A blind flange is a solid disc with the same drilling and facing as the flange it bolts to, but no bore - it closes off a line end, a vessel nozzle or a valve port. Spectacle blinds, paddle blanks and spacer rings are machined from the same forged plate stock. We forge and machine them at our own plant in Shanxi, China, and sell direct, from a single blind to a mixed line list.
Published ASME blind-flange scope depends on both size and class: B16.5 covers NPS 1/2 to 24 in Classes 150 to 1500 and NPS 1/2 to 12 in Class 2500; B16.47 covers NPS 26 to 60 in Classes 75 to 900. These are standard scope boundaries for RFQ routing; BLD confirms feasibility for each size/class combination against the exact standard or drawing, material and inspection requirements. EN 1092-1 Type 05, DIN 2527 and GOST 33259 / 12820 / 12821 items follow the specified DN/PN table or project drawing, with RF, FF or RTJ facing. Grades are ASTM A105 and A105N, A350 LF2, A182 stainless, duplex and super duplex, and project-specified alloys.
Because a blind carries full line pressure across an unsupported disc, thickness is the dimension that matters most, and a non-table thickness has to be stated rather than assumed. OD, drilling, facing and the gasket contact surface follow the mating flange. Inspection covers thickness, drilling, face finish and marking, with MTC 3.1, PMI and NDT where high-pressure service requires it.
Product family: Flanges
Blind flange RFQs are checked by standard, size, class or PN, facing, material grade, thickness, marking, inspection documents and destination country before quotation.
Paddle blanks are machined from the same forged plate stock as the blinds on this page.
A blind flange is quoted correctly only when its face and any opening are stated. Settle these five points before comparing prices.
| Detail | Technical basis | RFQ data to send | Risk if missing |
|---|---|---|---|
| Plain blind / no bore | A standard blind flange is a solid closure without a central opening | Say blind flange, no bore unless a tapped hole, center opening or drawing detail is required | Supplier may quote a catalogue blind while the buyer expects a custom testing or drain connection |
| RF - raised face | RF uses a raised sealing area and is common in many ASME flange orders | State RF, standard, class, material, gasket or surface-finish note, and mating flange route | Offer may assume the wrong face or omit surface-finish requirements |
| FF - flat face | FF provides a flat gasket contact surface and is often used where the mating equipment requires flat-face contact | State FF, full-face gasket requirement, mating valve / equipment note and bolt-up restrictions if the project has them | Raised-face supply can be incompatible with the mating equipment |
| RTJ - ring type joint | RTJ uses a ring groove for a metal ring gasket and is often selected for higher-pressure or severe-service sealing | State RTJ, ring number or groove requirement, Class, material, hardness / NDT notes and inspection hold points | Groove machining, inspection time and document scope may be missed |
| Tapped, center-bored or custom blind | Not part of a standard blind flange: a tapping, centre bore or hub is a drawing detail, machined to the buyer's drawing | Attach drawing with thread, bore, hub, thickness and tolerance notes | The price comparison will mix standard blinds with custom machined parts |
Put the controls your project needs in the first RFQ, so that every offer is priced on the same inspection scope.
| Control | When it matters | Evidence to request | RFQ note |
|---|---|---|---|
| MTC 3.1 | Most EPC, oil and gas, petrochemical, marine and pressure-equipment RFQs | Material grade, heat number, chemical / mechanical test results and authorized inspection representative validation | Ask for EN 10204 3.1 or project certificate wording in the first RFQ |
| Dimensional report | Any standard blind where bolt circle, thickness, OD, facing or RTJ groove must be accepted before shipment | Measured dimensions against ASME, EN/DIN, GOST or drawing basis | List the critical dimensions instead of asking only for photos |
| NDT | High-pressure, large-diameter, heavy forged, RTJ or project-critical blind flanges | UT, MT, PT, RT or other method per project acceptance criteria and qualified personnel route | Specify method, acceptance level, report language and witness need |
| PMI / hardness | Stainless, duplex, alloy, NACE or material-mix orders | PMI report, hardness record or project-specific material verification | Do not wait until pre-shipment inspection to add alloy verification |
| Marking and packing | Export shipments, mixed line-item orders and project receiving checks | Heat number, material, size, class / PN, face, item number, packing list and case mark | Match product marks with MTC, dimensional report and packing list |
| Scope and rating | |
|---|---|
| Size and rating review | Published ASME scope for RFQ routing: B16.5 Classes 150 to 1500 at NPS 1/2 to 24 and Class 2500 at NPS 1/2 to 12; B16.47 Classes 75 to 900 at NPS 26 to 60. Confirm BLD feasibility and EN/DIN/GOST DN/PN against the exact specification or drawing. |
| Supplied variants |
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| Standards and materials | |
| Standards / drawings |
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| Material grades |
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| Geometry, tolerance and inspection | |
| Critical dimensions | OD, thickness, bolt pattern, RF/FF/RTJ face, gasket contact surface and pressure-test requirement. |
| Inspection depth | Thickness check, drilling, face finish, marking, MTC 3.1, PMI and NDT when high-pressure service requires it. |
| Reviewed before quotation |
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| Buying logic | |
| Best-fit RFQ | Best for closed-end pipe, vessel nozzle and pressure isolation line items. |
| Buyer application | Pipeline isolation, pressure vessel nozzles, valve end closures and maintenance blinds. |
Your standard, drawing revision and project specification govern.
Also known as
We confirm each step against your drawing or standard before we quote.
Material grade, heat number, certificate basis and substitution limits are checked against the Blind Flanges drawing or standard before procurement is released.
The forging route is selected around flange type, section thickness, bore allowance, hub or neck geometry and pressure-service requirements.
Heat treatment is planned with the required record package, mechanical testing basis and impact-test condition where low-temperature or alloy service applies.
Rough machining opens reference faces, bore, hub, neck or sealing-face stock needed to control allowance before final flange machining.
Final machining controls facing, bore, bolt pattern, groove, sealing surface and flange-table or drawing tolerances before dimensional inspection is issued.
Inspection covers dimensional report, MTC 3.1, PMI and required UT, MT or PT records before the release documents are matched to the purchase order.
Marking, packing and export documents are prepared by PO line item so the Blind Flanges shipment can clear customs and be identified at site receiving.
List document requirements in the first RFQ; they affect price and schedule.
From us: we forge and machine blind flanges at our own plant in Dingxiang, Shanxi, China, and quote direct. The minimum order is 1 piece, every RFQ gets a reply within 8 hours, the lead time is 9 to 30 days after drawing approval, and shipment is FOB the Chinese port you designate, with CFR or CIF on request. Every order ships with an EN 10204 3.1 MTC.
Yes. Figure-8 spectacle blinds, paddle blanks and spacer rings are machined from the same forged plate stock as blind flanges, to line class or drawing. State standard or drawing, line size, pressure class, thickness, material grade and inspection documents in the RFQ.
MSS SP-44 covers steel pipeline flanges from NPS 12 through NPS 60 in Classes 150, 300, 400, 600 and 900, and its published scope notes that blind flanges can be forged steel or steel plate. Use it only when the pipeline specification names MSS SP-44, and state in the RFQ whether forged supply is required or plate is accepted. It does not replace ASME B16.5 or B16.47 unless the project permits it.
Email quote@bldforgedirect.com with standard, drawing, material, quantity and inspection requirements.