Heat Resistant & Cr-Mo
ER90S-B91 for P91 Steel
ER90S-B91 welding wire is an AWS A5.28 low-alloy welding wire for P91, T91 and other compatible Grade 91 steels used in high-temperature and creep-resistant applications. ER90S-B91 is a 9Cr-1Mo-V-Nb welding wire designed for compatible P91, T91 and F91 steels. It is commonly used for high-temperature steam piping, boilers, headers, superheaters, reheaters and power-generation equipment where weld-metal chemistry, creep resistance and controlled heat treatment are important.
ER90S-B91 Welding Wire
ER90S-B91 is an AWS A5.28 low-alloy solid welding wire for compatible P91, T91 and other Grade 91 steels used in high-temperature service.
It belongs to the modified 9Cr-1Mo-V-Nb welding consumable system and is designed for applications where weld-metal chemistry, high-temperature performance and compatibility with Grade 91 steels are critical.
Typical applications include:
- P91 and T91 pipe welding
- Main steam and hot reheat piping
- Boiler headers and pressure components
- Superheater and reheater systems
- High-temperature power-generation equipment
- Other compatible Grade 91 components
ER90S-B91 can be supplied for GMAW/MIG and GTAW/TIG, depending on product form and the qualified welding procedure.
ER90S-B91 at a Glance
Item | Details |
|---|---|
AWS Classification | ER90S-B91 |
Specification | AWS A5.28 / ASME SFA-5.28 |
Product Type | Solid welding wire / TIG filler rod |
Alloy System | 9Cr-1Mo-V-Nb |
Typical Base Materials | P91, T91, F91 and compatible Grade 91 steels |
Strength Class | ER90 |
Welding Processes | GMAW/MIG, GTAW/TIG |
Main Service | High-temperature / creep-resistant applications |
Typical Industries | Power generation, boilers, high-temperature piping |
Product Form | Spool / TIG rod |
Documentation | TDS, MTC/CoA and project documentation as required |
AWS A5.28 covers classification requirements for low-alloy steel electrodes and rods used with gas-shielded processes including GMAW, GTAW and plasma arc welding. The current published edition is A5.28/A5.28M:2026.
Grade 91 Welding: Where ER90S-B91 Fits
The key application for ER90S-B91 is the Grade 91 material system.
Grade 91 steels are modified 9Cr steels containing controlled additions of chromium, molybdenum, vanadium, niobium and nitrogen.
Typical materials include:
- P91
- T91
- F91
- A387 Grade 91
- Other compatible Grade 91 steels
These materials are used in high-temperature pressure and power-generation components.
The consumable should therefore be selected based on base-metal grade + weld-metal chemistry + welding procedure, rather than tensile strength alone.
ER90S-B91 Chemical Composition
ER90S-B91 is based on the 9Cr-1Mo-V-Nb alloy system.
Typical classification limits are:
Element | wt.% |
|---|---|
C | 0.07–0.13 |
Mn | ≤1.20 |
Si | 0.15–0.50 |
Cr | 8.00–10.50 |
Ni | ≤0.80 |
Mo | 0.85–1.20 |
V | 0.15–0.30 |
Nb | 0.02–0.10 |
N | 0.03–0.07 |
Cu | ≤0.20 |
P | ≤0.010 |
S | ≤0.010 |
Al | ≤0.04 |
Mn + Ni | ≤1.50 |
A commercial ER90S-B91 product can have a more tightly controlled chemistry within the classification range. For example, Kobelco's MG-S90B91 lists typical values of approximately 8.36% Cr, 0.97% Mo, 0.18% V and 0.06% Nb.
For procurement, always verify the actual MTC/CoA against the applicable AWS/ASME specification and project requirements.
ER90S-B91 Mechanical Properties
ER90S-B91 belongs to the ER90 strength classification.
Typical minimum classification requirements include:
Property | Minimum |
|---|---|
Tensile Strength | 620 MPa / 90 ksi |
Yield Strength | 414 MPa / 60 ksi |
Elongation | 16% |
Actual weld-metal properties depend on:
- Welding process
- Shielding gas
- Heat input
- Welding parameters
- PWHT
- Testing condition
Manufacturer-specific typical values can be considerably higher than the classification minimums. For example, published Kobelco data reports typical post-PWHT values around 620 MPa yield strength and 750 MPa tensile strength for its ER90S-B91 product.
For project purchasing, use the actual product TDS and MTC rather than generic typical values.
ER90S-B91 for P91 and T91 Welding
P91 Welding
ER90S-B91 welding wire for P91 steel is the primary application focus of this product.
