable; ER2553 is commercially common and sufficient |
| Repair welding, field conditions | E2594-15 / -16 (SMAW) or E2594T1 (FCAW) | Same metallurgy as ER2594 in stick or tubular form |
Available Forms (AWS Classifications)
| Process | AWS Classification | Common Diameters |
|---|---|---|
| GTAW (TIG) bare wire | ER2594 (AWS A5.9), ER2553 (AWS A5.9) | 1.6, 2.0, 2.4, 3.2 mm |
| GMAW (MIG) bare wire | ER2594 (AWS A5.9), ER2553 (AWS A5.9) | 0.9, 1.0, 1.2, 1.6 mm spool |
| SMAW (stick) electrode | E2594-15 / -16 (AWS A5.4), E2553-15 / -16 (AWS A5.4) | 2.5, 3.2, 4.0, 5.0 mm |
| FCAW (flux-cored) wire | E2594T1 (AWS A5.22), E2553T1 (AWS A5.22) | 1.2, 1.6 mm |
| SAW solid wire plus flux | ER2594 wire plus matching basic flux | 2.4, 3.2, 4.0 mm |
SMAW Electrode Coatings
For SMAW (stick) welding, both rutile (E2594-16, E2553-16) and basic (E2594-15, E2553-15) coatings are commercially available. Basic-coated electrodes (E2594-15) offer higher Charpy toughness in the as-welded condition and better hydrogen control, at the cost of more demanding handling: they require back-baking at 250 to 300 deg C for 1 to 2 hours before use, must be held in a heated quiver at 100 to 120 deg C during welding, and are not recommended for any electrode left exposed for more than 2 hours.
Rutile-coated electrodes (E2594-16) are easier to handle, give a smoother bead, and run in all positions, but have slightly lower Charpy toughness in the as-welded condition and are not normally specified for low-temperature service or for repair work where the highest toughness margin is required. Both coatings provide nitrogen pickup from the coating decomposition, supplementing the wire-core nitrogen and helping balance the weld-metal microstructure.
Storage and Handling
- Bare wire (GTAW, GMAW): store in original sealed packaging at controlled temperature and humidity (15 to 25 deg C, below 60 percent relative humidity). Once opened, use within 30 days; otherwise re-condition.
- Basic-coated SMAW electrodes (E2594-15, E2553-15): back-bake at 250 to 300 deg C for 1 to 2 hours before use; transfer immediately to a heated quiver at 100 to 120 deg C; discard any electrode exposed beyond 2 hours.
- Rutile-coated SMAW electrodes (E2594-16, E2553-16): lower humidity sensitivity; back-bake recommended but not always mandatory per electrode datasheet.
- FCAW (flux-cored) wire: store sealed; once opened, return spool to a sealed cabinet between shifts; replace spool if welding pauses for more than 24 hours in humid conditions.
- Cleanliness: no carbon-steel storage racks, no carbon-steel cutting tools, no carbon-steel grinding wheels in the welding area. Iron contamination on the wire surface transfers to the weld pool and degrades corrosion resistance.
Related Super Duplex 2507 References
- UNS S32750 reference page
- Welding procedure
- Sigma-phase embrittlement
- Ferrite content (NORSOK M-630)
- Heat treatment
- Mechanical properties
- Super duplex pipe and fasteners
Super Duplex 2507 Welding Filler FAQ
Which filler is correct for welding super duplex 2507?
ER2594 is the default first-choice filler for super duplex 2507 in chloride or sour service. It is overmatching, with PREN approximately 43, slightly above the base-material PREN of 41 to 43. ER2553 is a matching filler with PREN approximately 38, used in less aggressive service or where ER2594 is commercially unavailable. Both are nitrogen-enhanced and classified under AWS A5.9.
What is the AWS classification for super duplex 2507 filler?
ER2594 and ER2553 (AWS A5.9 / ASME SFA-5.9) for GTAW and GMAW bare wire. E2594-15 and E2594-16 (AWS A5.4) for SMAW basic and rutile-coated electrodes respectively, with parallel E2553-15 and E2553-16 classifications. E2594T1 and E2553T1 (AWS A5.22) for FCAW flux-cored wire.
Why is ER2594 called overmatching?
The chromium, nickel, and molybdenum content of ER2594 is set so that the deposited weld metal PREN is 1 to 3 points above the base metal PREN. Overmatching ensures that any pitting initiation occurs preferentially in the base metal rather than in the weld; weld geometry and residual stress would otherwise concentrate corrosion at the weld and accelerate failure.
Can ER316L be used to weld super duplex 2507?
No. ER316L (austenitic) is metallurgically incompatible with the duplex base material and produces a weld with mismatched ferrite content (well below 35 percent), insufficient PREN (below 25), and reduced strength. Project specifications for super duplex 2507 invariably require a matching or overmatching duplex filler (ER2594 or ER2553).
Why are super duplex fillers nitrogen-enhanced?
Nitrogen is the strongest austenite stabiliser in the super duplex chemistry. The high-temperature welding cycle drives nitrogen out of the weld metal toward the gas phase; without compensation, the weld solidifies with ferrite excess and reduced corrosion resistance. The nitrogen content of the filler (0.10 to 0.30 percent depending on classification) replaces the nitrogen lost during welding and helps the weld metal balance to the 35 to 65 percent ferrite acceptance range.
What handling controls apply to basic-coated SMAW electrodes?
Basic-coated electrodes (E2594-15, E2553-15) are hygroscopic. They require back-baking at 250 to 300 deg C for 1 to 2 hours before use to drive off absorbed moisture, transfer to a heated quiver at 100 to 120 deg C during welding, and discard if exposed beyond 2 hours of welding-floor humidity. Inadequate handling produces hydrogen pickup that promotes hydrogen-induced cracking in the as-welded duplex microstructure.
Is there a super duplex filler designed specifically for sour service?
ER2594 is the standard choice for NACE MR0175 sour service applications welded with super duplex 2507. The filler chemistry maintains the duplex microstructure with hardness controlled below 28 HRC after welding (verified by Vickers hardness traverse on the WPS qualification), and the overmatching PREN preserves the chloride-pitting margin in H2S-containing environments. Some mills offer a tightened-tolerance variant (sometimes called ER2594-LowFe or ER2594-S) for the most demanding sour-service projects.
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