Use exact ASTM A182 grade wording such as F51, F53, F55 or the project-specified grade
BLD Forge Direct
Duplex and Super Duplex Forged Flange RFQ Guide
Duplex and super duplex flange RFQs should define the exact grade wording, dimensional standard, service condition, corrosion or sour-service requirement, PMI, ferrite or project test notes, heat treatment, inspection package and approval route before quotation.
Summary
Duplex and super duplex flange RFQs should define the exact grade wording, dimensional standard, service condition, corrosion or sour-service requirement, PMI, ferrite or project test notes, heat treatment, inspection package and approval route before quotation.
Confirm whether the service requires NACE MR0175 / ISO 15156 review or other corrosion-service notes
Plan PMI, ferrite, heat treatment and MTC 3.1 evidence before price comparison
Attach drawing, line class or project material specification for any substitution review
Engineering Selection Notes
Duplex and super duplex are not simply stainless upgrades. Buyers usually specify them because strength, chloride exposure, sour service, offshore conditions or corrosion allowance make ordinary stainless language too weak. That means the RFQ must carry the service logic, not just the word duplex.
The commercial risk is hidden in verification. ASTM A182 grade wording gives the material route, but the project may also require PMI, ferrite checks, solution treatment evidence, NACE MR0175 / ISO 15156 review, hardness limits or third-party witness points. Those checks change cost and lead time, so they belong in the first RFQ.
If a supplier proposes a nearby duplex or super duplex grade, the buyer should treat it as a controlled alternate. Quote the specified grade first, then show the alternate with chemistry, mechanical, corrosion-service and document assumptions separated for engineering approval.
Duplex / Super Duplex RFQ Review Matrix
| Decision point | Duplex route | Super duplex route | Buyer action |
|---|---|---|---|
| Grade wording | ASTM A182 F51 or project-specified duplex grade | ASTM A182 F53 / F55 or project-specified super duplex grade | State exact grade and whether alternates are allowed |
| Service driver | Strength and corrosion resistance beyond common stainless needs | More severe chloride, offshore or project corrosion-service requirement | Send service note, line class or material specification |
| Verification | MTC 3.1, PMI and project material checks | MTC 3.1, PMI, ferrite/hardness or project checks when specified | List evidence before quotation |
| Sour service | Review if NACE MR0175 / ISO 15156 is specified | Review if NACE MR0175 / ISO 15156 is specified | Do not assume compliance without the project requirement |
| Substitution | Nearby grade may not satisfy corrosion or approval basis | Higher grade may still require approval | Quote specified grade first, alternate grade separately |
Duplex RFQ Data Checklist
| RFQ field | Minimum detail | Why it matters | Document evidence |
|---|---|---|---|
| Standard | ASME, EN, GOST or drawing | Controls dimensions and rating route | Dimensional report |
| Material | Exact ASTM A182 or project grade | Controls certificate and approval basis | MTC 3.1 and heat traceability |
| Corrosion service | Chloride, seawater, sour service or project note | Controls whether extra material review is needed | Project material specification |
| PMI / ferrite / hardness | Required, not required, or by project | Affects inspection route and lead time | Inspection report or third-party release |
| Substitution rule | Allowed, not allowed, or subject to approval | Prevents unauthorized grade changes | Written buyer or end-user approval |
Practical Checklist
Use this list before sending drawings or line items for quotation review.
Exact grade: ASTM A182 F51, F53, F55 or project-specified duplex / super duplex wording
Dimensional standard: ASME B16.5, ASME B16.47, EN 1092-1, GOST or drawing
Flange type, size, pressure class or PN, facing and bore / schedule requirement
Service condition: chloride exposure, seawater, sour service, temperature or project corrosion note
Inspection and documents: MTC 3.1, PMI, ferrite, hardness, NDT and dimensional report
NACE MR0175 / ISO 15156 or end-user material approval requirement where applicable
Whether substitution between duplex and super duplex grades is allowed
Common RFQ Mistakes
These points often cause repeated clarification, price revisions or document mismatch.
- Writing only duplex flange without the exact ASTM A182 grade or UNS/project wording
- Assuming F51, F53 and F55 can be substituted without end-user approval
- Leaving NACE MR0175 / ISO 15156 or sour-service notes out of the first RFQ
- Requesting PMI or ferrite evidence only after production price has been agreed
- Comparing duplex and stainless quotes without matching service condition and inspection scope
FAQ
Short answers for buyers preparing this RFQ topic.
Is duplex the same as super duplex in an RFQ?
No. Use the exact grade or project wording. Any substitution between duplex and super duplex grades should be treated as an engineering alternate and approved before production.
When should NACE MR0175 / ISO 15156 be mentioned?
Mention it whenever the project involves sour service, H2S-containing oil and gas environments or an end-user material approval note. It affects material selection and verification scope.
What inspection evidence is useful for duplex forged flanges?
Common evidence includes MTC 3.1, PMI, ferrite or project material checks, hardness where specified, dimensional report, NDT if required and third-party release documents.
PDF Datasheets for RFQ Review
Use these direct PDF links with the article before sending line items. The PDFs are generated from published product-page RFQ scope tables and do not invent standard dimensions.
Stainless Steel Forged Flanges RFQ Datasheet
Use this PDF when stainless, duplex, PMI or corrosion-service requirements are part of the RFQ.
High Pressure Flanges RFQ Datasheet
Use this PDF when duplex or super duplex flanges also carry high-pressure, RTJ, NDT or third-party inspection scope.
Send your RFQ or drawing directly to BLD Forge Direct.
Email quote@bldforgedirect.com with standard, drawing, material, quantity and inspection requirements.