Typical P91 applications include:
- Main steam piping
- Hot reheat piping
- Headers
- Boiler components
- Superheaters
- Reheaters
- High-temperature pressure piping
T91 Welding
T91 is the corresponding Grade 91 tube material used in high-temperature boiler and heat-transfer applications.
Typical applications include:
- Boiler tubes
- Superheater tubes
- Reheater tubes
- High-temperature pressure components
- Power-generation equipment
For both P91 and T91, the welding consumable must be compatible with the base material and qualified under the applicable welding procedure.
Why Choose a Grade 91 Consumable?
The important point with P91/T91 welding is not simply achieving ER90-level tensile strength.
The consumable needs to provide a suitable weld-metal chemistry for the Grade 91 system.
Key alloying elements include:
Cr + Mo + V + Nb + N
These controlled additions are part of the modified 9Cr alloy system used for Grade 91 applications.
For critical components, welding procedure control is equally important, including:
Preheat → Interpass Control → Heat Input → Hydrogen Control → Cooling → PWHT
The consumable and welding procedure should therefore be considered as one qualified welding system.
High-Temperature Applications
ER90S-B91 is primarily relevant to power-generation and high-temperature pressure applications.
Typical applications include:
Steam Piping
- Main steam lines
- Hot reheat lines
- High-temperature pressure piping
Boiler Components
- Headers
- Superheater components
- Reheater components
- T91 tubes
Power-Generation Equipment
- High-temperature pressure components
- Boiler systems
- Other compatible Grade 91 equipment
The suitability of ER90S-B91 for a particular component depends on the material specification, service conditions, applicable code and qualified WPS/PQR.
Welding Processes
GMAW / MIG
ER90S-B91 can be supplied as solid wire for GMAW/MIG welding.
Important welding variables include:
- Wire diameter
- Shielding gas
- Current
- Voltage
- Wire-feed speed
- Travel speed
- Heat input
The actual welding parameters should follow the qualified WPS.
Kobelco, for example, lists its ER90S-B91 solid wire for GMAW with specified shielding-gas ranges and DCEP polarity. These parameters are product-specific and should not be treated as universal settings.
GTAW / TIG
ER90S-B91 is also available as TIG filler rod.
GTAW can be used where controlled deposition and precise weld-metal placement are required, including suitable pipe and critical-joint applications.
Filler diameter, shielding gas, purge requirements and welding parameters should follow the qualified procedure.
P91 Welding Procedure and PWHT
P91/T91 welding requires strict control of the welding thermal cycle.
Important variables include:
- Preheat
- Interpass temperature
- Heat input
- Hydrogen control
- Cooling conditions
- PWHT
- Hardness control
P91 weld-metal systems can be sensitive to welding thermal history, so generic temperatures from a product page should not replace a qualified procedure.
Manufacturer literature may provide reference PWHT conditions, but the actual requirements must be established by the applicable code and WPS/PQR. Kobelco, for example, publishes specific PWHT ranges for its Grade 91 consumable systems.
Always follow the approved welding procedure for the actual project.
ER90S-B91 vs ER90S-B9
This comparison is important because ER90S-B9 remains an older search term.
AWS A5.28/A5.28M:2020 states that ER90S-B91 was added and replaced ER90S-B9.
| ER90S-B91 | ER90S-B9 |
|---|---|---|
Classification | Current designation | Earlier designation |
Typical Material | P91 / T91 | P91 / T91 |
Alloy System | 9Cr-1Mo-V-Nb | 9Cr-1Mo-V-Nb |
AWS A5.28:2020 | Added | Replaced |
Application | Grade 91 | Grade 91 |
For new projects, use the classification specified by the applicable current standard and project documentation.
ER90S-B91 vs ER90S-B92
This is one of the most useful comparisons for buyers choosing between Grade 91 and Grade 92 consumables.
| ER90S-B91 | ER90S-B92 |
|---|---|---|
Typical Material | P91 / T91 | P92 / T92 |
Alloy System | 9Cr-1Mo-V-Nb | Modified 9Cr-W-V-Nb |
Strength Class | ER90 | ER90 |
Main Material System | Grade 91 | Grade 92 |
Typical Service | High-temperature | High-temperature |
Main Selection Factor | P91/T91 compatibility | P92/T92 compatibility |
P91/T91 → B91
P92/T92 → B92
The two classifications should not be treated as interchangeable merely because both are ER90-class 9Cr consumables.
ER90S-B91 vs ER80S-B8
| ER90S-B91 | ER80S-B8 |
|---|---|---|
Typical Material | P91 / T91 | P9 / T9 |
Alloy System | 9Cr-1Mo-V-Nb | 9Cr-1Mo |
Strength Class | ER90 | ER80 |
Material System | Modified Grade 91 | Conventional Grade 9 |
Typical Service | High-temperature / creep | High-temperature |
Main Selection Factor | Grade 91 compatibility | Grade 9 compatibility |
Both contain approximately 9% chromium, but similar chromium content does not make the two consumables interchangeable.
ER90S-B91 vs ER90S-B3
| ER90S-B91 | ER90S-B3 |
|---|---|---|
Typical Material | P91 / T91 | P22 / T22 |
Alloy System | 9Cr-1Mo-V-Nb | 2.25Cr-1Mo |
Strength Class | ER90 | ER90 |
Material System | Grade 91 | Grade 22 |
Typical Service | High-temperature / creep | High-temperature |
Main Selection Factor | Grade 91 compatibility | P22/T22 compatibility |
P91/T91 ≠ P22/T22
How to Select ER90S-B91
Before ordering, confirm:
1. Base Material
P91, T91, F91 or another compatible Grade 91 steel?
2. Required Classification
Does the WPS specify ER90S-B91?
3. Welding Process
GMAW/MIG or GTAW/TIG?
4. Diameter
What filler diameter is specified by the qualified procedure?
5. Service Conditions
What temperature, pressure and operating environment apply?
6. PWHT
What heat-treatment requirements are specified?
7. Mechanical Requirements
Are tensile, hardness, impact or other requirements specified?
8. Certification
Is MTC, CoA, third-party inspection or additional project documentation required?
9. Packaging
Spool, TIG rod or another packaging format?
Diameter and Packaging
ER90S-B91 can be supplied in different diameters and packaging formats according to the welding process and customer requirements.
Possible forms include:
- GMAW/MIG spools
- GTAW/TIG rods
- Different wire diameters
- Standard industrial packaging
- Customized packaging where available
For quotation, provide:
AWS Classification + Base Material + Diameter + Welding Process + Quantity + Packaging
Quality and Technical Documentation
For Grade 91 projects, buyers may request:
- Technical Data Sheet (TDS)
- Mill Test Certificate (MTC)
- Certificate of Analysis (CoA)
- Chemical composition
- Mechanical properties
- Impact test data where applicable
- Certificate of Conformity
- Packaging information
- Heat/batch traceability
- Project-specific documentation
For power-generation and pressure-equipment projects, confirm documentation and traceability requirements before ordering.
Frequently Asked Questions
What is ER90S-B91 welding wire?
ER90S-B91 is an AWS A5.28 low-alloy solid welding wire for compatible Grade 91 steels such as P91 and T91.
What is ER90S-B91 used for?
It is primarily associated with P91/T91 welding in high-temperature piping, boilers, headers, superheaters, reheaters and power-generation equipment.
Is ER90S-B91 suitable for P91 steel?
ER90S-B91 is designed for compatible P91 applications, subject to the applicable material specification, qualified WPS/PQR and project code.
Is ER90S-B91 suitable for T91 steel?
Yes, it is associated with compatible T91 applications. The final welding procedure must be qualified for the actual project.
What is the difference between ER90S-B91 and ER90S-B9?
ER90S-B91 replaced ER90S-B9 in AWS A5.28:2020. Both designations are associated with the Grade 91 consumable system.
What is the difference between ER90S-B91 and ER90S-B92?
B91 is associated with P91/T91 Grade 91 steels, while B92 is associated with P92/T92 Grade 92 steels. Their alloy systems are different.
What is the difference between ER90S-B91 and ER80S-B8?
B91 is associated with modified Grade 91 steels, while B8 is associated with conventional 9Cr-1Mo Grade 9 materials such as P9/T9.
What is the difference between ER90S-B91 and ER90S-B3?
B91 is associated with the 9Cr-1Mo-V-Nb Grade 91 system, while B3 is associated with the 2.25Cr-1Mo system used with materials such as P22/T22.
Does ER90S-B91 require PWHT?
P91/T91 welding requires procedure-specific control of PWHT and other thermal variables. The exact requirements must follow the qualified WPS/PQR and applicable code.
Can ER90S-B91 be used for P92?
Do not assume substitution. P92/T92 requires the appropriate Grade 92 consumable system and qualified welding procedure.
ER90S-B91 Welding Wire for P91 and T91
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